gpui-whiteboard 0.5.1

//! An infinite, pannable/zoomable whiteboard canvas for GPUI.
//!
//! Host-agnostic — depends only on `gpui`, `serde`, and `ttf-parser` (no
//! `gpui-component`, no native libraries). Two layers: a serializable scene model
//! ([`Scene`] / [`Element`]) the host persists as opaque JSON, and a
//! [`WhiteboardView`] entity that renders the board *and* its editing UI (toolbar,
//! color picker, flyouts, templates gallery, context menu) and drives all
//! interaction. The host supplies a theme ([`WhiteboardStyle`]) and optional
//! callbacks (persist on change, open a page, fetch an image bitmap, read/write the
//! clipboard, store templates); with none installed it's still a working board.
//!
//! Elements: freehand pen, rect / ellipse / diamond / triangle / rounded-rect /
//! hexagon / star, line, arrow, text, images, and page-cards — sharing one select /
//! move / resize / rotate / fill / z-order machinery, plus copy-paste, templates,
//! and undo/redo. Text renders as **vector outlines** (the `font` module, via
//! `ttf-parser`) rather than gpui overlay glyphs, so it rotates + scales with the
//! camera and a host can supply a custom face ([`Font`]). See `README.md` for the
//! full API and usage; design notes in `docs/whiteboard-architecture.md`.
//!
//! Perf note: element geometry is re-tessellated when painted (as GPUI's own
//! `painting`/`brush` examples do), but rendering is viewport-culled and text
//! glyph layouts are cached. A built-`Path` cache remains a further optimization
//! for extremely dense visible scenes.

mod font;
mod geometry;
mod input;
mod paint;
mod render_perf;
mod scene;

use std::cell::Cell;
use std::collections::{HashMap, HashSet};
use std::hash::{DefaultHasher, Hash, Hasher};
use std::ops::Range;
use std::rc::Rc;
use std::sync::Arc;

pub use font::Font;
use geometry::*;
use input::WhiteboardInputElement;
use paint::*;
use render_perf::WorldViewport;
pub use scene::*;

use gpui::{
    AnyElement, AnyView, App, AppContext, Bounds, Context, CursorStyle, Div, ElementId,
    ElementInputHandler, Entity, EntityInputHandler, FocusHandle, GlobalElementId, Hsla,
    InspectorElementId, InteractiveElement, IntoElement, KeyDownEvent, LayoutId, MouseButton,
    MouseDownEvent, MouseMoveEvent, MouseUpEvent, ObjectFit, ParentElement, PathBuilder,
    PinchEvent, Pixels, Point, Render, Rgba, ScrollDelta, ScrollWheelEvent, SharedString,
    StatefulInteractiveElement, Style, Styled, StyledImage, TransformationMatrix, UTF16Selection,
    Window, canvas, div, fill, hsla, linear_color_stop, linear_gradient, point, px, relative, rgba,
    size,
};
use serde::{Deserialize, Serialize};

/// Zoom is clamped to this range (also guards the world↔screen math against a
/// zero/negative factor from hand-edited JSON).
const MIN_ZOOM: f32 = 0.1;
const MAX_ZOOM: f32 = 8.0;
/// World-space distance between grid dots.
const GRID: f32 = 24.0;
/// Smallest on-screen dot spacing before the grid is coarsened (×4).
const MIN_DOT_SPACING: f32 = 16.0;
/// Dot size in screen px (constant — dots don't grow with zoom).
const DOT: f32 = 2.0;
/// Screen px per scroll "line" for inexact (`Lines`) scroll deltas.
const LINE_PX: f32 = 16.0;
const VIEWPORT_CULL_MARGIN_PX: f32 = 96.0;

fn accepts_wheel_input(read_only: bool) -> bool {
    !read_only
}
/// Pen nib in screen px. A stored width is world-space (`NIB / zoom` at draw
/// time) so strokes/shapes feel like a constant nib yet scale with the content.
/// Also the default of [`WhiteboardView::active_width`].
const NIB: f32 = 2.5;
/// Stroke-thickness presets (screen px) offered by the toolbar thickness flyout.
/// `NIB` (the default) is one of them.
const WIDTH_PRESETS: [f32; 5] = [1.0, 2.5, 4.0, 6.0, 9.0];
/// Range (screen px) of the custom-width slider in the thickness flyout.
const WIDTH_MIN: f32 = 1.0;
const WIDTH_MAX: f32 = 20.0;
/// Slider track width, px (matches the preset row: 5 × 30 + gaps).
const WIDTH_SLIDER_W: f32 = 156.0;
/// Minimum on-screen gap between recorded freehand points (input thinning).
const MIN_POINT_PX: f32 = 2.0;
/// Hit-test tolerance around an element's bounds, in screen px.
const SELECT_PAD: f32 = 6.0;
/// Most undo steps kept (bounds memory; each step is a scene snapshot).
const UNDO_CAP: usize = 50;
/// Half-size of a corner resize handle, screen px.
const HANDLE_HALF: f32 = 4.0;
/// Grab radius for a corner handle, screen px.
const HANDLE_GRAB: f32 = 10.0;
/// Distance in screen pixels from a selected shape edge to its connector button.
const CONNECTOR_BUTTON_GAP: f32 = 24.0;
const CONNECTOR_BUTTON_SIZE: f32 = 20.0;
/// Color picker: saturation/brightness square + hue strip dimensions, px.
const SV_W: f32 = 216.0;
const SV_H: f32 = 140.0;
const HUE_H: f32 = 14.0;
/// Below this absolute rotation (radians), a box is treated as upright — it
/// shows resize corners. Rotated past it, only the rotate handle is offered
/// (rotated-frame resize is intentionally out of scope; rotate back to resize).
const ROT_EPS: f32 = 0.05;
/// While rotating, an orientation within this many radians (~6°) of horizontal
/// or vertical snaps to it, so boxes square up to the grid easily.
const ROT_SNAP: f32 = 0.105;
/// Default text size at creation, screen px (stored world size is this / zoom).
const TEXT_SIZE: f32 = 18.0;

/// Inset (world units) kept between a shape's inscribed text rectangle and its
/// border, so the auto-shrunk label never touches the edge.
const LABEL_PAD: f32 = 8.0;

/// Default highlighter color (packed `0xRRGGBBAA`) for the highlight toggle —
/// translucent yellow so the text stays readable.
const HIGHLIGHT_DEFAULT: u32 = 0xffe06680;
/// Rough per-character advance and line height, as fractions of the font size,
/// for an approximate text bounding box (hit-testing / selection).
const TEXT_CHAR_W: f32 = 0.55;
const TEXT_LINE_H: f32 = 1.3;
/// Default page-card size at creation, screen px (stored world size is / zoom).
const EMBED_W: f32 = 210.0;
const EMBED_H: f32 = 76.0;
const MINDMAP_ROOT_W: f32 = 196.0;
const MINDMAP_ROOT_H: f32 = 60.0;
const MINDMAP_NODE_W: f32 = 164.0;
const MINDMAP_NODE_H: f32 = 48.0;
const MINDMAP_BRANCH_GAP_X: f32 = 120.0;
const MINDMAP_BRANCH_GAP_Y: f32 = 84.0;
const FLOWCHART_NODE_W: f32 = 180.0;
const FLOWCHART_NODE_H: f32 = 52.0;
const FLOWCHART_GAP_Y: f32 = 92.0;
const FLOWCHART_BRANCH_GAP_X: f32 = 240.0;
/// Longest edge of a freshly placed image, screen px (aspect preserved).
const IMAGE_PLACE_PX: f32 = 280.0;

/// The active tool. UI state — not part of the persisted scene.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum Tool {
    /// Drag to pan the canvas (the default — navigation before drawing).
    Pan,
    Select,
    Pen,
    Rect,
    Ellipse,
    Diamond,
    Triangle,
    RoundRect,
    Star,
    Hexagon,
    Line,
    Arrow,
    DashedArrow,
    Text,
    MindMap,
    Flowchart,
    Embed,
    Image,
}

impl Tool {
    /// A glyph for the toolbar button (dependency-free; the host has no icon set
    /// in this crate).
    fn glyph(self) -> &'static str {
        match self {
            // A dingbat hand (pre-emoji, so it always renders flat/monochrome —
            // unlike ✋, which macOS re-colors even with a VS15 text request).
            Tool::Pan => "☞",
            Tool::Select => "↖",
            Tool::Pen => "✎",
            Tool::Rect => "▭",
            Tool::Ellipse => "◯",
            Tool::Diamond => "◇",
            Tool::Triangle => "△",
            Tool::RoundRect => "▢",
            Tool::Star => "☆",
            Tool::Hexagon => "⬡",
            Tool::Line => "╱",
            Tool::Arrow => "↗",
            Tool::DashedArrow => "⇢",
            Tool::Text => "T",
            Tool::MindMap => "◎",
            Tool::Flowchart => "⇅",
            Tool::Embed => "▤",
            Tool::Image => "▦",
        }
    }

    /// A human label for the tooltip (the toolbar is icon-only), with the
    /// keyboard shortcut where one exists (see [`shortcut`](Tool::shortcut)).
    fn label(self) -> &'static str {
        match self {
            Tool::Pan => "Pan — drag to move (H)",
            Tool::Select => "Select (V)",
            Tool::Pen => "Pen (P)",
            Tool::Rect => "Rectangle (R)",
            Tool::Ellipse => "Ellipse (O)",
            Tool::Diamond => "Diamond (D)",
            Tool::Triangle => "Triangle (G)",
            Tool::RoundRect => "Rounded rectangle (U)",
            Tool::Star => "Star (S)",
            Tool::Hexagon => "Hexagon (X)",
            Tool::Line => "Line (L)",
            Tool::Arrow => "Arrow (A)",
            Tool::DashedArrow => "Dashed arrow (K)",
            Tool::Text => "Text (T)",
            Tool::MindMap => "Mind map (M)",
            Tool::Flowchart => "Flowchart (F)",
            Tool::Embed => "Page card",
            Tool::Image => "Image (I) — click to place",
        }
    }

    /// The single-key shortcut that selects this tool, if any.
    fn shortcut(key: &str) -> Option<Tool> {
        Some(match key {
            "h" => Tool::Pan,
            "v" => Tool::Select,
            "p" => Tool::Pen,
            "r" => Tool::Rect,
            "o" => Tool::Ellipse,
            "d" => Tool::Diamond,
            "g" => Tool::Triangle,
            "u" => Tool::RoundRect,
            "s" => Tool::Star,
            "x" => Tool::Hexagon,
            "l" => Tool::Line,
            "a" => Tool::Arrow,
            "k" => Tool::DashedArrow,
            "t" => Tool::Text,
            "m" => Tool::MindMap,
            "f" => Tool::Flowchart,
            "i" => Tool::Image,
            _ => return None,
        })
    }

    /// The bundled SVG icon for this tool as `(cache-key, bytes)`, or `None` to
    /// fall back to [`glyph`]. Rendered flat in the theme color via gpui's SVG
    /// rasterizer (the SVG's own colors are ignored — it's tinted as an alpha
    /// mask). Lucide, ISC-licensed (see `assets/icons/LICENSE`).
    ///
    /// [`glyph`]: Tool::glyph
    fn icon(self) -> Option<(&'static str, &'static [u8])> {
        const PAN: &[u8] = include_bytes!("../assets/icons/pan.svg");
        const SELECT: &[u8] = include_bytes!("../assets/icons/select.svg");
        const PEN: &[u8] = include_bytes!("../assets/icons/pen.svg");
        const RECT: &[u8] = include_bytes!("../assets/icons/rect.svg");
        const ELLIPSE: &[u8] = include_bytes!("../assets/icons/ellipse.svg");
        const DIAMOND: &[u8] = include_bytes!("../assets/icons/diamond.svg");
        const TRIANGLE: &[u8] = include_bytes!("../assets/icons/triangle.svg");
        const ROUND_RECT: &[u8] = include_bytes!("../assets/icons/round-rect.svg");
        const STAR: &[u8] = include_bytes!("../assets/icons/star.svg");
        const HEXAGON: &[u8] = include_bytes!("../assets/icons/hexagon.svg");
        const LINE: &[u8] = include_bytes!("../assets/icons/line.svg");
        const ARROW: &[u8] = include_bytes!("../assets/icons/arrow.svg");
        const TEXT: &[u8] = include_bytes!("../assets/icons/text.svg");
        const MINDMAP: &[u8] = include_bytes!("../assets/icons/mindmap.svg");
        const FLOWCHART: &[u8] = include_bytes!("../assets/icons/flowchart.svg");
        const EMBED: &[u8] = include_bytes!("../assets/icons/embed.svg");
        const IMAGE: &[u8] = include_bytes!("../assets/icons/image.svg");
        match self {
            Tool::Pan => Some(("wb-icon-pan", PAN)),
            Tool::Select => Some(("wb-icon-select", SELECT)),
            Tool::Pen => Some(("wb-icon-pen", PEN)),
            Tool::Rect => Some(("wb-icon-rect", RECT)),
            Tool::Ellipse => Some(("wb-icon-ellipse", ELLIPSE)),
            Tool::Diamond => Some(("wb-icon-diamond", DIAMOND)),
            Tool::Triangle => Some(("wb-icon-triangle", TRIANGLE)),
            Tool::RoundRect => Some(("wb-icon-round-rect", ROUND_RECT)),
            Tool::Star => Some(("wb-icon-star", STAR)),
            Tool::Hexagon => Some(("wb-icon-hexagon", HEXAGON)),
            Tool::Line => Some(("wb-icon-line", LINE)),
            Tool::Arrow => Some(("wb-icon-arrow", ARROW)),
            Tool::DashedArrow => None,
            Tool::Text => Some(("wb-icon-text", TEXT)),
            Tool::MindMap => Some(("wb-icon-mindmap", MINDMAP)),
            Tool::Flowchart => Some(("wb-icon-flowchart", FLOWCHART)),
            Tool::Embed => Some(("wb-icon-embed", EMBED)),
            Tool::Image => Some(("wb-icon-image", IMAGE)),
        }
    }
}

/// A toolbar category whose tools live in a click-to-open flyout, keeping the
/// main bar trim. The category button shows the active tool of the group (or a
/// representative when none is active).
#[derive(Clone, Copy, PartialEq, Eq)]
enum ToolGroup {
    /// Freehand pen and the closed shapes.
    Shapes,
    /// Line and arrow connectors.
    Lines,
    /// Page-cards (and, later, images).
    PagesImages,
}

impl ToolGroup {
    const ALL: [ToolGroup; 3] = [ToolGroup::Shapes, ToolGroup::Lines, ToolGroup::PagesImages];

    /// The tools shown in this group's flyout.
    fn tools(self) -> &'static [Tool] {
        match self {
            ToolGroup::Shapes => &[
                Tool::Rect,
                Tool::RoundRect,
                Tool::Ellipse,
                Tool::Diamond,
                Tool::Triangle,
                Tool::Hexagon,
                Tool::Star,
            ],
            ToolGroup::Lines => &[Tool::Pen, Tool::Line, Tool::Arrow, Tool::DashedArrow],
            ToolGroup::PagesImages => &[Tool::MindMap, Tool::Flowchart, Tool::Embed, Tool::Image],
        }
    }

    fn contains(self, t: Tool) -> bool {
        self.tools().contains(&t)
    }

    /// The icon shown on the category button when none of its tools is active.
    fn representative(self) -> Tool {
        match self {
            ToolGroup::Shapes => Tool::Rect,
            ToolGroup::Lines => Tool::Arrow,
            ToolGroup::PagesImages => Tool::Flowchart,
        }
    }

    fn label(self) -> &'static str {
        match self {
            ToolGroup::Shapes => "Shapes",
            ToolGroup::Lines => "Lines",
            ToolGroup::PagesImages => "Pages & images",
        }
    }
}

/// A flat, theme-colored toolbar icon: render the bundled SVG `bytes` (a 16×16
/// Lucide glyph) tinted to `color` via gpui's rasterizer, in a `size`-px box.
/// `key` is a stable per-icon cache id.
fn svg_icon(key: &'static str, bytes: &'static [u8], color: Hsla, sz: f32) -> impl IntoElement {
    canvas(
        |_, _, _| {},
        move |bounds, _, window, cx| {
            let _ = window.paint_svg(
                bounds,
                SharedString::from(key),
                Some(bytes),
                TransformationMatrix::default(),
                color,
                cx,
            );
        },
    )
    .w(px(sz))
    .h(px(sz))
}

/// A hairline vertical divider separating toolbar tool groups.
fn toolbar_divider(color: Hsla, vertical: bool) -> gpui::AnyElement {
    let d = div().bg(color);
    // A row's dividers are vertical bars; a column's are horizontal.
    if vertical {
        d.h(px(1.0)).w(px(16.0)).my(px(3.0))
    } else {
        d.w(px(1.0)).h(px(16.0)).mx(px(3.0))
    }
    .into_any_element()
}

/// A minimal themed tooltip view. gpui has the `.tooltip()` *hook* but no
/// tooltip *view* (those live in UI crates this crate doesn't depend on), so —
/// like `gpui-pdf` — we render our own small label.
struct Tip {
    text: SharedString,
    fg: Hsla,
    bg: Hsla,
    border: Hsla,
}

impl Render for Tip {
    fn render(&mut self, _window: &mut Window, _cx: &mut Context<Self>) -> impl IntoElement {
        // gpui anchors the tooltip at the cursor; a small transparent top
        // padding drops the visible box just clear of the hovered button.
        div().pt(px(16.0)).child(
            div()
                .px(px(6.0))
                .py(px(2.0))
                .rounded(px(4.0))
                .border_1()
                .border_color(self.border)
                .bg(self.bg)
                .text_color(self.fg)
                .text_size(px(11.0))
                .child(self.text.clone()),
        )
    }
}

/// Theme colors, read at paint time (via [`WhiteboardStyleFn`]) so the board
/// follows live theme changes per window.
#[derive(Clone, Debug)]
pub struct WhiteboardStyle {
    /// The canvas background.
    pub bg: Hsla,
    /// The background grid dots.
    pub grid: Hsla,
    /// HUD / muted on-canvas text.
    pub text: Hsla,
    /// Ink (stroke/shape color). Per-element color comes with the color picker.
    pub ink: Hsla,
    /// Toolbar / flyout panel background — small pills, so it can be quite glassy.
    pub panel: Hsla,
    /// Background for the larger color-picker panel. Wants to stay readable over
    /// a busy canvas, so it should be much more opaque than `panel`.
    pub panel_strong: Hsla,
    /// Active-tool highlight (a subtle fill behind the current tool button).
    pub accent: Hsla,
    /// Selection outline — wants to be clearly visible, so a strong color.
    pub selection: Hsla,
    /// Palette shown as quick swatches in the color picker. The host supplies
    /// these (typically its theme colors) so the picker matches the app.
    pub swatches: Vec<Hsla>,
}

/// A `() -> WhiteboardStyle` the host supplies; called each paint so the board
/// tracks theme changes without the host pushing updates.
pub type WhiteboardStyleFn = Rc<dyn Fn() -> WhiteboardStyle>;

/// Called when the board changes (an element committed/moved/deleted, the camera
/// moved), with the serialized scene JSON, so the host can persist it.
pub type ChangeFn = Rc<dyn Fn(String, &mut Window, &mut App)>;

/// Called when the page-card tool is clicked at world `(x, y)` — the host picks
/// a page and calls [`WhiteboardView::add_embed`].
pub type PlaceEmbedFn = Rc<dyn Fn(f32, f32, &mut Window, &mut App)>;

/// Called to open a page (double-clicking a card) — the host opens it in a tab.
pub type OpenPageFn = Rc<dyn Fn(i64, &mut Window, &mut App)>;

/// Called when the user saves the current selection as a template, with the
/// selected elements serialized (normalized to origin). The host names + stores
/// it, then feeds the updated list back via [`WhiteboardView::set_templates`].
pub type SaveTemplateFn = Rc<dyn Fn(String, &mut Window, &mut App)>;

/// Called to delete a stored template by its host id (right-click a card).
pub type DeleteTemplateFn = Rc<dyn Fn(i64, &mut Window, &mut App)>;

/// Called on ⌘C / ⌘X with the selection serialized (same format as
/// [`SaveTemplateFn`]); the host writes it to the system clipboard. Paste is the
/// reverse: the host reads the clipboard and calls [`WhiteboardView::paste_elements`].
pub type CopyFn = Rc<dyn Fn(String, &mut Window, &mut App)>;

/// Called by the context-menu **Paste**: the host reads the clipboard and returns
/// previously copied whiteboard elements (the JSON a [`CopyFn`] wrote — same format
/// as [`SaveTemplateFn`]), or `None` if it holds no board elements. Pass the JSON to
/// [`WhiteboardView::paste_elements`]. (Keyboard ⌘V is handled internally.)
pub type PasteFn = Rc<dyn Fn(&mut Window, &mut App) -> Option<String>>;

/// Called when the user's saved-color palette changes (a swatch added or removed),
/// with the full list (packed `0xRRGGBBAA`). The host persists it and feeds it back
/// via [`WhiteboardView::set_saved_colors`]. Without it, the palette is per-session.
pub type SavedColorsFn = Rc<dyn Fn(Vec<u32>, &mut Window, &mut App)>;

/// Called each render to fetch the decoded bitmap for an image element's `src`,
/// rotated by `rotation` radians (0 = upright). The host serves it from its image
/// cache, decoding/rotating on demand (returning `None` until ready, then
/// re-rendering the board); a steady angle hits the cache, so it only re-rotates
/// when the angle changes.
pub type ImageFn = Rc<dyn Fn(&str, f32, &mut Window, &mut App) -> Option<gpui::ImageSource>>;

/// Called when the image tool is clicked at world `(x, y)` — the host picks a
/// file and calls [`WhiteboardView::add_image_at`].
pub type PlaceImageFn = Rc<dyn Fn(f32, f32, &mut Window, &mut App)>;

/// Called when files are dropped onto the canvas at world `(x, y)` — the host
/// imports any images and places them via [`WhiteboardView::add_image_at`].
pub type DropFilesFn = Rc<dyn Fn(Vec<std::path::PathBuf>, f32, f32, &mut Window, &mut App)>;

/// Which face the Font flyout offers — upload one from disk or revert to the
/// bundled default.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum FontPick {
    /// Pick a `.ttf`/`.otf` from disk (the host shows the file dialog).
    Upload,
    /// Revert to the bundled default face.
    Default,
}

/// Called when the user picks from the Font flyout. The host loads the face and
/// calls [`WhiteboardView::set_font`] (and persists the per-board choice). Without
/// it, the Font toolbar button is hidden.
pub type PickFontFn = Rc<dyn Fn(FontPick, &mut Window, &mut App)>;

/// Called when the toolbar is moved, reset, or re-oriented, with its new
/// board-relative top-left (`None` = default top-center) and whether it's vertical.
/// The host persists both and feeds them back via [`WhiteboardView::set_toolbar_pos`]
/// / [`set_toolbar_vertical`](WhiteboardView::set_toolbar_vertical). Without it, the
/// layout is per-session.
pub type MoveToolbarFn = Rc<dyn Fn(Option<(f32, f32)>, bool, &mut Window, &mut App)>;

/// Host callback fired by an embed view when the user requests "open / maximize
/// for editing". The host owns the actual layout transition.
pub type ExpandEmbedFn = Rc<dyn Fn(&mut Window, &mut App)>;

/// A reusable group of elements the user can stamp onto a board. Element
/// positions are normalized so the group's bounding box starts at the origin;
/// applying re-bases them to the viewport. The host owns persistence and the
/// `id`; the crate renders the preview + instantiates on click.
#[derive(Clone, Debug)]
pub struct Template {
    pub id: i64,
    pub name: String,
    pub elements: Vec<Element>,
}

impl Template {
    /// Build from the host's stored row. `elements_json` is a serialized
    /// `Vec<Element>` (the JSON a [`SaveTemplateFn`] handed the host); malformed
    /// JSON yields an empty (still-listable) template.
    pub fn from_json(id: i64, name: impl Into<String>, elements_json: &str) -> Self {
        Template {
            id,
            name: name.into(),
            elements: serde_json::from_str(elements_json).unwrap_or_default(),
        }
    }
}

/// An element being created by the current left-drag.
struct Pending {
    anchor: [f32; 2],
    kind: ElementKind,
}

/// A connector point shown on a hovered shape. `index` is 0/1/2/3 = top/right/bottom/left.
#[derive(Clone, Copy, PartialEq)]
struct ConnectPoint {
    id: u64,
    index: usize,
    pos: [f32; 2],
}

/// A line being dragged from a shape connector while the Select tool is active.
#[derive(Clone, Copy)]
struct ConnectDrag {
    from: ConnectPoint,
}

#[derive(Clone, Copy, Debug, Default, PartialEq)]
struct AlignmentGuides {
    vertical: Option<f32>,
    horizontal: Option<f32>,
}

/// An in-progress resize of a single selected element by one of its handles.
struct Resizing {
    id: u64,
    /// Which handle is being dragged (corner = free/proportional, edge = one axis).
    handle: ResizeHandle,
    /// The fixed (opposite) corner/edge the scale is about, world space.
    anchor: [f32; 2],
    /// The dragged handle's original position, world space.
    from: [f32; 2],
    /// World offset from the cursor to the dragged handle at grab time, kept so
    /// it tracks the cursor 1:1 (no jump on grab).
    grab: [f32; 2],
    /// The element's geometry at the start of the resize.
    orig: ElementKind,
}

/// Which handle drives a resize ([`Resizing`] or [`GroupResizing`]): a corner
/// (both axes together) or an edge midpoint (one axis only).
#[derive(Clone, Copy)]
enum ResizeHandle {
    /// A corner grip — uniform scale about the opposite corner.
    Corner,
    /// A left/right edge grip — scales x only, about the opposite edge.
    EdgeX,
    /// A top/bottom edge grip — scales y only, about the opposite edge.
    EdgeY,
}

/// An in-progress resize of a multi-selection by a handle of its (axis-aligned)
/// group bounds. A corner scales uniformly about the opposite corner (the group
/// grows as one); an edge midpoint stretches a single axis about the opposite
/// edge. Each member is scaled from its geometry at grab so it never compounds.
struct GroupResizing {
    /// Which handle is being dragged (corner = both axes, edge = one).
    handle: ResizeHandle,
    /// The fixed point the scale is about, world space (opposite corner/edge).
    anchor: [f32; 2],
    /// The dragged handle's original position, world space.
    from: [f32; 2],
    /// Cursor → dragged-handle offset at grab (1:1 tracking, no jump).
    grab: [f32; 2],
    /// Each selected element's id + geometry at the start of the resize.
    orig: Vec<(u64, ElementKind)>,
}

/// An in-progress drag of one endpoint of a selected line/arrow.
#[derive(Clone, Copy)]
struct EndpointDrag {
    id: u64,
    /// Which endpoint: 0 = (x1,y1), 1 = (x2,y2).
    which: usize,
}

/// An in-progress rotation of the selection (one element or a group) about a
/// fixed center. Drives every selected element, so it needs no element id.
#[derive(Clone, Copy)]
struct Rotating {
    /// Pivot (world), captured at grab so it can't drift between frames.
    center: [f32; 2],
    /// Pointer angle about `center` at grab (radians).
    start_pointer: f32,
    /// Rotation already applied since grab (radians).
    applied: f32,
    /// Orientation to snap to horizontal/vertical: a single element's angle (box
    /// / text) or line direction; `Some(0)` for a group (snaps quarter-turns);
    /// `None` when there's nothing meaningful to snap (a lone freehand stroke).
    base: Option<f32>,
}

/// What a press on a selection handle begins.
enum HandleGrab {
    Corner(Resizing),
    Endpoint(EndpointDrag),
    Rotate,
    GroupCorner(GroupResizing),
}

/// Which property the picker is editing.
#[derive(Clone, Copy, PartialEq)]
enum PickerTarget {
    /// Outline / ink color (`None` = theme ink).
    Stroke,
    /// Shape fill (`None` = unfilled).
    Fill,
    /// Shape label color (`None` follows the stroke / theme ink).
    Text,
}

/// Open color-picker state: the HSVA the controls currently reflect, and which
/// property (stroke or fill) it edits. Recolors the selection live.
#[derive(Clone, Copy)]
struct Picker {
    target: PickerTarget,
    h: f32,
    s: f32,
    v: f32,
    a: f32,
}

/// Which picker control an in-progress drag is manipulating.
#[derive(Clone, Copy, PartialEq)]
enum PickerDrag {
    /// The saturation/brightness square.
    Sv,
    /// The hue strip.
    Hue,
    /// The alpha (opacity) strip.
    Alpha,
    /// The thickness flyout's custom-width slider.
    Width,
}

/// The whiteboard view entity. The host holds it in an `Entity<WhiteboardView>`
/// (keyed by board id) and renders it into a tab.
pub struct WhiteboardView {
    scene: Scene,
    style: WhiteboardStyleFn,
    read_only: bool,
    on_change: Option<ChangeFn>,
    on_place_embed: Option<PlaceEmbedFn>,
    on_open: Option<OpenPageFn>,
    on_save_template: Option<SaveTemplateFn>,
    on_delete_template: Option<DeleteTemplateFn>,
    on_image: Option<ImageFn>,
    on_place_image: Option<PlaceImageFn>,
    on_drop_files: Option<DropFilesFn>,
    on_copy: Option<CopyFn>,
    on_paste: Option<PasteFn>,
    on_save_colors: Option<SavedColorsFn>,
    on_pick_font: Option<PickFontFn>,
    on_move_toolbar: Option<MoveToolbarFn>,
    /// The user's saved colors (packed `0xRRGGBBAA`), shown in the picker's palette.
    /// Supplied + persisted by the host (see [`SavedColorsFn`]).
    saved_colors: Vec<u32>,
    /// Stored templates, supplied by the host; shown as cards in the Pages &
    /// Images flyout.
    templates: Vec<Template>,
    /// Screen position of an open right-click context menu (a selection's
    /// "save as template"), or `None`.
    context_menu: Option<Point<Pixels>>,
    /// Whether the context menu's "Text ▸" formatting submenu is expanded.
    ctx_text_sub: bool,
    /// Whether the toolbar's text-formatting fly-out is open.
    format_flyout: bool,
    /// The face used to render text as vector outlines. Defaults to the bundled
    /// JetBrains Mono; the host can swap in a custom/user-uploaded font.
    font: Font,
    /// Camera-independent glyph outlines keyed by element id and text/style
    /// signature. Panning and zooming can reuse these directly.
    text_layout_cache: HashMap<u64, CachedTextLayout>,
    label_layout_cache: HashMap<u64, CachedLabelLayout>,
    tool: Tool,
    /// Keyboard focus — grabbed while editing a text element.
    focus: FocusHandle,
    /// The text element currently being edited (Text tool / double-click).
    editing: Option<u64>,
    /// Caret position (byte offset into the editing text's content).
    caret: usize,
    /// The fixed end of the text selection (byte offset); `== caret` means no
    /// selection, just the caret.
    sel_anchor: usize,
    /// A click-drag text selection is in progress (extends the selection on move).
    text_selecting: bool,
    /// Active IME marked/composition byte range in the editing text.
    marked_range: Option<Range<usize>>,
    /// Canvas bounds in window coords, captured each paint so input handlers can
    /// map window-relative event positions into the board.
    bounds: Rc<Cell<Bounds<Pixels>>>,
    /// The element being created by the in-progress left-drag.
    pending: Option<Pending>,
    /// The currently selected elements (Select tool).
    selected: Vec<u64>,
    /// In-progress marquee box (start, current) in world coords.
    marquee: Option<([f32; 2], [f32; 2])>,
    /// Connector point currently under/near the mouse, painted on hovered shapes.
    hovered_connector: Option<ConnectPoint>,
    /// Line creation started by pressing a connector point.
    connecting: Option<ConnectDrag>,
    /// The world point where an in-progress move-drag was grabbed (a *fixed*
    /// anchor — the move uses the total cursor delta from here, so grid-snapping
    /// stays cursor-synced and doesn't lose sub-grid motion).
    drag_from: Option<[f32; 2]>,
    /// The primary (first-selected) element's top-left at move-grab, the
    /// reference the move drives toward (`move_origin + total_delta`).
    move_origin: [f32; 2],
    /// Whether the current move-drag has actually moved (undo is pushed once).
    moved: bool,
    /// Active world-space smart-alignment guides while moving a selection.
    alignment_guides: AlignmentGuides,
    /// In-progress corner-resize of the selected box/stroke.
    resizing: Option<Resizing>,
    /// In-progress proportional resize of a multi-selection.
    group_resizing: Option<GroupResizing>,
    /// In-progress endpoint-drag of the selected line/arrow.
    endpoint: Option<EndpointDrag>,
    /// In-progress rotation of the selected element.
    rotating: Option<Rotating>,
    /// Current ink color for new elements (`None` follows the theme ink).
    active_stroke: Option<u32>,
    /// Current fill for new shapes (`None` = unfilled).
    active_fill: Option<u32>,
    /// Current label color for new shapes (`None` follows the stroke / theme ink).
    active_text: Option<u32>,
    /// Formatting to apply to the next typed text when there's no selection (set
    /// by a ⌘B/etc. toggle with a collapsed caret); cleared on caret move.
    pending_style: Option<RunStyle>,
    /// Current stroke thickness for new elements, in screen px (stored world-space
    /// as `active_width / zoom`, like [`NIB`]). Defaults to `NIB`.
    active_width: f32,
    /// Open color picker, if any.
    picker: Option<Picker>,
    /// The tool category whose flyout is open, if any.
    open_group: Option<ToolGroup>,
    /// Whether the thickness-preset flyout is open.
    width_open: bool,
    /// Whether the font flyout (upload / default) is open.
    font_open: bool,
    /// Whether the templates gallery modal is open.
    templates_open: bool,
    /// In-progress drag inside the open picker.
    picker_drag: Option<PickerDrag>,
    /// Screen bounds of the picker panel and its draggable regions, captured each
    /// paint so press/drag handlers can hit-test them.
    picker_bounds: Rc<Cell<Bounds<Pixels>>>,
    sv_bounds: Rc<Cell<Bounds<Pixels>>>,
    hue_bounds: Rc<Cell<Bounds<Pixels>>>,
    alpha_bounds: Rc<Cell<Bounds<Pixels>>>,
    /// Screen bounds of the thickness flyout panel and its width slider (captured
    /// each paint), so a press can route to the slider or dismiss the flyout.
    width_panel_bounds: Rc<Cell<Bounds<Pixels>>>,
    width_bounds: Rc<Cell<Bounds<Pixels>>>,
    /// Screen bounds of the toolbar pill and its drag grip (captured each paint),
    /// so a press routes to a drag (grip) or is consumed (pill) — the pill isn't
    /// occluded, like the picker.
    toolbar_bounds: Rc<Cell<Bounds<Pixels>>>,
    toolbar_grip_bounds: Rc<Cell<Bounds<Pixels>>>,
    /// The toolbar's board-relative top-left when the user has dragged it; `None`
    /// keeps the default top-center. Persisted by the host.
    toolbar_pos: Option<(f32, f32)>,
    /// Whether the toolbar is laid out vertically (a column) rather than as a row.
    /// Toggled with `R` while dragging it; persisted by the host.
    toolbar_vertical: bool,
    /// In-progress toolbar drag: the (pill origin − cursor) offset, board-relative.
    toolbar_drag: Option<(f32, f32)>,
    /// Undo / redo stacks of scene snapshots.
    history: Vec<Scene>,
    redo: Vec<Scene>,
    /// True while a middle-drag pan is in progress.
    panning: bool,
    /// Last pointer position (window coords) during a pan.
    last: Point<Pixels>,
    /// Next element id.
    next_id: u64,
    /// Unsaved changes since the last flush (flushed on mouse-up).
    dirty: bool,
}

/// A read-only whiteboard embedding surface for use inside rich-text editors and
/// other host containers. It overlays a small "edit / maximize" affordance and
/// delegates the actual expansion behavior back to the host.
pub struct BoardEmbedView {
    board: Entity<WhiteboardView>,
    style: WhiteboardStyleFn,
    on_expand: Option<ExpandEmbedFn>,
}

/// A lightweight, chrome-free thumbnail renderer for embedding a local board
/// snapshot in documents, lists, and rich-text blocks.
pub struct BoardThumbnailView {
    snapshot: LocalThumbnailSnapshot,
    style: WhiteboardStyleFn,
    font: Font,
}

impl WhiteboardView {
    /// Build a view over `scene`. Call inside `cx.new(|cx| WhiteboardView::new(..))`.
    pub fn new(scene: Scene, style: WhiteboardStyleFn, cx: &mut Context<Self>) -> Self {
        let next_id = scene
            .elements
            .iter()
            .map(|e| e.id)
            .max()
            .map_or(0, |m| m + 1);
        Self {
            scene,
            style,
            read_only: false,
            on_change: None,
            on_place_embed: None,
            on_open: None,
            on_save_template: None,
            on_delete_template: None,
            on_image: None,
            on_place_image: None,
            on_drop_files: None,
            on_copy: None,
            on_paste: None,
            on_save_colors: None,
            on_pick_font: None,
            on_move_toolbar: None,
            saved_colors: Vec::new(),
            templates: Vec::new(),
            context_menu: None,
            ctx_text_sub: false,
            format_flyout: false,
            font: Font::default(),
            text_layout_cache: HashMap::new(),
            label_layout_cache: HashMap::new(),
            tool: Tool::Pan,
            focus: cx.focus_handle(),
            editing: None,
            caret: 0,
            sel_anchor: 0,
            text_selecting: false,
            marked_range: None,
            bounds: Rc::new(Cell::new(Bounds::default())),
            pending: None,
            selected: Vec::new(),
            marquee: None,
            hovered_connector: None,
            connecting: None,
            drag_from: None,
            move_origin: [0.0, 0.0],
            moved: false,
            alignment_guides: AlignmentGuides::default(),
            resizing: None,
            group_resizing: None,
            endpoint: None,
            rotating: None,
            active_stroke: None,
            active_fill: None,
            active_text: None,
            pending_style: None,
            active_width: NIB,
            picker: None,
            open_group: None,
            width_open: false,
            font_open: false,
            templates_open: false,
            picker_drag: None,
            picker_bounds: Rc::new(Cell::new(Bounds::default())),
            sv_bounds: Rc::new(Cell::new(Bounds::default())),
            hue_bounds: Rc::new(Cell::new(Bounds::default())),
            alpha_bounds: Rc::new(Cell::new(Bounds::default())),
            width_panel_bounds: Rc::new(Cell::new(Bounds::default())),
            width_bounds: Rc::new(Cell::new(Bounds::default())),
            toolbar_bounds: Rc::new(Cell::new(Bounds::default())),
            toolbar_grip_bounds: Rc::new(Cell::new(Bounds::default())),
            toolbar_pos: None,
            toolbar_vertical: false,
            toolbar_drag: None,
            history: Vec::new(),
            redo: Vec::new(),
            panning: false,
            last: Point::default(),
            next_id,
            dirty: false,
        }
    }

    /// Build a read-only board view. Useful when embedding inside other editors
    /// that should only preview the board and allow viewport movement.
    pub fn new_read_only(scene: Scene, style: WhiteboardStyleFn, cx: &mut Context<Self>) -> Self {
        let mut this = Self::new(scene, style, cx);
        this.read_only = true;
        this.tool = Tool::Pan;
        this
    }

    /// Install the persistence hook (called with the serialized scene on change).
    pub fn set_on_change(&mut self, f: ChangeFn) {
        self.on_change = Some(f);
    }

    /// Install the page-card placement hook (page-card tool click).
    pub fn set_on_place_embed(&mut self, f: PlaceEmbedFn) {
        self.on_place_embed = Some(f);
    }

    /// Install the open-page hook (double-click a card).
    pub fn set_on_open(&mut self, f: OpenPageFn) {
        self.on_open = Some(f);
    }

    /// Install the save-template hook (right-click selection → save).
    pub fn set_on_save_template(&mut self, f: SaveTemplateFn) {
        self.on_save_template = Some(f);
    }

    /// Install the delete-template hook (right-click a template card → delete).
    pub fn set_on_delete_template(&mut self, f: DeleteTemplateFn) {
        self.on_delete_template = Some(f);
    }

    /// Install the image-fetch hook (decoded bitmap for an element's `src`).
    pub fn set_on_image(&mut self, f: ImageFn) {
        self.on_image = Some(f);
    }

    /// Install the place-image hook (image tool click → host file picker).
    pub fn set_on_place_image(&mut self, f: PlaceImageFn) {
        self.on_place_image = Some(f);
    }

    /// Install the file-drop hook (files dropped on the canvas).
    pub fn set_on_drop_files(&mut self, f: DropFilesFn) {
        self.on_drop_files = Some(f);
    }

    /// Install the copy hook (⌘C / ⌘X → write the selection to the clipboard).
    pub fn set_on_copy(&mut self, f: CopyFn) {
        self.on_copy = Some(f);
    }

    /// Install the paste hook (context-menu Paste → read board elements from the
    /// clipboard). Without it, the Paste menu item is hidden.
    pub fn set_on_paste(&mut self, f: PasteFn) {
        self.on_paste = Some(f);
    }

    /// Install the saved-colors hook (the palette changed → host persists it).
    pub fn set_on_save_colors(&mut self, f: SavedColorsFn) {
        self.on_save_colors = Some(f);
    }

    /// Install the font-picker hook (the Font toolbar button). Without it, the
    /// Font button is hidden. The host shows the file dialog, builds the face, and
    /// calls [`set_font`](Self::set_font).
    pub fn set_on_pick_font(&mut self, f: PickFontFn) {
        self.on_pick_font = Some(f);
    }

    /// Install the toolbar-moved hook (the host persists the new position).
    pub fn set_on_move_toolbar(&mut self, f: MoveToolbarFn) {
        self.on_move_toolbar = Some(f);
    }

    /// Toggle read-only mode. In this mode the board behaves like a fixed move
    /// tool: left-drag pans the canvas and edit interactions are ignored.
    pub fn set_read_only(&mut self, read_only: bool, cx: &mut Context<Self>) {
        self.read_only = read_only;
        if read_only {
            self.tool = Tool::Pan;
            self.selected.clear();
            self.editing = None;
            self.pending = None;
            self.connecting = None;
            self.hovered_connector = None;
            self.context_menu = None;
            self.open_group = None;
            self.font_open = false;
            self.width_open = false;
            self.templates_open = false;
            self.picker = None;
            self.format_flyout = false;
            self.text_selecting = false;
            self.marked_range = None;
        }
        cx.notify();
    }

    /// Whether the board is currently in read-only (forced pan) mode.
    pub fn read_only(&self) -> bool {
        self.read_only
    }

    /// Set the toolbar's board-relative top-left (`None` = default top-center). The
    /// host pushes the persisted position on open and after a change.
    pub fn set_toolbar_pos(&mut self, pos: Option<(f32, f32)>, cx: &mut Context<Self>) {
        self.toolbar_pos = pos;
        cx.notify();
    }

    /// Set the toolbar orientation (vertical = a column). The host pushes the
    /// persisted value on open and after a change.
    pub fn set_toolbar_vertical(&mut self, vertical: bool, cx: &mut Context<Self>) {
        self.toolbar_vertical = vertical;
        cx.notify();
    }

    /// Flip the toolbar orientation (row ↔ column) and persist. Bound to `R` while
    /// the bar is being dragged.
    fn toggle_toolbar_orientation(&mut self, window: &mut Window, cx: &mut Context<Self>) {
        self.toolbar_vertical = !self.toolbar_vertical;
        if let Some(f) = self.on_move_toolbar.clone() {
            f(self.toolbar_pos, self.toolbar_vertical, window, cx);
        }
        cx.notify();
    }

    /// Clamp a board-relative toolbar top-left so the pill stays fully on-board.
    fn clamp_toolbar(&self, x: f32, y: f32) -> (f32, f32) {
        let board = self.bounds.get().size;
        let pill = self.toolbar_bounds.get().size;
        let maxx = (f32::from(board.width) - f32::from(pill.width)).max(0.0);
        let maxy = (f32::from(board.height) - f32::from(pill.height)).max(0.0);
        (x.clamp(0.0, maxx), y.clamp(0.0, maxy))
    }

    /// Start dragging the toolbar from a grip press (window coords). A double-click
    /// resets it to the default top-center.
    fn start_toolbar_drag(
        &mut self,
        p: Point<Pixels>,
        double: bool,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        if double {
            self.toolbar_drag = None;
            self.toolbar_pos = None;
            if let Some(f) = self.on_move_toolbar.clone() {
                f(None, self.toolbar_vertical, window, cx);
            }
            cx.notify();
            return;
        }
        // Close any popover so it doesn't trail the bar while it's dragged.
        self.picker = None;
        self.open_group = None;
        self.width_open = false;
        self.font_open = false;
        self.templates_open = false;
        self.context_menu = None;
        // Take focus so `R` (flip orientation) reaches the key handler mid-drag.
        self.focus.focus(window, cx);
        let pill = self.toolbar_bounds.get().origin;
        self.toolbar_drag = Some((
            f32::from(pill.x) - f32::from(p.x),
            f32::from(pill.y) - f32::from(p.y),
        ));
        cx.notify();
    }

    /// Update the toolbar position while dragging (window-coords cursor).
    fn drag_toolbar(&mut self, p: Point<Pixels>, cx: &mut Context<Self>) {
        let Some((ox, oy)) = self.toolbar_drag else {
            return;
        };
        let board = self.bounds.get().origin;
        let x = f32::from(p.x) + ox - f32::from(board.x);
        let y = f32::from(p.y) + oy - f32::from(board.y);
        self.toolbar_pos = Some(self.clamp_toolbar(x, y));
        cx.notify();
    }

    /// Finish a toolbar drag and persist the new position.
    fn commit_toolbar_drag(&mut self, window: &mut Window, cx: &mut Context<Self>) {
        if self.toolbar_drag.take().is_none() {
            return;
        }
        if let Some(f) = self.on_move_toolbar.clone() {
            f(self.toolbar_pos, self.toolbar_vertical, window, cx);
        }
    }

    /// Replace the user's saved-color palette (the host pushes the persisted list
    /// on open and after a change).
    pub fn set_saved_colors(&mut self, colors: Vec<u32>, cx: &mut Context<Self>) {
        self.saved_colors = colors;
        cx.notify();
    }

    /// Save the picker's current color to the palette (the `+` in the picker),
    /// then notify the host to persist. Ignores duplicates.
    fn save_current_color(&mut self, window: &mut Window, cx: &mut Context<Self>) {
        if let Some(c) = self.picker_u32()
            && !self.saved_colors.contains(&c)
        {
            self.saved_colors.push(c);
            if let Some(f) = self.on_save_colors.clone() {
                f(self.saved_colors.clone(), window, cx);
            }
        }
        cx.notify();
    }

    /// Remove a saved color from the palette (right-click a swatch), then persist.
    fn remove_saved_color(&mut self, c: u32, window: &mut Window, cx: &mut Context<Self>) {
        self.saved_colors.retain(|&x| x != c);
        if let Some(f) = self.on_save_colors.clone() {
            f(self.saved_colors.clone(), window, cx);
        }
        cx.notify();
    }

    /// Replace the stored templates shown in the Pages & Images flyout. The host
    /// calls this on open and after any save/delete.
    pub fn set_templates(&mut self, templates: Vec<Template>, cx: &mut Context<Self>) {
        self.templates = templates;
        cx.notify();
    }

    /// Swap the font used to render text (e.g. a user-uploaded face). Build one
    /// with [`Font::from_bytes`].
    pub fn set_font(&mut self, font: Font, cx: &mut Context<Self>) {
        self.font = font;
        self.text_layout_cache.clear();
        self.label_layout_cache.clear();
        cx.notify();
    }

    /// Build a `.tooltip(..)` closure for a toolbar control — a small themed
    /// [`Tip`], reading colors through the style closure at show time.
    fn tip(
        &self,
        text: impl Into<SharedString>,
    ) -> impl Fn(&mut Window, &mut App) -> AnyView + 'static {
        let style_fn = self.style.clone();
        let text = text.into();
        move |_window, cx| {
            let s = style_fn();
            let text = text.clone();
            cx.new(move |_| Tip {
                text,
                fg: s.ink,
                bg: s.panel,
                border: s.grid,
            })
            .into()
        }
    }

    /// Insert a page-card at world `(x, y)` and select it. Called by the host
    /// after the user picks a page (in response to [`PlaceEmbedFn`]). Does *not*
    /// fire `on_change` — the host calls this mid-update, so a re-entrant save
    /// would panic; the host persists explicitly via [`scene`](Self::scene).
    pub fn add_embed(
        &mut self,
        page_id: i64,
        title: impl Into<String>,
        x: f32,
        y: f32,
        cx: &mut Context<Self>,
    ) {
        self.push_undo();
        let id = self.next_id;
        self.next_id += 1;
        let zoom = self.scene.camera.zoom.max(MIN_ZOOM);
        self.scene.elements.push(Element {
            id,
            kind: ElementKind::Embed(EmbedGeom {
                page_id,
                title: title.into(),
                x,
                y,
                w: EMBED_W / zoom,
                h: EMBED_H / zoom,
            }),
            stroke: None,
            fill: None,
            label: None,
            label_color: None,
            styles: Vec::new(),
            mindmap: None,
        });
        self.selected = vec![id];
        self.tool = Tool::Select;
        cx.notify();
    }

    /// Add an image element referencing `src`, centered at world `(cx_world,
    /// cy_world)` and sized from its pixel dimensions (`px_w`/`px_h`) so the longest
    /// edge gets a sensible default on-screen size (aspect preserved). Like
    /// [`add_embed`], the host persists afterward (this is called mid-host-update).
    ///
    /// [`add_embed`]: Self::add_embed
    pub fn add_image_at(
        &mut self,
        src: impl Into<String>,
        px_w: f32,
        px_h: f32,
        cx_world: f32,
        cy_world: f32,
        cx: &mut Context<Self>,
    ) {
        self.push_undo();
        let id = self.next_id;
        self.next_id += 1;
        let zoom = self.scene.camera.zoom.max(MIN_ZOOM);
        let longest = px_w.max(px_h).max(1.0);
        let scale = IMAGE_PLACE_PX / longest / zoom;
        let (w, h) = (px_w * scale, px_h * scale);
        self.scene.elements.push(Element {
            id,
            kind: ElementKind::Image(ImageGeom {
                src: src.into(),
                x: cx_world - w / 2.0,
                y: cy_world - h / 2.0,
                w,
                h,
                rotation: 0.0,
            }),
            stroke: None,
            fill: None,
            label: None,
            label_color: None,
            styles: Vec::new(),
            mindmap: None,
        });
        self.selected = vec![id];
        self.tool = Tool::Select;
        cx.notify();
    }

    /// Insert a native mind-map seed built from whiteboard round-rect nodes and
    /// anchored arrows. This stays entirely inside the whiteboard scene model, so
    /// selection, movement, text editing, IME, and connector-follow all reuse the
    /// existing whiteboard machinery.
    pub fn add_mindmap_seed(&mut self, center_x: f32, center_y: f32, cx: &mut Context<Self>) {
        self.push_undo();
        let zoom = self.scene.camera.zoom.max(MIN_ZOOM);
        let root_w = MINDMAP_ROOT_W / zoom;
        let root_h = MINDMAP_ROOT_H / zoom;
        let node_w = MINDMAP_NODE_W / zoom;
        let node_h = MINDMAP_NODE_H / zoom;
        let gap_x = MINDMAP_BRANCH_GAP_X / zoom;
        let gap_y = MINDMAP_BRANCH_GAP_Y / zoom;
        let stroke = Some(0x2563ebff);
        let root_fill = Some(0xdbeafeff);
        let node_fill = Some(0xffffffff);

        let add_node = |scene: &mut Scene,
                        next_id: &mut u64,
                        x: f32,
                        y: f32,
                        w: f32,
                        h: f32,
                        label: &str,
                        fill: Option<u32>,
                        mindmap: Option<MindMapNodeMeta>| {
            let id = *next_id;
            *next_id += 1;
            scene.elements.push(Element {
                id,
                kind: ElementKind::RoundRect(BoxGeom {
                    x,
                    y,
                    w,
                    h,
                    width: NIB / zoom,
                    rotation: 0.0,
                }),
                stroke,
                fill,
                label: Some(label.to_string()),
                label_color: Some(0x0f172aff),
                styles: Vec::new(),
                mindmap,
            });
            id
        };

        let root_id = add_node(
            &mut self.scene,
            &mut self.next_id,
            center_x - root_w / 2.0,
            center_y - root_h / 2.0,
            root_w,
            root_h,
            "Central topic",
            root_fill,
            Some(MindMapNodeMeta {
                parent: None,
                side: MindMapSide::Right,
                order: 0,
                root_direction: MindMapRootDirection::Both,
                connector_style: MindMapConnectorStyle::Bezier,
            }),
        );
        let right_top_id = add_node(
            &mut self.scene,
            &mut self.next_id,
            center_x + root_w / 2.0 + gap_x,
            center_y - gap_y - node_h / 2.0,
            node_w,
            node_h,
            "Branch 1",
            node_fill,
            Some(MindMapNodeMeta {
                parent: Some(root_id),
                side: MindMapSide::Right,
                order: 0,
                root_direction: MindMapRootDirection::Both,
                connector_style: MindMapConnectorStyle::Bezier,
            }),
        );
        let right_bottom_id = add_node(
            &mut self.scene,
            &mut self.next_id,
            center_x + root_w / 2.0 + gap_x,
            center_y + gap_y - node_h / 2.0,
            node_w,
            node_h,
            "Branch 2",
            node_fill,
            Some(MindMapNodeMeta {
                parent: Some(root_id),
                side: MindMapSide::Right,
                order: 1,
                root_direction: MindMapRootDirection::Both,
                connector_style: MindMapConnectorStyle::Bezier,
            }),
        );
        let left_top_id = add_node(
            &mut self.scene,
            &mut self.next_id,
            center_x - root_w / 2.0 - gap_x - node_w,
            center_y - gap_y - node_h / 2.0,
            node_w,
            node_h,
            "Branch 3",
            node_fill,
            Some(MindMapNodeMeta {
                parent: Some(root_id),
                side: MindMapSide::Left,
                order: 0,
                root_direction: MindMapRootDirection::Both,
                connector_style: MindMapConnectorStyle::Bezier,
            }),
        );
        let left_bottom_id = add_node(
            &mut self.scene,
            &mut self.next_id,
            center_x - root_w / 2.0 - gap_x - node_w,
            center_y + gap_y - node_h / 2.0,
            node_w,
            node_h,
            "Branch 4",
            node_fill,
            Some(MindMapNodeMeta {
                parent: Some(root_id),
                side: MindMapSide::Left,
                order: 1,
                root_direction: MindMapRootDirection::Both,
                connector_style: MindMapConnectorStyle::Bezier,
            }),
        );

        let add_branch = |scene: &mut Scene,
                          next_id: &mut u64,
                          from_id: u64,
                          from_connector: usize,
                          to_id: u64,
                          to_connector: usize| {
            let start_anchor = SegmentAnchor {
                element_id: from_id,
                connector: from_connector,
            };
            let end_anchor = SegmentAnchor {
                element_id: to_id,
                connector: to_connector,
            };
            let [x1, y1] =
                connector_world_pos_in(&scene.elements, start_anchor).unwrap_or([0.0, 0.0]);
            let [x2, y2] =
                connector_world_pos_in(&scene.elements, end_anchor).unwrap_or([0.0, 0.0]);
            let id = *next_id;
            *next_id += 1;
            scene.elements.push(Element {
                id,
                kind: ElementKind::Arrow(SegGeom {
                    x1,
                    y1,
                    x2,
                    y2,
                    width: NIB / zoom,
                    style: SegmentStyle::Solid,
                    start_anchor: Some(start_anchor),
                    end_anchor: Some(end_anchor),
                }),
                stroke,
                fill: None,
                label: None,
                label_color: None,
                styles: Vec::new(),
                mindmap: None,
            });
        };

        add_branch(
            &mut self.scene,
            &mut self.next_id,
            root_id,
            1,
            right_top_id,
            3,
        );
        add_branch(
            &mut self.scene,
            &mut self.next_id,
            root_id,
            1,
            right_bottom_id,
            3,
        );
        add_branch(
            &mut self.scene,
            &mut self.next_id,
            root_id,
            3,
            left_top_id,
            1,
        );
        add_branch(
            &mut self.scene,
            &mut self.next_id,
            root_id,
            3,
            left_bottom_id,
            1,
        );

        self.selected = vec![root_id];
        self.tool = Tool::Select;
        cx.notify();
    }

    pub fn add_mindmap_seed_at_viewport_center(&mut self, cx: &mut Context<Self>) {
        let center = self.viewport_center();
        self.add_mindmap_seed(center[0], center[1], cx);
    }

    /// Insert a native flowchart seed made from regular whiteboard nodes and
    /// anchored arrows. This is the first structured flowchart primitive inside
    /// the board and can later grow auto-layout / auto-branch behavior.
    pub fn add_flowchart_seed(&mut self, center_x: f32, center_y: f32, cx: &mut Context<Self>) {
        self.push_undo();
        let zoom = self.scene.camera.zoom.max(MIN_ZOOM);
        let node_w = FLOWCHART_NODE_W / zoom;
        let node_h = FLOWCHART_NODE_H / zoom;
        let gap_y = FLOWCHART_GAP_Y / zoom;
        let branch_gap_x = FLOWCHART_BRANCH_GAP_X / zoom;
        let stroke = Some(0x0f172aff);
        let fill = Some(0xffffffff);

        let add_box = |scene: &mut Scene, next_id: &mut u64, kind: ElementKind, label: &str| {
            let id = *next_id;
            *next_id += 1;
            scene.elements.push(Element {
                id,
                kind,
                stroke,
                fill,
                label: Some(label.to_string()),
                label_color: Some(0x0f172aff),
                styles: Vec::new(),
                mindmap: None,
            });
            id
        };
        let add_arrow = |scene: &mut Scene,
                         next_id: &mut u64,
                         from_id: u64,
                         from_connector: usize,
                         to_id: u64,
                         to_connector: usize| {
            let start_anchor = SegmentAnchor {
                element_id: from_id,
                connector: from_connector,
            };
            let end_anchor = SegmentAnchor {
                element_id: to_id,
                connector: to_connector,
            };
            let [x1, y1] =
                connector_world_pos_in(&scene.elements, start_anchor).unwrap_or([0.0, 0.0]);
            let [x2, y2] =
                connector_world_pos_in(&scene.elements, end_anchor).unwrap_or([0.0, 0.0]);
            let id = *next_id;
            *next_id += 1;
            scene.elements.push(Element {
                id,
                kind: ElementKind::Arrow(SegGeom {
                    x1,
                    y1,
                    x2,
                    y2,
                    width: NIB / zoom,
                    style: SegmentStyle::Solid,
                    start_anchor: Some(start_anchor),
                    end_anchor: Some(end_anchor),
                }),
                stroke,
                fill: None,
                label: None,
                label_color: None,
                styles: Vec::new(),
                mindmap: None,
            });
        };

        let start_id = add_box(
            &mut self.scene,
            &mut self.next_id,
            ElementKind::Ellipse(BoxGeom {
                x: center_x - node_w / 2.0,
                y: center_y - gap_y - node_h * 1.5,
                w: node_w,
                h: node_h,
                width: NIB / zoom,
                rotation: 0.0,
            }),
            "Start",
        );
        let process_id = add_box(
            &mut self.scene,
            &mut self.next_id,
            ElementKind::RoundRect(BoxGeom {
                x: center_x - node_w / 2.0,
                y: center_y - node_h / 2.0,
                w: node_w,
                h: node_h,
                width: NIB / zoom,
                rotation: 0.0,
            }),
            "Process",
        );
        let decision_id = add_box(
            &mut self.scene,
            &mut self.next_id,
            ElementKind::Diamond(BoxGeom {
                x: center_x - node_w / 2.0,
                y: center_y + gap_y - node_h / 2.0,
                w: node_w,
                h: node_h,
                width: NIB / zoom,
                rotation: 0.0,
            }),
            "Decision",
        );
        let branch_yes_id = add_box(
            &mut self.scene,
            &mut self.next_id,
            ElementKind::RoundRect(BoxGeom {
                x: center_x + branch_gap_x - node_w / 2.0,
                y: center_y + gap_y - node_h / 2.0,
                w: node_w,
                h: node_h,
                width: NIB / zoom,
                rotation: 0.0,
            }),
            "Yes",
        );
        let branch_no_id = add_box(
            &mut self.scene,
            &mut self.next_id,
            ElementKind::RoundRect(BoxGeom {
                x: center_x - branch_gap_x - node_w / 2.0,
                y: center_y + gap_y - node_h / 2.0,
                w: node_w,
                h: node_h,
                width: NIB / zoom,
                rotation: 0.0,
            }),
            "No",
        );
        let end_id = add_box(
            &mut self.scene,
            &mut self.next_id,
            ElementKind::Ellipse(BoxGeom {
                x: center_x - node_w / 2.0,
                y: center_y + gap_y * 2.0 + node_h * 0.5,
                w: node_w,
                h: node_h,
                width: NIB / zoom,
                rotation: 0.0,
            }),
            "End",
        );

        add_arrow(
            &mut self.scene,
            &mut self.next_id,
            start_id,
            2,
            process_id,
            0,
        );
        add_arrow(
            &mut self.scene,
            &mut self.next_id,
            process_id,
            2,
            decision_id,
            0,
        );
        add_arrow(
            &mut self.scene,
            &mut self.next_id,
            decision_id,
            1,
            branch_yes_id,
            3,
        );
        add_arrow(
            &mut self.scene,
            &mut self.next_id,
            decision_id,
            3,
            branch_no_id,
            1,
        );
        add_arrow(
            &mut self.scene,
            &mut self.next_id,
            branch_yes_id,
            2,
            end_id,
            1,
        );
        add_arrow(
            &mut self.scene,
            &mut self.next_id,
            branch_no_id,
            2,
            end_id,
            3,
        );

        self.selected = vec![process_id];
        self.tool = Tool::Select;
        cx.notify();
    }

    pub fn add_flowchart_seed_at_viewport_center(&mut self, cx: &mut Context<Self>) {
        let center = self.viewport_center();
        self.add_flowchart_seed(center[0], center[1], cx);
    }

    fn mindmap_meta(&self, id: u64) -> Option<MindMapNodeMeta> {
        self.scene
            .elements
            .iter()
            .find(|element| element.id == id)
            .and_then(|element| element.mindmap)
    }

    fn is_mindmap_node(&self, id: u64) -> bool {
        self.mindmap_meta(id).is_some()
    }

    fn is_mindmap_root(&self, id: u64) -> bool {
        self.mindmap_meta(id)
            .is_some_and(|meta| meta.parent.is_none())
    }

    fn selected_mindmap_root(&self) -> Option<u64> {
        self.selected_single()
            .filter(|id| self.is_mindmap_root(*id))
    }

    fn mindmap_root_direction(&self, root_id: u64) -> MindMapRootDirection {
        self.mindmap_meta(root_id)
            .map(|meta| meta.root_direction)
            .unwrap_or_default()
    }

    fn mindmap_connector_style_for_root(&self, root_id: u64) -> MindMapConnectorStyle {
        self.mindmap_meta(root_id)
            .map(|meta| meta.connector_style)
            .unwrap_or_default()
    }

    fn mindmap_root_of(&self, id: u64) -> Option<u64> {
        let mut current = id;
        loop {
            let meta = self.mindmap_meta(current)?;
            match meta.parent {
                Some(parent) => current = parent,
                None => return Some(current),
            }
        }
    }

    fn mindmap_children(&self, parent: u64, side: MindMapSide) -> Vec<u64> {
        let mut children: Vec<(usize, u64)> = self
            .scene
            .elements
            .iter()
            .filter_map(|element| {
                let meta = element.mindmap?;
                (meta.parent == Some(parent) && meta.side == side)
                    .then_some((meta.order, element.id))
            })
            .collect();
        children.sort_by_key(|(order, id)| (*order, *id));
        children.into_iter().map(|(_, id)| id).collect()
    }

    fn set_mindmap_node_side(&mut self, id: u64, side: MindMapSide) {
        if let Some(element) = self
            .scene
            .elements
            .iter_mut()
            .find(|element| element.id == id)
            && let Some(meta) = &mut element.mindmap
        {
            meta.side = side;
        }
        self.sync_mindmap_parent_link(id);
    }

    fn sync_mindmap_parent_link(&mut self, child_id: u64) {
        let Some(meta) = self.mindmap_meta(child_id) else {
            return;
        };
        let Some(parent_id) = meta.parent else {
            return;
        };
        let parent_connector = match meta.side {
            MindMapSide::Right => 1,
            MindMapSide::Left => 3,
        };
        let child_connector = match meta.side {
            MindMapSide::Right => 3,
            MindMapSide::Left => 1,
        };
        for element in &mut self.scene.elements {
            let segment = match &mut element.kind {
                ElementKind::Line(segment) | ElementKind::Arrow(segment) => segment,
                _ => continue,
            };
            let start_id = segment.start_anchor.map(|anchor| anchor.element_id);
            let end_id = segment.end_anchor.map(|anchor| anchor.element_id);
            let links_parent_child = matches!((start_id, end_id), (Some(a), Some(b)) if (a == parent_id && b == child_id) || (a == child_id && b == parent_id));
            if !links_parent_child {
                continue;
            }
            if let Some(anchor) = &mut segment.start_anchor {
                if anchor.element_id == parent_id {
                    anchor.connector = parent_connector;
                } else if anchor.element_id == child_id {
                    anchor.connector = child_connector;
                }
            }
            if let Some(anchor) = &mut segment.end_anchor {
                if anchor.element_id == parent_id {
                    anchor.connector = parent_connector;
                } else if anchor.element_id == child_id {
                    anchor.connector = child_connector;
                }
            }
        }
        self.sync_segment_anchors_for(&[parent_id, child_id]);
    }

    fn sync_mindmap_links_for_root(&mut self, root_id: u64) {
        let child_ids: Vec<u64> = self
            .scene
            .elements
            .iter()
            .filter_map(|element| {
                let meta = element.mindmap?;
                meta.parent?;
                (self.mindmap_root_of(element.id) == Some(root_id)).then_some(element.id)
            })
            .collect();
        for child_id in &child_ids {
            let Some(meta) = self.mindmap_meta(*child_id) else {
                continue;
            };
            let Some(parent_id) = meta.parent else {
                continue;
            };
            let parent_connector = match meta.side {
                MindMapSide::Right => 1,
                MindMapSide::Left => 3,
            };
            let child_connector = match meta.side {
                MindMapSide::Right => 3,
                MindMapSide::Left => 1,
            };
            for element in &mut self.scene.elements {
                let segment = match &mut element.kind {
                    ElementKind::Line(segment) | ElementKind::Arrow(segment) => segment,
                    _ => continue,
                };
                let start_id = segment.start_anchor.map(|anchor| anchor.element_id);
                let end_id = segment.end_anchor.map(|anchor| anchor.element_id);
                let links_parent_child = matches!((start_id, end_id), (Some(a), Some(b)) if (a == parent_id && b == *child_id) || (a == *child_id && b == parent_id));
                if !links_parent_child {
                    continue;
                }
                if let Some(anchor) = &mut segment.start_anchor {
                    if anchor.element_id == parent_id {
                        anchor.connector = parent_connector;
                    } else if anchor.element_id == *child_id {
                        anchor.connector = child_connector;
                    }
                }
                if let Some(anchor) = &mut segment.end_anchor {
                    if anchor.element_id == parent_id {
                        anchor.connector = parent_connector;
                    } else if anchor.element_id == *child_id {
                        anchor.connector = child_connector;
                    }
                }
            }
        }
        self.sync_segment_anchors_for(&child_ids);
    }

    fn ordered_mindmap_children(&self, parent: u64) -> Vec<u64> {
        let mut children: Vec<(f32, f32, usize, u64)> = self
            .scene
            .elements
            .iter()
            .filter_map(|element| {
                let meta = element.mindmap?;
                (meta.parent == Some(parent)).then(|| {
                    let (x, y, _, h, _) =
                        box_like(&element.kind).unwrap_or((0.0, 0.0, 0.0, 0.0, 0.0));
                    (y + h / 2.0, x, meta.order, element.id)
                })
            })
            .collect();
        children.sort_by(|a, b| {
            a.0.total_cmp(&b.0)
                .then_with(|| a.1.total_cmp(&b.1))
                .then_with(|| a.2.cmp(&b.2))
                .then_with(|| a.3.cmp(&b.3))
        });
        children.into_iter().map(|(_, _, _, id)| id).collect()
    }

    fn set_mindmap_children_side(&mut self, parent: u64, side: MindMapSide) {
        for child_id in self.ordered_mindmap_children(parent) {
            self.set_mindmap_node_side(child_id, side);
        }
    }

    fn set_mindmap_children_side_alternating(&mut self, parent: u64) {
        for (index, child_id) in self
            .ordered_mindmap_children(parent)
            .into_iter()
            .enumerate()
        {
            let side = if index % 2 == 0 {
                MindMapSide::Right
            } else {
                MindMapSide::Left
            };
            self.set_mindmap_node_side(child_id, side);
        }
    }

    fn reindex_mindmap_children(&mut self, parent: u64) {
        for side in [MindMapSide::Left, MindMapSide::Right] {
            let children = self.mindmap_children(parent, side);
            for (order, child_id) in children.into_iter().enumerate() {
                if let Some(element) = self
                    .scene
                    .elements
                    .iter_mut()
                    .find(|element| element.id == child_id)
                    && let Some(meta) = &mut element.mindmap
                {
                    meta.order = order;
                }
                self.reindex_mindmap_children(child_id);
            }
        }
    }

    fn set_mindmap_root_direction(
        &mut self,
        root_id: u64,
        direction: MindMapRootDirection,
        cx: &mut Context<Self>,
    ) {
        if let Some(element) = self
            .scene
            .elements
            .iter_mut()
            .find(|element| element.id == root_id)
            && let Some(meta) = &mut element.mindmap
        {
            meta.root_direction = direction;
        }
        match direction {
            MindMapRootDirection::Left => {
                self.set_mindmap_children_side(root_id, MindMapSide::Left)
            }
            MindMapRootDirection::Right => {
                self.set_mindmap_children_side(root_id, MindMapSide::Right)
            }
            MindMapRootDirection::Both => self.set_mindmap_children_side_alternating(root_id),
        }
        self.reindex_mindmap_children(root_id);
        self.relayout_mindmap_tree(root_id);
        cx.notify();
    }

    fn set_mindmap_connector_style(
        &mut self,
        root_id: u64,
        style: MindMapConnectorStyle,
        cx: &mut Context<Self>,
    ) {
        if let Some(element) = self
            .scene
            .elements
            .iter_mut()
            .find(|element| element.id == root_id)
            && let Some(meta) = &mut element.mindmap
        {
            meta.connector_style = style;
        }
        cx.notify();
    }

    fn set_mindmap_node_position(&mut self, id: u64, x: f32, y: f32) {
        if let Some(element) = self
            .scene
            .elements
            .iter_mut()
            .find(|element| element.id == id)
            && let ElementKind::RoundRect(geom) = &mut element.kind
        {
            geom.x = x;
            geom.y = y;
        }
    }

    fn mindmap_node_size(&self, id: u64, zoom: f32) -> (f32, f32) {
        self.scene
            .elements
            .iter()
            .find(|element| element.id == id)
            .and_then(|element| box_like(&element.kind).map(|(_, _, w, h, _)| (w, h)))
            .unwrap_or((MINDMAP_NODE_W / zoom, MINDMAP_NODE_H / zoom))
    }

    fn side_stack_height(&self, parent: u64, side: MindMapSide, zoom: f32) -> f32 {
        let children = self.mindmap_children(parent, side);
        if children.is_empty() {
            return 0.0;
        }
        let gap_y = MINDMAP_BRANCH_GAP_Y / zoom;
        children
            .into_iter()
            .enumerate()
            .fold(0.0, |acc, (index, child_id)| {
                acc + if index > 0 { gap_y } else { 0.0 }
                    + self.mindmap_subtree_height(child_id, zoom)
            })
    }

    fn mindmap_subtree_height(&self, id: u64, zoom: f32) -> f32 {
        let (_, node_h) = self.mindmap_node_size(id, zoom);
        node_h.max(
            self.side_stack_height(id, MindMapSide::Left, zoom)
                .max(self.side_stack_height(id, MindMapSide::Right, zoom)),
        )
    }

    fn relayout_mindmap_subtree(&mut self, node_id: u64, moved: &mut Vec<u64>, zoom: f32) {
        self.relayout_mindmap_children(node_id, MindMapSide::Left, moved, zoom);
        self.relayout_mindmap_children(node_id, MindMapSide::Right, moved, zoom);
    }

    fn relayout_mindmap_children(
        &mut self,
        parent_id: u64,
        side: MindMapSide,
        moved: &mut Vec<u64>,
        zoom: f32,
    ) {
        let children = self.mindmap_children(parent_id, side);
        if children.is_empty() {
            return;
        }
        let Some((px, py, pw, ph, _)) = self
            .scene
            .elements
            .iter()
            .find(|element| element.id == parent_id)
            .and_then(|element| box_like(&element.kind))
        else {
            return;
        };
        let gap_x = MINDMAP_BRANCH_GAP_X / zoom;
        let gap_y = MINDMAP_BRANCH_GAP_Y / zoom;
        let total_h = children
            .iter()
            .enumerate()
            .fold(0.0, |acc, (index, child_id)| {
                acc + if index > 0 { gap_y } else { 0.0 }
                    + self.mindmap_subtree_height(*child_id, zoom)
            });
        let mut cursor_y = py + ph / 2.0 - total_h / 2.0;
        for child_id in children {
            let subtree_h = self.mindmap_subtree_height(child_id, zoom);
            let (cw, ch) = self.mindmap_node_size(child_id, zoom);
            let cy = cursor_y + subtree_h / 2.0;
            let x = match side {
                MindMapSide::Right => px + pw + gap_x,
                MindMapSide::Left => px - gap_x - cw,
            };
            self.set_mindmap_node_position(child_id, x, cy - ch / 2.0);
            moved.push(child_id);
            self.relayout_mindmap_subtree(child_id, moved, zoom);
            cursor_y += subtree_h + gap_y;
        }
    }

    fn relayout_mindmap_tree(&mut self, root_id: u64) {
        let zoom = self.scene.camera.zoom.max(MIN_ZOOM);
        let mut moved = vec![root_id];
        self.relayout_mindmap_subtree(root_id, &mut moved, zoom);
        self.sync_mindmap_links_for_root(root_id);
        self.sync_segment_anchors_for(&moved);
    }

    fn bump_mindmap_sibling_orders(&mut self, parent: u64, side: MindMapSide, from_order: usize) {
        for element in &mut self.scene.elements {
            if let Some(meta) = &mut element.mindmap
                && meta.parent == Some(parent)
                && meta.side == side
                && meta.order >= from_order
            {
                meta.order += 1;
            }
        }
    }

    fn create_mindmap_node(
        &mut self,
        parent: u64,
        side: MindMapSide,
        order: usize,
        label: &str,
    ) -> u64 {
        self.bump_mindmap_sibling_orders(parent, side, order);
        let zoom = self.scene.camera.zoom.max(MIN_ZOOM);
        let id = self.next_id;
        self.next_id += 1;
        let w = MINDMAP_NODE_W / zoom;
        let h = MINDMAP_NODE_H / zoom;
        let (x, y) = self
            .scene
            .elements
            .iter()
            .find(|element| element.id == parent)
            .and_then(|element| box_like(&element.kind))
            .map(|(px, py, pw, ph, _)| match side {
                MindMapSide::Right => (
                    px + pw + MINDMAP_BRANCH_GAP_X / zoom,
                    py + ph / 2.0 - h / 2.0,
                ),
                MindMapSide::Left => (
                    px - MINDMAP_BRANCH_GAP_X / zoom - w,
                    py + ph / 2.0 - h / 2.0,
                ),
            })
            .unwrap_or((0.0, 0.0));
        self.scene.elements.push(Element {
            id,
            kind: ElementKind::RoundRect(BoxGeom {
                x,
                y,
                w,
                h,
                width: NIB / zoom,
                rotation: 0.0,
            }),
            stroke: Some(0x2563ebff),
            fill: Some(0xffffffff),
            label: Some(label.to_string()),
            label_color: Some(0x0f172aff),
            styles: Vec::new(),
            mindmap: Some(MindMapNodeMeta {
                parent: Some(parent),
                side,
                order,
                root_direction: MindMapRootDirection::Both,
                connector_style: MindMapConnectorStyle::Bezier,
            }),
        });
        let start_anchor = SegmentAnchor {
            element_id: parent,
            connector: match side {
                MindMapSide::Right => 1,
                MindMapSide::Left => 3,
            },
        };
        let end_anchor = SegmentAnchor {
            element_id: id,
            connector: match side {
                MindMapSide::Right => 3,
                MindMapSide::Left => 1,
            },
        };
        let [x1, y1] = connector_world_pos_in(&self.scene.elements, start_anchor).unwrap_or([x, y]);
        let [x2, y2] = connector_world_pos_in(&self.scene.elements, end_anchor).unwrap_or([x, y]);
        let line_id = self.next_id;
        self.next_id += 1;
        self.scene.elements.push(Element {
            id: line_id,
            kind: ElementKind::Arrow(SegGeom {
                x1,
                y1,
                x2,
                y2,
                width: NIB / zoom,
                style: SegmentStyle::Solid,
                start_anchor: Some(start_anchor),
                end_anchor: Some(end_anchor),
            }),
            stroke: Some(0x2563ebff),
            fill: None,
            label: None,
            label_color: None,
            styles: Vec::new(),
            mindmap: None,
        });
        if let Some(root_id) = self.mindmap_root_of(parent) {
            self.relayout_mindmap_tree(root_id);
        }
        id
    }

    fn add_mindmap_relative(
        &mut self,
        source_id: u64,
        sibling: bool,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) -> bool {
        let Some(meta) = self.mindmap_meta(source_id) else {
            return false;
        };
        let (parent, side, order) = if sibling {
            match meta.parent {
                Some(parent) => (parent, meta.side, meta.order + 1),
                None => (
                    source_id,
                    MindMapSide::Right,
                    self.mindmap_children(source_id, MindMapSide::Right).len(),
                ),
            }
        } else {
            (
                source_id,
                meta.side,
                self.mindmap_children(source_id, meta.side).len(),
            )
        };
        self.push_undo();
        let new_id = self.create_mindmap_node(parent, side, order, "");
        self.selected = vec![new_id];
        self.begin_text_edit(new_id, 0, window, cx);
        self.dirty = true;
        cx.notify();
        true
    }

    fn mindmap_connector_style_for_element(
        &self,
        kind: &ElementKind,
    ) -> Option<MindMapConnectorStyle> {
        let seg = match kind {
            ElementKind::Line(seg) | ElementKind::Arrow(seg) => seg,
            _ => return None,
        };
        let start_root = seg
            .start_anchor
            .and_then(|anchor| self.mindmap_root_of(anchor.element_id));
        let end_root = seg
            .end_anchor
            .and_then(|anchor| self.mindmap_root_of(anchor.element_id));
        match (start_root, end_root) {
            (Some(a), Some(b)) if a == b => Some(self.mindmap_connector_style_for_root(a)),
            _ => None,
        }
    }

    /// The world point at the center of the current viewport — where paste drops
    /// an image (the host has no access to the camera otherwise).
    pub fn viewport_center(&self) -> [f32; 2] {
        let b = self.bounds.get();
        let cam = self.scene.camera;
        let z = cam.zoom.max(MIN_ZOOM);
        [
            cam.x + f32::from(b.size.width) / 2.0 / z,
            cam.y + f32::from(b.size.height) / 2.0 / z,
        ]
    }

    /// The current board document (for the host to persist).
    pub fn scene(&self) -> &Scene {
        &self.scene
    }

    /// Build a local-thumbnail focus spec for the board. The board default has
    /// no natural root, so `Auto` means:
    ///
    /// - selected content, if any
    /// - otherwise the current viewport
    /// - otherwise all content
    pub fn local_thumbnail_spec(
        &self,
        width_px: f32,
        height_px: f32,
    ) -> Option<LocalThumbnailSpec> {
        self.local_thumbnail_spec_for_mode(LocalThumbnailMode::Auto, width_px, height_px)
    }

    pub fn local_thumbnail_snapshot(
        &self,
        width_px: f32,
        height_px: f32,
    ) -> Option<LocalThumbnailSnapshot> {
        self.local_thumbnail_snapshot_for_mode(LocalThumbnailMode::Auto, width_px, height_px)
    }

    pub fn local_thumbnail_spec_for_mode(
        &self,
        mode: LocalThumbnailMode,
        width_px: f32,
        height_px: f32,
    ) -> Option<LocalThumbnailSpec> {
        let scene_bounds = self.scene_bbox();
        let (anchor_element_id, focus) = match mode {
            LocalThumbnailMode::Auto => self
                .selection_bbox()
                .map(|bb| (self.selected_single(), bb))
                .or_else(|| self.viewport_world_bbox().map(|bb| (None, bb)))
                .or_else(|| scene_bounds.map(|bb| (None, bb)))?,
            LocalThumbnailMode::Selection => {
                let bb = self.selection_bbox()?;
                (self.selected_single(), bb)
            }
            LocalThumbnailMode::Viewport => (None, self.viewport_world_bbox()?),
            LocalThumbnailMode::AllContent => (None, scene_bounds?),
            LocalThumbnailMode::Element(id) => (Some(id), self.element_bbox(id)?),
        };
        Some(self.thumbnail_spec_from_bbox(
            anchor_element_id,
            focus,
            scene_bounds,
            width_px,
            height_px,
        ))
    }

    pub fn local_thumbnail_snapshot_for_mode(
        &self,
        mode: LocalThumbnailMode,
        width_px: f32,
        height_px: f32,
    ) -> Option<LocalThumbnailSnapshot> {
        Some(LocalThumbnailSnapshot {
            scene: self.scene.clone(),
            spec: self.local_thumbnail_spec_for_mode(mode, width_px, height_px)?,
        })
    }

    /// The lone selected id, if exactly one element is selected. Single-element
    /// manipulation (resize, endpoints, edit) only applies then.
    fn selected_single(&self) -> Option<u64> {
        match self.selected.as_slice() {
            [id] => Some(*id),
            _ => None,
        }
    }

    fn is_selected(&self, id: u64) -> bool {
        self.selected.contains(&id)
    }

    fn element_bbox(&self, id: u64) -> Option<(f32, f32, f32, f32)> {
        self.scene
            .elements
            .iter()
            .find(|e| e.id == id)
            .map(|e| bbox(&e.kind))
    }

    fn scene_bbox(&self) -> Option<(f32, f32, f32, f32)> {
        scene_bbox_for_local_thumbnail(&self.scene)
    }

    fn viewport_world_bbox(&self) -> Option<(f32, f32, f32, f32)> {
        let b = self.bounds.get();
        let vw = f32::from(b.size.width);
        let vh = f32::from(b.size.height);
        if vw <= 1.0 || vh <= 1.0 {
            return None;
        }
        let cam = self.scene.camera;
        let z = cam.zoom.max(MIN_ZOOM);
        Some((cam.x, cam.y, cam.x + vw / z, cam.y + vh / z))
    }

    fn render_viewport(&self, fallback_size: Option<gpui::Size<Pixels>>) -> Option<WorldViewport> {
        let bounds = self.bounds.get();
        let size = if f32::from(bounds.size.width) > 1.0 && f32::from(bounds.size.height) > 1.0 {
            bounds.size
        } else {
            fallback_size?
        };
        let camera = self.scene.camera;
        WorldViewport::from_canvas(
            f32::from(size.width),
            f32::from(size.height),
            camera.x,
            camera.y,
            camera.zoom.max(MIN_ZOOM),
            VIEWPORT_CULL_MARGIN_PX,
        )
    }

    fn thumbnail_spec_from_bbox(
        &self,
        anchor_element_id: Option<u64>,
        focus: (f32, f32, f32, f32),
        scene_bounds: Option<(f32, f32, f32, f32)>,
        width_px: f32,
        height_px: f32,
    ) -> LocalThumbnailSpec {
        local_thumbnail_spec_from_bbox(anchor_element_id, focus, scene_bounds, width_px, height_px)
    }

    /// World-space bounds enclosing the whole selection, or `None` if empty.
    fn selection_bbox(&self) -> Option<(f32, f32, f32, f32)> {
        let mut it = self
            .scene
            .elements
            .iter()
            .filter(|e| self.selected.contains(&e.id))
            .map(|e| bbox(&e.kind));
        let first = it.next()?;
        Some(it.fold(first, |a, b| {
            (a.0.min(b.0), a.1.min(b.1), a.2.max(b.2), a.3.max(b.3))
        }))
    }

    fn aligned_move_delta(&self, dx: f32, dy: f32) -> (f32, f32, AlignmentGuides) {
        const SNAP_PX: f32 = 6.0;
        let Some(selection) = self.selection_bbox() else {
            return (dx, dy, AlignmentGuides::default());
        };
        let threshold = SNAP_PX / self.scene.camera.zoom.max(MIN_ZOOM);
        let moving_x = [
            selection.0 + dx,
            (selection.0 + selection.2) / 2.0 + dx,
            selection.2 + dx,
        ];
        let moving_y = [
            selection.1 + dy,
            (selection.1 + selection.3) / 2.0 + dy,
            selection.3 + dy,
        ];
        let mut best_x: Option<(f32, f32)> = None;
        let mut best_y: Option<(f32, f32)> = None;

        for element in self
            .scene
            .elements
            .iter()
            .filter(|element| !self.selected.contains(&element.id))
        {
            let bb = bbox(&element.kind);
            for moving in moving_x {
                for target in [bb.0, (bb.0 + bb.2) / 2.0, bb.2] {
                    let correction = target - moving;
                    if correction.abs() <= threshold
                        && best_x.is_none_or(|(best, _)| correction.abs() < best.abs())
                    {
                        best_x = Some((correction, target));
                    }
                }
            }
            for moving in moving_y {
                for target in [bb.1, (bb.1 + bb.3) / 2.0, bb.3] {
                    let correction = target - moving;
                    if correction.abs() <= threshold
                        && best_y.is_none_or(|(best, _)| correction.abs() < best.abs())
                    {
                        best_y = Some((correction, target));
                    }
                }
            }
        }

        (
            dx + best_x.map_or(0.0, |(correction, _)| correction),
            dy + best_y.map_or(0.0, |(correction, _)| correction),
            AlignmentGuides {
                vertical: best_x.map(|(_, target)| target),
                horizontal: best_y.map(|(_, target)| target),
            },
        )
    }

    fn sync_segment_anchors_for(&mut self, changed_ids: &[u64]) {
        if changed_ids.is_empty() {
            return;
        }
        let elements = self.scene.elements.clone();
        for element in &mut self.scene.elements {
            let segment = match &mut element.kind {
                ElementKind::Line(segment) | ElementKind::Arrow(segment) => segment,
                _ => continue,
            };
            if let Some(anchor) = segment.start_anchor
                && changed_ids.contains(&anchor.element_id)
                && let Some(pos) = connector_world_pos_in(&elements, anchor)
            {
                segment.x1 = pos[0];
                segment.y1 = pos[1];
            }
            if let Some(anchor) = segment.end_anchor
                && changed_ids.contains(&anchor.element_id)
                && let Some(pos) = connector_world_pos_in(&elements, anchor)
            {
                segment.x2 = pos[0];
                segment.y2 = pos[1];
            }
        }
    }

    fn detach_segment_bindings_for_move(&mut self, ids: &[u64]) {
        for element in &mut self.scene.elements {
            if !ids.contains(&element.id) {
                continue;
            }
            if let ElementKind::Line(segment) | ElementKind::Arrow(segment) = &mut element.kind {
                if segment
                    .start_anchor
                    .is_some_and(|anchor| !ids.contains(&anchor.element_id))
                {
                    segment.start_anchor = None;
                }
                if segment
                    .end_anchor
                    .is_some_and(|anchor| !ids.contains(&anchor.element_id))
                {
                    segment.end_anchor = None;
                }
            }
        }
    }

    fn set_segment_endpoint_anchor(
        &mut self,
        segment_id: u64,
        endpoint: usize,
        anchor: Option<SegmentAnchor>,
    ) {
        let pos = anchor.and_then(|anchor| {
            connector_world_pos_in(&self.scene.elements, anchor).map(|pos| (anchor, pos))
        });
        let Some(element) = self
            .scene
            .elements
            .iter_mut()
            .find(|element| element.id == segment_id)
        else {
            return;
        };
        let segment = match &mut element.kind {
            ElementKind::Line(segment) | ElementKind::Arrow(segment) => segment,
            _ => return,
        };
        if endpoint == 0 {
            segment.start_anchor = anchor;
            if let Some((_, pos)) = pos {
                segment.x1 = pos[0];
                segment.y1 = pos[1];
            }
        } else {
            segment.end_anchor = anchor;
            if let Some((_, pos)) = pos {
                segment.x2 = pos[0];
                segment.y2 = pos[1];
            }
        }
    }

    /// Whether a *group* rotation applies: more than one element selected, at
    /// least one of which can rotate (so an all-cards group offers no grip).
    fn group_rotatable(&self) -> bool {
        self.selected.len() > 1
            && self
                .scene
                .elements
                .iter()
                .any(|e| self.selected.contains(&e.id) && rotatable(&e.kind))
    }

    /// The active tool (e.g. for host-driven chrome).
    pub fn tool(&self) -> Tool {
        self.tool
    }

    /// Switch the active drawing tool. Leaving Select clears the selection.
    /// Always closes an open tool flyout (the tool was just chosen).
    pub fn set_tool(&mut self, tool: Tool, cx: &mut Context<Self>) {
        if self.read_only {
            self.tool = Tool::Pan;
            self.selected.clear();
            self.open_group = None;
            cx.notify();
            return;
        }
        self.open_group = None;
        if self.tool != tool {
            self.tool = tool;
            if tool != Tool::Select {
                self.selected.clear();
            }
        }
        cx.notify();
    }

    /// Reset the viewport to the origin at 100% (also bound to double-click).
    pub fn reset_view(&mut self, cx: &mut Context<Self>) {
        self.scene.camera = Camera::default();
        self.dirty = true;
        cx.notify();
    }

    /// Zoom in/out a step, centered on the canvas.
    pub fn zoom_in(&mut self, cx: &mut Context<Self>) {
        self.zoom_centered(1.2, cx);
    }
    pub fn zoom_out(&mut self, cx: &mut Context<Self>) {
        self.zoom_centered(1.0 / 1.2, cx);
    }

    fn zoom_centered(&mut self, factor: f32, cx: &mut Context<Self>) {
        let b = self.bounds.get();
        let rx = f32::from(b.size.width) / 2.0;
        let ry = f32::from(b.size.height) / 2.0;
        self.scene.camera.zoom_about(rx, ry, factor);
        self.dirty = true;
        cx.notify();
    }

    /// Snapshot the scene for undo (before a mutation), capping history.
    fn push_undo(&mut self) {
        self.history.push(self.scene.clone());
        if self.history.len() > UNDO_CAP {
            self.history.remove(0);
        }
        self.redo.clear();
    }

    /// Revert the last change.
    pub fn undo(&mut self, window: &mut Window, cx: &mut Context<Self>) {
        if let Some(prev) = self.history.pop() {
            self.redo.push(std::mem::replace(&mut self.scene, prev));
            self.selected.clear();
            self.dirty = true;
            cx.notify();
            self.flush(window, cx);
        }
    }

    /// Re-apply the last undone change.
    pub fn redo(&mut self, window: &mut Window, cx: &mut Context<Self>) {
        if let Some(next) = self.redo.pop() {
            self.history.push(std::mem::replace(&mut self.scene, next));
            self.selected.clear();
            self.dirty = true;
            cx.notify();
            self.flush(window, cx);
        }
    }

    /// Delete the selected elements.
    fn delete_selected(&mut self, window: &mut Window, cx: &mut Context<Self>) {
        if self.selected.is_empty() {
            return;
        }
        self.push_undo();
        let gone = std::mem::take(&mut self.selected);
        self.scene.elements.retain(|e| !gone.contains(&e.id));
        self.editing = None;
        self.dirty = true;
        cx.notify();
        self.flush(window, cx);
    }

    /// Move the selected elements through the paint order (their position in
    /// `elements`; later = painted on top, so it can cover earlier ones). One step
    /// or all the way, per `op`. A no-op (already at that edge) leaves undo/redo
    /// untouched.
    fn reorder_selection(&mut self, op: ZOrder, window: &mut Window, cx: &mut Context<Self>) {
        if self.selected.is_empty() {
            return;
        }
        let sel = self.selected.clone();
        let on = |id: u64| sel.contains(&id);
        self.push_undo();
        let before: Vec<u64> = self.scene.elements.iter().map(|e| e.id).collect();
        let els = &mut self.scene.elements;
        match op {
            // Stable partition: the non-selected keep their order and the selected
            // keep theirs, so a multi-selection moves as a block.
            ZOrder::ToFront => els.sort_by_key(|e| on(e.id)),
            ZOrder::ToBack => els.sort_by_key(|e| !on(e.id)),
            // One step: swap each selected past its adjacent non-selected neighbor,
            // walking away from the destination edge so an element isn't moved twice
            // and selected elements don't leapfrog each other.
            ZOrder::Forward => {
                for i in (0..els.len().saturating_sub(1)).rev() {
                    if on(els[i].id) && !on(els[i + 1].id) {
                        els.swap(i, i + 1);
                    }
                }
            }
            ZOrder::Backward => {
                for i in 1..els.len() {
                    if on(els[i].id) && !on(els[i - 1].id) {
                        els.swap(i, i - 1);
                    }
                }
            }
        }
        if self.scene.elements.iter().map(|e| e.id).eq(before) {
            self.history.pop(); // nothing moved — drop the speculative snapshot
            return;
        }
        self.dirty = true;
        cx.notify();
        self.flush(window, cx);
    }

    /// Flush pending changes through the host's persistence hook.
    fn flush(&mut self, window: &mut Window, cx: &mut Context<Self>) {
        if !self.dirty {
            return;
        }
        self.dirty = false;
        if let Some(f) = self.on_change.clone() {
            f(self.scene.to_json(), window, cx);
        }
    }

    // --- templates ---------------------------------------------------------

    /// Serialize the current selection: the selected elements translated so their
    /// collective bounding box starts at the origin (so the group can be re-based
    /// anywhere when applied). `None` if nothing is selected. Used for both saving
    /// a template and copying to the clipboard — the two share this format, so a
    /// copied selection can be pasted on any board (see [`Self::paste_elements`]).
    fn selection_json(&self) -> Option<String> {
        let sel: Vec<&Element> = self
            .scene
            .elements
            .iter()
            .filter(|e| self.selected.contains(&e.id))
            .collect();
        if sel.is_empty() {
            return None;
        }
        let (minx, miny) = sel
            .iter()
            .fold((f32::INFINITY, f32::INFINITY), |(mx, my), e| {
                let (x0, y0, ..) = bbox(&e.kind);
                (mx.min(x0), my.min(y0))
            });
        let elems: Vec<Element> = sel
            .iter()
            .map(|e| {
                let mut c = (*e).clone();
                translate(&mut c.kind, -minx, -miny);
                c
            })
            .collect();
        serde_json::to_string(&elems).ok()
    }

    /// Hand the current selection to the host to be saved as a named template.
    fn save_selection_as_template(&mut self, window: &mut Window, cx: &mut Context<Self>) {
        self.context_menu = None;
        if let Some(json) = self.selection_json()
            && let Some(f) = self.on_save_template.clone()
        {
            f(json, window, cx);
        }
        cx.notify();
    }

    /// Stamp template `index` onto the board, centered in the current viewport,
    /// with fresh ids; the new elements become the selection.
    fn apply_template(&mut self, index: usize, window: &mut Window, cx: &mut Context<Self>) {
        let Some(elems) = self.templates.get(index).map(|t| t.elements.clone()) else {
            return;
        };
        self.templates_open = false;
        self.stamp_elements(&elems, window, cx);
    }

    /// Place `elems` (origin-normalized, as produced by [`Self::selection_json`])
    /// onto the board, centered in the current viewport with fresh ids; they
    /// become the new selection. Shared by template apply and clipboard paste.
    /// No-op for an empty group.
    fn stamp_elements(&mut self, elems: &[Element], window: &mut Window, cx: &mut Context<Self>) {
        if elems.is_empty() {
            return;
        }
        self.open_group = None;
        self.push_undo();
        // Center the (origin-normalized) group in the viewport.
        let b = self.bounds.get();
        let cam = self.scene.camera;
        let z = cam.zoom.max(MIN_ZOOM);
        let (tw, th) = elements_extent(elems);
        let off = [
            cam.x + (f32::from(b.size.width) / 2.0) / z - tw / 2.0,
            cam.y + (f32::from(b.size.height) / 2.0) / z - th / 2.0,
        ];
        let mut new_ids = Vec::with_capacity(elems.len());
        for e in elems {
            let mut c = e.clone();
            translate(&mut c.kind, off[0], off[1]);
            c.id = self.next_id;
            self.next_id += 1;
            new_ids.push(c.id);
            self.scene.elements.push(c);
        }
        self.selected = new_ids;
        self.tool = Tool::Select;
        self.dirty = true;
        self.flush(window, cx);
        cx.notify();
    }

    /// Copy the selection to the clipboard via the host's `on_copy` hook (the
    /// crate can't touch the system clipboard). Returns whether anything was
    /// copied. `⌘X` reuses this, then deletes.
    fn copy_selection(&self, window: &mut Window, cx: &mut Context<Self>) -> bool {
        let Some(json) = self.selection_json() else {
            return false;
        };
        if let Some(f) = self.on_copy.clone() {
            f(json, window, cx);
        }
        true
    }

    /// Paste a serialized `Vec<Element>` (the JSON a [`CopyFn`] wrote) onto the
    /// board — centered in the viewport, selected, with fresh ids. Ignores invalid
    /// JSON. The host calls this from its [`PasteFn`] when the clipboard holds
    /// whiteboard elements rather than an image.
    pub fn paste_elements(&mut self, json: &str, window: &mut Window, cx: &mut Context<Self>) {
        if let Ok(elems) = serde_json::from_str::<Vec<Element>>(json) {
            self.stamp_elements(&elems, window, cx);
        }
    }

    /// Ask the host to delete a stored template (right-click a card). The host
    /// confirms, removes it, and feeds the updated list back.
    fn delete_template(&mut self, id: i64, window: &mut Window, cx: &mut Context<Self>) {
        if let Some(f) = self.on_delete_template.clone() {
            f(id, window, cx);
        }
    }

    /// A template preview card for the gallery modal: a scaled mini-paint of the
    /// template's shapes over its name. Click to stamp it; right-click to delete.
    /// (Text and page-cards don't appear in the mini-paint — only drawn shapes —
    /// but they're still placed on apply.)
    fn template_card(
        &self,
        index: usize,
        ink: Hsla,
        text: Hsla,
        grid: Hsla,
        bg: Hsla,
        cx: &mut Context<Self>,
    ) -> gpui::AnyElement {
        let t = &self.templates[index];
        let id = t.id;
        let name: SharedString = t.name.clone().into();
        let elems = t.elements.clone();
        let (tw, th) = elements_extent(&elems);
        let preview = canvas(
            |_, _, _| {},
            move |bounds, _, window: &mut Window, _: &mut App| {
                let pad = 8.0;
                let aw = f32::from(bounds.size.width) - 2.0 * pad;
                let ah = f32::from(bounds.size.height) - 2.0 * pad;
                if tw <= 0.0 || th <= 0.0 || aw <= 0.0 || ah <= 0.0 {
                    return;
                }
                // Fit the (origin-normalized) template into the card, centered,
                // never magnifying past 1:1.
                let scale = (aw / tw).min(ah / th).min(1.0);
                let ox = (f32::from(bounds.size.width) - tw * scale) / 2.0;
                let oy = (f32::from(bounds.size.height) - th * scale) / 2.0;
                let cam = Camera {
                    x: -ox / scale,
                    y: -oy / scale,
                    zoom: scale,
                };
                for e in &elems {
                    let stroke = e.stroke.map_or(ink, u32_to_hsla);
                    let fill = e.fill.map(u32_to_hsla);
                    paint_element(&e.kind, None, cam, bounds.origin, stroke, fill, window);
                }
            },
        )
        .size_full();
        div()
            .id(("wb-template", index))
            .flex()
            .flex_col()
            .items_center()
            .gap(px(5.0))
            .p(px(6.0))
            .rounded(px(8.0))
            .hover(|s| s.bg(grid))
            .child(
                div()
                    .w(px(150.0))
                    .h(px(104.0))
                    .rounded(px(6.0))
                    .bg(bg)
                    .border_1()
                    .border_color(grid)
                    .child(preview),
            )
            .child(
                div()
                    .w(px(150.0))
                    .h(px(15.0))
                    .overflow_hidden()
                    .text_size(px(11.0))
                    .text_color(text)
                    .child(name),
            )
            .on_click(
                cx.listener(move |this, _ev, window, cx| this.apply_template(index, window, cx)),
            )
            .on_mouse_down(
                MouseButton::Right,
                cx.listener(move |this, _ev, window, cx| this.delete_template(id, window, cx)),
            )
            .into_any_element()
    }

    // --- color picker ------------------------------------------------------

    /// The color the picker should start from for `target`: the single
    /// selection's color (if any), else the active color, else a default.
    fn seed_color(&self, target: PickerTarget) -> u32 {
        let from_sel = self
            .selected_single()
            .and_then(|id| self.scene.elements.iter().find(|e| e.id == id))
            .and_then(|e| match target {
                PickerTarget::Stroke => e.stroke,
                PickerTarget::Fill => e.fill,
                PickerTarget::Text => e.label_color,
            });
        let active = match target {
            PickerTarget::Stroke => self.active_stroke,
            PickerTarget::Fill => self.active_fill,
            PickerTarget::Text => self.active_text,
        };
        from_sel.or(active).unwrap_or(0x4080f0ff)
    }

    /// Point the picker's HSVA controls at `target`'s current color.
    fn seed_picker(&mut self, target: PickerTarget) {
        let c = self.seed_color(target);
        let (h, s, v) = u32_to_hsv(c);
        self.picker = Some(Picker {
            target,
            h,
            s,
            v,
            a: u32_alpha(c),
        });
    }

    /// Open or close the color picker. Opening seeds the controls from the
    /// stroke color (selection's, else active, else a default).
    fn toggle_picker(&mut self, cx: &mut Context<Self>) {
        self.open_group = None;
        self.templates_open = false;
        self.width_open = false;
        self.font_open = false;
        if self.picker.is_some() {
            self.picker = None;
        } else {
            self.seed_picker(PickerTarget::Stroke);
        }
        cx.notify();
    }

    /// Open / close the thickness-preset flyout (closing the other popovers).
    fn toggle_width(&mut self, cx: &mut Context<Self>) {
        self.picker = None;
        self.open_group = None;
        self.templates_open = false;
        self.context_menu = None;
        self.font_open = false;
        self.width_open = !self.width_open;
        cx.notify();
    }

    /// Set the active stroke thickness (screen px) for new elements and apply it to
    /// the selection, *without* undo/flush — used for live slider drags (undo is
    /// pushed at drag start, flush on release, like the color strips).
    fn set_width_live(&mut self, w: f32, cx: &mut Context<Self>) {
        self.active_width = w;
        if !self.selected.is_empty() {
            let zoom = self.scene.camera.zoom.max(MIN_ZOOM);
            let sel = self.selected.clone();
            for e in self.scene.elements.iter_mut() {
                if sel.contains(&e.id) {
                    set_kind_width(&mut e.kind, w / zoom);
                }
            }
            self.dirty = true;
        }
        cx.notify();
    }

    /// A discrete thickness choice (a preset swatch): pushes undo, applies, and
    /// flushes, then closes the flyout.
    fn set_width(&mut self, w: f32, window: &mut Window, cx: &mut Context<Self>) {
        self.width_open = false;
        if !self.selected.is_empty() {
            self.push_undo();
        }
        self.set_width_live(w, cx);
        self.flush(window, cx);
    }

    /// Map a 0..1 slider fraction to a width (screen px), snapped to 0.5px steps.
    fn width_from_frac(frac: f32) -> f32 {
        let w = WIDTH_MIN + frac.clamp(0.0, 1.0) * (WIDTH_MAX - WIDTH_MIN);
        (w * 2.0).round() / 2.0
    }

    /// Open the given tool category's flyout (or close it if already open).
    /// Closes the color picker so only one popover shows at a time.
    fn toggle_group(&mut self, group: ToolGroup, cx: &mut Context<Self>) {
        self.picker = None;
        self.templates_open = false;
        self.width_open = false;
        self.font_open = false;
        self.open_group = if self.open_group == Some(group) {
            None
        } else {
            Some(group)
        };
        cx.notify();
    }

    /// Open / close the templates gallery modal (closing the other popovers).
    fn toggle_templates(&mut self, cx: &mut Context<Self>) {
        self.picker = None;
        self.open_group = None;
        self.width_open = false;
        self.context_menu = None;
        self.font_open = false;
        self.templates_open = !self.templates_open;
        cx.notify();
    }

    /// Open / close the font flyout (upload a face / revert to default), closing
    /// the other popovers.
    fn toggle_font(&mut self, cx: &mut Context<Self>) {
        self.picker = None;
        self.open_group = None;
        self.width_open = false;
        self.templates_open = false;
        self.context_menu = None;
        self.font_open = !self.font_open;
        cx.notify();
    }

    /// Switch which property (stroke / fill) the picker edits, re-seeding its
    /// controls from that property's current color.
    fn set_picker_target(&mut self, target: PickerTarget, cx: &mut Context<Self>) {
        if self.picker.map(|p| p.target) != Some(target) {
            self.seed_picker(target);
            cx.notify();
        }
    }

    /// The picker's current target (stroke unless the picker says otherwise).
    fn picker_target(&self) -> PickerTarget {
        self.picker.map_or(PickerTarget::Stroke, |p| p.target)
    }

    /// Apply `color` to the active target on the active swatch and the selection,
    /// *without* undo/flush — used for live picker drags (undo is pushed once at
    /// drag start; the flush happens on release).
    fn set_color_live(&mut self, color: Option<u32>, cx: &mut Context<Self>) {
        let target = self.picker_target();
        match target {
            PickerTarget::Stroke => self.active_stroke = color,
            PickerTarget::Fill => self.active_fill = color,
            PickerTarget::Text => self.active_text = color,
        }
        if !self.selected.is_empty() {
            let sel = self.selected.clone();
            for e in self.scene.elements.iter_mut() {
                if !sel.contains(&e.id) {
                    continue;
                }
                match target {
                    PickerTarget::Stroke => e.stroke = color,
                    // Fill + label color only attach to closed shapes.
                    PickerTarget::Fill => {
                        if is_closed_shape(&e.kind) {
                            e.fill = color;
                        }
                    }
                    PickerTarget::Text => {
                        if is_closed_shape(&e.kind) {
                            e.label_color = color;
                        }
                    }
                }
            }
            self.dirty = true;
        }
        cx.notify();
    }

    /// A discrete, undoable color choice (a swatch, or the Auto / None reset).
    /// Recolors the selection and syncs the picker controls to the chosen color.
    fn pick_color(&mut self, color: Option<u32>, window: &mut Window, cx: &mut Context<Self>) {
        if !self.selected.is_empty() {
            self.push_undo();
        }
        if let (Some(c), Some(p)) = (color, self.picker.as_mut()) {
            let (h, s, v) = u32_to_hsv(c);
            // Keep the hue stable on greys (s == 0) so the strip thumb won't jump.
            if s > 0.0 {
                p.h = h;
            }
            p.s = s;
            p.v = v;
            p.a = u32_alpha(c);
        }
        self.set_color_live(color, cx);
        self.flush(window, cx);
    }

    /// Saturation/brightness under a window-coords position in the SV square.
    fn sv_from_pos(&self, pos: Point<Pixels>) -> (f32, f32) {
        let b = self.sv_bounds.get();
        let w = f32::from(b.size.width).max(1.0);
        let h = f32::from(b.size.height).max(1.0);
        let s = ((f32::from(pos.x) - f32::from(b.origin.x)) / w).clamp(0.0, 1.0);
        let v = 1.0 - ((f32::from(pos.y) - f32::from(b.origin.y)) / h).clamp(0.0, 1.0);
        (s, v)
    }

    /// A 0..1 fraction along a horizontal strip (hue or alpha) under `pos`.
    fn frac_x(&self, bounds: Bounds<Pixels>, pos: Point<Pixels>) -> f32 {
        let w = f32::from(bounds.size.width).max(1.0);
        ((f32::from(pos.x) - f32::from(bounds.origin.x)) / w).clamp(0.0, 1.0)
    }

    /// The picker's current color as a packed int (for live application).
    fn picker_u32(&self) -> Option<u32> {
        self.picker.map(|p| hsva_to_u32(p.h, p.s, p.v, p.a))
    }

    /// World point under a window-coords event position.
    fn event_to_world(&self, p: Point<Pixels>) -> [f32; 2] {
        let (rx, ry) = self.relative(p);
        let (wx, wy) = self.scene.camera.screen_to_world(rx, ry);
        [wx, wy]
    }

    /// If `pos` (window coords) is on a manipulation handle of the current
    /// selection, what to begin. Lines/arrows manipulate by their two
    /// endpoints; everything else by its bounding-box corners (a line's bbox is
    /// degenerate, which would make corner-resize wildly imprecise).
    fn handle_hit(&self, pos: Point<Pixels>) -> Option<HandleGrab> {
        let cam = self.scene.camera;
        let origin = self.bounds.get().origin;
        let cursor = self.event_to_world(pos);
        let near = |wx: f32, wy: f32, ox: f32, oy: f32| {
            let s = to_screen(wx, wy, cam, origin);
            let (dx, dy) = (
                f32::from(pos.x) - (f32::from(s.x) + ox),
                f32::from(pos.y) - (f32::from(s.y) + oy),
            );
            dx * dx + dy * dy <= HANDLE_GRAB * HANDLE_GRAB
        };

        // A multi-selection offers a group rotate grip (if anything's rotatable)
        // and proportional corner-resize of the group bounds.
        if self.selected.len() > 1 {
            let bb = self.selection_bbox()?;
            if self.group_rotatable() {
                let (rx, ry) = rotate_handle_for_bbox(bb, cam, origin);
                let (dx, dy) = (f32::from(pos.x) - rx, f32::from(pos.y) - ry);
                if dx * dx + dy * dy <= HANDLE_GRAB * HANDLE_GRAB {
                    return Some(HandleGrab::Rotate);
                }
            }
            let wc = [(bb.0, bb.1), (bb.2, bb.1), (bb.0, bb.3), (bb.2, bb.3)];
            let collect_orig = || -> Vec<(u64, ElementKind)> {
                self.scene
                    .elements
                    .iter()
                    .filter(|e| self.is_selected(e.id))
                    .map(|e| (e.id, e.kind.clone()))
                    .collect()
            };
            for i in 0..4 {
                if near(wc[i].0, wc[i].1, 0.0, 0.0) {
                    let opp = wc[3 - i];
                    return Some(HandleGrab::GroupCorner(GroupResizing {
                        handle: ResizeHandle::Corner,
                        anchor: [opp.0, opp.1],
                        from: [wc[i].0, wc[i].1],
                        grab: [wc[i].0 - cursor[0], wc[i].1 - cursor[1]],
                        orig: collect_orig(),
                    }));
                }
            }
            // Edge midpoints stretch one axis (per-axis group resize), each about
            // the opposite edge: a left/right grip scales x, a top/bottom grip y.
            let (mx, my) = ((bb.0 + bb.2) / 2.0, (bb.1 + bb.3) / 2.0);
            let edges = [
                (ResizeHandle::EdgeX, [bb.0, my], (0.0, 0.0), [bb.2, my]),
                (ResizeHandle::EdgeX, [bb.2, my], (0.0, 0.0), [bb.0, my]),
                (ResizeHandle::EdgeY, [mx, bb.1], (0.0, 0.0), [mx, bb.3]),
                (ResizeHandle::EdgeY, [mx, bb.3], (0.0, 0.0), [mx, bb.1]),
            ];
            for (handle, from, (ox, oy), anchor) in edges {
                if near(from[0], from[1], ox, oy) {
                    return Some(HandleGrab::GroupCorner(GroupResizing {
                        handle,
                        anchor,
                        from,
                        grab: [from[0] - cursor[0], from[1] - cursor[1]],
                        orig: collect_orig(),
                    }));
                }
            }
            return None;
        }

        let id = self.selected_single()?;
        let kind = &self.scene.elements.iter().find(|e| e.id == id)?.kind;

        // The rotate handle floats above every rotatable element (not text/cards).
        if rotatable(kind) {
            let (rx, ry) = rotate_handle_screen(kind, cam, origin);
            let (dx, dy) = (f32::from(pos.x) - rx, f32::from(pos.y) - ry);
            if dx * dx + dy * dy <= HANDLE_GRAB * HANDLE_GRAB {
                return Some(HandleGrab::Rotate);
            }
        }

        if let ElementKind::Line(s) | ElementKind::Arrow(s) = kind {
            for (which, (wx, wy)) in [(s.x1, s.y1), (s.x2, s.y2)].into_iter().enumerate() {
                if near(wx, wy, 0.0, 0.0) {
                    return Some(HandleGrab::Endpoint(EndpointDrag { id, which }));
                }
            }
            return None;
        }

        // Box-like (rect/ellipse/text): corners on the (possibly rotated) box.
        // Upright resizes about the opposite corner (free aspect ratio); rotated
        // resizes proportionally about the center — a similarity transform that
        // stays correct under rotation (set up here, applied in `on_move`).
        if let Some((x, y, w, h, rot)) = box_like(kind) {
            let cu = box_padded_corners(x, y, w, h, rot, 0.0);
            let cp = cu;
            let center = [x + w / 2.0, y + h / 2.0];
            let rotated = rot.abs() > ROT_EPS;
            for i in 0..4 {
                if near(cp[i][0], cp[i][1], 0.0, 0.0) {
                    let anchor = if rotated { center } else { cu[(i + 2) % 4] };
                    return Some(HandleGrab::Corner(Resizing {
                        id,
                        handle: ResizeHandle::Corner,
                        anchor,
                        from: cu[i],
                        grab: [cu[i][0] - cursor[0], cu[i][1] - cursor[1]],
                        orig: kind.clone(),
                    }));
                }
            }
            // Edge midpoints stretch one axis. Offered only upright (a rotated
            // box's edges aren't world-axis-aligned) and not for text — a single
            // font size can't stretch one axis, so its edges would just duplicate
            // the proportional corners.
            if !rotated && !matches!(kind, ElementKind::Text(_)) {
                let mid = |a: [f32; 2], b: [f32; 2]| [(a[0] + b[0]) / 2.0, (a[1] + b[1]) / 2.0];
                if let Some(r) = self.edge_handle_hit(
                    id,
                    kind,
                    &near,
                    cursor,
                    mid(cu[0], cu[1]),
                    mid(cu[1], cu[2]),
                    mid(cu[2], cu[3]),
                    mid(cu[3], cu[0]),
                ) {
                    return Some(r);
                }
            }
            return None;
        }

        // Draw / Embed: corners on the padded AABB (offset the hit to match).
        let bb = bbox(kind);
        let wc = [(bb.0, bb.1), (bb.2, bb.1), (bb.0, bb.3), (bb.2, bb.3)];
        for i in 0..4 {
            if near(wc[i].0, wc[i].1, 0.0, 0.0) {
                let opp = wc[3 - i];
                return Some(HandleGrab::Corner(Resizing {
                    id,
                    handle: ResizeHandle::Corner,
                    anchor: [opp.0, opp.1],
                    from: [wc[i].0, wc[i].1],
                    grab: [wc[i].0 - cursor[0], wc[i].1 - cursor[1]],
                    orig: kind.clone(),
                }));
            }
        }
        // Edge midpoints stretch one axis (these kinds are always upright).
        let (mx, my) = ((bb.0 + bb.2) / 2.0, (bb.1 + bb.3) / 2.0);
        self.edge_handle_hit(
            id,
            kind,
            &near,
            cursor,
            [mx, bb.1],
            [bb.2, my],
            [mx, bb.3],
            [bb.0, my],
        )
    }

    /// Shared edge-handle hit-test for a single element: the four edge midpoints
    /// (`top`/`right`/`bottom`/`left`, world space) each stretch one axis about the
    /// opposite edge. `near` is the caller's screen-space proximity test.
    #[allow(clippy::too_many_arguments)]
    fn edge_handle_hit(
        &self,
        id: u64,
        kind: &ElementKind,
        near: &dyn Fn(f32, f32, f32, f32) -> bool,
        cursor: [f32; 2],
        top: [f32; 2],
        right: [f32; 2],
        bottom: [f32; 2],
        left: [f32; 2],
    ) -> Option<HandleGrab> {
        let edges = [
            (ResizeHandle::EdgeY, top, (0.0, 0.0), bottom),
            (ResizeHandle::EdgeY, bottom, (0.0, 0.0), top),
            (ResizeHandle::EdgeX, right, (0.0, 0.0), left),
            (ResizeHandle::EdgeX, left, (0.0, 0.0), right),
        ];
        for (handle, from, (ox, oy), anchor) in edges {
            if near(from[0], from[1], ox, oy) {
                return Some(HandleGrab::Corner(Resizing {
                    id,
                    handle,
                    anchor,
                    from,
                    grab: [from[0] - cursor[0], from[1] - cursor[1]],
                    orig: kind.clone(),
                }));
            }
        }
        None
    }

    /// The topmost connector point under the cursor. Connectors are exposed on
    /// box-like visual elements (closed shapes, text, image) at the midpoints of
    /// their rotated top/right/bottom/left edges.
    fn connector_at(&self, pos: Point<Pixels>) -> Option<ConnectPoint> {
        let origin = self.bounds.get().origin;
        let near_px = CONNECTOR_BUTTON_SIZE * 0.65;
        let (sx, sy) = (f32::from(pos.x), f32::from(pos.y));
        let id = self.selected_single()?;
        let element = self
            .scene
            .elements
            .iter()
            .find(|element| element.id == id && connector_capable(&element.kind))?;
        let points = connector_points(&element.kind);
        let buttons = connector_button_centers(&element.kind, self.scene.camera, origin);
        buttons.into_iter().enumerate().find_map(|(index, button)| {
            let dx = f32::from(button.x) - sx;
            let dy = f32::from(button.y) - sy;
            (dx * dx + dy * dy <= near_px * near_px).then_some(ConnectPoint {
                id,
                index,
                pos: points[index],
            })
        })
    }

    /// Update hover connector state and request repaint only when it changes.
    fn update_hover_connector(&mut self, pos: Point<Pixels>, cx: &mut Context<Self>) {
        let next = if self.tool == Tool::Select
            && self.editing.is_none()
            && self.pending.is_none()
            && self.connecting.is_none()
            && self.drag_from.is_none()
            && self.resizing.is_none()
            && self.group_resizing.is_none()
            && self.endpoint.is_none()
            && self.rotating.is_none()
            && self.marquee.is_none()
        {
            self.connector_at(pos)
        } else {
            None
        };
        if self.hovered_connector != next {
            self.hovered_connector = next;
            cx.notify();
        }
    }

    /// The topmost text element under a world point (within `pad`), if any.
    fn text_at(&self, p: [f32; 2], pad: f32) -> Option<u64> {
        self.scene
            .elements
            .iter()
            .rev()
            .find(|e| matches!(e.kind, ElementKind::Text(_)) && hit_test(&e.kind, p[0], p[1], pad))
            .map(|e| e.id)
    }

    /// The topmost closed shape (rect / ellipse / …) under a world point — for
    /// editing its centered label.
    fn shape_at(&self, p: [f32; 2], pad: f32) -> Option<u64> {
        self.scene
            .elements
            .iter()
            .rev()
            .find(|e| is_closed_shape(&e.kind) && hit_test(&e.kind, p[0], p[1], pad))
            .map(|e| e.id)
    }

    /// The topmost page-card under a world point: `(element id, page id)`.
    fn embed_at(&self, p: [f32; 2], pad: f32) -> Option<(u64, i64)> {
        self.scene
            .elements
            .iter()
            .rev()
            .find_map(|e| match &e.kind {
                ElementKind::Embed(em) if hit_test(&e.kind, p[0], p[1], pad) => {
                    Some((e.id, em.page_id))
                }
                _ => None,
            })
    }

    /// Nearest edge connector on another shape while a connection is being
    /// dragged. This path is intentionally separate from `connector_at`, whose
    /// hit targets are the selected source shape's outward arrow buttons.
    fn snap_connector_at(
        &self,
        pos: Point<Pixels>,
        source_id: u64,
    ) -> Option<(ConnectPoint, bool)> {
        const SHOW_DISTANCE_PX: f32 = 64.0;
        const SNAP_DISTANCE_PX: f32 = 20.0;
        let origin = self.bounds.get().origin;
        let (sx, sy) = (f32::from(pos.x), f32::from(pos.y));
        let world = self.event_to_world(pos);
        let target = self
            .scene
            .elements
            .iter()
            .rev()
            .filter(|element| element.id != source_id && connector_capable(&element.kind))
            .find(|element| {
                hit_test(
                    &element.kind,
                    world[0],
                    world[1],
                    SHOW_DISTANCE_PX / self.scene.camera.zoom.max(MIN_ZOOM),
                )
            })?;
        connector_points(&target.kind)
            .into_iter()
            .enumerate()
            .map(|(index, point)| {
                let screen = to_screen(point[0], point[1], self.scene.camera, origin);
                let dx = f32::from(screen.x) - sx;
                let dy = f32::from(screen.y) - sy;
                let distance_sq = dx * dx + dy * dy;
                (
                    distance_sq,
                    ConnectPoint {
                        id: target.id,
                        index,
                        pos: point,
                    },
                )
            })
            .min_by(|a, b| a.0.total_cmp(&b.0))
            .map(|(distance_sq, connector)| {
                (
                    connector,
                    distance_sq <= SNAP_DISTANCE_PX * SNAP_DISTANCE_PX,
                )
            })
    }

    fn on_left_down(&mut self, ev: &MouseDownEvent, window: &mut Window, cx: &mut Context<Self>) {
        if self.panning {
            return;
        }
        if self.read_only {
            self.panning = true;
            self.last = ev.position;
            return;
        }

        // The draggable toolbar (its pill isn't occluded — like the picker): a
        // press on the grip starts a drag (double-click resets to top-center); a
        // press anywhere else on the pill is consumed so its buttons handle their
        // own clicks. Both must be caught before any canvas logic below.
        if self.toolbar_grip_bounds.get().contains(&ev.position) {
            self.start_toolbar_drag(ev.position, ev.click_count >= 2, window, cx);
            return;
        }
        if self.toolbar_bounds.get().contains(&ev.position) {
            return;
        }

        // A press dismisses an open right-click menu (its own button is occluded,
        // so a press reaching here is outside it).
        if self.context_menu.take().is_some() {
            cx.notify();
            return;
        }
        // A press on the canvas closes an open tool flyout (the flyout itself is
        // occluded, so a press reaching here is outside it).
        if self.open_group.is_some() {
            self.open_group = None;
            cx.notify();
            return;
        }
        // Same for the font flyout (occluded; a press here is outside it).
        if self.font_open {
            self.font_open = false;
            cx.notify();
            return;
        }
        // The thickness flyout: a press on its slider starts a width drag; a press
        // elsewhere on the panel is consumed (presets fire via their own `on_click`);
        // a press outside dismisses it. The panel isn't occluded so drags reach here,
        // like the color picker.
        if self.width_open {
            let pos = ev.position;
            if self.width_bounds.get().contains(&pos) {
                if !self.selected.is_empty() {
                    self.push_undo();
                }
                self.picker_drag = Some(PickerDrag::Width);
                let w = Self::width_from_frac(self.frac_x(self.width_bounds.get(), pos));
                self.set_width_live(w, cx);
                return;
            }
            if self.width_panel_bounds.get().contains(&pos) {
                return;
            }
            self.width_open = false;
            cx.notify();
            return;
        }

        // The color picker takes input priority while open. Its draggable regions
        // (SV square, hue strip) start a drag here; presses on the rest of the
        // panel are consumed (the swatch / Auto buttons fire via their own
        // `on_click`); a press anywhere else closes it.
        if self.picker.is_some() {
            let pos = ev.position;
            if self.sv_bounds.get().contains(&pos) {
                if !self.selected.is_empty() {
                    self.push_undo();
                }
                self.picker_drag = Some(PickerDrag::Sv);
                let (s, v) = self.sv_from_pos(pos);
                if let Some(p) = self.picker.as_mut() {
                    (p.s, p.v) = (s, v);
                }
                if let Some(c) = self.picker_u32() {
                    self.set_color_live(Some(c), cx);
                }
                return;
            }
            if self.hue_bounds.get().contains(&pos) {
                if !self.selected.is_empty() {
                    self.push_undo();
                }
                self.picker_drag = Some(PickerDrag::Hue);
                let h = self.frac_x(self.hue_bounds.get(), pos);
                if let Some(p) = self.picker.as_mut() {
                    p.h = h;
                }
                if let Some(c) = self.picker_u32() {
                    self.set_color_live(Some(c), cx);
                }
                return;
            }
            if self.alpha_bounds.get().contains(&pos) {
                if !self.selected.is_empty() {
                    self.push_undo();
                }
                self.picker_drag = Some(PickerDrag::Alpha);
                let a = self.frac_x(self.alpha_bounds.get(), pos);
                if let Some(p) = self.picker.as_mut() {
                    p.a = a;
                }
                if let Some(c) = self.picker_u32() {
                    self.set_color_live(Some(c), cx);
                }
                return;
            }
            if self.picker_bounds.get().contains(&pos) {
                return;
            }
            self.picker = None;
            cx.notify();
            return;
        }

        // Take keyboard focus so the board's shortcuts (tool keys, ⌫, ⌘Z…) work
        // after a click on the canvas.
        self.focus.focus(window, cx);

        let p = self.event_to_world(ev.position);
        let zoom = self.scene.camera.zoom.max(MIN_ZOOM);

        // A press inside the text being edited drives its caret / selection (no
        // commit). A press anywhere else commits the edit, then falls through.
        if let Some(id) = self.editing {
            if self.point_in_editing_text(id, p) {
                self.place_caret_from_click(id, p, ev, window, cx);
                return;
            }
            self.commit_text(window, cx);
        }

        // Ctrl + left-drag always pans the canvas, regardless of the active tool
        // or what's under the pointer. Reuses the same panning state as the Pan
        // tool and middle-button drag.
        if ev.modifiers.control {
            self.panning = true;
            self.last = ev.position;
            return;
        }

        if ev.click_count >= 2 {
            self.pending = None;
            // Existing text and shape labels have one consistent edit gesture:
            // double-click, regardless of which tool happened to be active.
            if let Some(id) = self.text_at(p, SELECT_PAD / zoom) {
                self.selected = vec![id];
                self.editing = Some(id);
                self.place_caret_from_click(id, p, ev, window, cx);
                return;
            }
            if let Some(id) = self.shape_at(p, SELECT_PAD / zoom) {
                self.selected = vec![id];
                self.editing = Some(id);
                self.place_caret_from_click(id, p, ev, window, cx);
                return;
            }
            if self.tool == Tool::Select {
                // Double-click a page-card opens its page.
                if let Some((id, page_id)) = self.embed_at(p, SELECT_PAD / zoom) {
                    self.selected = vec![id];
                    if let Some(f) = self.on_open.clone() {
                        f(page_id, window, cx);
                    }
                    cx.notify();
                    return;
                }
            }
            self.reset_view(cx);
            return;
        }

        // A single click on any existing element always means selection, even if
        // a drawing/text tool is currently active. This prevents accidentally
        // drawing over a shape when the user only meant to select it. A second
        // click (handled above) is the sole path into text/label editing.
        if self.tool != Tool::Select {
            let pad = SELECT_PAD / zoom;
            let hit = self
                .scene
                .elements
                .iter()
                .rev()
                .find(|element| hit_test(&element.kind, p[0], p[1], pad))
                .map(|element| element.id);
            if let Some(id) = hit {
                self.tool = Tool::Select;
                if ev.modifiers.shift {
                    if let Some(index) = self.selected.iter().position(|&selected| selected == id) {
                        self.selected.remove(index);
                    } else {
                        self.selected.push(id);
                    }
                } else {
                    self.selected = vec![id];
                }
                self.drag_from = None;
                cx.notify();
                return;
            }
        }

        // Pan tool: a left-drag pans the canvas (the default navigation tool;
        // double-click above still recenters). Reuses the middle-drag machinery.
        if self.tool == Tool::Pan {
            self.panning = true;
            self.last = ev.position;
            return;
        }

        if self.tool == Tool::Text {
            // A single click on existing text only selects it. Editing existing
            // content is deliberately double-click-only; clicking empty canvas
            // still creates a fresh text element and immediately edits that.
            if let Some(id) = self.text_at(p, SELECT_PAD / zoom) {
                self.selected = vec![id];
                cx.notify();
            } else {
                self.push_undo();
                let id = self.next_id;
                self.next_id += 1;
                self.scene.elements.push(Element {
                    id,
                    kind: ElementKind::Text(TextGeom {
                        x: p[0],
                        y: p[1],
                        content: String::new(),
                        size: TEXT_SIZE / zoom,
                        rotation: 0.0,
                        measured_w: 0.0,
                        measured_h: 0.0,
                    }),
                    stroke: self.active_stroke,
                    fill: None,
                    label: None,
                    label_color: None,
                    styles: Vec::new(),
                    mindmap: None,
                });
                self.selected = vec![id];
                self.begin_text_edit(id, 0, window, cx);
                self.dirty = true;
                cx.notify();
            }
            return;
        }

        if self.tool == Tool::MindMap {
            self.add_mindmap_seed(p[0], p[1], cx);
            return;
        }

        if self.tool == Tool::Flowchart {
            self.add_flowchart_seed(p[0], p[1], cx);
            return;
        }

        if self.tool == Tool::Embed {
            // The host picks a page, then calls back into `add_embed`.
            if let Some(f) = self.on_place_embed.clone() {
                f(p[0], p[1], window, cx);
            }
            return;
        }

        if self.tool == Tool::Image {
            // The host picks an image file, then calls back into `add_image_at`.
            if let Some(f) = self.on_place_image.clone() {
                f(p[0], p[1], window, cx);
            }
            return;
        }

        if self.tool == Tool::Select {
            // A connector point on a hovered shape starts drawing a line from that
            // exact side/midpoint without switching away from Select.
            if let Some(cp) = self.connector_at(ev.position) {
                let width = self.active_width / zoom;
                self.pending = Some(Pending {
                    anchor: cp.pos,
                    kind: ElementKind::Arrow(SegGeom {
                        x1: cp.pos[0],
                        y1: cp.pos[1],
                        x2: cp.pos[0],
                        y2: cp.pos[1],
                        width,
                        style: SegmentStyle::Solid,
                        start_anchor: Some(SegmentAnchor {
                            element_id: cp.id,
                            connector: cp.index,
                        }),
                        end_anchor: None,
                    }),
                });
                self.connecting = Some(ConnectDrag { from: cp });
                self.hovered_connector = Some(cp);
                cx.notify();
                return;
            }
            // A handle on the current selection takes priority.
            if let Some(grab) = self.handle_hit(ev.position) {
                self.push_undo();
                match grab {
                    HandleGrab::Corner(rs) => self.resizing = Some(rs),
                    HandleGrab::GroupCorner(gr) => self.group_resizing = Some(gr),
                    HandleGrab::Endpoint(ep) => self.endpoint = Some(ep),
                    HandleGrab::Rotate => {
                        // Pivot = the whole selection's bounds center (a single
                        // element's own center, or the group's). Snap on the lone
                        // element's orientation, or — for a group — the first
                        // oriented member's, so it squares to horizontal/vertical
                        // (falling back to quarter-turns if nothing's oriented).
                        if let Some(bb) = self.selection_bbox() {
                            let center = [(bb.0 + bb.2) / 2.0, (bb.1 + bb.3) / 2.0];
                            let base = match self.selected_single() {
                                Some(id) => self
                                    .scene
                                    .elements
                                    .iter()
                                    .find(|e| e.id == id)
                                    .and_then(|e| reference_angle(&e.kind)),
                                None => self
                                    .scene
                                    .elements
                                    .iter()
                                    .filter(|e| self.is_selected(e.id))
                                    .find_map(|e| reference_angle(&e.kind))
                                    .or(Some(0.0)),
                            };
                            let start_pointer = (p[1] - center[1]).atan2(p[0] - center[0]);
                            self.rotating = Some(Rotating {
                                center,
                                start_pointer,
                                applied: 0.0,
                                base,
                            });
                        }
                    }
                }
                cx.notify();
                return;
            }
            // Otherwise hit-test topmost-first.
            let pad = SELECT_PAD / zoom;
            let hit = self
                .scene
                .elements
                .iter()
                .rev()
                .find(|e| hit_test(&e.kind, p[0], p[1], pad))
                .map(|e| e.id);
            match hit {
                Some(id) if ev.modifiers.shift => {
                    // Shift-click toggles membership (no move).
                    if let Some(pos) = self.selected.iter().position(|&s| s == id) {
                        self.selected.remove(pos);
                    } else {
                        self.selected.push(id);
                    }
                    self.drag_from = None;
                }
                Some(id) => {
                    // Click an unselected element selects only it; clicking one
                    // already in the selection keeps the group (so a drag moves
                    // them all). Either way, arm a move.
                    if !self.is_selected(id) {
                        self.selected = vec![id];
                    }
                    self.drag_from = Some(p);
                    // Capture the primary element's top-left so the move can drive
                    // an absolute target (and snap it) without drifting.
                    self.move_origin = self
                        .selected
                        .first()
                        .and_then(|&pid| self.scene.elements.iter().find(|e| e.id == pid))
                        .map(|e| {
                            let (x, y, ..) = bbox(&e.kind);
                            [x, y]
                        })
                        .unwrap_or(p);
                    self.moved = false;
                }
                None => {
                    // Empty space: clear (unless extending) and start a marquee.
                    if !ev.modifiers.shift {
                        self.selected.clear();
                    }
                    self.marquee = Some((p, p));
                    self.drag_from = None;
                }
            }
            cx.notify();
            return;
        }

        let width = self.active_width / zoom;
        // While the snap modifier (Option) is held, start the shape on a grid
        // line; the move handler snaps the opposite corner / endpoint too.
        let anchor = if ev.modifiers.alt {
            [snap_grid(p[0]), snap_grid(p[1])]
        } else {
            p
        };
        // A zero-size box anchored at the press; the move handler grows it.
        let box0 = BoxGeom {
            x: anchor[0],
            y: anchor[1],
            w: 0.0,
            h: 0.0,
            width,
            rotation: 0.0,
        };
        let kind = match self.tool {
            // Freehand keeps the raw point — strokes aren't grid-aligned.
            Tool::Pen => ElementKind::Draw(Stroke {
                points: vec![p],
                width,
            }),
            Tool::Rect => ElementKind::Rect(box0),
            Tool::Ellipse => ElementKind::Ellipse(box0),
            Tool::Diamond => ElementKind::Diamond(box0),
            Tool::Triangle => ElementKind::Triangle(box0),
            Tool::RoundRect => ElementKind::RoundRect(box0),
            Tool::Star => ElementKind::Star(box0),
            Tool::Hexagon => ElementKind::Hexagon(box0),
            Tool::Line => ElementKind::Line(SegGeom {
                x1: anchor[0],
                y1: anchor[1],
                x2: anchor[0],
                y2: anchor[1],
                width,
                style: SegmentStyle::Solid,
                start_anchor: None,
                end_anchor: None,
            }),
            Tool::Arrow => ElementKind::Arrow(SegGeom {
                x1: anchor[0],
                y1: anchor[1],
                x2: anchor[0],
                y2: anchor[1],
                width,
                style: SegmentStyle::Solid,
                start_anchor: None,
                end_anchor: None,
            }),
            Tool::DashedArrow => ElementKind::Arrow(SegGeom {
                x1: anchor[0],
                y1: anchor[1],
                x2: anchor[0],
                y2: anchor[1],
                width,
                style: SegmentStyle::Dashed,
                start_anchor: None,
                end_anchor: None,
            }),
            // These tools don't create a drag-element here (handled earlier).
            Tool::Pan
            | Tool::Select
            | Tool::Text
            | Tool::MindMap
            | Tool::Flowchart
            | Tool::Embed
            | Tool::Image => return,
        };
        self.pending = Some(Pending { anchor, kind });
        cx.notify();
    }

    fn on_left_up(&mut self, _ev: &MouseUpEvent, window: &mut Window, cx: &mut Context<Self>) {
        // Finish a toolbar drag (persist the new position).
        if self.toolbar_drag.is_some() {
            self.commit_toolbar_drag(window, cx);
            return;
        }
        // End a text-selection drag (the selection is applied live in `on_move`).
        if self.text_selecting {
            self.text_selecting = false;
            return;
        }
        // End a Pan-tool drag (left-button pan).
        if self.panning {
            self.panning = false;
            cx.notify();
            self.flush(window, cx);
            return;
        }
        // End a picker drag: the live changes are already applied; just persist.
        if self.picker_drag.take().is_some() {
            self.flush(window, cx);
            return;
        }
        if self.resizing.take().is_some()
            || self.group_resizing.take().is_some()
            || self.endpoint.take().is_some()
            || self.rotating.take().is_some()
        {
            self.dirty = true;
            cx.notify();
            self.flush(window, cx);
            return;
        }
        if self.drag_from.take().is_some() {
            if self.moved {
                self.dirty = true;
            }
            self.moved = false;
            self.alignment_guides = AlignmentGuides::default();
            cx.notify();
            self.flush(window, cx);
            return;
        }
        // Finish a marquee: add every element whose bounds intersect the box.
        if let Some((a, b)) = self.marquee.take() {
            let (x0, x1) = (a[0].min(b[0]), a[0].max(b[0]));
            let (y0, y1) = (a[1].min(b[1]), a[1].max(b[1]));
            for e in &self.scene.elements {
                let bb = bbox(&e.kind);
                let hits = bb.0 <= x1 && bb.2 >= x0 && bb.1 <= y1 && bb.3 >= y0;
                if hits && !self.selected.contains(&e.id) {
                    self.selected.push(e.id);
                }
            }
            cx.notify();
            return;
        }
        if let Some(pending) = self.pending.take() {
            let completed_connection = self.connecting.take().is_some();
            if committable(&pending.kind) {
                self.push_undo();
                let id = self.next_id;
                self.next_id += 1;
                // Fill applies only to closed shapes.
                let fill = if is_closed_shape(&pending.kind) {
                    self.active_fill
                } else {
                    None
                };
                self.scene.elements.push(Element {
                    id,
                    kind: pending.kind,
                    stroke: self.active_stroke,
                    fill,
                    label: None,
                    label_color: self.active_text,
                    styles: Vec::new(),
                    mindmap: None,
                });
                if completed_connection {
                    // The newly-created connector becomes the active object so
                    // its endpoints can be adjusted immediately.
                    self.selected = vec![id];
                    self.focus.focus(window, cx);
                }
                self.dirty = true;
            }
            cx.notify();
        }
        self.flush(window, cx);
    }

    /// Right-click: with a selection (and a host save hook), open a small menu to
    /// save it as a template; otherwise just dismiss any open menu.
    fn on_right_down(&mut self, ev: &MouseDownEvent, _window: &mut Window, cx: &mut Context<Self>) {
        if self.read_only {
            self.context_menu = None;
            cx.notify();
            return;
        }
        // A right-click inside the open color picker (e.g. removing a saved swatch)
        // shouldn't also open the board context menu.
        if self.picker.is_some() && self.picker_bounds.get().contains(&ev.position) {
            return;
        }
        // Show the menu when there's a selection (copy / cut / z-order / save) or
        // paste is wired (so you can paste onto empty canvas). Positioned at the click.
        if self.selected.is_empty() && self.on_paste.is_none() {
            self.context_menu = None;
        } else {
            let b = self.bounds.get();
            self.context_menu = Some(point(
                ev.position.x - b.origin.x,
                ev.position.y - b.origin.y,
            ));
            self.ctx_text_sub = false;
        }
        cx.notify();
    }

    /// Paste board elements from the clipboard (via the host's `on_paste` hook),
    /// centered + selected. Returns whether anything was pasted, so ⌘V can fall
    /// through to image paste when the clipboard holds no board elements.
    fn try_paste(&mut self, window: &mut Window, cx: &mut Context<Self>) -> bool {
        if let Some(f) = self.on_paste.clone()
            && let Some(json) = f(window, cx)
        {
            self.paste_elements(&json, window, cx);
            true
        } else {
            false
        }
    }

    /// Context-menu Paste.
    fn paste_from_menu(&mut self, window: &mut Window, cx: &mut Context<Self>) {
        self.context_menu = None;
        self.try_paste(window, cx);
    }

    fn on_middle_down(
        &mut self,
        ev: &MouseDownEvent,
        _window: &mut Window,
        _cx: &mut Context<Self>,
    ) {
        if self.pending.is_some()
            || self.drag_from.is_some()
            || self.resizing.is_some()
            || self.group_resizing.is_some()
            || self.endpoint.is_some()
            || self.rotating.is_some()
            || self.picker_drag.is_some()
            || self.marquee.is_some()
        {
            return;
        }
        self.panning = true;
        self.last = ev.position;
    }

    fn on_middle_up(&mut self, _ev: &MouseUpEvent, window: &mut Window, cx: &mut Context<Self>) {
        if self.panning {
            self.panning = false;
            cx.notify();
        }
        self.flush(window, cx);
    }

    fn on_move(&mut self, ev: &MouseMoveEvent, _window: &mut Window, cx: &mut Context<Self>) {
        // Dragging the toolbar (its pill follows the cursor).
        if self.toolbar_drag.is_some() {
            self.drag_toolbar(ev.position, cx);
            return;
        }
        // Extending a text selection by dragging — the caret tracks the cursor
        // while the anchor stays put.
        if self.text_selecting
            && let Some(id) = self.editing
            && let Some(tg) = self.edit_target(id)
        {
            let local = block_local(
                tg.x,
                tg.y,
                tg.rotation,
                tg.pivot,
                self.event_to_world(ev.position),
            );
            self.caret = self
                .font
                .index_at_wrapped(&tg.content, tg.size, tg.wrap, local);
            cx.notify();
            return;
        }
        // Dragging a line out of a connector point. Snaps the endpoint to another
        // connector if the cursor is close to one, so shape-to-shape links land cleanly.
        if let Some(conn) = self.connecting {
            let target = self.snap_connector_at(ev.position, conn.from.id);
            let cur = if let Some((target, snapped)) = target {
                self.hovered_connector = Some(target);
                if snapped {
                    target.pos
                } else {
                    self.event_to_world(ev.position)
                }
            } else {
                self.hovered_connector = None;
                self.event_to_world(ev.position)
            };
            if let Some(pending) = self.pending.as_mut()
                && let ElementKind::Line(s) | ElementKind::Arrow(s) = &mut pending.kind
            {
                s.x1 = conn.from.pos[0];
                s.y1 = conn.from.pos[1];
                s.x2 = cur[0];
                s.y2 = cur[1];
                s.start_anchor = Some(SegmentAnchor {
                    element_id: conn.from.id,
                    connector: conn.from.index,
                });
                s.end_anchor = target.and_then(|(target, snapped)| {
                    snapped.then_some(SegmentAnchor {
                        element_id: target.id,
                        connector: target.index,
                    })
                });
            }
            cx.notify();
            return;
        }
        // Dragging inside the color picker (SV square, hue strip, alpha strip) or
        // the thickness flyout's width slider.
        if let Some(drag) = self.picker_drag {
            let pos = ev.position;
            if drag == PickerDrag::Width {
                let w = Self::width_from_frac(self.frac_x(self.width_bounds.get(), pos));
                self.set_width_live(w, cx);
                return;
            }
            match drag {
                PickerDrag::Sv => {
                    let (s, v) = self.sv_from_pos(pos);
                    if let Some(p) = self.picker.as_mut() {
                        (p.s, p.v) = (s, v);
                    }
                }
                PickerDrag::Hue => {
                    let h = self.frac_x(self.hue_bounds.get(), pos);
                    if let Some(p) = self.picker.as_mut() {
                        p.h = h;
                    }
                }
                PickerDrag::Alpha => {
                    let a = self.frac_x(self.alpha_bounds.get(), pos);
                    if let Some(p) = self.picker.as_mut() {
                        p.a = a;
                    }
                }
                PickerDrag::Width => unreachable!("handled above"),
            }
            if let Some(c) = self.picker_u32() {
                self.set_color_live(Some(c), cx);
            }
            return;
        }
        // Rotating the selection (rotate-handle drag). Shift snaps to 15° steps.
        if let Some(mut rot) = self.rotating.take() {
            let cur = self.event_to_world(ev.position);
            let ang = (cur[1] - rot.center[1]).atan2(cur[0] - rot.center[0]);
            let mut total = ang - rot.start_pointer;
            match rot.base {
                // Box/text/line: work in absolute orientation so Shift gives
                // clean 15° angles and, unmodified, it snaps to horizontal /
                // vertical when within ROT_SNAP (the easy-squaring the user wants).
                Some(base) => total = snap_angle(base + total, ev.modifiers.shift) - base,
                // Freehand: no absolute orientation; Shift still steps relatively.
                None => {
                    if ev.modifiers.shift {
                        let step = std::f32::consts::PI / 12.0;
                        total = (total / step).round() * step;
                    }
                }
            }
            // Apply only the change since last frame, normalized to [-π, π] so the
            // atan2 wrap-around at ±π doesn't spin the element a full turn.
            let tau = std::f32::consts::TAU;
            let mut delta = total - rot.applied;
            delta -= (delta / tau).round() * tau;
            // Every selected element turns about the shared pivot (a single
            // selection is just the one, pivoting on its own center).
            let sel = self.selected.clone();
            for e in self.scene.elements.iter_mut() {
                if sel.contains(&e.id) {
                    rotate_element(&mut e.kind, rot.center[0], rot.center[1], delta);
                }
            }
            self.sync_segment_anchors_for(&sel);
            rot.applied += delta;
            self.rotating = Some(rot);
            cx.notify();
            return;
        }
        // Resizing a multi-selection by a group-bounds corner: scale every
        // member uniformly (proportional) about the opposite corner, each from
        // its geometry at grab so the scaling never compounds.
        if let Some(gr) = self.group_resizing.take() {
            let cur = self.event_to_world(ev.position);
            let mut target = [cur[0] + gr.grab[0], cur[1] + gr.grab[1]];
            if ev.modifiers.alt {
                target = [snap_grid(target[0]), snap_grid(target[1])];
            }
            // A corner scales both axes together (proportional); an edge stretches
            // just its own axis, the other held at 1.
            let (sx, sy) = match gr.handle {
                ResizeHandle::Corner => {
                    let s = diagonal_scale(gr.anchor, gr.from, target);
                    (s, s)
                }
                ResizeHandle::EdgeX => (axis_scale(gr.anchor[0], gr.from[0], target[0]), 1.0),
                ResizeHandle::EdgeY => (1.0, axis_scale(gr.anchor[1], gr.from[1], target[1])),
            };
            let font = self.font.clone();
            for (id, orig) in &gr.orig {
                let mut kind = orig.clone();
                resize_about(&mut kind, gr.anchor[0], gr.anchor[1], sx, sy);
                if let ElementKind::Text(t) = &mut kind {
                    let (w, h) = font.measure(&t.content, t.size);
                    (t.measured_w, t.measured_h) = (w, h);
                }
                if let Some(e) = self.scene.elements.iter_mut().find(|e| e.id == *id) {
                    e.kind = kind;
                }
            }
            let changed: Vec<u64> = gr.orig.iter().map(|(id, _)| *id).collect();
            self.sync_segment_anchors_for(&changed);
            self.group_resizing = Some(gr);
            cx.notify();
            return;
        }
        // Resizing the selection (corner- or edge-handle drag).
        if let Some(r) = self.resizing.as_ref() {
            let (id, handle, anchor, from, grab, mut kind) =
                (r.id, r.handle, r.anchor, r.from, r.grab, r.orig.clone());
            let cur = self.event_to_world(ev.position);
            // Where the dragged handle should sit: cursor + the grab offset, so it
            // tracks the cursor without jumping when the drag starts. The snap
            // modifier (Option) lands it on the grid.
            let mut target = [cur[0] + grab[0], cur[1] + grab[1]];
            if ev.modifiers.alt {
                target = [snap_grid(target[0]), snap_grid(target[1])];
            }
            let (sx, sy) = match handle {
                // An edge grip stretches just its axis (the explicit per-axis ask,
                // so it overrides the proportional defaults — even for text/image).
                ResizeHandle::EdgeX => (axis_scale(anchor[0], from[0], target[0]), 1.0),
                ResizeHandle::EdgeY => (1.0, axis_scale(anchor[1], from[1], target[1])),
                // A corner: text and images scale proportionally (text is a single
                // font size; an image would distort otherwise); Shift does so for
                // shapes; and a *rotated* box-like element must (its anchor is the
                // center, so a uniform scale keeps it correct under rotation). All
                // use the diagonal projection so the corner tracks the cursor at the
                // right rate. Otherwise free resize is per-axis.
                ResizeHandle::Corner => {
                    let rotated = box_like(&kind).is_some_and(|(.., r)| r.abs() > ROT_EPS);
                    let proportional = ev.modifiers.shift
                        || rotated
                        || matches!(kind, ElementKind::Text(_) | ElementKind::Image(_));
                    if proportional {
                        let s = diagonal_scale(anchor, from, target);
                        (s, s)
                    } else {
                        (
                            axis_scale(anchor[0], from[0], target[0]),
                            axis_scale(anchor[1], from[1], target[1]),
                        )
                    }
                }
            };
            resize_about(&mut kind, anchor[0], anchor[1], sx, sy);
            let font = self.font.clone();
            if let Some(e) = self.scene.elements.iter_mut().find(|e| e.id == id) {
                e.kind = kind;
                // Re-measure text now so its box tracks the cursor this frame.
                if let ElementKind::Text(t) = &mut e.kind {
                    let (w, h) = font.measure(&t.content, t.size);
                    t.measured_w = w;
                    t.measured_h = h;
                }
            }
            self.sync_segment_anchors_for(&[id]);
            cx.notify();
            return;
        }
        // Dragging a line/arrow endpoint (Shift snaps the angle to 45°, Option
        // snaps the endpoint to the grid).
        if let Some(ep) = self.endpoint {
            let cur = self.event_to_world(ev.position);
            let shift = ev.modifiers.shift;
            if let Some(e) = self.scene.elements.iter_mut().find(|e| e.id == ep.id)
                && let ElementKind::Line(s) | ElementKind::Arrow(s) = &mut e.kind
            {
                let (ox, oy) = if ep.which == 0 {
                    (s.x2, s.y2)
                } else {
                    (s.x1, s.y1)
                };
                let (nx, ny) = if shift {
                    snap_45(ox, oy, cur[0], cur[1])
                } else if ev.modifiers.alt {
                    (snap_grid(cur[0]), snap_grid(cur[1]))
                } else {
                    (cur[0], cur[1])
                };
                if ep.which == 0 {
                    s.x1 = nx;
                    s.y1 = ny;
                    s.start_anchor = None;
                } else {
                    s.x2 = nx;
                    s.y2 = ny;
                    s.end_anchor = None;
                }
            }
            if !ev.modifiers.shift && !ev.modifiers.alt {
                if let Some((target, snapped)) = self.snap_connector_at(ev.position, ep.id)
                    && snapped
                {
                    self.hovered_connector = Some(target);
                    self.set_segment_endpoint_anchor(
                        ep.id,
                        ep.which,
                        Some(SegmentAnchor {
                            element_id: target.id,
                            connector: target.index,
                        }),
                    );
                } else {
                    self.hovered_connector = None;
                }
            } else {
                self.hovered_connector = None;
            }
            cx.notify();
            return;
        }
        // Moving the selection (all selected elements together). The target is
        // the primary's grab position plus the *total* cursor delta from the
        // fixed grab anchor; the snap modifier (Option) rounds that target to the
        // grid. Computing the absolute target each frame (vs. snapping the
        // per-frame delta) keeps the shape under the cursor and never loses
        // sub-grid motion — so it moves on every axis, not just one.
        if let Some(from) = self.drag_from {
            let cur = self.event_to_world(ev.position);
            let target = move_target(self.move_origin, from, cur, ev.modifiers.alt);
            // Where the primary sits now → the delta to apply this frame. Every
            // element kind's bbox-min translates 1:1, so this tracks exactly.
            let cur_min = self
                .selected
                .first()
                .and_then(|&pid| self.scene.elements.iter().find(|e| e.id == pid))
                .map(|e| {
                    let (x, y, ..) = bbox(&e.kind);
                    [x, y]
                })
                .unwrap_or(self.move_origin);
            let (raw_dx, raw_dy) = (target[0] - cur_min[0], target[1] - cur_min[1]);
            let (dx, dy, guides) = if ev.modifiers.alt {
                (raw_dx, raw_dy, AlignmentGuides::default())
            } else {
                self.aligned_move_delta(raw_dx, raw_dy)
            };
            self.alignment_guides = guides;
            if dx != 0.0 || dy != 0.0 {
                if !self.moved {
                    self.push_undo();
                    self.moved = true;
                }
                let sel = self.selected.clone();
                self.detach_segment_bindings_for_move(&sel);
                for e in self.scene.elements.iter_mut() {
                    if sel.contains(&e.id) {
                        translate(&mut e.kind, dx, dy);
                    }
                }
                self.sync_segment_anchors_for(&sel);
                cx.notify();
            }
            return;
        }
        // Dragging a marquee box (started on empty space).
        if let Some((start, _)) = self.marquee {
            let cur = self.event_to_world(ev.position);
            self.marquee = Some((start, cur));
            cx.notify();
            return;
        }
        // Creating an element.
        if self.pending.is_some() {
            let cur = self.event_to_world(ev.position);
            let z = self.scene.camera.zoom.max(MIN_ZOOM);
            let Some(pending) = self.pending.as_mut() else {
                return;
            };
            let anchor = pending.anchor;
            // Snap the growing corner / endpoint to the grid while Option is held
            // (freehand strokes keep the raw point).
            let c = if ev.modifiers.alt {
                [snap_grid(cur[0]), snap_grid(cur[1])]
            } else {
                cur
            };
            match &mut pending.kind {
                ElementKind::Draw(s) => {
                    if let Some(last) = s.points.last() {
                        let (ddx, ddy) = ((cur[0] - last[0]) * z, (cur[1] - last[1]) * z);
                        if ddx * ddx + ddy * ddy < MIN_POINT_PX * MIN_POINT_PX {
                            return;
                        }
                    }
                    s.points.push(cur);
                }
                ElementKind::Rect(b)
                | ElementKind::Ellipse(b)
                | ElementKind::Diamond(b)
                | ElementKind::Triangle(b)
                | ElementKind::RoundRect(b)
                | ElementKind::Star(b)
                | ElementKind::Hexagon(b) => {
                    b.x = anchor[0].min(c[0]);
                    b.y = anchor[1].min(c[1]);
                    b.w = (c[0] - anchor[0]).abs();
                    b.h = (c[1] - anchor[1]).abs();
                }
                ElementKind::Line(s) | ElementKind::Arrow(s) => {
                    s.x2 = c[0];
                    s.y2 = c[1];
                }
                // Text/cards/images aren't created by dragging, never pending here.
                ElementKind::Text(_) | ElementKind::Embed(_) | ElementKind::Image(_) => {}
            }
            cx.notify();
            return;
        }
        self.update_hover_connector(ev.position, cx);
        // Panning.
        if self.panning {
            let dx = f32::from(ev.position.x - self.last.x);
            let dy = f32::from(ev.position.y - self.last.y);
            self.last = ev.position;
            self.scene.camera.pan_by(dx, dy);
            self.dirty = true;
            cx.notify();
        }
    }

    fn on_scroll(&mut self, ev: &ScrollWheelEvent, _window: &mut Window, cx: &mut Context<Self>) {
        let (dx, dy) = match ev.delta {
            ScrollDelta::Pixels(p) => (f32::from(p.x), f32::from(p.y)),
            ScrollDelta::Lines(p) => (p.x * LINE_PX, p.y * LINE_PX),
        };
        if ev.modifiers.platform || ev.modifiers.control {
            let (rx, ry) = self.relative(ev.position);
            let factor = (1.0 + dy * 0.0025).clamp(0.5, 2.0);
            self.scene.camera.zoom_about(rx, ry, factor);
        } else {
            self.scene.camera.pan_by(dx, dy);
        }
        self.dirty = true;
        cx.notify();
    }

    fn on_pinch(&mut self, ev: &PinchEvent, _window: &mut Window, cx: &mut Context<Self>) {
        let (rx, ry) = self.relative(ev.position);
        self.scene.camera.zoom_about(rx, ry, 1.0 + ev.delta);
        self.dirty = true;
        cx.notify();
    }

    /// Canvas-relative position of a window-coords event point.
    fn relative(&self, p: Point<Pixels>) -> (f32, f32) {
        let o = self.bounds.get().origin;
        (f32::from(p.x - o.x), f32::from(p.y - o.y))
    }

    /// A clone of the text element being edited (its content + size + placement).
    /// The text currently being edited — a `Text` element's content, or a closed
    /// shape's centered label — with everything the caret math and click
    /// hit-testing need. `wrap` is `None` for free text, `Some(inner_width)` for a
    /// label (which word-wraps inside its shape). `x`/`y`/`w`/`h`/`rotation` place
    /// the laid-out block in the world.
    fn edit_target(&self, id: u64) -> Option<EditTarget> {
        let e = self.scene.elements.iter().find(|e| e.id == id)?;
        match &e.kind {
            ElementKind::Text(t) => Some(EditTarget {
                content: t.content.clone(),
                size: t.size,
                wrap: None,
                x: t.x,
                y: t.y,
                rotation: t.rotation,
                pivot: [t.x + t.measured_w / 2.0, t.y + t.measured_h / 2.0],
            }),
            kind if is_closed_shape(kind) => {
                let (bx, by, bw, bh, rot) = box_like(kind)?;
                let label = e.label.clone().unwrap_or_default();
                let blk = shape_label_block(&self.font, kind, bx, by, bw, bh, &label);
                Some(EditTarget {
                    content: label,
                    size: blk.size,
                    wrap: Some(blk.wrap),
                    x: blk.x,
                    y: blk.y,
                    rotation: rot,
                    pivot: [bx + bw / 2.0, by + bh / 2.0],
                })
            }
            _ => None,
        }
    }

    /// The selection as an ordered byte range `[start, end)` (empty when the caret
    /// and anchor coincide).
    fn sel_range(&self) -> (usize, usize) {
        (
            self.caret.min(self.sel_anchor),
            self.caret.max(self.sel_anchor),
        )
    }

    /// Move the caret to byte offset `to`; unless `extend` (Shift), collapse the
    /// selection there too.
    fn move_caret(&mut self, to: usize, extend: bool, cx: &mut Context<Self>) {
        self.caret = to;
        if !extend {
            self.sel_anchor = to;
        }
        self.pending_style = None; // a deliberate move ends a pending toggle
        cx.notify();
    }

    /// Replace the editing text's `[s, e)` with `ins`, landing the caret just after
    /// it (collapsed). The single mutation point for typing, deletion, and paste.
    fn replace_range(&mut self, id: u64, s: usize, e: usize, ins: &str, cx: &mut Context<Self>) {
        let pending = self.pending_style;
        let Some(el) = self.scene.elements.iter_mut().find(|el| el.id == id) else {
            return;
        };
        // The inserted text takes a pending toggle (⌘B with no selection), else it
        // inherits the run to the left of the caret.
        let insert_style = pending.unwrap_or_else(|| style_at(&el.styles, s.saturating_sub(1)));
        // Mutate the text — a `Text` element's content, or a closed shape's label.
        let edited = if let ElementKind::Text(t) = &mut el.kind {
            t.content.replace_range(s..e, ins);
            true
        } else if is_closed_shape(&el.kind) {
            el.label
                .get_or_insert_with(String::new)
                .replace_range(s..e, ins);
            true
        } else {
            false
        };
        if edited {
            // Keep the styling aligned to the edited text.
            el.styles = splice_styles(&el.styles, s, e, ins.len(), insert_style);
            self.caret = s + ins.len();
            self.sel_anchor = self.caret;
            self.marked_range = None;
            self.dirty = true;
            cx.notify();
        }
    }

    /// Replace the current selection (or insert at the caret) with `ins`.
    fn replace_selection(&mut self, id: u64, ins: &str, cx: &mut Context<Self>) {
        let (s, e) = self.sel_range();
        self.replace_range(id, s, e, ins, cx);
    }

    fn editing_content(&self) -> Option<String> {
        self.editing
            .and_then(|id| self.edit_target(id).map(|tg| tg.content))
    }

    // Kept byte-for-byte equivalent to zorite-markdown-editor's UTF-16 bridge.
    fn utf16_to_utf8_in(text: &str, offset: usize) -> usize {
        let mut utf8_offset = 0;
        let mut utf16_count = 0;

        for ch in text.chars() {
            if utf16_count >= offset {
                break;
            }
            utf16_count += ch.len_utf16();
            utf8_offset += ch.len_utf8();
        }

        utf8_offset
    }

    fn utf8_to_utf16_in(text: &str, offset: usize) -> usize {
        let mut utf16_offset = 0;
        let mut utf8_count = 0;

        for ch in text.chars() {
            if utf8_count >= offset {
                break;
            }
            utf8_count += ch.len_utf8();
            utf16_offset += ch.len_utf16();
        }

        utf16_offset
    }

    fn utf16_range_to_utf8_in(text: &str, range_utf16: &Range<usize>) -> Range<usize> {
        Self::utf16_to_utf8_in(text, range_utf16.start)
            ..Self::utf16_to_utf8_in(text, range_utf16.end)
    }

    fn utf8_range_to_utf16_in(text: &str, range: &Range<usize>) -> Range<usize> {
        Self::utf8_to_utf16_in(text, range.start)..Self::utf8_to_utf16_in(text, range.end)
    }

    /// Whiteboard storage adapter for the editor's `replace_text_in_visible_range`.
    /// The full inserted text is the marked range; the IME's relative selection is
    /// tracked independently, exactly as in zorite-markdown-editor.
    fn replace_text_in_visible_range(
        &mut self,
        visible_range: Range<usize>,
        new_text: &str,
        selected_range_relative: Option<Range<usize>>,
        mark_inserted_text: bool,
        cx: &mut Context<Self>,
    ) {
        let Some(id) = self.editing else {
            return;
        };
        let insert_start = visible_range.start;
        self.replace_range(id, visible_range.start, visible_range.end, new_text, cx);

        self.marked_range = if mark_inserted_text && !new_text.is_empty() {
            Some(insert_start..insert_start + new_text.len())
        } else {
            None
        };
        let selected_range = selected_range_relative
            .map(|relative| insert_start + relative.start..insert_start + relative.end);
        self.caret = selected_range
            .as_ref()
            .map(|range| range.end)
            .unwrap_or(insert_start + new_text.len());
        self.sel_anchor = selected_range
            .as_ref()
            .map(|range| range.start)
            .unwrap_or(self.caret);
        cx.notify();
    }

    /// The formatting active across the current selection (or, collapsed, the
    /// pending toggle / the run left of the caret) — for menu checkmarks. Plain
    /// when not editing text.
    fn selection_style(&self) -> RunStyle {
        let Some(id) = self.editing else {
            return RunStyle::default();
        };
        let (s, e) = self.sel_range();
        if s >= e
            && let Some(p) = self.pending_style
        {
            return p;
        }
        self.scene
            .elements
            .iter()
            .find(|el| el.id == id)
            .map_or(RunStyle::default(), |el| active_style(&el.styles, s, e))
    }

    /// Toggle a boolean format over the selection while editing text; with a
    /// collapsed caret, arm a pending toggle for the next typed text instead.
    fn apply_format(&mut self, format: Format, cx: &mut Context<Self>) {
        let Some(id) = self.editing else {
            return;
        };
        let (s, e) = self.sel_range();
        if s < e {
            if let Some(el) = self.scene.elements.iter_mut().find(|el| el.id == id) {
                el.styles = toggle_format(&el.styles, s, e, format);
                self.dirty = true;
            }
        } else {
            let mut p = self.selection_style();
            let on = !format.get(&p);
            format.set(&mut p, on);
            self.pending_style = Some(p);
        }
        cx.notify();
    }

    /// Like [`apply_format`](Self::apply_format) for the highlight color.
    fn apply_highlight(&mut self, color: u32, cx: &mut Context<Self>) {
        let Some(id) = self.editing else {
            return;
        };
        let (s, e) = self.sel_range();
        if s < e {
            if let Some(el) = self.scene.elements.iter_mut().find(|el| el.id == id) {
                el.styles = toggle_highlight(&el.styles, s, e, color);
                self.dirty = true;
            }
        } else {
            let mut p = self.selection_style();
            p.highlight = (p.highlight != Some(color)).then_some(color);
            self.pending_style = Some(p);
        }
        cx.notify();
    }

    /// The formatting menu panel — a ✓-marked toggle per format — shared by the
    /// right-click submenu and the toolbar fly-out. Toggling a row keeps the menu
    /// open so the checkmarks update live.
    fn format_menu(
        &self,
        ink: Hsla,
        text: Hsla,
        grid: Hsla,
        bg: Hsla,
        cx: &mut Context<Self>,
    ) -> Div {
        let st = self.selection_style();
        let frow = |id: &'static str, label: &'static str, sc: &'static str, on: bool| {
            div()
                .id(id)
                .flex()
                .items_center()
                .gap(px(8.0))
                .px(px(10.0))
                .py(px(5.0))
                .mx(px(4.0))
                .rounded(px(6.0))
                .text_size(px(12.0))
                .text_color(ink)
                .hover(|s| s.bg(grid))
                .child(div().w(px(12.0)).child(if on { "✓" } else { "" }))
                .child(div().flex_1().child(label))
                .child(div().text_size(px(11.0)).text_color(text).child(sc))
        };
        div()
            .min_w(px(184.0))
            .py(px(4.0))
            .rounded(px(8.0))
            .bg(bg)
            .shadow_lg()
            .border_1()
            .border_color(grid)
            .flex()
            .flex_col()
            .child(
                frow("wb-fmt-bold", "Bold", "⌘B", st.bold)
                    .on_click(cx.listener(|this, _ev, _w, cx| this.apply_format(Format::Bold, cx))),
            )
            .child(
                frow("wb-fmt-italic", "Italic", "⌘I", st.italic).on_click(
                    cx.listener(|this, _ev, _w, cx| this.apply_format(Format::Italic, cx)),
                ),
            )
            .child(
                frow("wb-fmt-underline", "Underline", "⌘U", st.underline).on_click(
                    cx.listener(|this, _ev, _w, cx| this.apply_format(Format::Underline, cx)),
                ),
            )
            .child(
                frow("wb-fmt-strike", "Strikethrough", "⇧⌘X", st.strike).on_click(
                    cx.listener(|this, _ev, _w, cx| this.apply_format(Format::Strike, cx)),
                ),
            )
            .child(
                frow(
                    "wb-fmt-highlight",
                    "Highlight",
                    "⇧⌘H",
                    st.highlight.is_some(),
                )
                .on_click(
                    cx.listener(|this, _ev, _w, cx| this.apply_highlight(HIGHLIGHT_DEFAULT, cx)),
                ),
            )
    }

    /// The caret offset one line up (`dir = -1`) or down (`dir = 1`), keeping the
    /// current column (x). Clamps at the first / last line.
    fn caret_vertical(&self, content: &str, size: f32, wrap: Option<f32>, dir: i32) -> usize {
        let pos = self.font.caret_pos_wrapped(content, size, wrap, self.caret);
        let lh = self.font.measure("", size).1.max(1.0);
        // Aim mid-target-line so `index_at`'s floor lands on it despite rounding.
        let y = (pos[1] + dir as f32 * lh + lh * 0.5).max(0.0);
        self.font.index_at_wrapped(content, size, wrap, [pos[0], y])
    }

    /// Apply one key press while editing text: caret navigation (arrows / Home /
    /// End, ⇧ extends), selection (⌘A, click-drag set elsewhere), clipboard
    /// (⌘C/X/V on the system clipboard), and insertion / deletion. Escape commits.
    fn text_edit_key(&mut self, ev: &KeyDownEvent, window: &mut Window, cx: &mut Context<Self>) {
        let Some(id) = self.editing else {
            return;
        };
        let Some(tg) = self.edit_target(id) else {
            self.commit_text(window, cx);
            return;
        };
        let (content, size, wrap) = (tg.content, tg.size, tg.wrap);
        // Keep the caret/anchor valid against the live content (defensive).
        self.caret = floor_boundary(&content, self.caret);
        self.sel_anchor = floor_boundary(&content, self.sel_anchor);
        let ks = &ev.keystroke;
        if ks.is_ime_in_progress() {
            return;
        }
        let cmd = ks.modifiers.platform || ks.modifiers.control;
        let shift = ks.modifiers.shift;

        if ks.key == "escape" {
            self.commit_text(window, cx);
            return;
        }
        if cmd {
            match ks.key.as_str() {
                "a" => {
                    self.sel_anchor = 0;
                    self.caret = content.len();
                    cx.notify();
                }
                "b" => self.apply_format(Format::Bold, cx),
                "i" => self.apply_format(Format::Italic, cx),
                "u" => self.apply_format(Format::Underline, cx),
                "x" if shift => self.apply_format(Format::Strike, cx),
                "h" if shift => self.apply_highlight(HIGHLIGHT_DEFAULT, cx),
                "c" | "x" => {
                    let (s, e) = self.sel_range();
                    if s < e {
                        cx.write_to_clipboard(gpui::ClipboardItem::new_string(
                            content[s..e].into(),
                        ));
                        if ks.key == "x" {
                            self.replace_range(id, s, e, "", cx);
                        }
                    }
                }
                "v" => {
                    if let Some(text) = cx.read_from_clipboard().and_then(|c| c.text()) {
                        self.replace_selection(id, &text, cx);
                    }
                }
                _ => cx.propagate(), // ⌘Z / ⌘W / … belong to the host
            }
            return;
        }

        if ks.key == "tab" && self.is_mindmap_node(id) {
            self.commit_text(window, cx);
            self.add_mindmap_relative(id, false, window, cx);
            return;
        }
        if ks.key == "enter" && self.is_mindmap_node(id) {
            self.commit_text(window, cx);
            self.add_mindmap_relative(id, true, window, cx);
            return;
        }

        match ks.key.as_str() {
            "left" => {
                let (s, e) = self.sel_range();
                let to = if !shift && s < e {
                    s
                } else {
                    caret_left(&content, self.caret)
                };
                self.move_caret(to, shift, cx);
            }
            "right" => {
                let (s, e) = self.sel_range();
                let to = if !shift && s < e {
                    e
                } else {
                    caret_right(&content, self.caret)
                };
                self.move_caret(to, shift, cx);
            }
            "up" => {
                let to = self.caret_vertical(&content, size, wrap, -1);
                self.move_caret(to, shift, cx);
            }
            "down" => {
                let to = self.caret_vertical(&content, size, wrap, 1);
                self.move_caret(to, shift, cx);
            }
            "home" => self.move_caret(line_start(&content, self.caret), shift, cx),
            "end" => self.move_caret(line_end(&content, self.caret), shift, cx),
            "backspace" => {
                let (s, e) = self.sel_range();
                if s < e {
                    self.replace_range(id, s, e, "", cx);
                } else if self.caret > 0 {
                    self.replace_range(id, caret_left(&content, self.caret), self.caret, "", cx);
                }
            }
            "delete" => {
                let (s, e) = self.sel_range();
                if s < e {
                    self.replace_range(id, s, e, "", cx);
                } else if self.caret < content.len() {
                    self.replace_range(id, self.caret, caret_right(&content, self.caret), "", cx);
                }
            }
            "enter" => self.replace_selection(id, "\n", cx),
            "tab" => cx.propagate(),
            _ => {
                // Printable text is handled by GPUI's ElementInputHandler path.
                // Inserting `key_char` here duplicates IME composition: pinyin is
                // inserted by keydown, then the committed Chinese text is inserted
                // by the input handler. Keep keydown for navigation/deletion only.
                if ks
                    .key_char
                    .as_deref()
                    .is_none_or(|c| c.chars().next().is_none_or(|ch| ch.is_control()))
                {
                    cx.propagate();
                }
            }
        }
    }

    /// Enter edit mode on text `id`, placing the caret at byte offset `at`.
    fn begin_text_edit(&mut self, id: u64, at: usize, window: &mut Window, cx: &mut Context<Self>) {
        self.editing = Some(id);
        self.caret = at;
        self.sel_anchor = at;
        self.marked_range = None;
        self.focus.focus(window, cx);
    }

    /// Whether world point `p` lands on the text being edited (its padded bounds).
    fn point_in_editing_text(&self, id: u64, p: [f32; 2]) -> bool {
        let pad = SELECT_PAD / self.scene.camera.zoom.max(MIN_ZOOM);
        self.scene
            .elements
            .iter()
            .find(|e| e.id == id)
            .is_some_and(|e| {
                let (x0, y0, x1, y1) = bbox(&e.kind);
                p[0] >= x0 - pad && p[0] <= x1 + pad && p[1] >= y0 - pad && p[1] <= y1 + pad
            })
    }

    /// A press inside the text being edited: place the caret at the nearest letter,
    /// extend on Shift, select the word on a double-click, else start a drag-select.
    fn place_caret_from_click(
        &mut self,
        id: u64,
        p: [f32; 2],
        ev: &MouseDownEvent,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        let Some(tg) = self.edit_target(id) else {
            return;
        };
        let local = block_local(tg.x, tg.y, tg.rotation, tg.pivot, p);
        let idx = self
            .font
            .index_at_wrapped(&tg.content, tg.size, tg.wrap, local);
        if ev.click_count >= 2 {
            let (s, e) = word_range(&tg.content, idx);
            self.sel_anchor = s;
            self.caret = e;
            self.text_selecting = false;
        } else {
            self.caret = idx;
            if !ev.modifiers.shift {
                self.sel_anchor = idx;
            }
            self.text_selecting = true;
        }
        // Clicking establishes a new native selection and cancels any stale
        // composition range left by an IME that did not send `unmark_text`.
        self.marked_range = None;
        self.focus.focus(window, cx);
        cx.notify();
    }

    /// Finish editing the current text element, dropping it if it's empty.
    fn commit_text(&mut self, window: &mut Window, cx: &mut Context<Self>) {
        self.text_selecting = false;
        self.pending_style = None;
        self.marked_range = None;
        self.format_flyout = false;
        let Some(id) = self.editing.take() else {
            return;
        };
        if let Some(e) = self.scene.elements.iter_mut().find(|e| e.id == id)
            && is_closed_shape(&e.kind)
            && e.label.as_deref().is_none_or(|s| s.trim().is_empty())
        {
            // A shape stays put; an empty label is just cleared (not persisted).
            e.label = None;
        }
        // An empty free-text element has no purpose of its own → remove it.
        self.scene.elements.retain(|e| {
            e.id != id || !matches!(&e.kind, ElementKind::Text(t) if t.content.trim().is_empty())
        });
        self.dirty = true;
        cx.notify();
        self.flush(window, cx);
    }

    /// Handle a board keyboard shortcut (the board has focus and isn't editing
    /// text). Returns whether the key was consumed. Single letters pick a tool;
    /// ⌫/Del clears the selection's elements; ⌘Z / ⌘⇧Z undo / redo; ⌘C / ⌘X / ⌘V
    /// copy / cut / paste; ⌘] / ⌘[ (± ⇧) reorder z-order; Esc deselects. ⌘V with no
    /// copied elements and other modified chords (⌘W, …) pass through to the host.
    fn handle_shortcut(
        &mut self,
        ev: &KeyDownEvent,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) -> bool {
        let ks = &ev.keystroke;
        let cmd = ks.modifiers.platform || ks.modifiers.control;
        if cmd && ks.key == "z" {
            if ks.modifiers.shift {
                self.redo(window, cx);
            } else {
                self.undo(window, cx);
            }
            return true;
        }
        // Z-order: ⌘] / ⌘[ nudge one step, ⌘⇧] / ⌘⇧[ go all the way. Some keymaps
        // report the shifted bracket as `}` / `{`, so treat that as "all the way"
        // too. Only consumed when something is selected.
        let close = ks.key == "]" || ks.key == "}";
        let open = ks.key == "[" || ks.key == "{";
        if cmd && (close || open) {
            if self.selected.is_empty() {
                return false;
            }
            let all_the_way = ks.modifiers.shift || ks.key == "}" || ks.key == "{";
            let op = match (close, all_the_way) {
                (true, true) => ZOrder::ToFront,
                (true, false) => ZOrder::Forward,
                (false, true) => ZOrder::ToBack,
                (false, false) => ZOrder::Backward,
            };
            self.reorder_selection(op, window, cx);
            return true;
        }
        // Copy / cut the selection to the clipboard (the host's `on_copy` writes
        // it). ⌘V paste is left to propagate so the host can read the clipboard and
        // prefer elements over an image. ⌘C/⌘X are consumed even with nothing
        // selected, so they never fall through to a text copy on the board.
        if cmd && ks.key == "c" {
            self.copy_selection(window, cx);
            return true;
        }
        if cmd && ks.key == "x" {
            if self.copy_selection(window, cx) {
                self.delete_selected(window, cx);
            }
            return true;
        }
        if cmd && ks.key == "v" {
            // Paste copied elements; if the clipboard holds none, fall through so
            // the host can paste a clipboard image instead.
            return self.try_paste(window, cx);
        }
        if cmd || ks.modifiers.alt {
            return false;
        }
        if let Some(tool) = Tool::shortcut(&ks.key) {
            self.set_tool(tool, cx);
            return true;
        }
        match ks.key.as_str() {
            "backspace" | "delete" => self.delete_selected(window, cx),
            "escape" if !self.selected.is_empty() => {
                self.selected.clear();
                cx.notify();
            }
            _ => return false,
        }
        true
    }

    fn on_key(&mut self, ev: &KeyDownEvent, window: &mut Window, cx: &mut Context<Self>) {
        if self.read_only {
            cx.propagate();
            return;
        }
        // Escape cancels an in-progress connector without losing the source
        // shape selection; its four direction buttons become visible again.
        if ev.keystroke.key == "escape" && self.connecting.is_some() {
            self.connecting = None;
            self.pending = None;
            self.hovered_connector = None;
            cx.notify();
            return;
        }
        // Escape closes an open color picker or the templates modal (when the
        // board holds focus).
        if ev.keystroke.key == "escape" && (self.picker.is_some() || self.templates_open) {
            self.picker = None;
            self.templates_open = false;
            cx.notify();
            return;
        }
        // While dragging the toolbar, `R` flips its orientation (row ↔ column);
        // other keys are swallowed so they can't change tools mid-drag.
        if self.toolbar_drag.is_some() {
            let ks = &ev.keystroke;
            if ks.key == "r" && !(ks.modifiers.platform || ks.modifiers.control || ks.modifiers.alt)
            {
                self.toggle_toolbar_orientation(window, cx);
            }
            return;
        }
        // Not editing text → keys are board shortcuts (tools, delete, undo/redo).
        if self.editing.is_none() {
            if !self.handle_shortcut(ev, window, cx) {
                cx.propagate();
            }
            return;
        }
        // Editing → full text-box key handling (caret, selection, edit, clipboard).
        self.text_edit_key(ev, window, cx);
    }
}

impl BoardEmbedView {
    /// Build a read-only embedded board view. The inner board starts in
    /// read-only forced-pan mode.
    pub fn new(scene: Scene, style: WhiteboardStyleFn, cx: &mut Context<Self>) -> Self {
        let board_style = style.clone();
        let board = cx.new(|cx| WhiteboardView::new_read_only(scene, board_style, cx));
        Self {
            board,
            style,
            on_expand: None,
        }
    }

    /// Access the inner board entity for host-driven inspection or updates.
    pub fn board(&self) -> Entity<WhiteboardView> {
        self.board.clone()
    }

    /// Install the callback fired by the embed view's "edit" affordance.
    pub fn set_on_expand(&mut self, f: ExpandEmbedFn) {
        self.on_expand = Some(f);
    }
}

impl Render for BoardEmbedView {
    fn render(&mut self, _window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
        let st = (self.style)();
        let ink = st.ink;
        let panel = st.panel_strong;
        let grid = st.grid;
        let accent = st.accent;
        let button = self.on_expand.as_ref().map(|_| {
            div()
                .id("board-embed-expand")
                .absolute()
                .top(px(10.0))
                .right(px(10.0))
                .h(px(30.0))
                .px(px(10.0))
                .flex()
                .items_center()
                .justify_center()
                .gap(px(6.0))
                .rounded(px(8.0))
                .bg(panel)
                .border_1()
                .border_color(grid.opacity(0.5))
                .hover(|s| s.bg(accent))
                .text_size(px(12.0))
                .text_color(ink)
                .child("↗")
                .child("Edit")
                .on_click(cx.listener(|this, _ev, window, cx| {
                    if let Some(f) = this.on_expand.clone() {
                        f(window, cx);
                    }
                }))
        });
        div()
            .size_full()
            .relative()
            .child(self.board.clone())
            .children(button)
    }
}

impl BoardThumbnailView {
    pub fn new(snapshot: LocalThumbnailSnapshot, style: WhiteboardStyleFn) -> Self {
        Self {
            snapshot,
            style,
            font: Font::default(),
        }
    }

    pub fn snapshot(&self) -> &LocalThumbnailSnapshot {
        &self.snapshot
    }

    pub fn set_snapshot(&mut self, snapshot: LocalThumbnailSnapshot) {
        self.snapshot = snapshot;
    }
}

impl Render for BoardThumbnailView {
    fn render(&mut self, _window: &mut Window, _cx: &mut Context<Self>) -> impl IntoElement {
        let WhiteboardStyle {
            bg,
            grid,
            text,
            ink,
            panel,
            ..
        } = (self.style)();
        let cam = self.snapshot.spec.camera;
        let layers = build_thumbnail_layers(
            &self.snapshot.scene,
            &self.font,
            cam,
            ink,
            text,
            grid,
            panel,
            None,
            None,
            None,
        );
        let board_layer = canvas(
            |_, _, _| {},
            move |bounds, _, window, _| paint_board(bounds, cam, bg, grid, window),
        )
        .absolute()
        .size_full();
        let element_layers: Vec<gpui::AnyElement> = layers
            .into_iter()
            .map(|l| match l {
                Layer::Band(es) => band_canvas(es, cam).into_any_element(),
                Layer::Overlay(el) => el,
            })
            .collect();
        div()
            .size_full()
            .relative()
            .overflow_hidden()
            .child(board_layer)
            .children(element_layers)
    }
}

/// How [`WhiteboardView::reorder_selection`] moves the selection through the
/// paint order (`elements` order; later = on top).
#[derive(Clone, Copy)]
enum ZOrder {
    ToFront,
    Forward,
    Backward,
    ToBack,
}

// --- Text-editing string navigation (byte offsets into the content) ---

/// The previous char boundary before byte offset `at` (0 at the start).
fn caret_left(content: &str, at: usize) -> usize {
    content[..at.min(content.len())]
        .chars()
        .next_back()
        .map_or(0, |c| at - c.len_utf8())
}

/// The next char boundary after byte offset `at` (clamped to the end).
fn caret_right(content: &str, at: usize) -> usize {
    content[at.min(content.len())..]
        .chars()
        .next()
        .map_or(content.len(), |c| at + c.len_utf8())
}

/// Start of the line holding `at` (just past the previous '\n', else 0).
fn line_start(content: &str, at: usize) -> usize {
    content[..at.min(content.len())]
        .rfind('\n')
        .map_or(0, |i| i + 1)
}

/// End of the line holding `at` (just before the next '\n', else the end).
fn line_end(content: &str, at: usize) -> usize {
    let at = at.min(content.len());
    content[at..].find('\n').map_or(content.len(), |i| at + i)
}

/// Round `idx` down to the nearest char boundary (clamped to the length), so a
/// stale offset can never split a multi-byte char and panic.
fn floor_boundary(content: &str, idx: usize) -> usize {
    let mut i = idx.min(content.len());
    while i > 0 && !content.is_char_boundary(i) {
        i -= 1;
    }
    i
}

/// The word (run of alphanumerics / `_`) around `at`, as a `[start, end)` range —
/// for double-click selection. Empty when `at` isn't on a word char.
fn word_range(content: &str, at: usize) -> (usize, usize) {
    let is_word = |c: char| c.is_alphanumeric() || c == '_';
    let at = floor_boundary(content, at);
    let start = content[..at]
        .char_indices()
        .rev()
        .take_while(|(_, c)| is_word(*c))
        .last()
        .map_or(at, |(i, _)| i);
    let end = content[at..]
        .char_indices()
        .take_while(|(_, c)| is_word(*c))
        .last()
        .map_or(at, |(i, c)| at + i + c.len_utf8());
    (start, end)
}

/// World point → text-local space (origin at the block's top-left), undoing the
/// text's rotation about its center so a click maps to the right glyph.
/// The text currently being edited, captured for the caret math + click
/// hit-testing. See [`WhiteboardView::edit_target`].
struct EditTarget {
    content: String,
    size: f32,
    wrap: Option<f32>,
    x: f32,
    y: f32,
    rotation: f32,
    /// Rotation pivot (world) for click → local mapping — the shape's center.
    pivot: [f32; 2],
}

/// A closed shape's label block: world top-left `(x, y)`, the auto-shrunk font
/// size, and the wrap width.
struct LabelBlock {
    x: f32,
    y: f32,
    size: f32,
    wrap: f32,
}

/// Map a model [`RunStyle`] to the renderer's [`font::GlyphStyle`].
fn glyph_style(s: RunStyle) -> font::GlyphStyle {
    font::GlyphStyle {
        bold: s.bold,
        italic: s.italic,
        underline: s.underline,
        strike: s.strike,
        highlight: s.highlight,
    }
}

/// Lay out a closed shape's label inside its box (minus [`LABEL_PAD`]): the
/// auto-shrunk font size, the wrap width, and the block's world placement,
/// centered. Shared by the paint path and the editor so the caret matches the
/// rendered glyphs exactly.
fn shape_label_block(
    font: &Font,
    kind: &ElementKind,
    bx: f32,
    by: f32,
    bw: f32,
    bh: f32,
    label: &str,
) -> LabelBlock {
    // The label wraps + shrinks to fit the shape's *inscribed rectangle* (a
    // fraction of the bounding box), not the box itself — so text never crosses a
    // slanted / round outline. Largest centered inscribed rect: ellipse 1/√2 each
    // axis, diamond ½. A triangle narrows toward its apex, so its band is ½×½
    // sitting on the base (text anchored low, not vertically centered). Star /
    // pointy-top hexagon use a safe central band. (Rect / round-rect = the box.)
    let (wf, hf, bottom) = match kind {
        ElementKind::Ellipse(_) => (
            std::f32::consts::FRAC_1_SQRT_2,
            std::f32::consts::FRAC_1_SQRT_2,
            false,
        ),
        ElementKind::Diamond(_) => (0.5, 0.5, false),
        ElementKind::Triangle(_) => (0.5, 0.5, true),
        ElementKind::Star(_) => (0.5, 0.4, false),
        ElementKind::Hexagon(_) => (0.8, 0.5, false),
        _ => (1.0, 1.0, false),
    };
    let wrap = (bw * wf - 2.0 * LABEL_PAD).max(1.0);
    let ih = (bh * hf - 2.0 * LABEL_PAD).max(1.0);
    let size = font.fit_size(label, wrap, ih, TEXT_SIZE);
    let (w, h) = font.measure_wrapped(label, size, Some(wrap));
    // Always horizontally centered; the triangle's band sits on the base, every
    // other shape is vertically centered too.
    let x = bx + (bw - w) / 2.0;
    let y = if bottom {
        by + bh - LABEL_PAD - h
    } else {
        by + (bh - h) / 2.0
    };
    LabelBlock { x, y, size, wrap }
}

impl WhiteboardView {
    fn render_read_only(&mut self, window: &Window, cx: &mut Context<Self>) -> AnyElement {
        let WhiteboardStyle {
            bg,
            grid,
            text,
            ink,
            panel,
            ..
        } = (self.style)();
        let camera = self.scene.camera;
        let bounds_cell = self.bounds.clone();
        let render_viewport = self.render_viewport(Some(window.viewport_size()));
        let visible_element_ids = self
            .scene
            .elements
            .iter()
            .filter(|element| {
                render_viewport.is_none_or(|viewport| viewport.intersects(bbox(&element.kind)))
            })
            .map(|element| element.id)
            .collect::<HashSet<_>>();
        self.text_layout_cache
            .retain(|element_id, _| visible_element_ids.contains(element_id));
        self.label_layout_cache
            .retain(|element_id, _| visible_element_ids.contains(element_id));
        let layers = build_thumbnail_layers(
            &self.scene,
            &self.font,
            camera,
            ink,
            text,
            grid,
            panel,
            render_viewport,
            Some(&mut self.text_layout_cache),
            Some(&mut self.label_layout_cache),
        );
        let board_layer = canvas(
            move |bounds, _, _| bounds_cell.set(bounds),
            move |bounds, _, window, _| paint_board(bounds, camera, bg, grid, window),
        )
        .absolute()
        .size_full();
        let element_layers = layers.into_iter().map(|layer| match layer {
            Layer::Band(elements) => band_canvas(elements, camera).into_any_element(),
            Layer::Overlay(element) => element,
        });

        div()
            .size_full()
            .relative()
            .overflow_hidden()
            .cursor(if self.panning {
                CursorStyle::ClosedHand
            } else {
                CursorStyle::OpenHand
            })
            .child(board_layer)
            .children(element_layers)
            .on_mouse_down(MouseButton::Left, cx.listener(Self::on_left_down))
            .on_mouse_up(MouseButton::Left, cx.listener(Self::on_left_up))
            .on_mouse_down(MouseButton::Middle, cx.listener(Self::on_middle_down))
            .on_mouse_up(MouseButton::Middle, cx.listener(Self::on_middle_up))
            .on_mouse_move(cx.listener(Self::on_move))
            .on_pinch(cx.listener(Self::on_pinch))
            .child(
                div()
                    .absolute()
                    .left(px(10.0))
                    .bottom(px(8.0))
                    .text_size(px(11.0))
                    .text_color(text)
                    .child(SharedString::from(format!("{:.0}%", camera.zoom * 100.0))),
            )
            .into_any_element()
    }
}

impl Render for WhiteboardView {
    fn render(&mut self, window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
        if self.read_only {
            return self.render_read_only(window, cx);
        }
        let WhiteboardStyle {
            bg,
            grid,
            text,
            ink,
            panel,
            panel_strong,
            accent,
            selection,
            swatches,
        } = (self.style)();
        let cam = self.scene.camera;
        let zoom = cam.zoom.max(MIN_ZOOM);
        let bounds_cell = self.bounds.clone();
        let board_bounds = self.bounds.get();
        let render_viewport = self.render_viewport(Some(window.viewport_size()));
        let visible_element_ids = self
            .scene
            .elements
            .iter()
            .filter(|element| {
                render_viewport.is_none_or(|viewport| viewport.intersects(bbox(&element.kind)))
            })
            .map(|element| element.id)
            .collect::<HashSet<_>>();
        self.text_layout_cache
            .retain(|element_id, _| visible_element_ids.contains(element_id));
        self.label_layout_cache
            .retain(|element_id, _| visible_element_ids.contains(element_id));

        // Decoded bitmaps for image elements, fetched from the host (which decodes
        // off-thread and re-renders when ready). Pre-fetched here — before the
        // element walk below — so the host callback can borrow `window`/`cx`
        // without clashing with the `iter_mut`.
        // Keyed by element id (not src) so two elements sharing a file but at
        // different angles don't collide. The rotation is snapped to a quarter
        // turn (images rotate in 90° steps), so a steady angle hits the host's
        // cache and only re-rotates as the drag crosses a 90° boundary.
        let img_sources: HashMap<u64, gpui::ImageSource> = {
            let items: Vec<(u64, String, f32)> = self
                .scene
                .elements
                .iter()
                .filter(|element| visible_element_ids.contains(&element.id))
                .filter_map(|e| match &e.kind {
                    ElementKind::Image(im) => {
                        Some((e.id, im.src.clone(), snap_quarter(im.rotation)))
                    }
                    _ => None,
                })
                .collect();
            let mut map = HashMap::new();
            if let Some(f) = self.on_image.clone() {
                for (id, src, rot) in items {
                    if let Some(s) = f(&src, rot, window, cx) {
                        map.insert(id, s);
                    }
                }
            }
            map
        };

        // One ordered pass over the elements, building the paint stack as a list
        // of layers in `elements` order (later = on top). Canvas-drawn kinds
        // (shapes / lines / pen / text) accumulate into a "band" canvas; an image
        // or page-card flushes the band and adds its overlay div, so a shape can
        // sit above or below an image. Text is laid out here (measured extent for
        // selection/hit-test + outline segments) so it z-orders and rotates with
        // shapes. Camera-independent glyph outlines are cached by content/style;
        // camera movement only rebuilds their screen-space paths.
        let font = self.font.clone();
        let editing = self.editing;
        let (caret_at, sel_anchor) = (self.caret, self.sel_anchor);
        // A translucent accent fills the selected glyphs (kept readable).
        let sel_fill = gpui::hsla(selection.h, selection.s, selection.l, 0.30);
        let mindmap_connector_styles: HashMap<u64, MindMapConnectorStyle> = self
            .scene
            .elements
            .iter()
            .filter(|element| visible_element_ids.contains(&element.id))
            .filter_map(|element| {
                self.mindmap_connector_style_for_element(&element.kind)
                    .map(|style| (element.id, style))
            })
            .collect();
        let text_layout_cache = &mut self.text_layout_cache;
        let label_layout_cache = &mut self.label_layout_cache;
        let mut layers: Vec<Layer> = Vec::new();
        let mut band: Vec<ElemPaint> = Vec::new();
        for e in self.scene.elements.iter_mut() {
            if !visible_element_ids.contains(&e.id) {
                continue;
            }
            let id = e.id;
            let stroke = e.stroke.map_or(ink, u32_to_hsla);
            let fill = e.fill.map(u32_to_hsla);
            // Disjoint field borrows (vs `&mut e.kind` below) so the text arms can
            // read the label, its color, and the styling without cloning.
            let label = e.label.as_deref();
            let label_color = e.label_color;
            let styles = e.styles.as_slice();
            match &mut e.kind {
                // Page-card: a titled box (top-aligned header + hint) that links
                // to a host page. Subtle border — the accent is the selection.
                ElementKind::Embed(em) => {
                    if !band.is_empty() {
                        layers.push(Layer::Band(std::mem::take(&mut band)));
                    }
                    layers.push(Layer::Overlay(
                        div()
                            .absolute()
                            .left(px((em.x - cam.x) * zoom))
                            .top(px((em.y - cam.y) * zoom))
                            .w(px(em.w * zoom))
                            .h(px(em.h * zoom))
                            .bg(panel)
                            .border_1()
                            .border_color(grid)
                            .rounded(px(8.0))
                            .overflow_hidden()
                            .p(px(10.0 * zoom))
                            .flex()
                            .flex_col()
                            .gap(px(3.0 * zoom))
                            .child(
                                div()
                                    .flex()
                                    .items_center()
                                    .gap(px(6.0 * zoom))
                                    .text_size(px(14.0 * zoom))
                                    .text_color(ink)
                                    .child(div().text_color(accent).child("▤"))
                                    .child(SharedString::from(em.title.clone())),
                            )
                            .child(
                                div()
                                    .text_size(px(11.0 * zoom))
                                    .text_color(text)
                                    .child("Double-click to open"),
                            )
                            .into_any_element(),
                    ));
                }
                // Image: the decoded bitmap (when the host has it ready), placed
                // in the element box's quarter-turn-rotated AABB; else a
                // placeholder while it loads.
                ElementKind::Image(im) => {
                    if !band.is_empty() {
                        layers.push(Layer::Band(std::mem::take(&mut band)));
                    }
                    let rot = snap_quarter(im.rotation);
                    let (bx, by, bw, bh) = if rot.abs() < ROT_EPS {
                        (im.x, im.y, im.w, im.h)
                    } else {
                        let c = box_padded_corners(im.x, im.y, im.w, im.h, rot, 0.0);
                        let (x0, y0, x1, y1) = aabb(&c);
                        (x0, y0, x1 - x0, y1 - y0)
                    };
                    let frame = div()
                        .absolute()
                        .left(px((bx - cam.x) * zoom))
                        .top(px((by - cam.y) * zoom))
                        .w(px(bw * zoom))
                        .h(px(bh * zoom))
                        .overflow_hidden()
                        .rounded(px(2.0));
                    let el = match img_sources.get(&id) {
                        // Set only the width and let gpui derive the height from the
                        // bitmap's aspect (its `Img` forces an `aspect_ratio` from the
                        // image, then ignores it unless a dimension is `Auto` — so
                        // `size_full` makes it overflow the box and clip). The bitmap is
                        // pre-rotated to the box's quarter-turn aspect, so width alone
                        // reproduces the rotated AABB exactly. `Contain` guards rounding.
                        Some(src) => frame.child(
                            gpui::img(src.clone())
                                .w(px(bw * zoom))
                                .object_fit(ObjectFit::Contain),
                        ),
                        None => frame
                            .bg(panel)
                            .border_1()
                            .border_color(grid)
                            .flex()
                            .items_center()
                            .justify_center()
                            .child(
                                div()
                                    .text_size(px(11.0 * zoom))
                                    .text_color(text)
                                    .child("Loading…"),
                            ),
                    };
                    layers.push(Layer::Overlay(el.into_any_element()));
                }
                // Canvas-drawn kinds: shapes / lines / pen / text.
                kind => {
                    let text = if let ElementKind::Text(t) = kind {
                        let layout = cached_text_layout(
                            text_layout_cache,
                            &font,
                            id,
                            &t.content,
                            t.size,
                            None,
                            styles,
                        );
                        t.measured_w = layout.width;
                        t.measured_h = layout.height;
                        // While editing: the caret at its byte offset and the
                        // selection rects (both text-local).
                        let active = editing == Some(id);
                        let caret = active.then(|| font.caret_pos(&t.content, t.size, caret_at));
                        let (s, e) = (caret_at.min(sel_anchor), caret_at.max(sel_anchor));
                        let selection = if active {
                            font.selection_rects(&t.content, t.size, s, e)
                        } else {
                            Vec::new()
                        };
                        Some(TextOutline {
                            segs: layout.segs.clone(),
                            bold_segs: layout.bold_segs.clone(),
                            bold_width: layout.bold_width,
                            color: stroke,
                            x: t.x,
                            y: t.y,
                            rotation: t.rotation,
                            pivot: [t.x + layout.width / 2.0, t.y + layout.height / 2.0],
                            line_height: layout.line_height,
                            caret,
                            selection,
                            sel_color: sel_fill,
                            decorations: layout.decorations.clone(),
                        })
                    } else if is_closed_shape(kind)
                        && let Some((bx, by, bw, bh, rot)) = box_like(kind)
                        && (editing == Some(id) || label.is_some_and(|s| !s.trim().is_empty()))
                    {
                        // Auto-shrink + word-wrap the label to fit inside the shape,
                        // centered. Its block center coincides with the box center, so
                        // it rotates with the shape. The shared `shape_label_block`
                        // keeps this identical to what the editor's caret math uses.
                        // Built while editing even when empty, so the caret shows the
                        // moment you double-click (before the first keystroke).
                        let active = editing == Some(id);
                        let text = label.map_or("", str::trim);
                        let label_layout = cached_label_layout(
                            label_layout_cache,
                            &font,
                            id,
                            kind,
                            bx,
                            by,
                            bw,
                            bh,
                            text,
                            styles,
                        );
                        let caret = active.then(|| {
                            font.caret_pos_wrapped(
                                text,
                                label_layout.size,
                                Some(label_layout.wrap),
                                caret_at,
                            )
                        });
                        let (s, e) = (caret_at.min(sel_anchor), caret_at.max(sel_anchor));
                        let selection = if active {
                            font.selection_rects_wrapped(
                                text,
                                label_layout.size,
                                Some(label_layout.wrap),
                                s,
                                e,
                            )
                        } else {
                            Vec::new()
                        };
                        Some(TextOutline {
                            segs: label_layout.text.segs.clone(),
                            bold_segs: label_layout.text.bold_segs.clone(),
                            bold_width: label_layout.text.bold_width,
                            color: label_color.map_or(stroke, u32_to_hsla),
                            x: bx + label_layout.offset_x,
                            y: by + label_layout.offset_y,
                            rotation: rot,
                            pivot: [bx + bw / 2.0, by + bh / 2.0],
                            line_height: label_layout.text.line_height,
                            caret,
                            selection,
                            sel_color: sel_fill,
                            decorations: label_layout.text.decorations.clone(),
                        })
                    } else {
                        None
                    };
                    band.push(ElemPaint {
                        kind: kind.clone(),
                        stroke,
                        fill,
                        text,
                        mindmap_connector_style: mindmap_connector_styles.get(&id).copied(),
                    });
                }
            }
        }
        if !band.is_empty() {
            layers.push(Layer::Band(band));
        }

        // The in-progress element previews in the current active color / fill.
        let pending_ink = self.active_stroke.map_or(ink, u32_to_hsla);
        let pending_fill = self.active_fill.map(u32_to_hsla);
        let pending = self.pending.as_ref().map(|p| p.kind.clone());
        // A single selection gets the full box + handles (unless it's the text
        // being edited — then just the caret). A multi-selection shows a single
        // enclosing group box instead of per-element outlines (one box stays
        // legible while rotating), with resize corners and — when at least one
        // member can rotate — a shared rotate grip.
        let single_sel = self
            .selected_single()
            .filter(|id| Some(*id) != self.editing)
            .and_then(|id| self.scene.elements.iter().find(|e| e.id == id))
            .map(|e| e.kind.clone());
        let group_sel = (self.selected.len() > 1)
            .then(|| self.selection_bbox())
            .flatten()
            .map(|bb| (bb, self.group_rotatable()));
        let marquee = self.marquee;
        let alignment_guides = self.alignment_guides;
        let snap_target = self.connecting.and_then(|connection| {
            self.hovered_connector
                .filter(|target| target.id != connection.from.id)
                .and_then(|target| {
                    self.scene
                        .elements
                        .iter()
                        .find(|element| element.id == target.id)
                        .map(|element| (element.kind.clone(), target.index))
                })
        });
        const CONNECTOR_ICONS: [(&str, &[u8]); 4] = [
            ("wb-connector-up", include_bytes!("../assets/icons/up.svg")),
            (
                "wb-connector-right",
                include_bytes!("../assets/icons/right.svg"),
            ),
            (
                "wb-connector-down",
                include_bytes!("../assets/icons/down.svg"),
            ),
            (
                "wb-connector-left",
                include_bytes!("../assets/icons/left.svg"),
            ),
        ];
        let connector_buttons: Vec<gpui::AnyElement> = single_sel
            .as_ref()
            .filter(|_| self.connecting.is_none() && self.pending.is_none())
            .filter(|kind| connector_capable(kind))
            .map(|kind| {
                connector_button_centers(kind, cam, board_bounds.origin)
                    .into_iter()
                    .enumerate()
                    .map(|(index, center)| {
                        let (key, bytes) = CONNECTOR_ICONS[index];
                        div()
                            .id(("wb-connector-button", index))
                            .absolute()
                            .left(
                                center.x - board_bounds.origin.x - px(CONNECTOR_BUTTON_SIZE / 2.0),
                            )
                            .top(center.y - board_bounds.origin.y - px(CONNECTOR_BUTTON_SIZE / 2.0))
                            .size(px(CONNECTOR_BUTTON_SIZE))
                            .flex()
                            .items_center()
                            .justify_center()
                            .rounded_full()
                            .bg(panel_strong)
                            .text_color(selection)
                            .shadow_sm()
                            .cursor_pointer()
                            .child(svg_icon(key, bytes, selection, CONNECTOR_BUTTON_SIZE))
                            .into_any_element()
                    })
                    .collect()
            })
            .unwrap_or_default();
        const ROTATE_ICON: &[u8] = include_bytes!("../assets/icons/refresh.svg");
        let rotate_position = single_sel
            .as_ref()
            .filter(|kind| rotatable(kind))
            .map(|kind| rotate_handle_screen(kind, cam, board_bounds.origin))
            .or_else(|| {
                group_sel
                    .filter(|(_, can_rotate)| *can_rotate)
                    .map(|(bounds, _)| rotate_handle_for_bbox(bounds, cam, board_bounds.origin))
            });
        let rotate_button = rotate_position.map(|(x, y)| {
            div()
                .id("wb-rotate-button")
                .absolute()
                .left(px(x) - board_bounds.origin.x - px(CONNECTOR_BUTTON_SIZE / 2.0))
                .top(px(y) - board_bounds.origin.y - px(CONNECTOR_BUTTON_SIZE / 2.0))
                .size(px(CONNECTOR_BUTTON_SIZE))
                .flex()
                .items_center()
                .justify_center()
                .rounded_full()
                .bg(panel_strong)
                .shadow_sm()
                .cursor_pointer()
                .child(svg_icon(
                    "wb-icon-refresh",
                    ROTATE_ICON,
                    selection,
                    CONNECTOR_BUTTON_SIZE - 4.0,
                ))
        });
        let selected_mindmap_root = self.selected_mindmap_root();

        // Tool palette + actions (top-center). The pill `occlude()`s so a press
        // on a button doesn't also act on the board beneath it. Layout, left→right:
        //   pan · select · mindmap · color │ shapes&text▾ · pages&images▾ │ undo · redo · delete
        // `MindMap` is promoted to a first-class toolbar button in the main tool area.
        let active = self.tool;
        let open_group = self.open_group;

        // A bare tool button (icon + active highlight). The caller attaches the
        // tooltip and click handler, so this borrows nothing from `self`/`cx` and
        // can be reused for both the main bar and the flyout.
        let tool_btn = |t: Tool| {
            let icon: gpui::AnyElement = match t.icon() {
                Some((key, bytes)) => svg_icon(key, bytes, ink, 16.0).into_any_element(),
                None => t.glyph().into_any_element(),
            };
            let mut b = div()
                .id(("wb-tool", t as usize))
                .size(px(30.0))
                .flex()
                .items_center()
                .justify_center()
                .rounded(px(6.0))
                .text_size(px(15.0))
                .text_color(ink)
                .child(icon);
            // The hover tint also makes gpui repaint on hover transitions, which
            // is what lets a tooltip dismiss when the cursor leaves the button
            // (the canvas doesn't repaint on a bare mouse-move otherwise).
            if t == active {
                b = b.bg(accent);
            } else {
                b = b.hover(|s| s.bg(grid));
            }
            b
        };

        // A category button: shows the group's active tool (else a representative)
        // with a ▾ affordance, and highlights while its group owns the active tool
        // or its flyout is open.
        let cat_btn = |g: ToolGroup| {
            let shown = if g.contains(active) {
                active
            } else {
                g.representative()
            };
            let icon: gpui::AnyElement = match shown.icon() {
                Some((key, bytes)) => svg_icon(key, bytes, ink, 16.0).into_any_element(),
                None => shown.glyph().into_any_element(),
            };
            let mut b = div()
                .id(("wb-group", g as usize))
                .h(px(30.0))
                .px(px(6.0))
                .flex()
                .items_center()
                .justify_center()
                .gap(px(1.0))
                .rounded(px(6.0))
                .text_color(ink)
                .child(icon)
                .child(div().text_size(px(8.0)).text_color(text).child("▾"));
            if open_group == Some(g) || g.contains(active) {
                b = b.bg(accent);
            } else {
                b = b.hover(|s| s.bg(grid));
            }
            b
        };

        // The category buttons (one per `ToolGroup`), with the standalone Text
        // tool slotted in right after the Lines group.
        let mut cats: Vec<gpui::AnyElement> = Vec::with_capacity(ToolGroup::ALL.len() + 1);
        for &g in ToolGroup::ALL.iter() {
            cats.push(
                cat_btn(g)
                    .tooltip(self.tip(g.label()))
                    .on_click(cx.listener(move |this, _ev, window, cx| {
                        this.focus.focus(window, cx);
                        this.toggle_group(g, cx);
                    }))
                    .into_any_element(),
            );
            if g == ToolGroup::Lines {
                cats.push(
                    tool_btn(Tool::Text)
                        .tooltip(self.tip(Tool::Text.label()))
                        .on_click(cx.listener(|this, _ev, _w, cx| this.set_tool(Tool::Text, cx)))
                        .into_any_element(),
                );
            }
        }

        const UNDO_ICON: &[u8] = include_bytes!("../assets/icons/undo.svg");
        const REDO_ICON: &[u8] = include_bytes!("../assets/icons/redo.svg");
        const DELETE_ICON: &[u8] = include_bytes!("../assets/icons/delete.svg");
        let act = |id: usize, key: &'static str, bytes: &'static [u8]| {
            div()
                .id(("wb-act", id))
                .size(px(30.0))
                .flex()
                .items_center()
                .justify_center()
                .rounded(px(6.0))
                .hover(|s| s.bg(grid))
                .child(svg_icon(key, bytes, ink, 16.0))
        };
        // Color button: a swatch of the current ink that toggles the picker.
        let cur_swatch = self.active_stroke.map_or(ink, u32_to_hsla);
        let mut color_btn = div()
            .id("wb-color")
            .size(px(30.0))
            .flex()
            .items_center()
            .justify_center()
            .rounded(px(6.0));
        if self.picker.is_some() {
            color_btn = color_btn.bg(accent);
        } else {
            color_btn = color_btn.hover(|s| s.bg(grid));
        }
        let color_btn = color_btn
            .child(
                div()
                    .size(px(16.0))
                    .rounded(px(4.0))
                    .bg(cur_swatch)
                    .border_1()
                    .border_color(grid),
            )
            .tooltip(self.tip("Color"))
            .on_click(cx.listener(|this, _ev, window, cx| {
                this.focus.focus(window, cx);
                this.toggle_picker(cx);
            }));
        // Thickness button: a bar of the current stroke weight (in the current ink)
        // that toggles the thickness flyout — sits next to color.
        let mut width_btn = div()
            .id("wb-width")
            .size(px(30.0))
            .flex()
            .items_center()
            .justify_center()
            .rounded(px(6.0));
        if self.width_open {
            width_btn = width_btn.bg(accent);
        } else {
            width_btn = width_btn.hover(|s| s.bg(grid));
        }
        let width_btn = width_btn
            .child(
                div()
                    .w(px(16.0))
                    .h(px(self.active_width.clamp(1.0, 8.0)))
                    .rounded_full()
                    .bg(cur_swatch),
            )
            .tooltip(self.tip("Thickness"))
            .on_click(cx.listener(|this, _ev, window, cx| {
                this.focus.focus(window, cx);
                this.toggle_width(cx);
            }));
        // Font button: a per-board text face ("Aa"); opens a small flyout to upload
        // a `.ttf`/`.otf` or revert to the default. Hidden without a host hook.
        let font_btn = self.on_pick_font.is_some().then(|| {
            let mut b = div()
                .id("wb-font")
                .size(px(30.0))
                .flex()
                .items_center()
                .justify_center()
                .rounded(px(6.0));
            if self.font_open {
                b = b.bg(accent);
            } else {
                b = b.hover(|s| s.bg(grid));
            }
            b.child(div().text_size(px(15.0)).text_color(ink).child("Aa"))
                .tooltip(self.tip("Font"))
                .on_click(cx.listener(|this, _ev, window, cx| {
                    this.focus.focus(window, cx);
                    this.toggle_font(cx);
                }))
        });
        // Templates button: opens the gallery modal (its own toolbar item, since
        // a gallery of cards doesn't belong among the tool icons).
        const TEMPLATES_ICON: &[u8] = include_bytes!("../assets/icons/templates.svg");
        let mut templates_btn = div()
            .id("wb-templates")
            .size(px(30.0))
            .flex()
            .items_center()
            .justify_center()
            .rounded(px(6.0))
            .child(svg_icon("wb-icon-templates", TEMPLATES_ICON, ink, 16.0));
        if self.templates_open {
            templates_btn = templates_btn.bg(accent);
        } else {
            templates_btn = templates_btn.hover(|s| s.bg(grid));
        }
        let templates_btn = templates_btn
            .tooltip(self.tip("Templates"))
            .on_click(cx.listener(|this, _ev, window, cx| {
                this.focus.focus(window, cx);
                this.toggle_templates(cx);
            }));
        // Dotted drag grip + bounds capture so the toolbar can be moved. The pill
        // is NOT occluded (like the color picker): a grip press starts a drag and a
        // press elsewhere on the pill is consumed in `on_left_down`, so the buttons
        // still fire their own clicks.
        let grip_cell = self.toolbar_grip_bounds.clone();
        let pill_cell = self.toolbar_bounds.clone();
        let vertical = self.toolbar_vertical;
        let dot_row = move || {
            div()
                .flex()
                .gap(px(3.0))
                .child(div().size(px(2.5)).rounded_full().bg(text))
                .child(div().size(px(2.5)).rounded_full().bg(text))
        };
        let grip = div()
            .id("wb-grip")
            .relative()
            .flex()
            .flex_col()
            .justify_center()
            .gap(px(3.0))
            .px(px(4.0))
            .h(px(30.0))
            .cursor(CursorStyle::OpenHand)
            .tooltip(self.tip("Drag to move · Tap R to flip · double-click to reset"))
            .child(
                canvas(move |b, _, _| grip_cell.set(b), |_, _, _, _| {})
                    .absolute()
                    .size_full(),
            )
            .child(dot_row())
            .child(dot_row())
            .child(dot_row());
        // A "Format" button — shown only while editing text — toggling the
        // text-formatting fly-out.
        let format_btn = self.editing.is_some().then(|| {
            let mut b = div()
                .id("wb-format-btn")
                .size(px(30.0))
                .flex()
                .items_center()
                .justify_center()
                .rounded(px(6.0))
                .text_size(px(14.0))
                .text_color(ink)
                .tooltip(self.tip("Text formatting"))
                .child("A");
            if self.format_flyout {
                b = b.bg(accent);
            } else {
                b = b.hover(|s| s.bg(grid));
            }
            b.on_click(cx.listener(|this, _ev, _w, cx| {
                this.format_flyout = !this.format_flyout;
                cx.notify();
            }))
        });
        let mut pill = div()
            .relative()
            .flex()
            .items_center()
            .gap(px(2.0))
            .p(px(3.0))
            .rounded(px(9.0))
            .bg(panel);
        if vertical {
            pill = pill.flex_col();
        }
        let mut pill = pill
            .child(
                canvas(move |b, _, _| pill_cell.set(b), |_, _, _, _| {})
                    .absolute()
                    .size_full(),
            )
            .child(grip)
            .child(toolbar_divider(grid, vertical))
            // navigate + color
            .child(
                tool_btn(Tool::Pan)
                    .tooltip(self.tip(Tool::Pan.label()))
                    .on_click(cx.listener(|this, _ev, _w, cx| this.set_tool(Tool::Pan, cx))),
            )
            .child(
                tool_btn(Tool::Select)
                    .tooltip(self.tip(Tool::Select.label()))
                    .on_click(cx.listener(|this, _ev, _w, cx| this.set_tool(Tool::Select, cx))),
            );
        if let Some(root_id) = selected_mindmap_root {
            let direction = self.mindmap_root_direction(root_id);
            let connector_style = self.mindmap_connector_style_for_root(root_id);
            let chip = |id: &'static str, active: bool, icon: gpui::AnyElement| {
                let mut d = div()
                    .id(id)
                    .px(px(8.0))
                    .h(px(24.0))
                    .flex()
                    .items_center()
                    .justify_center()
                    .rounded(px(6.0))
                    .text_size(px(11.0))
                    .text_color(ink);
                if active {
                    d = d.bg(accent);
                } else {
                    d = d.hover(|s| s.bg(grid));
                }
                d.child(icon)
            };
            let icon_color = ink;
            let draw_mm_icon = move |_id: &'static str, kind: &'static str| -> gpui::AnyElement {
                canvas(
                    |_, _, _| {},
                    move |bounds, _, window, _| {
                        let w = f32::from(bounds.size.width);
                        let h = f32::from(bounds.size.height);
                        let ox = f32::from(bounds.origin.x);
                        let oy = f32::from(bounds.origin.y);
                        let p = |x: f32, y: f32| point(px(ox + x), px(oy + y));
                        let mut stroke = |segments: &[([f32; 2], [f32; 2])]| {
                            let mut pb = PathBuilder::stroke(px(1.75));
                            for &([x1, y1], [x2, y2]) in segments {
                                pb.move_to(p(x1, y1));
                                pb.line_to(p(x2, y2));
                            }
                            if let Ok(path) = pb.build() {
                                window.paint_path(path, icon_color);
                            }
                        };
                        match kind {
                            "dir-both" => stroke(&[
                                ([3.0, h / 2.0], [w - 3.0, h / 2.0]),
                                ([3.0, h / 2.0], [6.0, h / 2.0 - 3.0]),
                                ([3.0, h / 2.0], [6.0, h / 2.0 + 3.0]),
                                ([w - 3.0, h / 2.0], [w - 6.0, h / 2.0 - 3.0]),
                                ([w - 3.0, h / 2.0], [w - 6.0, h / 2.0 + 3.0]),
                            ]),
                            "dir-right" => stroke(&[
                                ([3.0, h / 2.0], [w - 3.0, h / 2.0]),
                                ([w - 3.0, h / 2.0], [w - 6.0, h / 2.0 - 3.0]),
                                ([w - 3.0, h / 2.0], [w - 6.0, h / 2.0 + 3.0]),
                            ]),
                            "dir-left" => stroke(&[
                                ([3.0, h / 2.0], [w - 3.0, h / 2.0]),
                                ([3.0, h / 2.0], [6.0, h / 2.0 - 3.0]),
                                ([3.0, h / 2.0], [6.0, h / 2.0 + 3.0]),
                            ]),
                            "line-straight" => stroke(&[([3.0, h / 2.0], [w - 3.0, h / 2.0])]),
                            "line-bezier" => {
                                let mut pb = PathBuilder::stroke(px(1.75));
                                pb.move_to(p(2.5, h - 4.0));
                                pb.cubic_bezier_to(
                                    p(w - 2.5, 4.0),
                                    p(w * 0.35, h - 4.0),
                                    p(w * 0.65, 4.0),
                                );
                                if let Ok(path) = pb.build() {
                                    window.paint_path(path, icon_color);
                                }
                            }
                            "line-orthogonal" => stroke(&[
                                ([3.0, h - 4.0], [w * 0.45, h - 4.0]),
                                ([w * 0.45, h - 4.0], [w * 0.45, 4.0]),
                                ([w * 0.45, 4.0], [w - 3.0, 4.0]),
                            ]),
                            _ => {}
                        }
                    },
                )
                .w(px(14.0))
                .h(px(14.0))
                .into_any_element()
            };
            pill = pill
                .child(toolbar_divider(grid, vertical))
                .child(
                    div()
                        .px(px(4.0))
                        .text_size(px(11.0))
                        .text_color(text)
                        .child("Direction"),
                )
                .child(
                    chip(
                        "wb-mm-dir-both",
                        direction == MindMapRootDirection::Both,
                        draw_mm_icon("wb-mm-dir-both-icon", "dir-both"),
                    )
                    .on_click(cx.listener(move |this, _ev, _window, cx| {
                        this.set_mindmap_root_direction(root_id, MindMapRootDirection::Both, cx);
                    })),
                )
                .child(
                    chip(
                        "wb-mm-dir-right",
                        direction == MindMapRootDirection::Right,
                        draw_mm_icon("wb-mm-dir-right-icon", "dir-right"),
                    )
                    .on_click(cx.listener(move |this, _ev, _window, cx| {
                        this.set_mindmap_root_direction(root_id, MindMapRootDirection::Right, cx);
                    })),
                )
                .child(
                    chip(
                        "wb-mm-dir-left",
                        direction == MindMapRootDirection::Left,
                        draw_mm_icon("wb-mm-dir-left-icon", "dir-left"),
                    )
                    .on_click(cx.listener(move |this, _ev, _window, cx| {
                        this.set_mindmap_root_direction(root_id, MindMapRootDirection::Left, cx);
                    })),
                )
                .child(toolbar_divider(grid, vertical))
                .child(
                    div()
                        .px(px(4.0))
                        .text_size(px(11.0))
                        .text_color(text)
                        .child("Connector"),
                )
                .child(
                    chip(
                        "wb-mm-line-straight",
                        connector_style == MindMapConnectorStyle::Straight,
                        draw_mm_icon("wb-mm-line-straight-icon", "line-straight"),
                    )
                    .on_click(cx.listener(move |this, _ev, _window, cx| {
                        this.set_mindmap_connector_style(
                            root_id,
                            MindMapConnectorStyle::Straight,
                            cx,
                        );
                    })),
                )
                .child(
                    chip(
                        "wb-mm-line-bezier",
                        connector_style == MindMapConnectorStyle::Bezier,
                        draw_mm_icon("wb-mm-line-bezier-icon", "line-bezier"),
                    )
                    .on_click(cx.listener(move |this, _ev, _window, cx| {
                        this.set_mindmap_connector_style(
                            root_id,
                            MindMapConnectorStyle::Bezier,
                            cx,
                        );
                    })),
                )
                .child(
                    chip(
                        "wb-mm-line-orthogonal",
                        connector_style == MindMapConnectorStyle::Orthogonal,
                        draw_mm_icon("wb-mm-line-orthogonal-icon", "line-orthogonal"),
                    )
                    .on_click(cx.listener(move |this, _ev, _window, cx| {
                        this.set_mindmap_connector_style(
                            root_id,
                            MindMapConnectorStyle::Orthogonal,
                            cx,
                        );
                    })),
                );
        } else {
            pill = pill
                .child(color_btn)
                .child(width_btn)
                .children(font_btn)
                .children(format_btn)
                .child(toolbar_divider(grid, vertical))
                // tool categories (each opens a flyout of its tools)
                .children(cats)
                .child(templates_btn);
        }
        let pill = pill
            .child(toolbar_divider(grid, vertical))
            // actions
            .child(
                act(0, "wb-icon-undo", UNDO_ICON)
                    .tooltip(self.tip("Undo (⌘Z)"))
                    .on_click(cx.listener(|this, _ev, window, cx| this.undo(window, cx))),
            )
            .child(
                act(1, "wb-icon-redo", REDO_ICON)
                    .tooltip(self.tip("Redo (⌘⇧Z)"))
                    .on_click(cx.listener(|this, _ev, window, cx| this.redo(window, cx))),
            )
            .child(
                act(2, "wb-icon-delete", DELETE_ICON)
                    .tooltip(self.tip("Delete selection (⌫)"))
                    .on_click(
                        cx.listener(|this, _ev, window, cx| this.delete_selected(window, cx)),
                    ),
            );
        // Default top-center; once dragged, an absolute board-relative position
        // (clamped to the board each paint, so a position persisted under a larger
        // window can't strand the bar — and its grip — off-screen).
        let tb_pos = self.toolbar_pos.map(|(x, y)| self.clamp_toolbar(x, y));
        let toolbar = match tb_pos {
            Some((x, y)) => div().absolute().left(px(x)).top(px(y)).child(pill),
            None => div()
                .absolute()
                .top(px(10.0))
                .left_0()
                .right_0()
                .flex()
                .justify_center()
                .child(pill),
        };
        // Flyouts / picker hang off the toolbar: under a horizontal bar (centered
        // by default, else under its top-left — 42px matches the 10→52 gap), or to
        // the right of a vertical bar (anchored to its captured bounds, so it works
        // whether centered or dragged). Call `.child(panel)` on the result.
        let pill_b = self.toolbar_bounds.get();
        let board_o = self.bounds.get().origin;
        let pill_top = f32::from(pill_b.origin.y) - f32::from(board_o.y);
        let pill_right =
            f32::from(pill_b.origin.x) - f32::from(board_o.x) + f32::from(pill_b.size.width);
        let has_bounds = f32::from(pill_b.size.width) > 1.0;
        let popover_anchor = move || -> Div {
            if vertical && has_bounds {
                div()
                    .absolute()
                    .left(px(pill_right + 6.0))
                    .top(px(pill_top))
            } else {
                match tb_pos {
                    Some((x, y)) => div().absolute().left(px(x)).top(px(y + 42.0)),
                    None => div()
                        .absolute()
                        .top(px(52.0))
                        .left_0()
                        .right_0()
                        .flex()
                        .justify_center(),
                }
            }
        };

        // Tool-category flyout (centered below the toolbar), built only while a
        // group is open. Occluded like the main bar; picking a tool activates it
        // and closes the flyout (via `set_tool`), and a press elsewhere on the
        // canvas closes it (see `on_left_down`).
        let flyout =
            open_group.map(|g| {
                let mut row = div()
                    .flex()
                    .items_center()
                    .gap(px(2.0))
                    .p(px(3.0))
                    .rounded(px(9.0))
                    .bg(panel_strong)
                    .shadow_lg()
                    .occlude();
                for &t in g.tools() {
                    row = row.child(tool_btn(t).tooltip(self.tip(t.label())).on_click(
                        cx.listener(move |this, _ev, window, cx| {
                            this.focus.focus(window, cx);
                            this.set_tool(t, cx);
                        }),
                    ));
                }
                popover_anchor().child(row)
            });

        // The toolbar's text-formatting fly-out (the same panel as the right-click
        // submenu), shown while the "Format" button is toggled on during a text edit.
        let format_panel = (self.editing.is_some() && self.format_flyout).then(|| {
            popover_anchor().child(
                self.format_menu(ink, text, grid, panel_strong, cx)
                    .occlude(),
            )
        });

        // Thickness flyout (centered below the toolbar): a row of preset weights
        // (the active one highlighted) over a slider for any custom width. Presets
        // fire via `on_click`; the slider drags via `on_left_down`/`on_move` (so the
        // panel is *not* occluded — presses fall through, like the color picker).
        // A press outside the panel dismisses it (see `on_left_down`).
        let width_cell = self.width_bounds.clone();
        let width_panel_cell = self.width_panel_bounds.clone();
        let width_frac =
            ((self.active_width - WIDTH_MIN) / (WIDTH_MAX - WIDTH_MIN)).clamp(0.0, 1.0);
        let width_flyout = self.width_open.then(|| {
            let mut presets = div().flex().items_center().gap(px(2.0));
            for (i, w) in WIDTH_PRESETS.into_iter().enumerate() {
                let active = (self.active_width - w).abs() < 0.01;
                let mut opt = div()
                    .id(("wb-width-opt", i))
                    .size(px(30.0))
                    .flex()
                    .items_center()
                    .justify_center()
                    .rounded(px(6.0));
                if active {
                    opt = opt.bg(accent);
                } else {
                    opt = opt.hover(|s| s.bg(grid));
                }
                presets = presets.child(
                    opt.child(
                        div()
                            .w(px(18.0))
                            .h(px(w.clamp(1.0, 9.0)))
                            .rounded_full()
                            .bg(cur_swatch),
                    )
                    .on_click(
                        cx.listener(move |this, _ev, window, cx| this.set_width(w, window, cx)),
                    ),
                );
            }
            // The custom-width slider: a bar whose height *is* the current weight,
            // with a thumb at the value. Dragging it lands in `on_left_down`/`on_move`.
            let slider = div()
                .relative()
                .w(px(WIDTH_SLIDER_W))
                .h(px(WIDTH_MAX + 6.0))
                .flex()
                .items_center()
                .child(
                    canvas(move |b, _, _| width_cell.set(b), |_, _, _, _| {})
                        .absolute()
                        .size_full(),
                )
                .child(
                    div()
                        .w_full()
                        .h(px(self.active_width.clamp(1.0, WIDTH_MAX)))
                        .rounded_full()
                        .bg(cur_swatch),
                )
                .child(
                    div()
                        .absolute()
                        .top_0()
                        .bottom_0()
                        .left(px(width_frac * WIDTH_SLIDER_W - 1.5))
                        .w(px(3.0))
                        .rounded(px(2.0))
                        .bg(hsla(0.0, 0.0, 1.0, 1.0))
                        .border_1()
                        .border_color(hsla(0.0, 0.0, 0.0, 0.45)),
                );
            let panel = div()
                .relative()
                .flex()
                .flex_col()
                .items_center()
                .gap(px(6.0))
                .p(px(6.0))
                .rounded(px(9.0))
                .bg(panel_strong)
                .shadow_lg()
                .child(
                    canvas(move |b, _, _| width_panel_cell.set(b), |_, _, _, _| {})
                        .absolute()
                        .size_full(),
                )
                .child(presets)
                .child(slider);
            popover_anchor().child(panel)
        });

        // Font flyout: upload a `.ttf`/`.otf`, or revert to the bundled default.
        // Occluded (a press outside dismisses it via `on_left_down`); each row fires
        // the host hook, which loads the face and calls `set_font` for this board.
        let font_flyout = (self.font_open && self.on_pick_font.is_some()).then(|| {
            let row = |id: &'static str, label: &'static str| {
                div()
                    .id(id)
                    .px(px(12.0))
                    .py(px(6.0))
                    .mx(px(4.0))
                    .rounded(px(6.0))
                    .text_size(px(12.0))
                    .text_color(ink)
                    .hover(|s| s.bg(grid))
                    .child(label)
            };
            let panel = div()
                .occlude()
                .py(px(4.0))
                .min_w(px(168.0))
                .rounded(px(9.0))
                .bg(panel_strong)
                .shadow_lg()
                .border_1()
                .border_color(grid)
                .flex()
                .flex_col()
                .child(row("wb-font-upload", "Upload font…").on_click(cx.listener(
                    |this, _ev, window, cx| {
                        this.font_open = false;
                        if let Some(f) = this.on_pick_font.clone() {
                            f(FontPick::Upload, window, cx);
                        }
                        cx.notify();
                    },
                )))
                .child(row("wb-font-default", "Use default").on_click(cx.listener(
                    |this, _ev, window, cx| {
                        this.font_open = false;
                        if let Some(f) = this.on_pick_font.clone() {
                            f(FontPick::Default, window, cx);
                        }
                        cx.notify();
                    },
                )));
            popover_anchor().child(panel)
        });

        // Right-click context menu (a selection's "Save as template"), anchored at
        // the cursor. Occluded so its button doesn't fall through to the canvas;
        // any other press dismisses it (see `on_left_down`).
        let menu =
            self.context_menu.map(|pos| {
                // One clickable row; clicking runs `act` and closes the menu.
                let row = |id: &'static str, label: &'static str, shortcut: &'static str| {
                    div()
                        .id(id)
                        .flex()
                        .items_center()
                        .justify_between()
                        .gap(px(16.0))
                        .px(px(10.0))
                        .py(px(5.0))
                        .mx(px(4.0))
                        .rounded(px(6.0))
                        .text_size(px(12.0))
                        .text_color(ink)
                        .hover(|s| s.bg(grid))
                        .child(label)
                        .child(div().text_size(px(11.0)).text_color(text).child(shortcut))
                };
                let divider = || div().my(px(4.0)).mx(px(8.0)).h(px(1.0)).bg(grid);
                let has_sel = !self.selected.is_empty();
                let mut panel = div()
                    .absolute()
                    .left(pos.x)
                    .top(pos.y)
                    .occlude()
                    .min_w(px(176.0))
                    .py(px(4.0))
                    .rounded(px(8.0))
                    .bg(panel_strong)
                    .shadow_lg()
                    .border_1()
                    .border_color(grid)
                    .flex()
                    .flex_col();
                // While editing text, a "Text ▸" row expands the formatting submenu.
                if self.editing.is_some() {
                    panel = panel
                        .child(row("wb-ctx-text", "Text", "▸").on_click(cx.listener(
                            |this, _ev, _w, cx| {
                                this.ctx_text_sub = !this.ctx_text_sub;
                                cx.notify();
                            },
                        )))
                        .child(divider());
                }
                // Z-order + copy / cut act on the selection, so they show only with one.
                if has_sel {
                    panel =
                        panel
                            .child(row("wb-ctx-front", "Bring to Front", "⌘⇧]").on_click(
                                cx.listener(|this, _ev, window, cx| {
                                    this.context_menu = None;
                                    this.reorder_selection(ZOrder::ToFront, window, cx);
                                }),
                            ))
                            .child(row("wb-ctx-forward", "Bring Forward", "⌘]").on_click(
                                cx.listener(|this, _ev, window, cx| {
                                    this.context_menu = None;
                                    this.reorder_selection(ZOrder::Forward, window, cx);
                                }),
                            ))
                            .child(row("wb-ctx-backward", "Send Backward", "⌘[").on_click(
                                cx.listener(|this, _ev, window, cx| {
                                    this.context_menu = None;
                                    this.reorder_selection(ZOrder::Backward, window, cx);
                                }),
                            ))
                            .child(
                                row("wb-ctx-back", "Send to Back", "⌘⇧[").on_click(cx.listener(
                                    |this, _ev, window, cx| {
                                        this.context_menu = None;
                                        this.reorder_selection(ZOrder::ToBack, window, cx);
                                    },
                                )),
                            )
                            .child(divider())
                            .child(row("wb-ctx-copy", "Copy", "⌘C").on_click(cx.listener(
                                |this, _ev, window, cx| {
                                    this.context_menu = None;
                                    this.copy_selection(window, cx);
                                },
                            )))
                            .child(row("wb-ctx-cut", "Cut", "⌘X").on_click(cx.listener(
                                |this, _ev, window, cx| {
                                    this.context_menu = None;
                                    if this.copy_selection(window, cx) {
                                        this.delete_selected(window, cx);
                                    }
                                },
                            )));
                }
                // Paste shows whenever the host wired it (so it works on empty canvas).
                if self.on_paste.is_some() {
                    panel = panel.child(row("wb-ctx-paste", "Paste", "⌘V").on_click(
                        cx.listener(|this, _ev, window, cx| this.paste_from_menu(window, cx)),
                    ));
                }
                // "Save as template" only with a selection and a wired host callback.
                if has_sel && self.on_save_template.is_some() {
                    panel = panel.child(divider()).child(
                        row("wb-ctx-save-template", "Save as template", "").on_click(cx.listener(
                            |this, _ev, window, cx| {
                                this.context_menu = None;
                                this.save_selection_as_template(window, cx);
                            },
                        )),
                    );
                }
                panel
            });

        // The "Text ▸" formatting submenu — a fly-out beside the context menu with
        // a ✓ on each active format. Toggling a row keeps the menu open so the
        // checkmarks update live; clicking off (anywhere else) dismisses it.
        let text_submenu = self
            .context_menu
            .filter(|_| self.ctx_text_sub && self.editing.is_some())
            .map(|pos| {
                self.format_menu(ink, text, grid, panel_strong, cx)
                    .absolute()
                    .left(pos.x + px(184.0))
                    .top(pos.y)
                    .occlude()
            });

        // Templates gallery modal: a dimming scrim (click to dismiss) centering a
        // panel of preview cards. The panel `occlude()`s so clicks on it don't
        // reach the scrim; a card stamps its template and closes (see
        // `apply_template`), and Escape closes it (see `on_key`).
        let templates_modal = self.templates_open.then(|| {
            let body = if self.templates.is_empty() {
                div()
                    .flex_1()
                    .flex()
                    .items_center()
                    .justify_center()
                    .p(px(28.0))
                    .child(
                        div()
                            .max_w(px(320.0))
                            .text_size(px(12.0))
                            .text_color(text)
                            .child(
                                "No templates yet. Select shapes on the canvas, right-click, \
                                 and choose “Save as template”.",
                            ),
                    )
                    .into_any_element()
            } else {
                let mut grid_el = div().flex().flex_wrap().gap(px(8.0)).justify_center();
                for i in 0..self.templates.len() {
                    grid_el = grid_el.child(self.template_card(i, ink, text, grid, bg, cx));
                }
                div()
                    .id("wb-tmpl-scroll")
                    .flex_1()
                    .min_h_0()
                    .overflow_y_scroll()
                    .p(px(12.0))
                    .child(grid_el)
                    .into_any_element()
            };
            let panel = div()
                .w(px(540.0))
                .max_h(px(460.0))
                .flex()
                .flex_col()
                .rounded(px(12.0))
                .bg(panel_strong)
                .shadow_lg()
                .border_1()
                .border_color(grid)
                .occlude()
                // header
                .child(
                    div()
                        .flex()
                        .items_center()
                        .justify_between()
                        .px(px(14.0))
                        .py(px(10.0))
                        .border_b_1()
                        .border_color(grid)
                        .child(div().text_size(px(14.0)).text_color(ink).child("Templates"))
                        .child(
                            div()
                                .id("wb-tmpl-close")
                                .size(px(22.0))
                                .flex()
                                .items_center()
                                .justify_center()
                                .rounded(px(6.0))
                                .text_size(px(15.0))
                                .text_color(text)
                                .hover(|s| s.bg(grid))
                                .child("✕")
                                .on_click(cx.listener(|this, _ev, _w, cx| {
                                    this.templates_open = false;
                                    cx.notify();
                                })),
                        ),
                )
                .child(body)
                // footer hint
                .child(
                    div()
                        .px(px(14.0))
                        .py(px(8.0))
                        .border_t_1()
                        .border_color(grid)
                        .text_size(px(10.0))
                        .text_color(text)
                        .child("Click to add · right-click to delete"),
                );
            div()
                .absolute()
                .size_full()
                .flex()
                .items_center()
                .justify_center()
                .bg(hsla(0.0, 0.0, 0.0, 0.35))
                .occlude()
                .on_mouse_down(
                    MouseButton::Left,
                    cx.listener(|this, _ev, _w, cx| {
                        this.templates_open = false;
                        cx.notify();
                    }),
                )
                .child(panel)
        });

        // Color picker panel (below the toolbar), built only while open. Not
        // occluded: presses fall through to `on_left_down`, which routes the SV
        // square / hue strip to drags (via the captured bounds), consumes presses
        // elsewhere on the panel, and closes on a press outside it.
        let sv_cell = self.sv_bounds.clone();
        let hue_cell = self.hue_bounds.clone();
        let alpha_cell = self.alpha_bounds.clone();
        let panel_cell = self.picker_bounds.clone();
        let swatch_list = swatches;
        let white = hsla(0.0, 0.0, 1.0, 1.0);
        // The stroke / fill colors backing the two target tabs (selection's, else
        // the active value). `None` = theme ink (stroke) or unfilled (fill).
        let stroke_disp = self
            .selected_single()
            .and_then(|id| self.scene.elements.iter().find(|e| e.id == id))
            .and_then(|e| e.stroke)
            .or(self.active_stroke);
        let fill_disp = self
            .selected_single()
            .and_then(|id| self.scene.elements.iter().find(|e| e.id == id))
            .and_then(|e| e.fill)
            .or(self.active_fill);
        let text_disp = self
            .selected_single()
            .and_then(|id| self.scene.elements.iter().find(|e| e.id == id))
            .and_then(|e| e.label_color)
            .or(self.active_text);
        let picker_panel = self.picker.map(|p| {
            let cur = hsva_to_u32(p.h, p.s, p.v, p.a);
            let hex = format!("#{:06X}", cur >> 8);
            let clear = hsla(0.0, 0.0, 0.0, 0.0);

            // Stroke / fill target tabs. The active one is highlighted; clicking
            // re-seeds the controls from that property's color.
            let tab = |active: bool, sw: Hsla, label: &'static str, id: &'static str| {
                let mut d = div()
                    .id(id)
                    .flex()
                    .items_center()
                    .gap(px(6.0))
                    .px(px(8.0))
                    .py(px(4.0))
                    .rounded(px(6.0))
                    .text_size(px(12.0))
                    .text_color(ink);
                if active {
                    d = d.bg(accent);
                }
                d.child(
                    div()
                        .size(px(12.0))
                        .rounded(px(3.0))
                        .bg(sw)
                        .border_1()
                        .border_color(grid),
                )
                .child(label)
            };
            let tabs = div()
                .flex()
                .gap(px(6.0))
                .child(
                    tab(
                        p.target == PickerTarget::Stroke,
                        stroke_disp.map_or(ink, u32_to_hsla),
                        "Stroke",
                        "wb-tab-stroke",
                    )
                    .on_click(cx.listener(|this, _ev, _w, cx| {
                        this.set_picker_target(PickerTarget::Stroke, cx)
                    })),
                )
                .child(
                    tab(
                        p.target == PickerTarget::Fill,
                        fill_disp.map_or(clear, u32_to_hsla),
                        "Fill",
                        "wb-tab-fill",
                    )
                    .on_click(cx.listener(|this, _ev, _w, cx| {
                        this.set_picker_target(PickerTarget::Fill, cx)
                    })),
                )
                .child(
                    tab(
                        p.target == PickerTarget::Text,
                        text_disp.map_or(ink, u32_to_hsla),
                        "Text",
                        "wb-tab-text",
                    )
                    .on_click(cx.listener(|this, _ev, _w, cx| {
                        this.set_picker_target(PickerTarget::Text, cx)
                    })),
                );

            let sv_square = div()
                .relative()
                .w(px(SV_W))
                .h(px(SV_H))
                .rounded(px(5.0))
                .overflow_hidden()
                .bg(hsla(p.h, 1.0, 0.5, 1.0))
                .child(div().absolute().size_full().bg(linear_gradient(
                    90.0,
                    linear_color_stop(white, 0.0),
                    linear_color_stop(hsla(0.0, 0.0, 1.0, 0.0), 1.0),
                )))
                .child(div().absolute().size_full().bg(linear_gradient(
                    180.0,
                    linear_color_stop(hsla(0.0, 0.0, 0.0, 0.0), 0.0),
                    linear_color_stop(hsla(0.0, 0.0, 0.0, 1.0), 1.0),
                )))
                .child(
                    canvas(move |b, _, _| sv_cell.set(b), |_, _, _, _| {})
                        .absolute()
                        .size_full(),
                )
                .child(
                    div()
                        .absolute()
                        .left(px(p.s * SV_W - 7.0))
                        .top(px((1.0 - p.v) * SV_H - 7.0))
                        .size(px(14.0))
                        .rounded_full()
                        .border_2()
                        .border_color(white),
                );

            let seg = |from: f32, to: f32| {
                div().flex_1().h_full().bg(linear_gradient(
                    90.0,
                    linear_color_stop(hsla(from, 1.0, 0.5, 1.0), 0.0),
                    linear_color_stop(hsla(to, 1.0, 0.5, 1.0), 1.0),
                ))
            };
            let hue_strip = div()
                .relative()
                .w(px(SV_W))
                .h(px(HUE_H))
                .rounded(px(4.0))
                .overflow_hidden()
                .flex()
                .child(seg(0.0, 1.0 / 6.0))
                .child(seg(1.0 / 6.0, 2.0 / 6.0))
                .child(seg(2.0 / 6.0, 3.0 / 6.0))
                .child(seg(3.0 / 6.0, 4.0 / 6.0))
                .child(seg(4.0 / 6.0, 5.0 / 6.0))
                .child(seg(5.0 / 6.0, 1.0))
                .child(
                    canvas(move |b, _, _| hue_cell.set(b), |_, _, _, _| {})
                        .absolute()
                        .size_full(),
                )
                .child(
                    div()
                        .absolute()
                        .left(px(p.h * SV_W - 1.5))
                        .top(px(-2.0))
                        .w(px(3.0))
                        .h(px(HUE_H + 4.0))
                        .rounded(px(2.0))
                        .bg(white)
                        .border_1()
                        .border_color(hsla(0.0, 0.0, 0.0, 0.5)),
                );

            // Alpha (opacity) strip: transparent → the current color, opaque.
            let alpha_strip = div()
                .relative()
                .w(px(SV_W))
                .h(px(HUE_H))
                .rounded(px(4.0))
                .overflow_hidden()
                .bg(linear_gradient(
                    90.0,
                    linear_color_stop(clear, 0.0),
                    linear_color_stop(u32_to_hsla(hsv_to_u32(p.h, p.s, p.v)), 1.0),
                ))
                .child(
                    canvas(move |b, _, _| alpha_cell.set(b), |_, _, _, _| {})
                        .absolute()
                        .size_full(),
                )
                .child(
                    div()
                        .absolute()
                        .left(px(p.a * SV_W - 1.5))
                        .top(px(-2.0))
                        .w(px(3.0))
                        .h(px(HUE_H + 4.0))
                        .rounded(px(2.0))
                        .bg(white)
                        .border_1()
                        .border_color(hsla(0.0, 0.0, 0.0, 0.5)),
                );

            // Reset means "back to theme ink" for stroke, "no fill" for fill.
            let reset_label = if p.target == PickerTarget::Fill {
                "None"
            } else {
                "Auto"
            };
            let info_row = div()
                .flex()
                .items_center()
                .gap(px(8.0))
                .child(
                    div()
                        .size(px(22.0))
                        .rounded(px(4.0))
                        .bg(u32_to_hsla(cur))
                        .border_1()
                        .border_color(grid),
                )
                .child(
                    div()
                        .flex_1()
                        .text_size(px(12.0))
                        .text_color(text)
                        .child(SharedString::from(hex)),
                )
                .child(
                    div()
                        .id("wb-color-auto")
                        .px(px(8.0))
                        .py(px(3.0))
                        .rounded(px(5.0))
                        .border_1()
                        .border_color(grid)
                        .text_size(px(12.0))
                        .text_color(ink)
                        .child(reset_label)
                        .on_click(
                            cx.listener(|this, _ev, window, cx| this.pick_color(None, window, cx)),
                        ),
                );

            let mut swatch_views = Vec::with_capacity(swatch_list.len());
            for (i, c) in swatch_list.iter().enumerate() {
                let col = *c;
                swatch_views.push(
                    div()
                        .id(("wb-swatch", i))
                        .size(px(20.0))
                        .rounded(px(4.0))
                        .bg(col)
                        .border_1()
                        .border_color(grid)
                        .on_click(cx.listener(move |this, _ev, window, cx| {
                            this.pick_color(Some(hsla_to_u32(col)), window, cx)
                        })),
                );
            }
            // Theme swatches, kept on one line. Its width (`n` swatches of 20px +
            // 6px gaps) sets the panel width, and the Saved column is sized to the
            // space it leaves beside the controls — so the panel crops to this row
            // (no dead space) and saved colors wrap rather than run off the edge.
            let theme_row_w = (swatch_views.len() as f32 * 26.0 - 6.0).max(0.0);
            let saved_col_w = (theme_row_w - SV_W - 12.0).max(64.0);
            let swatch_grid = div().flex().flex_wrap().gap(px(6.0)).children(swatch_views);

            // The gradient controls (the swatch row spans the full panel below).
            let controls_col = div()
                .flex()
                .flex_col()
                .gap(px(10.0))
                .child(tabs)
                .child(sv_square)
                .child(hue_strip)
                .child(alpha_strip)
                .child(info_row);

            // The user's saved palette: the right column (filling the dead space). A
            // `+` saves the current color; each swatch applies on click, removes on
            // right-click. Persisted by the host via `on_save_colors`.
            let mut saved_grid = div().flex().flex_wrap().gap(px(6.0));
            if self.saved_colors.is_empty() {
                saved_grid = saved_grid.child(
                    div()
                        .w_full()
                        .text_size(px(11.0))
                        .text_color(text)
                        .child("Tap + to save a color"),
                );
            } else {
                for (i, &c) in self.saved_colors.iter().enumerate() {
                    saved_grid = saved_grid.child(
                        div()
                            .id(("wb-saved", i))
                            .size(px(20.0))
                            .rounded(px(4.0))
                            .bg(u32_to_hsla(c))
                            .border_1()
                            .border_color(grid)
                            .tooltip(self.tip("Click to use · right-click to remove"))
                            .on_click(cx.listener(move |this, _ev, window, cx| {
                                this.pick_color(Some(c), window, cx)
                            }))
                            .on_mouse_down(
                                MouseButton::Right,
                                cx.listener(move |this, _ev, window, cx| {
                                    this.remove_saved_color(c, window, cx)
                                }),
                            ),
                    );
                }
            }
            // Sized to the space the one-line swatch row leaves beside the controls,
            // so the panel crops to that row (no dead space) and the saved swatches
            // wrap within this column instead of forming one long row.
            let saved_col = div()
                .flex()
                .flex_col()
                .flex_none()
                .w(px(saved_col_w))
                .gap(px(8.0))
                .child(
                    div()
                        .flex()
                        .items_center()
                        .justify_between()
                        .child(div().text_size(px(11.0)).text_color(text).child("Saved"))
                        .child(
                            div()
                                .id("wb-save-color")
                                .size(px(20.0))
                                .flex()
                                .items_center()
                                .justify_center()
                                .rounded(px(4.0))
                                .border_1()
                                .border_color(grid)
                                .text_size(px(14.0))
                                .text_color(ink)
                                .hover(|s| s.bg(grid))
                                .child("+")
                                .tooltip(self.tip("Save current color"))
                                .on_click(cx.listener(|this, _ev, window, cx| {
                                    this.save_current_color(window, cx)
                                })),
                        ),
                )
                .child(saved_grid);

            // Top: the gradient controls with the Saved palette beside them (in the
            // space the one-line swatch row leaves free). Swatch row spans below.
            let top_row = div()
                .flex()
                .flex_row()
                .items_start()
                .gap(px(12.0))
                .child(controls_col)
                .child(saved_col);

            popover_anchor().child(
                div()
                    .relative()
                    .flex()
                    .flex_col()
                    .gap(px(10.0))
                    .p(px(10.0))
                    .rounded(px(10.0))
                    .bg(panel_strong)
                    .shadow_lg()
                    .border_1()
                    .border_color(grid)
                    .child(
                        canvas(move |b, _, _| panel_cell.set(b), |_, _, _, _| {})
                            .absolute()
                            .size_full(),
                    )
                    .child(top_row)
                    .child(swatch_grid),
            )
        });

        // Pan tool shows a grab cursor (closed while dragging) to read as "drag
        // to move the canvas"; other tools use the default arrow.
        let board_cursor = if self.panning {
            CursorStyle::ClosedHand
        } else if self.tool == Tool::Pan {
            CursorStyle::OpenHand
        } else {
            CursorStyle::Arrow
        };

        // The board paints as a stack of layers (back → front): the grid /
        // background; then the element layers (canvas "bands" interleaved with
        // image / page-card overlays, in z-order); then a top "chrome" canvas for
        // the in-progress element, selection box, and marquee — kept above the
        // content so handles stay visible over images.
        let board_layer = canvas(
            move |bounds, _, _| bounds_cell.set(bounds),
            move |bounds, _, window, _| paint_board(bounds, cam, bg, grid, window),
        )
        .absolute()
        .size_full();
        let element_layers: Vec<gpui::AnyElement> = layers
            .into_iter()
            .map(|l| match l {
                Layer::Band(es) => band_canvas(es, cam).into_any_element(),
                Layer::Overlay(el) => el,
            })
            .collect();
        let chrome_layer = canvas(
            |_, _, _| {},
            move |bounds, _, window, _| {
                if let Some(k) = &pending {
                    paint_element(
                        k,
                        None,
                        cam,
                        bounds.origin,
                        pending_ink,
                        pending_fill,
                        window,
                    );
                }
                if let Some(k) = &single_sel {
                    paint_selection(k, cam, bounds.origin, selection, window);
                }
                if let Some((kind, active)) = &snap_target {
                    paint_snap_points(kind, *active, cam, bounds.origin, selection, window);
                }
                // Group: resize handles without an enclosing blue frame, plus a
                // shared rotate grip when the group can rotate.
                if let Some((bb, _can_rotate)) = group_sel {
                    let tl = to_screen(bb.0, bb.1, cam, bounds.origin);
                    let br = to_screen(bb.2, bb.3, cam, bounds.origin);
                    let m = 0.0;
                    let (x0, y0) = (f32::from(tl.x) - m, f32::from(tl.y) - m);
                    let (x1, y1) = (f32::from(br.x) + m, f32::from(br.y) + m);
                    // Four corners (proportional) plus four edge midpoints (per-axis
                    // stretch). The midpoints align with `handle_hit`'s edge grips.
                    let (mx, my) = ((x0 + x1) / 2.0, (y0 + y1) / 2.0);
                    for (hx, hy) in [
                        (x0, y0),
                        (x1, y0),
                        (x0, y1),
                        (x1, y1),
                        (mx, y0),
                        (mx, y1),
                        (x0, my),
                        (x1, my),
                    ] {
                        draw_handle(hx, hy, selection, window);
                    }
                }
                if let Some((a, b)) = marquee {
                    paint_marquee(a, b, cam, bounds.origin, selection, window);
                }
                paint_alignment_guides(alignment_guides, bounds, cam, selection, window);
            },
        )
        .absolute()
        .size_full();

        let root = div()
            .track_focus(&self.focus)
            .size_full()
            .relative()
            .overflow_hidden()
            .cursor(board_cursor)
            .child(board_layer)
            .children(connector_buttons)
            .children(rotate_button)
            .child(
                div()
                    .absolute()
                    .size_full()
                    .child(WhiteboardInputElement::new(cx.entity())),
            )
            .on_mouse_down(MouseButton::Left, cx.listener(Self::on_left_down))
            .on_mouse_up(MouseButton::Left, cx.listener(Self::on_left_up))
            .on_mouse_down(MouseButton::Right, cx.listener(Self::on_right_down))
            .on_mouse_down(MouseButton::Middle, cx.listener(Self::on_middle_down))
            .on_mouse_up(MouseButton::Middle, cx.listener(Self::on_middle_up))
            .on_mouse_move(cx.listener(Self::on_move));
        let root = if accepts_wheel_input(self.read_only) {
            root.on_scroll_wheel(cx.listener(Self::on_scroll))
        } else {
            root
        };
        root.on_pinch(cx.listener(Self::on_pinch))
            .on_key_down(cx.listener(Self::on_key))
            // Files dragged from the OS land as `ExternalPaths`; hand them to the
            // host (which imports any images) at the drop point.
            .on_drop::<gpui::ExternalPaths>(cx.listener(
                |this, paths: &gpui::ExternalPaths, window, cx| {
                    if let Some(f) = this.on_drop_files.clone() {
                        let w = this.event_to_world(window.mouse_position());
                        f(paths.paths().to_vec(), w[0], w[1], window, cx);
                    }
                },
            ))
            .children(element_layers)
            .child(chrome_layer)
            .child(toolbar)
            .children(flyout)
            .children(format_panel)
            .children(width_flyout)
            .children(font_flyout)
            .children(menu)
            .children(text_submenu)
            .children(picker_panel)
            .children(templates_modal)
            .child(
                div()
                    .absolute()
                    .left(px(10.0))
                    .bottom(px(8.0))
                    .text_size(px(11.0))
                    .text_color(text)
                    .child(SharedString::from(format!("{:.0}%", cam.zoom * 100.0))),
            )
            .into_any_element()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn text_layout_cache_reuses_outlines_until_content_changes() {
        let font = Font::default();
        let mut cache = HashMap::new();
        let first = cached_text_layout(&mut cache, &font, 9, "hello", 16.0, None, &[]);
        let reused = cached_text_layout(&mut cache, &font, 9, "hello", 16.0, None, &[]);
        let changed = cached_text_layout(&mut cache, &font, 9, "hello!", 16.0, None, &[]);

        assert!(Arc::ptr_eq(&first.segs, &reused.segs));
        assert!(!Arc::ptr_eq(&first.segs, &changed.segs));
    }

    #[test]
    fn shape_label_cache_survives_movement_and_invalidates_on_resize() {
        let font = Font::default();
        let mut cache = HashMap::new();
        let kind = ElementKind::RoundRect(BoxGeom {
            x: 10.0,
            y: 20.0,
            w: 180.0,
            h: 60.0,
            width: 2.0,
            rotation: 0.0,
        });
        let first = cached_label_layout(
            &mut cache,
            &font,
            3,
            &kind,
            10.0,
            20.0,
            180.0,
            60.0,
            "Node",
            &[],
        );
        let moved = cached_label_layout(
            &mut cache,
            &font,
            3,
            &kind,
            80.0,
            90.0,
            180.0,
            60.0,
            "Node",
            &[],
        );
        let resized = cached_label_layout(
            &mut cache,
            &font,
            3,
            &kind,
            80.0,
            90.0,
            240.0,
            80.0,
            "Node",
            &[],
        );

        assert!(Arc::ptr_eq(&first.text.segs, &moved.text.segs));
        assert!(!Arc::ptr_eq(&first.text.segs, &resized.text.segs));
    }

    #[test]
    fn read_only_embed_does_not_accept_wheel_input() {
        assert!(!accepts_wheel_input(true));
        assert!(accepts_wheel_input(false));
    }

    #[test]
    fn empty_or_garbage_loads_a_blank_board() {
        for s in ["", "   ", "not json", "{}", r#"{"camera":{"zoom":0}}"#] {
            let scene = Scene::from_json(s);
            assert_eq!(scene.camera.zoom, 1.0, "input {s:?}");
            assert!(scene.elements.is_empty(), "input {s:?}");
        }
    }

    #[test]
    fn ime_offsets_bridge_utf16_and_utf8() {
        // Chinese uses one UTF-16 code unit but three UTF-8 bytes; emoji uses a
        // surrogate pair. These are the offsets GPUI's native IME APIs exchange.
        let text = "A中😀B";
        let utf8_boundaries = [0, 1, 4, 8, 9];
        let utf16_boundaries = [0, 1, 2, 4, 5];
        for (utf8, utf16) in utf8_boundaries.into_iter().zip(utf16_boundaries) {
            assert_eq!(WhiteboardView::utf8_to_utf16_in(text, utf8), utf16);
            assert_eq!(WhiteboardView::utf16_to_utf8_in(text, utf16), utf8);
        }

        // Like the editor bridge, offsets inside a code point advance to the next
        // valid boundary, so slicing the scene's UTF-8 string remains safe.
        assert_eq!(WhiteboardView::utf8_to_utf16_in(text, 3), 2);
        assert_eq!(WhiteboardView::utf16_to_utf8_in(text, 3), 8);
    }

    #[test]
    fn camera_round_trips_through_json() {
        let scene = Scene {
            camera: Camera {
                x: 12.5,
                y: -4.0,
                zoom: 2.0,
            },
            ..Default::default()
        };
        let restored = Scene::from_json(&scene.to_json());
        assert_eq!(restored.camera.x, 12.5);
        assert_eq!(restored.camera.zoom, 2.0);
    }

    #[test]
    fn all_content_thumbnail_snapshot_uses_scene_bounds_without_mounting_view() {
        let scene = Scene {
            elements: vec![Element {
                id: 1,
                kind: ElementKind::Rect(BoxGeom {
                    x: 10.0,
                    y: 20.0,
                    w: 100.0,
                    h: 60.0,
                    width: 2.0,
                    rotation: 0.0,
                }),
                stroke: None,
                fill: None,
                label: None,
                label_color: None,
                styles: Vec::new(),
                mindmap: None,
            }],
            ..Scene::default()
        };

        let snapshot = LocalThumbnailSnapshot::for_scene_all_content(scene, 320.0, 180.0);

        assert_eq!(snapshot.spec.scene_bounds, Some([10.0, 20.0, 110.0, 80.0]));
        assert_eq!(snapshot.spec.focus_bounds, [10.0, 20.0, 110.0, 80.0]);
        assert!(snapshot.spec.camera.zoom > 0.0);
    }

    #[test]
    fn empty_scene_still_builds_a_renderable_thumbnail_snapshot() {
        let snapshot =
            LocalThumbnailSnapshot::for_scene_all_content(Scene::default(), 320.0, 180.0);

        assert_eq!(snapshot.spec.scene_bounds, None);
        assert_eq!(snapshot.spec.focus_bounds, [0.0, 0.0, 320.0, 180.0]);
        assert_eq!(snapshot.spec.camera.zoom, 1.0);
    }

    #[test]
    fn every_element_kind_round_trips_through_json() {
        let scene = Scene {
            camera: Camera::default(),
            elements: vec![
                Element {
                    id: 1,
                    kind: ElementKind::Draw(Stroke {
                        points: vec![[0.0, 0.0], [10.0, 5.0]],
                        width: 3.0,
                    }),
                    stroke: None,
                    fill: None,
                    label: None,
                    label_color: None,
                    styles: Vec::new(),
                    mindmap: None,
                },
                Element {
                    id: 2,
                    kind: ElementKind::Rect(BoxGeom {
                        x: 1.0,
                        y: 2.0,
                        w: 30.0,
                        h: 40.0,
                        width: 2.0,
                        rotation: 0.0,
                    }),
                    stroke: Some(0xff0000ff),
                    fill: Some(0x00ff0080),
                    label: Some("hi".into()),
                    label_color: Some(0x112233ff),
                    styles: Vec::new(),
                    mindmap: None,
                },
                Element {
                    id: 3,
                    kind: ElementKind::Arrow(SegGeom {
                        x1: 1.0,
                        y1: 1.0,
                        x2: 2.0,
                        y2: 8.0,
                        width: 2.5,
                        style: SegmentStyle::Solid,
                        start_anchor: None,
                        end_anchor: None,
                    }),
                    stroke: None,
                    fill: None,
                    label: None,
                    label_color: None,
                    styles: Vec::new(),
                    mindmap: None,
                },
            ],
        };
        let restored = Scene::from_json(&scene.to_json());
        assert_eq!(restored.elements.len(), 3);
        match &restored.elements[2].kind {
            ElementKind::Arrow(s) => assert_eq!(s.y2, 8.0),
            other => panic!("expected arrow, got {other:?}"),
        }
        // Per-element color round-trips; an uncolored element stays `None`.
        assert_eq!(restored.elements[1].stroke, Some(0xff0000ff));
        assert_eq!(restored.elements[1].fill, Some(0x00ff0080));
        // The shape label + its color round-trip too.
        assert_eq!(restored.elements[1].label.as_deref(), Some("hi"));
        assert_eq!(restored.elements[1].label_color, Some(0x112233ff));
        assert_eq!(restored.elements[0].stroke, None);
        assert_eq!(restored.elements[0].fill, None);
    }

    #[test]
    fn label_defaults_to_none_for_older_boards() {
        // A board saved before labels existed has no `label` key → `None`, and an
        // unlabeled element never writes the key back.
        let old = r#"{"id":2,"kind":{"rect":{"x":0.0,"y":0.0,"w":1.0,"h":1.0,"width":1.0}}}"#;
        let back: Element = serde_json::from_str(old).unwrap();
        assert_eq!(back.label, None);
        assert!(!serde_json::to_string(&back).unwrap().contains("label"));
    }

    #[test]
    fn shape_label_block_fits_inscribed_region() {
        let font = Font::default();
        let bg = BoxGeom {
            x: 0.0,
            y: 0.0,
            w: 0.0,
            h: 0.0,
            width: 0.0,
            rotation: 0.0,
        };
        let (bx, by, bw, bh) = (10.0, 20.0, 200.0, 120.0);

        // Rect: default size for a roomy box; wraps to ~the full padded width.
        let rect = shape_label_block(&font, &ElementKind::Rect(bg), bx, by, bw, bh, "hello world");
        assert!(rect.size <= TEXT_SIZE + 0.01, "size {}", rect.size);
        assert!(
            (rect.wrap - (bw - 2.0 * LABEL_PAD)).abs() < 0.5,
            "rect wraps full width: {}",
            rect.wrap
        );

        // Diamond: wraps to the central inscribed rectangle (½ width), so it wraps
        // narrower and shrinks at least as much as the rect.
        let dia = shape_label_block(
            &font,
            &ElementKind::Diamond(bg),
            bx,
            by,
            bw,
            bh,
            "hello world",
        );
        assert!(
            (dia.wrap - (bw * 0.5 - 2.0 * LABEL_PAD)).abs() < 0.5,
            "diamond half width: {}",
            dia.wrap
        );
        assert!(
            dia.size <= rect.size,
            "diamond shrinks ≥ rect: {} vs {}",
            dia.size,
            rect.size
        );

        // Triangle: its band sits in the lower half (anchored near the base).
        let tri = shape_label_block(
            &font,
            &ElementKind::Triangle(bg),
            bx,
            by,
            bw,
            bh,
            "hello world",
        );
        assert!(
            tri.y >= by + bh / 2.0 - 0.5,
            "triangle label low: y={}",
            tri.y
        );

        // A long label in a small box shrinks below the default to avoid overflow.
        let tiny = shape_label_block(
            &font,
            &ElementKind::Rect(bg),
            0.0,
            0.0,
            44.0,
            28.0,
            "a long label that must shrink",
        );
        assert!(tiny.size < TEXT_SIZE, "shrinks: {}", tiny.size);
    }

    #[test]
    fn style_span_toggle_and_layer() {
        let bold = RunStyle {
            bold: true,
            ..Default::default()
        };
        let s = toggle_format(&[], 0, 4, Format::Bold);
        assert_eq!(s.len(), 1);
        assert_eq!((s[0].start, s[0].end, s[0].style), (0, 4, bold));
        assert!(style_at(&s, 2).bold && !style_at(&s, 4).bold);
        // Toggling the same range off clears it.
        assert!(toggle_format(&s, 0, 4, Format::Bold).is_empty());
        // Extending past the run (partly unstyled) adds, merging into one run.
        let s2 = toggle_format(&s, 2, 6, Format::Bold);
        assert_eq!((s2.len(), s2[0].start, s2[0].end), (1, 0, 6));
        // Layering italic over part of the bold run yields three runs.
        let s3 = toggle_format(&s, 1, 3, Format::Italic);
        assert_eq!(s3.len(), 3, "{s3:?}");
        assert!(style_at(&s3, 1).bold && style_at(&s3, 1).italic);
        assert!(style_at(&s3, 0).bold && !style_at(&s3, 0).italic);
        // Highlight toggles its color independently.
        let h = toggle_highlight(&[], 0, 3, 0xffff00ff);
        assert_eq!(style_at(&h, 1).highlight, Some(0xffff00ff));
        assert!(toggle_highlight(&h, 0, 3, 0xffff00ff).is_empty());
    }

    #[test]
    fn active_style_reports_common_formatting() {
        let s = toggle_format(&[], 2, 5, Format::Bold); // bytes 2..5 bold
        assert!(active_style(&s, 2, 5).bold, "whole selection bold");
        assert!(
            !active_style(&s, 0, 5).bold,
            "selection spills onto plain text"
        );
        // Collapsed caret inherits the char to its left.
        assert!(
            active_style(&s, 5, 5).bold,
            "just after the run inherits bold"
        );
        assert!(!active_style(&s, 2, 2).bold, "just before it is plain");
    }

    #[test]
    fn splice_keeps_runs_aligned() {
        let plain = RunStyle::default();
        let s = toggle_format(&[], 2, 5, Format::Bold);
        // Insert two chars at the start → the run shifts right.
        let a = splice_styles(&s, 0, 0, 2, plain);
        assert_eq!((a[0].start, a[0].end), (4, 7));
        // Delete a char inside the run → it shrinks by one.
        let b = splice_styles(&s, 3, 4, 0, plain);
        assert_eq!((b[0].start, b[0].end), (2, 4), "{b:?}");
        // Replacing a middle slice of a bold run with plain text splits it.
        let full = toggle_format(&[], 0, 6, Format::Bold);
        let c = splice_styles(&full, 2, 4, 2, plain);
        assert_eq!(c.len(), 2, "{c:?}");
        assert_eq!(
            ((c[0].start, c[0].end), (c[1].start, c[1].end)),
            ((0, 2), (4, 6))
        );
    }

    #[test]
    fn styles_round_trip_and_back_compat() {
        let el = Element {
            id: 1,
            kind: ElementKind::Text(TextGeom {
                x: 0.0,
                y: 0.0,
                content: "hello world".into(),
                size: 12.0,
                rotation: 0.0,
                measured_w: 0.0,
                measured_h: 0.0,
            }),
            stroke: None,
            fill: None,
            label: None,
            label_color: None,
            styles: vec![StyleSpan {
                start: 0,
                end: 5,
                style: RunStyle {
                    bold: true,
                    highlight: Some(0xffff00ff),
                    ..Default::default()
                },
            }],
            mindmap: None,
        };
        let back: Element = serde_json::from_str(&serde_json::to_string(&el).unwrap()).unwrap();
        assert_eq!(back.styles.len(), 1);
        assert!(back.styles[0].style.bold);
        assert_eq!(back.styles[0].style.highlight, Some(0xffff00ff));
        // A board saved before rich text loads with no styles.
        let old = r#"{"id":2,"kind":{"rect":{"x":0.0,"y":0.0,"w":1.0,"h":1.0,"width":1.0}}}"#;
        assert!(
            serde_json::from_str::<Element>(old)
                .unwrap()
                .styles
                .is_empty()
        );
    }

    #[test]
    fn pan_and_zoom_math() {
        let mut c = Camera::default();
        c.pan_by(50.0, -20.0);
        assert_eq!((c.x, c.y), (-50.0, 20.0));

        let mut c = Camera {
            x: 10.0,
            y: 5.0,
            zoom: 1.0,
        };
        let before = c.screen_to_world(300.0, 200.0);
        c.zoom_about(300.0, 200.0, 2.5);
        let after = c.screen_to_world(300.0, 200.0);
        assert!((before.0 - after.0).abs() < 1e-3);
        assert!((before.1 - after.1).abs() < 1e-3);
        assert_eq!(c.zoom, 2.5);
    }

    #[test]
    fn bbox_translate_and_hit_test() {
        let mut k = ElementKind::Line(SegGeom {
            x1: 0.0,
            y1: 0.0,
            x2: 10.0,
            y2: 4.0,
            width: 1.0,
            style: SegmentStyle::Solid,
            start_anchor: None,
            end_anchor: None,
        });
        assert_eq!(bbox(&k), (0.0, 0.0, 10.0, 4.0));
        translate(&mut k, 5.0, -2.0);
        assert_eq!(bbox(&k), (5.0, -2.0, 15.0, 2.0));
        // Within the padded bounds hits; far away misses.
        assert!(hit_test(&k, 5.0, -2.0, 1.0));
        assert!(hit_test(&k, 4.5, -2.5, 1.0)); // inside pad
        assert!(!hit_test(&k, 100.0, 100.0, 1.0));
    }

    #[test]
    fn diagonal_scale_projects_the_cursor_onto_the_diagonal() {
        // On the diagonal: cursor twice as far from the anchor → 2×.
        let s = diagonal_scale([0.0, 0.0], [10.0, 10.0], [20.0, 20.0]);
        assert!((s - 2.0).abs() < 1e-4, "{s}");
        // Off-diagonal projects onto it: (20,0) onto the (10,10) line → 1×.
        let s = diagonal_scale([0.0, 0.0], [10.0, 10.0], [20.0, 0.0]);
        assert!((s - 1.0).abs() < 1e-4, "{s}");
    }

    #[test]
    fn snap_45_locks_angle_and_keeps_length() {
        // Near 45° snaps onto the exact diagonal (x == y).
        let (x, y) = snap_45(0.0, 0.0, 10.0, 9.0);
        assert!((x - y).abs() < 1e-3, "{x} vs {y}");
        // Near-horizontal snaps flat, preserving the distance.
        let (x, y) = snap_45(0.0, 0.0, 10.0, 1.0);
        assert!(y.abs() < 1e-3);
        assert!((x - 101.0f32.sqrt()).abs() < 1e-2);
    }

    #[test]
    fn snap_grid_rounds_to_nearest_line() {
        // GRID is 24: values round to the nearest multiple, halves away from zero.
        assert_eq!(snap_grid(0.0), 0.0);
        assert_eq!(snap_grid(11.0), 0.0);
        assert_eq!(snap_grid(13.0), GRID);
        assert_eq!(snap_grid(GRID), GRID);
        assert_eq!(snap_grid(-13.0), -GRID);
        assert_eq!(snap_grid(1.5 * GRID), 2.0 * GRID);
    }

    #[test]
    fn move_target_drives_an_absolute_snapped_target() {
        // Origin off-grid (100 % 24 == 4); grab anchor at the cursor's start.
        let origin = [100.0, 100.0];
        let anchor = [0.0, 0.0];

        // Free move tracks the cursor exactly on both axes.
        assert_eq!(
            move_target(origin, anchor, [37.0, -11.0], false),
            [137.0, 89.0]
        );

        // Snapped: the target is `snap(origin + total)`, computed fresh each
        // frame — never the running position, so it can't stick. A 50,50 total
        // lands on snap(150) = 144 (150/24 = 6.25 → 6).
        assert_eq!(
            move_target(origin, anchor, [50.0, 50.0], true),
            [144.0, 144.0]
        );

        // Regression: twelve sub-threshold 4px steps (each < half a grid cell)
        // must still accumulate across grid lines on BOTH axes — the old logic
        // snapped each tiny step from the already-snapped spot and stuck.
        let mut cursor = [0.0, 0.0];
        for _ in 0..12 {
            cursor = [cursor[0] + 4.0, cursor[1] + 4.0];
        }
        // 48px total → snap(148) = 144 on each axis.
        assert_eq!(move_target(origin, anchor, cursor, true), [144.0, 144.0]);
    }

    #[test]
    fn resize_scales_geometry_about_the_anchor() {
        // Drag the bottom-right corner of a 20×20 rect to double it, anchored
        // at the top-left — origin stays put, size doubles.
        let mut k = ElementKind::Rect(BoxGeom {
            x: 10.0,
            y: 10.0,
            w: 20.0,
            h: 20.0,
            width: 1.0,
            rotation: 0.0,
        });
        resize_about(&mut k, 10.0, 10.0, 2.0, 2.0);
        match k {
            ElementKind::Rect(b) => {
                assert_eq!((b.x, b.y), (10.0, 10.0));
                assert_eq!((b.w, b.h), (40.0, 40.0));
            }
            other => panic!("expected rect, got {other:?}"),
        }
    }

    #[test]
    fn axis_scale_measures_one_axis_about_the_anchor() {
        // `target` twice as far from the anchor as `from` → 2×.
        assert!((axis_scale(0.0, 10.0, 20.0) - 2.0).abs() < 1e-4);
        // Halfway back toward the anchor → 0.5×.
        assert!((axis_scale(0.0, 10.0, 5.0) - 0.5).abs() < 1e-4);
        // Degenerate (anchor == from) → 1.0, no divide-by-zero.
        assert!((axis_scale(7.0, 7.0, 99.0) - 1.0).abs() < 1e-6);
    }

    #[test]
    fn per_axis_resize_stretches_one_axis_and_keeps_text_uniform() {
        // A rect stretched on x only (sx=2, sy=1): width doubles, height holds.
        let mut k = ElementKind::Rect(BoxGeom {
            x: 10.0,
            y: 10.0,
            w: 20.0,
            h: 20.0,
            width: 1.0,
            rotation: 0.0,
        });
        resize_about(&mut k, 10.0, 10.0, 2.0, 1.0);
        match k {
            ElementKind::Rect(b) => {
                assert_eq!((b.x, b.y), (10.0, 10.0));
                assert_eq!((b.w, b.h), (40.0, 20.0));
            }
            other => panic!("expected rect, got {other:?}"),
        }
        // Text under a per-axis (4×, 1×) stretch keeps a single size: the geometric
        // mean (sqrt(4) = 2×), never distorted to the raw 4× horizontal factor.
        let mut t = ElementKind::Text(TextGeom {
            x: 0.0,
            y: 0.0,
            content: "hi".into(),
            size: 10.0,
            rotation: 0.0,
            measured_w: 0.0,
            measured_h: 0.0,
        });
        resize_about(&mut t, 0.0, 0.0, 4.0, 1.0);
        match t {
            ElementKind::Text(t) => assert!((t.size - 20.0).abs() < 1e-3, "{}", t.size),
            other => panic!("expected text, got {other:?}"),
        }
    }

    #[test]
    fn color_round_trips_through_hsv_and_packed_ints() {
        // Pure primaries survive HSV → packed → HSV.
        for c in [0xff0000ff, 0x00ff00ff, 0x0000ffff, 0x808080ff, 0xffffffff] {
            let (h, s, v) = u32_to_hsv(c);
            assert_eq!(hsv_to_u32(h, s, v), c, "{c:#010x}");
        }
        // Hue endpoints both land on red.
        assert_eq!(hsv_to_u32(0.0, 1.0, 1.0), 0xff0000ff);
        assert_eq!(hsv_to_u32(1.0, 1.0, 1.0), 0xff0000ff);
        // A 2/3 hue is pure blue.
        assert_eq!(hsv_to_u32(2.0 / 3.0, 1.0, 1.0), 0x0000ffff);
        // pack clamps out-of-range and rounds to 0..255.
        assert_eq!(pack_rgba(1.5, -0.2, 0.5, 1.0), 0xff0080ff);
    }

    #[test]
    fn rotation_accumulates_on_boxes_and_bakes_into_segments() {
        use std::f32::consts::FRAC_PI_2;
        // A box stores the angle and its center-anchored bounds don't move.
        let mut k = ElementKind::Rect(BoxGeom {
            x: -10.0,
            y: -10.0,
            w: 20.0,
            h: 20.0,
            width: 1.0,
            rotation: 0.0,
        });
        rotate_element(&mut k, 0.0, 0.0, FRAC_PI_2);
        match &k {
            ElementKind::Rect(b) => assert!((b.rotation - FRAC_PI_2).abs() < 1e-5),
            other => panic!("expected rect, got {other:?}"),
        }
        // A square's bounds are unchanged by a 90° turn about its center.
        let bb = bbox(&k);
        assert!(
            (bb.0 + 10.0).abs() < 1e-3 && (bb.2 - 10.0).abs() < 1e-3,
            "{bb:?}"
        );

        // A line bakes the rotation into its endpoints: +90° about the origin
        // sends (10,0) → (0,10).
        let mut seg = ElementKind::Line(SegGeom {
            x1: 0.0,
            y1: 0.0,
            x2: 10.0,
            y2: 0.0,
            width: 1.0,
            style: SegmentStyle::Solid,
            start_anchor: None,
            end_anchor: None,
        });
        rotate_element(&mut seg, 0.0, 0.0, FRAC_PI_2);
        match seg {
            ElementKind::Line(s) => {
                assert!(s.x2.abs() < 1e-3 && (s.y2 - 10.0).abs() < 1e-3, "{s:?}");
            }
            other => panic!("expected line, got {other:?}"),
        }

        // Text rotates like a box: spun about its own center, it accumulates an
        // angle and stays put (centered on the pivot here, so no orbit).
        let mut txt = ElementKind::Text(TextGeom {
            x: -20.0,
            y: -8.0,
            content: "hi".into(),
            size: 16.0,
            rotation: 0.0,
            measured_w: 40.0,
            measured_h: 16.0,
        });
        rotate_element(&mut txt, 0.0, 0.0, FRAC_PI_2);
        match txt {
            ElementKind::Text(t) => {
                assert!((t.rotation - FRAC_PI_2).abs() < 1e-5);
                assert!(
                    (t.x + 20.0).abs() < 1e-3 && (t.y + 8.0).abs() < 1e-3,
                    "{t:?}"
                );
            }
            other => panic!("expected text, got {other:?}"),
        }

        // Orbiting: rotating a box about a *different* pivot moves its center
        // along the arc. A unit box at (1,0) turned 90° about the origin → (0,1).
        let mut orb = ElementKind::Rect(BoxGeom {
            x: 0.5,
            y: -0.5,
            w: 1.0,
            h: 1.0,
            width: 1.0,
            rotation: 0.0,
        });
        rotate_element(&mut orb, 0.0, 0.0, FRAC_PI_2);
        match orb {
            ElementKind::Rect(b) => {
                let (ccx, ccy) = (b.x + 0.5, b.y + 0.5);
                assert!(ccx.abs() < 1e-3 && (ccy - 1.0).abs() < 1e-3, "{b:?}");
            }
            other => panic!("expected rect, got {other:?}"),
        }
    }

    #[test]
    fn rotation_snaps_to_horizontal_and_vertical() {
        use std::f32::consts::{FRAC_PI_2, FRAC_PI_4};
        let step = std::f32::consts::PI / 12.0;
        // Within the snap zone of a cardinal snaps onto it...
        assert!((snap_angle(FRAC_PI_2 - 0.05, false) - FRAC_PI_2).abs() < 1e-6);
        assert!(snap_angle(0.04, false).abs() < 1e-6);
        assert!((snap_angle(-FRAC_PI_2 + 0.03, false) + FRAC_PI_2).abs() < 1e-6);
        // ...but a hair outside it, and at 45°, the angle is left free.
        assert!((snap_angle(FRAC_PI_2 - 0.2, false) - (FRAC_PI_2 - 0.2)).abs() < 1e-6);
        assert!((snap_angle(FRAC_PI_4, false) - FRAC_PI_4).abs() < 1e-6);
        // Shift snaps to the nearest 15° everywhere.
        assert!((snap_angle(0.30, true) - step).abs() < 1e-4);
    }

    #[test]
    fn caret_navigation_walks_chars_and_lines() {
        // Multi-byte: "é" is 2 bytes, so caret steps by whole chars, never panics.
        let s = "aébc";
        assert_eq!(caret_right(s, 0), 1); // past 'a'
        assert_eq!(caret_right(s, 1), 3); // past 'é' (2 bytes)
        assert_eq!(caret_left(s, 3), 1); // back over 'é'
        assert_eq!(caret_left(s, 0), 0); // clamps at start
        assert_eq!(caret_right(s, s.len()), s.len()); // clamps at end
        // Line edges around a newline.
        let m = "ab\ncde";
        assert_eq!(line_start(m, 5), 3); // within "cde" → after the '\n'
        assert_eq!(line_end(m, 0), 2); // end of "ab" (before '\n')
        assert_eq!(line_start(m, 1), 0);
        assert_eq!(line_end(m, 4), m.len());
        // floor_boundary never splits a char.
        assert_eq!(floor_boundary(s, 2), 1); // mid-'é' → its start
        assert_eq!(floor_boundary(s, 99), s.len());
    }

    #[test]
    fn word_range_selects_the_word_under_the_caret() {
        let s = "foo bar_baz qux";
        assert_eq!(word_range(s, 1), (0, 3)); // inside "foo"
        assert_eq!(word_range(s, 7), (4, 11)); // "bar_baz" (underscore is a word char)
        // At a word/space boundary the adjacent word wins (caret just after "foo").
        assert_eq!(word_range(s, 3), (0, 3));
        // Between two spaces → empty (no word under the caret).
        assert_eq!(word_range("a  b", 2), (2, 2));
    }

    #[test]
    fn text_bbox_anchors_at_origin_and_grows() {
        let t = TextGeom {
            x: 5.0,
            y: 6.0,
            content: "ab\ncde".into(),
            size: 10.0,
            rotation: 0.0,
            measured_w: 0.0,
            measured_h: 0.0,
        };
        let bb = bbox(&ElementKind::Text(t));
        assert_eq!((bb.0, bb.1), (5.0, 6.0));
        assert!(bb.2 > bb.0 && bb.3 > bb.1);
    }

    #[test]
    fn tiny_drags_are_not_committed() {
        assert!(!committable(&ElementKind::Draw(Stroke {
            points: vec![[0.0, 0.0]],
            width: 1.0,
        })));
        assert!(committable(&ElementKind::Rect(BoxGeom {
            x: 0.0,
            y: 0.0,
            w: 20.0,
            h: 5.0,
            width: 1.0,
            rotation: 0.0,
        })));
    }

    #[test]
    fn image_round_trips_and_behaves_like_a_box() {
        let kind = ElementKind::Image(ImageGeom {
            src: "images/x.png".into(),
            x: 10.0,
            y: 20.0,
            w: 100.0,
            h: 60.0,
            rotation: 0.0,
        });
        // Bounds = the box; not a fillable closed shape.
        assert_eq!(bbox(&kind), (10.0, 20.0, 110.0, 80.0));
        assert!(!is_closed_shape(&kind));
        // Round-trips through JSON under the "image" tag, keeping its src.
        let elem = Element {
            id: 1,
            kind,
            stroke: None,
            fill: None,
            label: None,
            label_color: None,
            styles: Vec::new(),
            mindmap: None,
        };
        let json = serde_json::to_string(&elem).unwrap();
        assert!(json.contains("\"image\""), "{json}");
        assert!(json.contains("images/x.png"));
        let mut back = serde_json::from_str::<Element>(&json).unwrap().kind;
        assert_eq!(bbox(&back), (10.0, 20.0, 110.0, 80.0));
        // Translates like the other box kinds.
        translate(&mut back, 5.0, -3.0);
        assert_eq!(bbox(&back), (15.0, 17.0, 115.0, 77.0));
    }

    #[test]
    fn new_box_shapes_share_box_behavior_and_round_trip() {
        let b = BoxGeom {
            x: 1.0,
            y: 2.0,
            w: 30.0,
            h: 40.0,
            width: 2.0,
            rotation: 0.5,
        };
        // (serde tag, kind) — the tag is what gets persisted in JSON.
        let cases = [
            ("diamond", ElementKind::Diamond(b)),
            ("triangle", ElementKind::Triangle(b)),
            ("round_rect", ElementKind::RoundRect(b)),
            ("star", ElementKind::Star(b)),
            ("hexagon", ElementKind::Hexagon(b)),
        ];
        for (tag, kind) in cases {
            // Every new shape is a fillable closed shape, commits like a box, and
            // flows through the shared `box_like` path (bounds / select / resize /
            // rotate) just like rect/ellipse.
            assert!(is_closed_shape(&kind), "{tag} should be fillable");
            assert!(committable(&kind), "{tag} should commit");
            assert_eq!(
                box_like(&kind),
                Some((1.0, 2.0, 30.0, 40.0, 0.5)),
                "{tag} box_like"
            );
            // Round-trips through JSON under its snake_case tag.
            let elem = Element {
                id: 7,
                kind,
                stroke: None,
                fill: None,
                label: None,
                label_color: None,
                styles: Vec::new(),
                mindmap: None,
            };
            let json = serde_json::to_string(&elem).unwrap();
            assert!(json.contains(tag), "{tag} not in json: {json}");
            let back: Element = serde_json::from_str(&json).unwrap();
            assert_eq!(box_like(&back.kind), Some((1.0, 2.0, 30.0, 40.0, 0.5)));
        }
    }
}