gpui-rhai 0.1.8

use std::cell::RefCell;
use std::collections::{BTreeMap, BTreeSet};
use std::rc::Rc;
use std::sync::atomic::{AtomicU64, Ordering};
use std::time::Duration;

use rhai::{
    Array, CustomType, Dynamic, Engine, EvalAltResult, FLOAT, FnPtr, INT, ImmutableString, Map,
    NativeCallContext, Position, TypeBuilder,
};
use thiserror::Error;

use crate::{
    ActionError, ActionId, ActionInvocation, ActionRegistry, AssetError, AssetId, AssetRegistry,
    AsyncRuntimeError, AsyncScope, CalendarClock, CapabilityError, CapabilityId,
    CapabilityRegistry, ComponentInstancePath, DateStyle, EventSchema, ImageDecodeHandle,
    LocaleError, LocaleManager, MotionKey, MotionRuntime, NumberFormatOptions, OpaqueHandle,
    ResponsiveError, ResponsiveRuntime, ScriptCallback, ScriptGeneration, ScriptWindowSpec,
    StateError, StateStore, StoreError, StoreId, StoreRegistry, SubscriptionCloseReason,
    SubscriptionDeliveryPolicy, SubscriptionHandle, SubscriptionOptions, SubscriptionRegistration,
    SubscriptionRegistry, TaskHandle, TaskRegistry, TextDirection, ThemeError, ThemeManager,
    ThemePreference, ThemeSelection, UiEvent, UiValue, UiValueError, UiValuePath, UiValuePathError,
    UiValuePathSegment, WindowCommandError, WindowCommandRegistry,
};

fn domain_is_within(domain: &str, scope: &str) -> bool {
    domain == scope
        || domain
            .strip_prefix(scope)
            .is_some_and(|suffix| suffix.starts_with('/'))
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum ExecutionPhase {
    Init,
    Render,
    Event,
    Suspend,
    Resume,
    Dispose,
}

/// Identity of one continuous component mount. Logical paths may be reused
/// after unmount, but an incarnation never is.
#[derive(Clone, Copy, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct ComponentIncarnation(u64);

impl ComponentIncarnation {
    pub(crate) const fn unscoped() -> Self {
        Self(0)
    }

    #[must_use]
    pub const fn get(self) -> u64 {
        self.0
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
struct RuntimeStateId(u64);

impl Default for RuntimeStateId {
    fn default() -> Self {
        static NEXT_ID: AtomicU64 = AtomicU64::new(1);
        Self(NEXT_ID.fetch_add(1, Ordering::Relaxed))
    }
}

enum ThemeTarget {
    App,
    Window(String),
    Local,
}

impl ExecutionPhase {
    const fn allows_mutation(self) -> bool {
        matches!(
            self,
            Self::Init | Self::Event | Self::Suspend | Self::Resume | Self::Dispose
        )
    }

    const fn allows_async_start(self) -> bool {
        matches!(self, Self::Init | Self::Event | Self::Resume)
    }
}

#[derive(Debug, Default)]
pub struct UiRuntimeState {
    runtime_id: RuntimeStateId,
    transaction_depth: usize,
    pub component_state: StateStore,
    pub stores: StoreRegistry,
    pub native_collections: crate::NativeCollectionRegistry,
    pub native_documents: crate::NativeTextDocumentRegistry,
    #[cfg(feature = "charts")]
    pub native_chart_data: BTreeMap<String, crate::NativeChartData>,
    pub actions: ActionRegistry,
    pub capabilities: CapabilityRegistry,
    pub tasks: TaskRegistry,
    pub subscriptions: SubscriptionRegistry,
    pub timers: crate::TimerRegistry,
    pub locale: Option<LocaleManager>,
    pub calendar_clock: CalendarClock,
    pub clock: crate::RuntimeClock,
    pub theme: Option<ThemeManager>,
    component_styles: crate::ComponentStyleSheet,
    pub assets: AssetRegistry,
    pub motions: MotionRuntime,
    pub effects: crate::EffectRegistry,
    pub signals: crate::SignalRegistry,
    pub element_refs: crate::ElementRefRegistry,
    pub(crate) geometry: crate::GeometryRegistry,
    pub(crate) pointer_capture: crate::PointerCaptureRegistry,
    presentations: BTreeMap<String, ViewPresentationState>,
    pub budgets: crate::RuntimeBudgets,
    pub virtual_requests: crate::VirtualRequestRegistry,
    pub windows: WindowCommandRegistry,
    pub responsive: ResponsiveRuntime,
    pub(crate) environment_dependencies:
        crate::environment_dependency::EnvironmentDependencyRegistry,
    pub motion_values: BTreeMap<MotionKey, f64>,
    pub(crate) motion_ghosts: Vec<crate::motion::MotionGhost>,
    pub(crate) window_appearances: BTreeMap<String, crate::SystemAppearance>,
    pub traces: crate::TraceBuffer,
    component_event_handlers: BTreeMap<(ComponentInstancePath, String), ScriptCallback>,
    component_incarnations: BTreeMap<ComponentInstancePath, ComponentIncarnation>,
    next_component_incarnation: u64,
    dirty: BTreeSet<ComponentInstancePath>,
    pending_events: Vec<PendingEvent>,
    pending_actions: Vec<ActionInvocation>,
    pending_async: Vec<crate::AsyncDelivery>,
    pending_element_commands: Vec<crate::element_ref::ElementCommand>,
    repaint_windows: BTreeSet<String>,
    component_style_generation: u64,
}

impl UiRuntimeState {
    pub(crate) fn update_window_appearance(
        &mut self,
        window: &str,
        appearance: crate::SystemAppearance,
    ) -> bool {
        let previous = self
            .window_appearances
            .insert(window.to_owned(), appearance)
            .unwrap_or(crate::SystemAppearance::Dark);
        let changed = previous != appearance;
        if changed {
            let invalidated = self
                .environment_dependencies
                .invalidate_theme_window(window);
            self.mark_dirty(invalidated);
        }
        changed
    }
    const SUSPENDED_DELIVERY_CAPACITY: usize = 256;
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    pub(crate) fn ensure_component_incarnation(
        &mut self,
        component: &ComponentInstancePath,
    ) -> ComponentIncarnation {
        if let Some(incarnation) = self.component_incarnations.get(component) {
            return *incarnation;
        }
        let next = self.next_component_incarnation.max(1);
        let incarnation = ComponentIncarnation(next);
        self.next_component_incarnation = next.saturating_add(1);
        self.component_incarnations
            .insert(component.clone(), incarnation);
        incarnation
    }

    pub(crate) fn component_incarnation(
        &self,
        component: &ComponentInstancePath,
    ) -> Option<ComponentIncarnation> {
        self.component_incarnations.get(component).copied()
    }

    pub(crate) fn component_incarnations_snapshot(
        &self,
    ) -> BTreeMap<ComponentInstancePath, ComponentIncarnation> {
        self.component_incarnations.clone()
    }

    pub(crate) fn ensure_presentation(&mut self, view: &str) {
        self.presentations.entry(view.to_owned()).or_default();
    }

    /// Return the geometry domain for one mounted view, creating it if needed.
    pub fn presentation_geometry(&mut self, view: &str) -> crate::GeometryRegistry {
        self.ensure_presentation(view);
        self.geometry_for(Some(view))
    }

    /// Return the pointer-capture domain for one mounted view, creating it if needed.
    pub fn presentation_pointer_capture(&mut self, view: &str) -> crate::PointerCaptureRegistry {
        self.ensure_presentation(view);
        self.pointer_capture_for(Some(view))
    }

    pub(crate) fn geometry_for(&self, view: Option<&str>) -> crate::GeometryRegistry {
        view.and_then(|view| self.presentations.get(view))
            .map_or_else(|| self.geometry.clone(), |state| state.geometry.clone())
    }

    pub(crate) fn pointer_capture_for(&self, view: Option<&str>) -> crate::PointerCaptureRegistry {
        view.and_then(|view| self.presentations.get(view))
            .map_or_else(
                || self.pointer_capture.clone(),
                |state| state.pointer_capture.clone(),
            )
    }

    pub(crate) fn remove_presentation(&mut self, view: &str) {
        self.presentations.remove(view);
    }

    /// Set one mounted component field from trusted host code and schedule its
    /// retained subtree for reevaluation.
    ///
    /// # Errors
    ///
    /// Returns the same schema and identity errors as [`StateStore::set`].
    pub fn set_component_state_from_host(
        &mut self,
        component: &ComponentInstancePath,
        field: &str,
        value: UiValue,
    ) -> Result<bool, crate::StateError> {
        let changed = self.component_state.set(component, field, value)?;
        if changed {
            self.dirty.insert(component.clone());
        }
        Ok(changed)
    }

    /// Replace one Rust-owned collection and invalidate only subscribed components.
    ///
    /// # Errors
    ///
    /// Returns an error when the collection name is not registered.
    pub fn replace_native_collection_from_host(
        &mut self,
        name: &str,
        collection: crate::NativeCollection,
    ) -> Result<bool, crate::NativeCollectionError> {
        let invalidated = self.native_collections.replace(name, collection)?;
        let changed = !invalidated.is_empty();
        self.dirty.extend(invalidated);
        Ok(changed)
    }

    /// Register one new Host-owned collection after mount and invalidate the
    /// owning view so its next render can resolve the new name.
    ///
    /// # Errors
    ///
    /// Returns an invalid-name or duplicate-collection error.
    pub fn register_native_collection_from_host(
        &mut self,
        _root: &ComponentInstancePath,
        name: &str,
        collection: crate::NativeCollection,
    ) -> Result<(), crate::NativeCollectionError> {
        let invalidated = self
            .native_collections
            .register_with_invalidated(name.to_owned(), collection)?;
        self.dirty.extend(invalidated);
        Ok(())
    }

    /// Replace one Host-owned text revision and invalidate exact readers.
    ///
    /// # Errors
    ///
    /// Returns when the document name is not registered.
    pub fn replace_native_text_document_from_host(
        &mut self,
        name: &str,
        document: crate::NativeTextDocument,
    ) -> Result<bool, crate::DocumentError> {
        let invalidated = self.native_documents.replace(name, document)?;
        let changed = !invalidated.is_empty();
        self.dirty.extend(invalidated);
        Ok(changed)
    }

    /// Register or replace one Host-owned streaming chart data handle.
    ///
    /// # Errors
    ///
    /// Returns an error when `name` is not a safe identifier.
    #[cfg(feature = "charts")]
    pub fn register_native_chart_data(
        &mut self,
        name: impl Into<String>,
        data: crate::NativeChartData,
    ) -> Result<(), UiContextError> {
        let name = name.into();
        if name.is_empty()
            || name.len() > 128
            || !name
                .chars()
                .next()
                .is_some_and(|character| character.is_ascii_alphabetic())
            || !name
                .chars()
                .all(|character| character.is_ascii_alphanumeric() || character == '_')
        {
            return Err(UiContextError::InvalidChartDataName(name));
        }
        self.native_chart_data.insert(name, data);
        Ok(())
    }

    /// Replace the active editable theme variant and invalidate mounted
    /// component subtrees without recompiling Rhai.
    ///
    /// # Errors
    ///
    /// Returns when no theme manager is installed or the variant is invalid.
    pub fn replace_theme_variant_from_host(
        &mut self,
        variant: crate::ThemeVariant,
    ) -> Result<(), crate::ThemeError> {
        self.theme
            .as_mut()
            .ok_or(crate::ThemeError::NoVariants)?
            .replace_variant(variant)?;
        self.dirty.extend(self.component_state.paths());
        Ok(())
    }

    /// Select the app-level theme from trusted Host code without resetting script state.
    ///
    /// # Errors
    ///
    /// Returns when no theme manager is installed or the selection is unknown.
    pub fn select_theme_from_host(
        &mut self,
        family: &str,
        variant: &str,
    ) -> Result<bool, crate::ThemeError> {
        let theme = self.theme.as_mut().ok_or(crate::ThemeError::NoVariants)?;
        let previous = theme.generation();
        theme.set_app(ThemePreference::Fixed {
            selection: ThemeSelection::new(family, variant),
        })?;
        let changed = theme.generation() != previous;
        if changed {
            let invalidated = self.environment_dependencies.invalidate_theme_app();
            self.dirty.extend(invalidated);
            self.mark_all_windows_dirty();
        }
        Ok(changed)
    }

    /// Select the app-level locale from trusted Host code without resetting script state.
    ///
    /// # Errors
    ///
    /// Returns when no locale manager is installed or the locale is unknown.
    pub fn select_locale_from_host(&mut self, locale: &str) -> Result<bool, crate::LocaleError> {
        let locales = self
            .locale
            .as_mut()
            .ok_or_else(|| crate::LocaleError::UnknownLocale(locale.to_owned()))?;
        let previous = locales.generation();
        locales.set_app(locale)?;
        let changed = locales.generation() != previous;
        if changed {
            let invalidated = self.environment_dependencies.invalidate_locale_app();
            self.dirty.extend(invalidated);
            self.mark_all_windows_repaint();
        }
        Ok(changed)
    }

    /// Replace the Host-owned motion preference without resetting script state.
    ///
    /// Returns whether the effective preference changed. Reduced and disabled
    /// motion settle active work through the same central runtime policy used
    /// during initial view construction.
    pub fn set_motion_preference_from_host(&mut self, preference: crate::MotionPreference) -> bool {
        let previous = self.motions.preference();
        self.motions.set_preference(preference);
        let changed = self.motions.preference() != previous;
        if changed {
            let now = self.clock.now();
            self.motion_values = self.motions.snapshot(now);
            self.mark_all_windows_dirty();
        }
        changed
    }

    /// Atomically replace application-wide formal-component style rules.
    ///
    /// Equal replacements are ignored. A changed sheet invalidates every
    /// mounted component because rules are keyed by formal component identity.
    pub fn replace_component_styles_from_host(
        &mut self,
        styles: crate::ComponentStyleSheet,
    ) -> bool {
        if self.component_styles == styles {
            return false;
        }
        self.component_styles = styles;
        self.component_style_generation = self.component_style_generation.saturating_add(1);
        self.dirty.extend(self.component_state.paths());
        true
    }

    pub(crate) const fn component_style_generation(&self) -> u64 {
        self.component_style_generation
    }

    pub(crate) const fn component_styles(&self) -> &crate::ComponentStyleSheet {
        &self.component_styles
    }

    pub(crate) fn trace_subscription_closures(&mut self) {
        for closure in self.subscriptions.take_closures() {
            let scope = match closure.scope {
                AsyncScope::App => "/App".to_owned(),
                AsyncScope::Window(window) => format!("window:{window}"),
                AsyncScope::Component(component) => component.to_string(),
                AsyncScope::Effect {
                    component,
                    key,
                    activation,
                } => format!("{component}/effect[{key}]#{activation}"),
            };
            self.traces.push(
                crate::RuntimeTraceKind::Subscription,
                scope,
                format!("close {}: {}", closure.label, closure.reason),
                None,
                false,
            );
        }
    }

    /// Release every window-owned runtime resource while retaining app scope.
    ///
    /// # Errors
    ///
    /// Returns an asset-registry borrow error if image work is being drained.
    pub fn release_window(
        &mut self,
        window: &str,
        root: &ComponentInstancePath,
    ) -> Result<(), AssetError> {
        self.tasks
            .cancel_scope(&AsyncScope::Window(window.to_owned()));
        self.tasks.cancel_component_scope(root);
        self.timers.cancel_component_scope(root);
        self.subscriptions
            .cancel_scope(&AsyncScope::Window(window.to_owned()));
        self.subscriptions.cancel_component_scope(root);
        self.assets.cancel_window_scope(window, root)?;
        self.stores.remove_window(window);
        self.native_collections.remove_reader_scope(root);
        self.native_documents.remove_reader_scope(root);
        self.component_state.remove_scope(root);
        self.component_event_handlers
            .retain(|(path, _), _| !path.is_within(root));
        self.component_incarnations
            .retain(|path, _| !path.is_within(root));
        self.actions.remove_component_scope(root);
        self.dirty.retain(|path| !path.is_within(root));
        self.pending_events
            .retain(|event| !event.target.is_within(root));
        self.pending_actions.retain(|action| {
            !action
                .callback
                .component()
                .is_some_and(|path| path.is_within(root))
        });
        self.pending_async.retain(|delivery| match &delivery.scope {
            AsyncScope::App => true,
            AsyncScope::Window(id) => id != window,
            AsyncScope::Component(_) | AsyncScope::Effect { .. } => {
                !delivery.scope.is_within_component(root)
            }
        });
        self.pending_element_commands
            .retain(|command| command.window() != window);
        self.environment_dependencies.remove_window(window);
        self.environment_dependencies.remove_scope(root);
        self.repaint_windows.remove(window);
        self.window_appearances.remove(window);
        if let Some(theme) = self.theme.as_mut() {
            theme.remove_window(window);
            theme.remove_scope(root);
        }
        if let Some(locale) = self.locale.as_mut() {
            locale.remove_window(window);
            locale.remove_scope(root);
        }
        let window_scope = format!("window:{window}");
        self.motions.release_node_scope(&window_scope);
        let removed_ghosts = self
            .motion_ghosts
            .iter()
            .filter(|ghost| domain_is_within(&ghost.domain, &window_scope))
            .map(|ghost| ghost.path.clone())
            .collect::<Vec<_>>();
        self.motion_ghosts
            .retain(|ghost| !domain_is_within(&ghost.domain, &window_scope));
        for path in removed_ghosts {
            self.motions.cancel_node_scope(&path);
        }
        self.motions.discard_timeline_events_in_scope(&window_scope);
        self.motion_values = self.motions.snapshot(self.clock.now());
        self.effects.remove_scope(root);
        self.signals.remove_scope(root);
        self.element_refs.remove_scope(root);
        self.geometry.remove_scope(root);
        for presentation in self.presentations.values() {
            presentation.geometry.remove_scope(root);
        }
        self.windows.remove(window);
        self.responsive.remove_window(window);
        Ok(())
    }

    pub(crate) fn queue_async(
        &mut self,
        deliveries: impl IntoIterator<Item = crate::AsyncDelivery>,
    ) {
        self.pending_async.extend(deliveries);
    }

    pub(crate) fn queue_suspended_async(
        &mut self,
        deliveries: impl IntoIterator<Item = crate::AsyncDelivery>,
    ) -> Result<(), AsyncRuntimeError> {
        for delivery in deliveries {
            if self.pending_async.len() >= Self::SUSPENDED_DELIVERY_CAPACITY {
                return Err(AsyncRuntimeError::SuspendedBackpressure {
                    capacity: Self::SUSPENDED_DELIVERY_CAPACITY,
                });
            }
            self.pending_async.push(delivery);
        }
        Ok(())
    }

    pub(crate) fn suspended_delivery_capacity_remaining(&self) -> usize {
        Self::SUSPENDED_DELIVERY_CAPACITY.saturating_sub(self.pending_async.len())
    }

    pub(crate) fn cancel_async_scope(&mut self, scope: &AsyncScope) -> Result<(), AssetError> {
        self.assets.cancel_scope(scope)?;
        self.tasks.cancel_scope(scope);
        self.subscriptions.cancel_scope(scope);
        self.pending_async
            .retain(|delivery| &delivery.scope != scope);
        self.trace_subscription_closures();
        Ok(())
    }

    pub(crate) fn take_window_async(
        &mut self,
        window: &str,
        root: &ComponentInstancePath,
    ) -> Vec<crate::AsyncDelivery> {
        let app_owner = self.windows.open_ids().into_iter().next();
        let pending = std::mem::take(&mut self.pending_async);
        let (accepted, retained) =
            pending
                .into_iter()
                .partition(|delivery| match &delivery.scope {
                    AsyncScope::App => app_owner.as_deref() == Some(window),
                    AsyncScope::Window(id) => id == window,
                    AsyncScope::Component(_) | AsyncScope::Effect { .. } => {
                        delivery.scope.is_within_component(root)
                    }
                });
        self.pending_async = retained;
        accepted
    }

    pub(crate) fn discard_component_async_before_generation(
        &mut self,
        root: &ComponentInstancePath,
        generation: crate::ScriptGeneration,
    ) {
        self.pending_async.retain(|delivery| {
            !delivery.scope.is_within_component(root)
                || delivery.callback.generation() == generation
        });
    }

    pub(crate) fn take_window_element_commands(
        &mut self,
        window: &str,
    ) -> Vec<crate::element_ref::ElementCommand> {
        let commands = std::mem::take(&mut self.pending_element_commands);
        let (selected, retained) = commands
            .into_iter()
            .partition(|command| command.window() == window);
        self.pending_element_commands = retained;
        selected
    }

    pub(crate) fn has_window_dirty(&self, root: &ComponentInstancePath) -> bool {
        self.dirty.iter().any(|path| path.is_within(root))
    }

    pub(crate) fn flush_geometry_dependencies(&mut self) {
        self.dirty.extend(self.element_refs.take_dirty());
        self.dirty.extend(self.geometry.take_dirty());
        for presentation in self.presentations.values() {
            self.dirty.extend(presentation.geometry.take_dirty());
        }
    }

    pub(crate) fn take_window_dirty_components(
        &mut self,
        root: &ComponentInstancePath,
    ) -> BTreeSet<ComponentInstancePath> {
        let all = std::mem::take(&mut self.dirty);
        let (selected, retained) = all.into_iter().partition(|path| path.is_within(root));
        self.dirty = retained;
        selected
    }

    pub(crate) fn drain_pending_actions(&mut self) -> Vec<ActionInvocation> {
        std::mem::take(&mut self.pending_actions)
    }

    pub(crate) fn drain_pending_events(&mut self) -> Vec<PendingEvent> {
        std::mem::take(&mut self.pending_events)
    }

    pub(crate) fn has_pending_dispatch(&self) -> bool {
        !self.pending_actions.is_empty() || !self.pending_events.is_empty()
    }

    pub(crate) fn has_virtual_requests(&self) -> bool {
        !self.virtual_requests.is_empty()
    }

    pub(crate) fn component_event_handler(
        &self,
        component: &ComponentInstancePath,
        event: &str,
    ) -> Option<ScriptCallback> {
        self.component_event_handlers
            .get(&(component.clone(), event.to_owned()))
            .cloned()
    }

    pub(crate) fn reset_component_readers(&mut self, component: &ComponentInstancePath) {
        self.stores.reset_reader(component);
        self.native_collections.reset_reader(component);
        self.native_documents.reset_reader(component);
        self.environment_dependencies.reset_reader(component);
        self.reset_geometry_read_contribution(&crate::read_dependency::ReadDependency::component(
            component,
        ));
    }

    pub(crate) fn retain_virtual_read_contributions(
        &mut self,
        scope: &ComponentInstancePath,
        active: &BTreeSet<crate::read_dependency::ReadContribution>,
    ) {
        self.native_collections.retain_contributions(scope, active);
        self.native_documents.retain_contributions(scope, active);
        self.stores.retain_contributions(scope, active);
        self.environment_dependencies
            .retain_contributions(scope, active);
        self.element_refs.retain_contributions(scope, active);
        self.geometry.retain_contributions(scope, active);
        for presentation in self.presentations.values() {
            presentation.geometry.retain_contributions(scope, active);
        }
    }

    fn reset_geometry_read_contribution(
        &mut self,
        reader: &crate::read_dependency::ReadDependency,
    ) {
        self.element_refs.reset_contribution(reader);
        self.geometry.reset_contribution(reader);
        for presentation in self.presentations.values() {
            presentation.geometry.reset_contribution(reader);
        }
    }

    pub(crate) fn component_event_handlers_in_scope(
        &self,
        root: &ComponentInstancePath,
    ) -> BTreeMap<(ComponentInstancePath, String), ScriptCallback> {
        self.component_event_handlers
            .iter()
            .filter(|((path, _), _)| path.is_within(root))
            .map(|(id, callback)| (id.clone(), callback.clone()))
            .collect()
    }

    pub(crate) fn replace_component_event_handlers(
        &mut self,
        root: &ComponentInstancePath,
        handlers: BTreeMap<(ComponentInstancePath, String), ScriptCallback>,
    ) {
        self.component_event_handlers
            .retain(|(path, _), _| !path.is_within(root));
        self.component_event_handlers.extend(handlers);
    }

    pub(crate) fn mark_all_windows_dirty(&mut self) {
        self.dirty.extend(
            self.windows
                .open_ids()
                .into_iter()
                .map(|window| ComponentInstancePath::root("App", window)),
        );
    }

    pub(crate) fn mark_dirty(
        &mut self,
        components: impl IntoIterator<Item = ComponentInstancePath>,
    ) {
        self.dirty.extend(components);
    }

    pub(crate) fn mark_all_windows_repaint(&mut self) {
        self.repaint_windows.extend(self.windows.open_ids());
    }

    pub(crate) fn mark_window_repaint(&mut self, window: impl Into<String>) {
        self.repaint_windows.insert(window.into());
    }

    pub(crate) fn take_window_repaint(&mut self, window: &str) -> bool {
        self.repaint_windows.remove(window)
    }

    pub(crate) fn reconcile_component_lifetimes(
        &mut self,
        root: &ComponentInstancePath,
        active: &BTreeSet<ComponentInstancePath>,
        previous: &BTreeSet<ComponentInstancePath>,
    ) -> Result<(), AssetError> {
        for removed in previous
            .iter()
            .filter(|path| path.is_within(root) && *path != root && !active.contains(*path))
        {
            self.tasks.cancel_component_scope(removed);
            self.subscriptions.cancel_component_scope(removed);
            self.timers.cancel_component_scope(removed);
            self.assets.cancel_component_scope(removed)?;
            self.actions.remove_component_scope(removed);
        }
        self.pending_async.retain(|delivery| {
            delivery
                .scope
                .component()
                .is_none_or(|path| !path.is_within(root) || active.contains(path))
        });
        self.pending_actions.retain(|action| {
            !action
                .callback
                .component()
                .is_some_and(|path| path.is_within(root) && !active.contains(path))
        });
        self.pending_events.retain(|event| {
            !event.target.is_within(root) || active.contains(&event.target) || event.target == *root
        });
        self.stores.retain_reader_scope(root, active);
        self.component_event_handlers
            .retain(|(path, _), _| !path.is_within(root) || path == root || active.contains(path));
        self.native_collections.retain_reader_scope(root, active);
        self.native_documents.retain_reader_scope(root, active);
        self.element_refs.retain_scope(root, active);
        self.geometry.retain_reader_scope(root, active);
        for presentation in self.presentations.values() {
            presentation.geometry.retain_reader_scope(root, active);
        }
        self.environment_dependencies.retain_scope(root, active);
        self.dirty
            .retain(|path| !path.is_within(root) || path == root || active.contains(path));
        self.component_incarnations
            .retain(|path, _| !path.is_within(root) || path == root || active.contains(path));
        Ok(())
    }

    #[must_use]
    pub fn drain_batch(&mut self) -> UiMutationBatch {
        UiMutationBatch {
            dirty: std::mem::take(&mut self.dirty),
            events: std::mem::take(&mut self.pending_events),
            actions: std::mem::take(&mut self.pending_actions),
        }
    }

    #[must_use]
    pub fn dirty_components(&self) -> &BTreeSet<ComponentInstancePath> {
        &self.dirty
    }

    pub(crate) fn snapshot(&self) -> Result<UiStateSnapshot, AssetError> {
        Ok(UiStateSnapshot {
            runtime_id: self.runtime_id,
            transaction_depth: self.transaction_depth,
            component_state: self.component_state.clone(),
            stores: self.stores.clone(),
            native_collections: self.native_collections.clone(),
            native_documents: self.native_documents.clone(),
            actions: self.actions.clone(),
            component_event_handlers: self.component_event_handlers.clone(),
            component_incarnations: self.component_incarnations.clone(),
            next_component_incarnation: self.next_component_incarnation,
            dirty: self.dirty.clone(),
            pending_events: self.pending_events.clone(),
            pending_actions: self.pending_actions.clone(),
            pending_async: self.pending_async.clone(),
            pending_element_commands: self.pending_element_commands.clone(),
            locale: self.locale.clone(),
            theme: self.theme.clone(),
            component_styles: self.component_styles.clone(),
            component_style_generation: self.component_style_generation,
            motions: self.motions.transaction_snapshot(),
            effects: self.effects.clone(),
            signals: self.signals.clone(),
            element_refs: self.element_refs.clone(),
            geometry: self.geometry.snapshot(),
            pointer_capture: self.pointer_capture.snapshot(),
            presentations: self
                .presentations
                .iter()
                .map(|(view, state)| (view.clone(), state.snapshot()))
                .collect(),
            budgets: self.budgets.clone(),
            virtual_requests: self.virtual_requests.snapshot(),
            motion_values: self.motion_values.clone(),
            motion_ghosts: self.motion_ghosts.clone(),
            windows: self.windows.clone(),
            responsive: self.responsive.clone(),
            environment_dependencies: self.environment_dependencies.clone(),
            repaint_windows: self.repaint_windows.clone(),
            tasks: self.tasks.snapshot(),
            subscriptions: self.subscriptions.snapshot(),
            timers: self.timers.clone(),
            image_decodes: self.assets.decode_snapshot()?,
        })
    }

    pub(crate) fn restore(&mut self, snapshot: UiStateSnapshot) -> Result<(), UiTransactionError> {
        if self.runtime_id != snapshot.runtime_id {
            return Err(UiTransactionError::ForeignSnapshot);
        }
        let expected_depth = snapshot.transaction_depth.saturating_add(1);
        if self.transaction_depth != expected_depth {
            return Err(UiTransactionError::Unbalanced {
                expected: expected_depth,
                actual: self.transaction_depth,
            });
        }
        self.tasks.restore(snapshot.tasks);
        self.subscriptions.restore(snapshot.subscriptions);
        self.timers = snapshot.timers;
        let decode_result = self.assets.restore_decode_snapshot(snapshot.image_decodes);
        self.component_state = snapshot.component_state;
        self.stores = snapshot.stores;
        self.native_collections = snapshot.native_collections;
        self.native_documents = snapshot.native_documents;
        self.actions = snapshot.actions;
        self.component_event_handlers = snapshot.component_event_handlers;
        self.component_incarnations = snapshot.component_incarnations;
        self.next_component_incarnation = snapshot.next_component_incarnation;
        self.dirty = snapshot.dirty;
        self.pending_events = snapshot.pending_events;
        self.pending_actions = snapshot.pending_actions;
        self.pending_async = snapshot.pending_async;
        self.pending_element_commands = snapshot.pending_element_commands;
        self.locale = snapshot.locale;
        self.theme = snapshot.theme;
        self.component_styles = snapshot.component_styles;
        self.component_style_generation = snapshot.component_style_generation;
        self.motions = snapshot.motions;
        self.effects = snapshot.effects;
        self.signals = snapshot.signals;
        self.element_refs = snapshot.element_refs;
        self.geometry.restore(snapshot.geometry);
        self.pointer_capture.restore(snapshot.pointer_capture);
        self.presentations
            .retain(|view, _| snapshot.presentations.contains_key(view));
        for (view, presentation) in snapshot.presentations {
            let state = self.presentations.entry(view).or_default();
            state.geometry.restore(presentation.geometry);
            state.pointer_capture.restore(presentation.pointer_capture);
        }
        self.budgets = snapshot.budgets;
        self.virtual_requests.restore(snapshot.virtual_requests);
        self.motion_values = snapshot.motion_values;
        self.motion_ghosts = snapshot.motion_ghosts;
        self.windows = snapshot.windows;
        self.responsive = snapshot.responsive;
        self.environment_dependencies = snapshot.environment_dependencies;
        self.repaint_windows = snapshot.repaint_windows;
        self.transaction_depth = snapshot.transaction_depth;
        decode_result.map_err(UiTransactionError::from)
    }

    /// Begin an explicit rollback-capable runtime transaction.
    ///
    /// Cancellation of existing tasks, subscriptions, and image decodes remains
    /// provisional until commit, so rollback restores their delivery ability.
    ///
    /// # Errors
    ///
    /// Returns an asset-registry error while decode state is in use.
    pub fn begin_transaction(&mut self) -> Result<UiStateSnapshot, UiTransactionError> {
        let snapshot = self.snapshot()?;
        let _ = self.assets.begin_transaction()?;
        self.tasks.begin_transaction();
        self.subscriptions.begin_transaction();
        self.transaction_depth = self.transaction_depth.saturating_add(1);
        Ok(snapshot)
    }

    /// Commit a transaction and publish deferred resource cancellation when the
    /// outermost nested transaction completes.
    ///
    /// # Errors
    ///
    /// Returns an asset-registry error or an unmatched-commit error.
    pub fn commit_transaction(&mut self) -> Result<(), UiTransactionError> {
        if self.transaction_depth == 0 {
            return Err(UiTransactionError::Unbalanced {
                expected: 1,
                actual: 0,
            });
        }
        self.assets.commit_transaction()?;
        self.tasks.commit_transaction();
        self.subscriptions.commit_transaction();
        self.transaction_depth -= 1;
        Ok(())
    }

    /// Roll back a transaction to its checkpoint.
    ///
    /// # Errors
    ///
    /// Returns an asset-registry error, foreign-checkpoint error, or an
    /// unbalanced transaction-depth error.
    pub fn rollback_transaction(
        &mut self,
        snapshot: UiStateSnapshot,
    ) -> Result<(), UiTransactionError> {
        self.restore(snapshot)
    }
}

#[derive(Debug, Default)]
struct ViewPresentationState {
    geometry: crate::GeometryRegistry,
    pointer_capture: crate::PointerCaptureRegistry,
}

impl ViewPresentationState {
    fn snapshot(&self) -> ViewPresentationSnapshot {
        ViewPresentationSnapshot {
            geometry: self.geometry.snapshot(),
            pointer_capture: self.pointer_capture.snapshot(),
        }
    }
}

#[derive(Clone, Debug)]
struct ViewPresentationSnapshot {
    geometry: crate::geometry::GeometrySnapshot,
    pointer_capture: BTreeMap<u64, crate::NodeId>,
}

#[derive(Debug, Error)]
pub enum UiTransactionError {
    #[error("transaction snapshot belongs to another UiRuntimeState")]
    ForeignSnapshot,
    #[error("unbalanced runtime transaction depth: expected {expected}, got {actual}")]
    Unbalanced { expected: usize, actual: usize },
    #[error(transparent)]
    Asset(#[from] AssetError),
}

pub struct UiStateSnapshot {
    runtime_id: RuntimeStateId,
    transaction_depth: usize,
    component_state: StateStore,
    stores: StoreRegistry,
    native_collections: crate::NativeCollectionRegistry,
    native_documents: crate::NativeTextDocumentRegistry,
    actions: ActionRegistry,
    component_event_handlers: BTreeMap<(ComponentInstancePath, String), ScriptCallback>,
    component_incarnations: BTreeMap<ComponentInstancePath, ComponentIncarnation>,
    next_component_incarnation: u64,
    dirty: BTreeSet<ComponentInstancePath>,
    pending_events: Vec<PendingEvent>,
    pending_actions: Vec<ActionInvocation>,
    pending_async: Vec<crate::AsyncDelivery>,
    pending_element_commands: Vec<crate::element_ref::ElementCommand>,
    locale: Option<LocaleManager>,
    theme: Option<ThemeManager>,
    component_styles: crate::ComponentStyleSheet,
    component_style_generation: u64,
    motions: MotionRuntime,
    effects: crate::EffectRegistry,
    signals: crate::SignalRegistry,
    element_refs: crate::ElementRefRegistry,
    geometry: crate::geometry::GeometrySnapshot,
    pointer_capture: BTreeMap<u64, crate::NodeId>,
    presentations: BTreeMap<String, ViewPresentationSnapshot>,
    budgets: crate::RuntimeBudgets,
    virtual_requests: crate::virtual_list::VirtualRequestSnapshot,
    motion_values: BTreeMap<MotionKey, f64>,
    motion_ghosts: Vec<crate::motion::MotionGhost>,
    windows: WindowCommandRegistry,
    responsive: ResponsiveRuntime,
    environment_dependencies: crate::environment_dependency::EnvironmentDependencyRegistry,
    repaint_windows: BTreeSet<String>,
    tasks: crate::async_runtime::TaskRegistrySnapshot,
    subscriptions: crate::async_runtime::SubscriptionRegistrySnapshot,
    timers: crate::TimerRegistry,
    image_decodes: crate::asset::ImageDecodeSnapshot,
}

impl Clone for UiStateSnapshot {
    fn clone(&self) -> Self {
        Self {
            runtime_id: self.runtime_id,
            transaction_depth: self.transaction_depth,
            component_state: self.component_state.clone(),
            stores: self.stores.clone(),
            native_collections: self.native_collections.clone(),
            native_documents: self.native_documents.clone(),
            actions: self.actions.clone(),
            component_event_handlers: self.component_event_handlers.clone(),
            component_incarnations: self.component_incarnations.clone(),
            next_component_incarnation: self.next_component_incarnation,
            dirty: self.dirty.clone(),
            pending_events: self.pending_events.clone(),
            pending_actions: self.pending_actions.clone(),
            pending_async: self.pending_async.clone(),
            pending_element_commands: self.pending_element_commands.clone(),
            locale: self.locale.clone(),
            theme: self.theme.clone(),
            component_styles: self.component_styles.clone(),
            component_style_generation: self.component_style_generation,
            motions: self.motions.transaction_snapshot(),
            effects: self.effects.clone(),
            signals: self.signals.clone(),
            element_refs: self.element_refs.clone(),
            geometry: self.geometry.clone(),
            pointer_capture: self.pointer_capture.clone(),
            presentations: self.presentations.clone(),
            budgets: self.budgets.clone(),
            virtual_requests: self.virtual_requests.clone(),
            motion_values: self.motion_values.clone(),
            motion_ghosts: self.motion_ghosts.clone(),
            windows: self.windows.clone(),
            responsive: self.responsive.clone(),
            environment_dependencies: self.environment_dependencies.clone(),
            repaint_windows: self.repaint_windows.clone(),
            tasks: self.tasks.clone(),
            subscriptions: self.subscriptions.clone(),
            timers: self.timers.clone(),
            image_decodes: self.image_decodes.clone(),
        }
    }
}

impl UiStateSnapshot {
    pub(crate) const fn component_state(&self) -> &StateStore {
        &self.component_state
    }
}

#[derive(Clone, Debug)]
pub struct PendingEvent {
    pub target: ComponentInstancePath,
    pub event: UiEvent,
}

#[derive(Clone, Debug, Default)]
pub struct UiMutationBatch {
    pub dirty: BTreeSet<ComponentInstancePath>,
    pub events: Vec<PendingEvent>,
    pub actions: Vec<ActionInvocation>,
}

#[derive(Clone, Debug)]
pub struct UiContext {
    runtime: Rc<RefCell<UiRuntimeState>>,
    component: ComponentInstancePath,
    incarnation: ComponentIncarnation,
    callback_component: ComponentInstancePath,
    callback_incarnation: ComponentIncarnation,
    callback_events: BTreeMap<String, EventSchema>,
    read_dependency: crate::read_dependency::ReadDependency,
    window: Option<String>,
    view: Option<String>,
    phase: ExecutionPhase,
    events: BTreeMap<String, EventSchema>,
    generation: ScriptGeneration,
    native_context: Option<crate::invocation::ScriptInvocationContext>,
    async_scope: Option<AsyncScope>,
    component_style: Option<crate::Style>,
    component_part_styles: BTreeMap<String, crate::Style>,
    global_component_part_styles: BTreeMap<String, crate::Style>,
    non_reusable_render_reads: Rc<RefCell<BTreeSet<ComponentInstancePath>>>,
    event_target: Option<crate::GeometryBounds>,
}

impl UiContext {
    #[must_use]
    pub fn new(
        runtime: Rc<RefCell<UiRuntimeState>>,
        component: ComponentInstancePath,
        window: Option<String>,
        phase: ExecutionPhase,
        events: BTreeMap<String, EventSchema>,
    ) -> Self {
        if let Some(window) = window.as_deref()
            && let Ok(mut runtime) = runtime.try_borrow_mut()
        {
            runtime.ensure_presentation(window);
        }
        let incarnation = runtime
            .try_borrow_mut()
            .map(|mut runtime| runtime.ensure_component_incarnation(&component))
            .unwrap_or_default();
        let read_dependency = crate::read_dependency::ReadDependency::component(&component);
        let context = Self {
            runtime,
            component: component.clone(),
            incarnation,
            callback_component: component,
            read_dependency,
            callback_incarnation: incarnation,
            callback_events: events.clone(),
            window,
            view: None,
            phase,
            events,
            generation: ScriptGeneration::default(),
            native_context: None,
            async_scope: None,
            component_style: None,
            component_part_styles: BTreeMap::new(),
            global_component_part_styles: BTreeMap::new(),
            non_reusable_render_reads: Rc::new(RefCell::new(BTreeSet::new())),
            event_target: None,
        };
        if phase == ExecutionPhase::Render
            && let Ok(mut runtime) = context.runtime.try_borrow_mut()
        {
            runtime.reset_component_readers(&context.component);
        }
        context
    }

    #[must_use]
    pub fn with_generation(mut self, generation: ScriptGeneration) -> Self {
        self.generation = generation;
        self
    }

    #[must_use]
    pub fn with_view_id(mut self, view: impl Into<String>) -> Self {
        let view = view.into();
        if let Ok(mut runtime) = self.runtime.try_borrow_mut() {
            runtime.ensure_presentation(&view);
        }
        self.view = Some(view);
        self
    }

    #[must_use]
    pub(crate) fn with_optional_view_id(mut self, view: Option<String>) -> Self {
        if let Some(view) = view.as_deref()
            && let Ok(mut runtime) = self.runtime.try_borrow_mut()
        {
            runtime.ensure_presentation(view);
        }
        self.view = view;
        self
    }

    pub(crate) fn for_component(
        &self,
        component: ComponentInstancePath,
        events: BTreeMap<String, EventSchema>,
    ) -> Self {
        let incarnation = self
            .runtime
            .try_borrow_mut()
            .map(|mut runtime| runtime.ensure_component_incarnation(&component))
            .unwrap_or_default();
        let read_dependency = crate::read_dependency::ReadDependency::component(&component);
        let context = Self {
            runtime: Rc::clone(&self.runtime),
            component: component.clone(),
            incarnation,
            callback_component: component,
            read_dependency,
            callback_incarnation: incarnation,
            callback_events: events.clone(),
            window: self.window.clone(),
            view: self.view.clone(),
            phase: self.phase,
            events,
            generation: self.generation,
            native_context: self.native_context.clone(),
            async_scope: self.async_scope.clone(),
            component_style: self.component_style.clone(),
            component_part_styles: self.component_part_styles.clone(),
            global_component_part_styles: self.global_component_part_styles.clone(),
            non_reusable_render_reads: Rc::clone(&self.non_reusable_render_reads),
            event_target: self.event_target,
        };
        if context.phase == ExecutionPhase::Render
            && let Ok(mut runtime) = context.runtime.try_borrow_mut()
        {
            runtime.reset_component_readers(&context.component);
        }
        context
    }

    pub(crate) fn for_structural_scope(
        &self,
        component: ComponentInstancePath,
        events: BTreeMap<String, EventSchema>,
    ) -> Self {
        // Structure supplies child identity, while callbacks and observable
        // reads must still belong to an executable formal/root component.
        let mut context = self.for_component(component, events);
        context.callback_component = self.callback_component.clone();
        context.callback_incarnation = self.callback_incarnation;
        context.callback_events = self.callback_events.clone();
        context.read_dependency = self.read_dependency.clone();
        context
    }

    pub(crate) fn for_virtual_item(
        &self,
        collection: &crate::VirtualCollectionId,
        key: &str,
    ) -> Self {
        let mut context = self.clone();
        context.read_dependency = crate::read_dependency::ReadDependency::virtual_item(
            &self.callback_component,
            collection,
            key,
        );
        if let Ok(mut runtime) = context.runtime.try_borrow_mut() {
            runtime
                .native_collections
                .reset_contribution(&context.read_dependency);
            runtime
                .native_documents
                .reset_contribution(&context.read_dependency);
            runtime.stores.reset_contribution(&context.read_dependency);
            runtime
                .environment_dependencies
                .reset_contribution(&context.read_dependency);
            runtime.reset_geometry_read_contribution(&context.read_dependency);
        }
        context
    }

    pub(crate) fn with_native_context(
        mut self,
        native_context: Option<crate::invocation::ScriptInvocationContext>,
    ) -> Self {
        self.native_context = native_context;
        self
    }

    pub(crate) const fn with_event_target(mut self, target: Option<crate::GeometryBounds>) -> Self {
        self.event_target = target;
        self
    }

    pub(crate) fn with_async_scope(mut self, scope: AsyncScope) -> Self {
        self.async_scope = Some(scope);
        self
    }

    pub(crate) fn with_component_styles(
        mut self,
        global_part_styles: BTreeMap<String, crate::Style>,
        style: Option<crate::Style>,
        part_styles: BTreeMap<String, crate::Style>,
    ) -> Self {
        self.global_component_part_styles = global_part_styles;
        self.component_style = style;
        self.component_part_styles = part_styles;
        self
    }

    pub(crate) fn reset_non_reusable_render_reads(&self) {
        self.non_reusable_render_reads.borrow_mut().clear();
    }

    pub(crate) fn component_render_is_reusable(&self) -> bool {
        !self
            .non_reusable_render_reads
            .borrow()
            .contains(&self.component)
    }

    fn mark_non_reusable_render_read(&self) {
        if self.phase == ExecutionPhase::Render {
            self.non_reusable_render_reads
                .borrow_mut()
                .insert(self.callback_component.clone());
        }
    }

    fn resolve_component_style(&self, part: &str, mut base: crate::Style) -> crate::Style {
        if let Some(style) = self.global_component_part_styles.get(part) {
            base = base.merged(style);
        }
        if part == "root"
            && let Some(style) = &self.component_style
        {
            base = base.merged(style);
        }
        if let Some(style) = self.component_part_styles.get(part) {
            base = base.merged(style);
        }
        base
    }

    fn scoped_callback(&self, function: FnPtr) -> Result<ScriptCallback, UiContextError> {
        let mut callback = ScriptCallback::try_from_fn_ptr(function, self.generation)?;
        callback.bind_component_scope_if_unset(
            &self.callback_component,
            self.callback_incarnation,
            self.callback_events.clone(),
        );
        if let Some(context) = &self.native_context {
            callback.bind_native_context_if_unset(context.clone());
        }
        Ok(callback)
    }

    #[must_use]
    pub fn runtime(&self) -> &Rc<RefCell<UiRuntimeState>> {
        &self.runtime
    }

    pub(crate) fn component_path(&self) -> &ComponentInstancePath {
        &self.component
    }

    pub(crate) const fn component_incarnation(&self) -> ComponentIncarnation {
        self.incarnation
    }

    pub(crate) fn event_schemas(&self) -> &BTreeMap<String, EventSchema> {
        &self.events
    }

    pub(crate) fn callback_component_path(&self) -> &ComponentInstancePath {
        &self.callback_component
    }

    pub(crate) const fn callback_component_incarnation(&self) -> ComponentIncarnation {
        self.callback_incarnation
    }

    pub(crate) fn callback_event_schemas(&self) -> &BTreeMap<String, EventSchema> {
        &self.callback_events
    }

    pub(crate) fn native_context(&self) -> Option<&crate::invocation::ScriptInvocationContext> {
        self.native_context.as_ref()
    }

    /// Read declared local component state.
    ///
    /// # Errors
    ///
    /// Returns [`UiContextError`] for a poisoned runtime, unknown instance, or
    /// unknown state field.
    pub fn get_state(&self, field: &str) -> Result<UiValue, UiContextError> {
        self.runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .component_state
            .get(&self.callback_component, field)
            .cloned()
            .ok_or_else(|| UiContextError::UnknownState {
                component: self.callback_component.clone(),
                field: field.to_owned(),
            })
    }

    /// Read one existing nested local-state path.
    ///
    /// Local state remains a component-scoped dependency: this accessor avoids
    /// copying an entire collection into Rhai but does not create a smaller
    /// rerender boundary than the owning component.
    ///
    /// # Errors
    ///
    /// Returns state, borrow, or nested-path errors.
    pub fn get_state_path(
        &self,
        field: &str,
        path: &UiValuePath,
    ) -> Result<UiValue, UiContextError> {
        Ok(self.get_state(field)?.get_path(path)?.clone())
    }

    /// Queue a schema-checked local state mutation.
    ///
    /// # Errors
    ///
    /// Returns [`UiContextError::MutationDuringRender`] in `view`, plus state
    /// and value-conversion errors.
    pub fn set_state(&self, field: &str, value: Dynamic) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let value = UiValue::from_dynamic(value)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let sensitive = runtime.component_state.is_sensitive(&self.component, field);
        let changed = runtime
            .component_state
            .set(&self.component, field, value.clone())?;
        if changed {
            runtime.dirty.insert(self.component.clone());
        }
        runtime.traces.push(
            crate::RuntimeTraceKind::State,
            self.component.to_string(),
            format!("set {field}"),
            Some(value),
            sensitive,
        );
        Ok(())
    }

    /// Replace one existing nested local-state path.
    ///
    /// # Errors
    ///
    /// Returns phase, state, conversion, borrow, or nested-path errors. The
    /// complete resulting field is checked against its declared schema.
    pub fn set_state_path(
        &self,
        field: &str,
        path: &UiValuePath,
        value: Dynamic,
    ) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let value = UiValue::from_dynamic(value)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let mut root = runtime
            .component_state
            .get(&self.component, field)
            .cloned()
            .ok_or_else(|| UiContextError::UnknownState {
                component: self.component.clone(),
                field: field.to_owned(),
            })?;
        root.set_path(path, value.clone())?;
        let sensitive = runtime.component_state.is_sensitive(&self.component, field);
        if runtime.component_state.set(&self.component, field, root)? {
            runtime.dirty.insert(self.component.clone());
        }
        runtime.traces.push(
            crate::RuntimeTraceKind::State,
            self.component.to_string(),
            format!("set nested {field}"),
            Some(value),
            sensitive,
        );
        Ok(())
    }

    /// Read a native hot value without establishing a component dependency.
    ///
    /// # Errors
    ///
    /// Returns a stale-signal or runtime borrow error.
    pub fn get_signal(&self, signal: &crate::NativeSignal) -> Result<Dynamic, UiContextError> {
        self.mark_non_reusable_render_read();
        Ok(self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .signals
            .read(signal)?
            .into_dynamic())
    }

    /// Update a native hot value without dirtying a formal component.
    ///
    /// # Errors
    ///
    /// Returns during render, for a stale signal, a type mismatch, or an
    /// unsupported value.
    pub fn set_signal(
        &self,
        signal: &crate::NativeSignal,
        value: Dynamic,
    ) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let value = crate::SignalValue::from_dynamic_for_kind(value, signal.id().kind())?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let changed =
            runtime
                .signals
                .write_from(signal, value.clone(), crate::SignalWriter::Script)?;
        runtime.traces.push(
            crate::RuntimeTraceKind::Signal,
            signal.id().component().to_string(),
            format!(
                "set {} ({}){}",
                signal.id().key(),
                signal.id().kind().as_str(),
                if changed { "" } else { " unchanged" }
            ),
            None,
            false,
        );
        Ok(())
    }

    /// Resolve and read a component-local signal key without tracking a dependency.
    ///
    /// # Errors
    ///
    /// Returns when the key is not mounted or runtime state is borrowed.
    pub fn get_signal_by_key(&self, key: &str) -> Result<Dynamic, UiContextError> {
        self.mark_non_reusable_render_read();
        let runtime = self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?;
        let signal = runtime.signals.resolve(&self.component, key)?;
        Ok(runtime.signals.read(&signal)?.into_dynamic())
    }

    /// Resolve an optional-float signal owned by the nearest parent component.
    /// This is intended for retained render scopes, such as virtual collection
    /// item renderers, that consume a signal declared by their owner while the
    /// owner's initial render transaction is still in progress.
    ///
    /// # Errors
    ///
    /// Returns a borrow, identity, type, or unknown-signal error.
    pub(crate) fn parent_optional_float_signal_ref(
        &self,
        key: &str,
    ) -> Result<crate::NativeSignal, UiContextError> {
        let runtime = self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?;
        let mut scope = self.component.parent();
        while let Some(component) = scope {
            if let Ok(signal) = runtime.signals.resolve(&component, key) {
                if signal.id().kind() == crate::SignalKind::OptionalFloat {
                    return Ok(signal);
                }
                return Err(crate::SignalError::TypeMismatch {
                    expected: crate::SignalKind::OptionalFloat,
                    actual: signal.id().kind(),
                }
                .into());
            }
            if let Some(incarnation) = runtime.component_incarnation(&component) {
                let id = crate::SignalId::new_scoped(
                    component,
                    incarnation,
                    key,
                    crate::SignalKind::OptionalFloat,
                )?;
                return Ok(crate::NativeSignal::new(id));
            }
            scope = component.parent();
        }
        Err(crate::SignalError::UnknownKey {
            component: self.component.clone(),
            key: key.to_owned(),
        }
        .into())
    }

    /// Resolve and write a component-local signal key.
    ///
    /// # Errors
    ///
    /// Returns during render, when the key is not mounted, or for a type mismatch.
    pub fn set_signal_by_key(&self, key: &str, value: Dynamic) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let signal = self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .signals
            .resolve(&self.component, key)?;
        self.set_signal(&signal, value)
    }

    /// Read last committed layout/visual geometry through a stable element ref.
    ///
    /// The exact node becomes a component dependency. The first render returns
    /// null until GPUI has committed prepaint, which then dirties the reader.
    ///
    /// # Errors
    ///
    /// Returns for stale refs, unavailable geometry, or runtime borrow conflicts.
    pub fn element_bounds(&self, reference: &crate::ElementRef) -> Result<UiValue, UiContextError> {
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let node = if self.phase == ExecutionPhase::Render {
            runtime
                .element_refs
                .resolve_and_track_geometry(reference, &self.read_dependency)
        } else {
            Some(runtime.element_refs.resolve(reference)?)
        };
        let Some(node) = node else {
            return Ok(UiValue::Null);
        };
        let geometry_registry =
            runtime.geometry_for(self.view.as_deref().or(self.window.as_deref()));
        drop(runtime);
        let geometry = if self.phase == ExecutionPhase::Render {
            geometry_registry.read_ref_tracked(reference.id(), node, &self.read_dependency)
        } else {
            geometry_registry.get(node)
        };
        let Some(geometry) = geometry else {
            return Ok(UiValue::Null);
        };
        Ok(UiValue::Map(BTreeMap::from([
            ("layout".to_owned(), geometry_bounds_value(geometry.layout)),
            ("visual".to_owned(), geometry_bounds_value(geometry.visual)),
            (
                "clip".to_owned(),
                geometry.clip.map_or(UiValue::Null, geometry_bounds_value),
            ),
        ])))
    }

    /// Resolve and read a committed component-local ref by its stable key.
    ///
    /// This is intended for event callbacks, which cannot retain the custom
    /// [`crate::ElementRef`] value created during render.
    ///
    /// # Errors
    ///
    /// Returns for unknown keys, unavailable geometry, or runtime borrow conflicts.
    pub fn element_bounds_by_key(&self, key: &str) -> Result<UiValue, UiContextError> {
        let reference = self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .element_refs
            .resolve_key(&self.component, key)?;
        self.element_bounds(&reference)
    }

    /// Read the current handler node's committed visual bounds without
    /// establishing a render dependency.
    ///
    /// This event-time snapshot is `null` for callbacks that were not
    /// dispatched from a retained node or whose geometry is unavailable.
    ///
    /// # Errors
    ///
    /// Returns [`UiContextError::EventTargetOutsideEvent`] during render,
    /// initialization, or disposal.
    pub fn event_target_bounds(&self) -> Result<UiValue, UiContextError> {
        if self.phase != ExecutionPhase::Event {
            return Err(UiContextError::EventTargetOutsideEvent);
        }
        Ok(self
            .event_target
            .map_or(UiValue::Null, crate::GeometryBounds::into_value))
    }

    /// Queue focus for a mounted element ref in the current window.
    ///
    /// # Errors
    ///
    /// Returns during render, outside a window, or for a stale ref.
    pub fn focus_element(&self, reference: &crate::ElementRef) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let window = self.window.clone().ok_or(UiContextError::MissingWindow)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let node = runtime.element_refs.resolve(reference)?;
        runtime
            .pending_element_commands
            .push(crate::element_ref::ElementCommand::Focus { window, node });
        Ok(())
    }

    /// Resolve and queue focus for a component-local ref key.
    ///
    /// # Errors
    ///
    /// Returns the same errors as [`Self::focus_element`] plus unknown keys.
    pub fn focus_element_by_key(&self, key: &str) -> Result<(), UiContextError> {
        let reference = self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .element_refs
            .resolve_key(&self.component, key)?;
        self.focus_element(&reference)
    }

    /// Queue a positive visible scroll offset for a retained scroll container.
    ///
    /// # Errors
    ///
    /// Returns during render, outside a window, for a stale ref, or for invalid
    /// offsets.
    pub fn scroll_element_to(
        &self,
        reference: &crate::ElementRef,
        x: f64,
        y: f64,
    ) -> Result<(), UiContextError> {
        self.require_mutation()?;
        if !x.is_finite() || !y.is_finite() || x < 0.0 || y < 0.0 {
            return Err(UiContextError::InvalidScrollOffset { x, y });
        }
        let window = self.window.clone().ok_or(UiContextError::MissingWindow)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let node = runtime.element_refs.resolve(reference)?;
        runtime
            .pending_element_commands
            .push(crate::element_ref::ElementCommand::ScrollTo { window, node, x, y });
        Ok(())
    }

    /// Resolve and queue scroll for a component-local ref key.
    ///
    /// # Errors
    ///
    /// Returns the same errors as [`Self::scroll_element_to`] plus unknown keys.
    pub fn scroll_element_to_by_key(
        &self,
        key: &str,
        x: f64,
        y: f64,
    ) -> Result<(), UiContextError> {
        let reference = self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .element_refs
            .resolve_key(&self.component, key)?;
        self.scroll_element_to(&reference, x, y)
    }

    /// Queue minimal ancestor scrolling that reveals a retained descendant.
    ///
    /// # Errors
    ///
    /// Returns during render, outside a window, or for a stale ref.
    pub fn scroll_element_into_view(
        &self,
        reference: &crate::ElementRef,
    ) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let window = self.window.clone().ok_or(UiContextError::MissingWindow)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let node = runtime.element_refs.resolve(reference)?;
        runtime
            .pending_element_commands
            .push(crate::element_ref::ElementCommand::ScrollIntoView { window, node });
        Ok(())
    }

    /// Resolve and reveal a component-local ref key.
    ///
    /// # Errors
    ///
    /// Returns the same errors as [`Self::scroll_element_into_view`] plus unknown keys.
    pub fn scroll_element_into_view_by_key(&self, key: &str) -> Result<(), UiContextError> {
        let reference = self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .element_refs
            .resolve_key(&self.component, key)?;
        self.scroll_element_into_view(&reference)
    }

    /// Read and subscribe to an app-scoped store field.
    ///
    /// # Errors
    ///
    /// Returns store or lock errors.
    pub fn get_app_store(&self, store: &str, field: &str) -> Result<UiValue, UiContextError> {
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        Ok(runtime
            .stores
            .read_dependency(&self.read_dependency, &StoreId::app(store), field)?)
    }

    /// Read one Rust-owned collection and subscribe the current component.
    ///
    /// The returned value is an opaque collection view: Rhai can pass it to
    /// collection-aware components but cannot enumerate and materialize all rows.
    ///
    /// # Errors
    ///
    /// Returns collection or borrow errors.
    pub fn get_native_collection(
        &self,
        name: &str,
    ) -> Result<crate::NativeCollection, UiContextError> {
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        Ok(runtime.native_collections.read_dependency(
            &self.read_dependency,
            name,
            self.phase == ExecutionPhase::Render,
        )?)
    }

    /// Read and subscribe to one immutable Host-owned text revision.
    ///
    /// # Errors
    ///
    /// Returns document or runtime borrow errors.
    pub fn get_native_text_document(
        &self,
        name: &str,
    ) -> Result<crate::NativeTextDocument, UiContextError> {
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        Ok(runtime
            .native_documents
            .read_dependency(&self.read_dependency, name)?)
    }

    /// Read one Host-owned chart data handle. The handle performs its own
    /// revision notifications, so this read does not create a Rhai rerender
    /// dependency for every streaming update.
    ///
    /// # Errors
    ///
    /// Returns a borrow error or an unknown-data diagnostic.
    #[cfg(feature = "charts")]
    pub fn get_native_chart_data(
        &self,
        name: &str,
    ) -> Result<crate::NativeChartData, UiContextError> {
        self.runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .native_chart_data
            .get(name)
            .cloned()
            .ok_or_else(|| UiContextError::UnknownChartData(name.to_owned()))
    }

    /// Read and subscribe to one exact app-store path.
    ///
    /// # Errors
    ///
    /// Returns store, path, or borrow errors.
    pub fn get_app_store_path(
        &self,
        store: &str,
        field: &str,
        path: &UiValuePath,
    ) -> Result<UiValue, UiContextError> {
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        Ok(runtime.stores.read_path_dependency(
            &self.read_dependency,
            &StoreId::app(store),
            field,
            path,
        )?)
    }

    /// Queue a schema-checked app store mutation.
    ///
    /// # Errors
    ///
    /// Returns phase, conversion, store, or lock errors.
    pub fn set_app_store(
        &self,
        store: &str,
        field: &str,
        value: Dynamic,
    ) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let value = UiValue::from_dynamic(value)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let id = StoreId::app(store);
        let sensitive = runtime.stores.is_sensitive(&id, field);
        let invalidated = runtime.stores.write(&id, field, value.clone())?;
        runtime.dirty.extend(invalidated);
        runtime.traces.push(
            crate::RuntimeTraceKind::Store,
            format!("app:{store}"),
            format!("set {field}"),
            Some(value),
            sensitive,
        );
        Ok(())
    }

    /// Replace one exact app-store path and invalidate only affected readers.
    ///
    /// # Errors
    ///
    /// Returns phase, conversion, store, path, schema, or borrow errors.
    pub fn set_app_store_path(
        &self,
        store: &str,
        field: &str,
        path: &UiValuePath,
        value: Dynamic,
    ) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let value = UiValue::from_dynamic(value)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let id = StoreId::app(store);
        let sensitive = runtime.stores.is_sensitive(&id, field);
        let invalidated = runtime.stores.write_path(&id, field, path, value.clone())?;
        runtime.dirty.extend(invalidated);
        runtime.traces.push(
            crate::RuntimeTraceKind::Store,
            format!("app:{store}"),
            format!("set nested {field}"),
            Some(value),
            sensitive,
        );
        Ok(())
    }

    /// Read and subscribe to a store scoped to this context's window.
    ///
    /// # Errors
    ///
    /// Returns [`UiContextError::MissingWindow`] outside a window, plus store
    /// and lock errors.
    pub fn get_window_store(&self, store: &str, field: &str) -> Result<UiValue, UiContextError> {
        let window = self.window.as_ref().ok_or(UiContextError::MissingWindow)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        Ok(runtime.stores.read_dependency(
            &self.read_dependency,
            &StoreId::window(window, store),
            field,
        )?)
    }

    /// Read and subscribe to one exact path in the current window's store.
    ///
    /// # Errors
    ///
    /// Returns missing-window, store, path, or borrow errors.
    pub fn get_window_store_path(
        &self,
        store: &str,
        field: &str,
        path: &UiValuePath,
    ) -> Result<UiValue, UiContextError> {
        let window = self.window.as_ref().ok_or(UiContextError::MissingWindow)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        Ok(runtime.stores.read_path_dependency(
            &self.read_dependency,
            &StoreId::window(window, store),
            field,
            path,
        )?)
    }

    /// Queue a schema-checked mutation in the current window's store.
    ///
    /// # Errors
    ///
    /// Returns phase, missing-window, conversion, store, or borrow errors.
    pub fn set_window_store(
        &self,
        store: &str,
        field: &str,
        value: Dynamic,
    ) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let window = self.window.as_ref().ok_or(UiContextError::MissingWindow)?;
        let value = UiValue::from_dynamic(value)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let id = StoreId::window(window, store);
        let sensitive = runtime.stores.is_sensitive(&id, field);
        let invalidated = runtime.stores.write(&id, field, value.clone())?;
        runtime.dirty.extend(invalidated);
        runtime.traces.push(
            crate::RuntimeTraceKind::Store,
            format!("window:{window}:{store}"),
            format!("set {field}"),
            Some(value),
            sensitive,
        );
        Ok(())
    }

    /// Replace one exact path in the current window's store.
    ///
    /// # Errors
    ///
    /// Returns phase, missing-window, conversion, store, path, schema, or
    /// borrow errors.
    pub fn set_window_store_path(
        &self,
        store: &str,
        field: &str,
        path: &UiValuePath,
        value: Dynamic,
    ) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let window = self.window.as_ref().ok_or(UiContextError::MissingWindow)?;
        let value = UiValue::from_dynamic(value)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let id = StoreId::window(window, store);
        let sensitive = runtime.stores.is_sensitive(&id, field);
        let invalidated = runtime.stores.write_path(&id, field, path, value.clone())?;
        runtime.dirty.extend(invalidated);
        runtime.traces.push(
            crate::RuntimeTraceKind::Store,
            format!("window:{window}:{store}"),
            format!("set nested {field}"),
            Some(value),
            sensitive,
        );
        Ok(())
    }

    /// Emit a declared semantic component event.
    ///
    /// # Errors
    ///
    /// Returns phase, schema, conversion, or lock errors.
    pub fn emit(&self, event: &str, payload: Dynamic) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let schema = self
            .events
            .get(event)
            .ok_or_else(|| UiContextError::UnknownEvent(event.to_owned()))?;
        schema
            .payload
            .validate(&payload)
            .map_err(UiContextError::InvalidEvent)?;
        let payload = UiValue::from_dynamic(payload)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime.pending_events.push(PendingEvent {
            target: self.component.clone(),
            event: UiEvent {
                name: event.to_owned(),
                payload,
            },
        });
        runtime.traces.push(
            crate::RuntimeTraceKind::Event,
            self.component.to_string(),
            format!("emit {event}"),
            None,
            true,
        );
        Ok(())
    }

    /// Dispatch a registered semantic action.
    ///
    /// # Errors
    ///
    /// Returns phase, action, conversion, or lock errors.
    pub fn dispatch_action(&self, action: &str, payload: Dynamic) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let id = ActionId::parse(action)?;
        let payload = UiValue::from_dynamic(payload)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let invocation = runtime.actions.dispatch(&id, payload)?;
        runtime.pending_actions.push(invocation);
        runtime.traces.push(
            crate::RuntimeTraceKind::Action,
            self.component.to_string(),
            format!("dispatch {action}"),
            None,
            true,
        );
        Ok(())
    }

    /// Register or refresh an app-scoped semantic action callback.
    ///
    /// # Errors
    ///
    /// Returns phase, identifier, or borrow errors.
    pub fn register_action(&self, action: &str, callback: FnPtr) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let id = ActionId::parse(action)?;
        let callback = self.scoped_callback(callback)?;
        self.runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?
            .actions
            .register_or_replace(id, callback);
        Ok(())
    }

    /// Enable or disable a registered semantic action.
    ///
    /// # Errors
    ///
    /// Returns phase, identifier, unknown-action, or borrow errors.
    pub fn set_action_enabled(&self, action: &str, enabled: bool) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let id = ActionId::parse(action)?;
        self.runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?
            .actions
            .set_enabled(&id, enabled)?;
        Ok(())
    }

    /// Invoke a manifest-declared Rust capability.
    ///
    /// # Errors
    ///
    /// Returns phase, identifier, schema, handler, conversion, or borrow errors.
    pub fn call_capability(
        &self,
        capability: &str,
        method: &str,
        input: Dynamic,
    ) -> Result<UiValue, UiContextError> {
        self.require_mutation()?;
        let id = CapabilityId::parse(capability)?;
        let input = UiValue::from_dynamic(input)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let output = runtime.capabilities.call(&id, method, input)?;
        runtime.traces.push(
            crate::RuntimeTraceKind::Capability,
            self.component.to_string(),
            format!("call {capability}.{method}"),
            None,
            true,
        );
        Ok(output)
    }

    fn read_locale<T>(
        &self,
        read: impl FnOnce(
            &LocaleManager,
            Option<&str>,
            &ComponentInstancePath,
        ) -> Result<T, LocaleError>,
    ) -> Result<T, UiContextError> {
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime
            .environment_dependencies
            .track_locale(self.window.as_deref(), &self.read_dependency);
        let locale = runtime
            .locale
            .as_ref()
            .ok_or(UiContextError::LocaleUnavailable)?;
        Ok(read(locale, self.window.as_deref(), &self.component)?)
    }

    /// Resolve one localized message for this window/component scope.
    ///
    /// # Errors
    ///
    /// Returns [`UiContextError::LocaleUnavailable`], locale, or borrow errors.
    pub fn text(&self, key: &str) -> Result<String, UiContextError> {
        self.read_locale(|locale, window, component| locale.text(window, Some(component), key))
    }

    /// Resolve the logical text direction for this component scope.
    ///
    /// # Errors
    ///
    /// Returns [`UiContextError::LocaleUnavailable`], locale, or borrow errors.
    pub fn text_direction(&self) -> Result<String, UiContextError> {
        match self
            .read_locale(|locale, window, component| locale.direction(window, Some(component)))?
        {
            TextDirection::LeftToRight => Ok("ltr".to_owned()),
            TextDirection::RightToLeft => Ok("rtl".to_owned()),
        }
    }

    /// Return today's strict ISO date from the host-injected calendar Clock.
    ///
    /// This is a read-only presentation input and is available during render.
    ///
    /// # Errors
    ///
    /// Returns a borrow error when another callback owns the runtime state.
    pub fn today(&self) -> Result<String, UiContextError> {
        Ok(self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .calendar_clock
            .today()
            .to_iso())
    }

    /// Format a strict ISO date through the selected locale.
    ///
    /// # Errors
    ///
    /// Returns locale, date, style, or runtime borrow errors.
    pub fn format_date(&self, iso_date: &str, style: &str) -> Result<String, UiContextError> {
        let style = DateStyle::parse(style)?;
        self.read_locale(|locale, window, component| {
            locale.format_date(window, Some(component), iso_date, style)
        })
    }

    /// Format a strict ISO date with the locale's month/year pattern.
    ///
    /// # Errors
    ///
    /// Returns locale, date, or runtime borrow errors.
    pub fn format_month_year(&self, iso_date: &str) -> Result<String, UiContextError> {
        self.read_locale(|locale, window, component| {
            locale.format_month_year(window, Some(component), iso_date)
        })
    }

    /// Return a detached read-only copy of selected calendar metadata.
    ///
    /// # Errors
    ///
    /// Returns locale, serialization, or runtime borrow errors.
    pub fn calendar_metadata(&self) -> Result<Map, UiContextError> {
        let calendar = self.read_locale(|locale, window, component| {
            locale.calendar(window, Some(component)).cloned()
        })?;
        let dynamic = rhai::serde::to_dynamic(calendar)
            .map_err(|error| LocaleError::Decode(error.to_string()))?;
        Ok(dynamic.cast::<Map>())
    }

    /// Return a detached read-only copy of selected number metadata.
    ///
    /// # Errors
    ///
    /// Returns locale, serialization, or runtime borrow errors.
    pub fn number_metadata(&self) -> Result<Map, UiContextError> {
        let number = self.read_locale(|locale, window, component| {
            locale.number(window, Some(component)).cloned()
        })?;
        let dynamic = rhai::serde::to_dynamic(number)
            .map_err(|error| LocaleError::Decode(error.to_string()))?;
        Ok(dynamic.cast::<Map>())
    }

    /// Format an integer through the selected locale.
    ///
    /// # Errors
    ///
    /// Returns locale, option, or runtime borrow errors.
    pub fn format_integer(
        &self,
        value: INT,
        options: NumberFormatOptions,
    ) -> Result<String, UiContextError> {
        self.read_locale(|locale, window, component| {
            locale.format_integer(window, Some(component), value, options)
        })
    }

    /// Format a finite decimal number through the selected locale.
    ///
    /// # Errors
    ///
    /// Returns locale, option, or runtime borrow errors.
    pub fn format_number(
        &self,
        value: FLOAT,
        options: NumberFormatOptions,
    ) -> Result<String, UiContextError> {
        self.read_locale(|locale, window, component| {
            locale.format_number(window, Some(component), value, options)
        })
    }

    /// Change the app locale at runtime without changing component state.
    ///
    /// # Errors
    ///
    /// Returns phase, locale, or borrow errors.
    pub fn set_locale(&self, locale: &str) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let changed = {
            let locales = runtime
                .locale
                .as_mut()
                .ok_or(UiContextError::LocaleUnavailable)?;
            let previous = locales.generation();
            locales.set_app(locale)?;
            locales.generation() != previous
        };
        if changed {
            let invalidated = runtime.environment_dependencies.invalidate_locale_app();
            runtime.dirty.extend(invalidated);
            runtime.mark_all_windows_repaint();
        }
        runtime.traces.push(
            crate::RuntimeTraceKind::Locale,
            self.component.to_string(),
            format!("select {locale}"),
            None,
            false,
        );
        Ok(())
    }

    /// Select an application theme without recompiling scripts or resetting state.
    ///
    /// # Errors
    ///
    /// Returns phase, theme availability, selection, or borrow errors.
    pub fn set_theme(&self, family: &str, variant: &str) -> Result<(), UiContextError> {
        self.set_theme_preference(
            ThemeTarget::App,
            ThemePreference::Fixed {
                selection: ThemeSelection::new(family, variant),
            },
            format!("select {family}/{variant}"),
        )
    }

    /// Select a theme for this context's window.
    ///
    /// # Errors
    ///
    /// Returns phase, missing-window, theme, or borrow errors.
    pub fn set_window_theme(&self, family: &str, variant: &str) -> Result<(), UiContextError> {
        let window = self.window.clone().ok_or(UiContextError::MissingWindow)?;
        self.set_theme_preference(
            ThemeTarget::Window(window),
            ThemePreference::Fixed {
                selection: ThemeSelection::new(family, variant),
            },
            format!("select window {family}/{variant}"),
        )
    }

    /// Return the stable script-visible ID of the current window.
    ///
    /// # Errors
    ///
    /// Returns [`UiContextError::MissingWindow`] outside a window lifecycle.
    pub fn window_id(&self) -> Result<String, UiContextError> {
        self.window.clone().ok_or(UiContextError::MissingWindow)
    }

    /// Return the stable identity of the mounted script view.
    ///
    /// # Errors
    ///
    /// Returns [`UiContextError::MissingView`] for manually constructed contexts
    /// that are not attached to a script view.
    pub fn view_id(&self) -> Result<String, UiContextError> {
        self.view.clone().ok_or(UiContextError::MissingView)
    }

    /// Return `compact`, `regular`, or `wide` for the current native window.
    ///
    /// # Errors
    ///
    /// Returns [`UiContextError::MissingWindow`] outside a window lifecycle.
    pub fn viewport_class(&self) -> Result<String, UiContextError> {
        let window = self.window.as_ref().ok_or(UiContextError::MissingWindow)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime
            .environment_dependencies
            .track_viewport(window, &self.read_dependency);
        Ok(runtime.responsive.class(window).as_str().to_owned())
    }

    /// Queue another native window running the same script entry.
    ///
    /// # Errors
    ///
    /// Returns phase, missing-window, validation, duplicate, or queue errors.
    pub fn open_window(&self, spec: ScriptWindowSpec) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let window = self.window.as_ref().ok_or(UiContextError::MissingWindow)?;
        let id = spec.id.clone();
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime.windows.request_open_from(window, spec)?;
        runtime.traces.push(
            crate::RuntimeTraceKind::Window,
            self.component.to_string(),
            format!("open {id}"),
            None,
            false,
        );
        Ok(())
    }

    /// Queue activation of a registered native window.
    ///
    /// # Errors
    ///
    /// Returns phase, registry, or queue errors.
    pub fn focus_window(&self, id: &str) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let window = self.window.as_ref().ok_or(UiContextError::MissingWindow)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime.windows.request_focus_from(window, id)?;
        runtime.traces.push(
            crate::RuntimeTraceKind::Window,
            self.component.to_string(),
            format!("focus {id}"),
            None,
            false,
        );
        Ok(())
    }

    /// Queue forced close after the script has performed any confirmation UI.
    ///
    /// # Errors
    ///
    /// Returns phase, registry, or queue errors.
    pub fn close_window(&self, id: &str) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let window = self.window.as_ref().ok_or(UiContextError::MissingWindow)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime.windows.request_close_from(window, id)?;
        runtime.traces.push(
            crate::RuntimeTraceKind::Window,
            self.component.to_string(),
            format!("close {id}"),
            None,
            false,
        );
        Ok(())
    }

    /// Intercept native close requests with a generation-bound script callback.
    /// The callback may show confirmation UI and later call `close_window`.
    ///
    /// # Errors
    ///
    /// Returns phase, missing-window, registry, or borrow errors.
    pub fn set_close_handler(&self, callback: FnPtr) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let window = self.window.as_ref().ok_or(UiContextError::MissingWindow)?;
        let callback = self.scoped_callback(callback)?;
        self.runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?
            .windows
            .set_close_handler(window, Some(callback))?;
        Ok(())
    }

    /// Remove the current window's close-request interception.
    ///
    /// # Errors
    ///
    /// Returns phase, missing-window, registry, or borrow errors.
    pub fn clear_close_handler(&self) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let window = self.window.as_ref().ok_or(UiContextError::MissingWindow)?;
        self.runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?
            .windows
            .set_close_handler(window, None)?;
        Ok(())
    }

    /// Select a locale override for the current window.
    ///
    /// # Errors
    ///
    /// Returns phase, missing-window, locale, or borrow errors.
    pub fn set_window_locale(&self, locale: &str) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let window = self.window.clone().ok_or(UiContextError::MissingWindow)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let changed = {
            let locales = runtime
                .locale
                .as_mut()
                .ok_or(UiContextError::LocaleUnavailable)?;
            let previous = locales.generation();
            locales.set_window(window.clone(), locale)?;
            locales.generation() != previous
        };
        if changed {
            let invalidated = runtime
                .environment_dependencies
                .invalidate_locale_window(&window);
            runtime.dirty.extend(invalidated);
            runtime.mark_window_repaint(window.clone());
        }
        runtime.traces.push(
            crate::RuntimeTraceKind::Locale,
            self.component.to_string(),
            format!("select window {window} locale {locale}"),
            None,
            false,
        );
        Ok(())
    }

    /// Select a locale override for the current component subtree.
    ///
    /// # Errors
    ///
    /// Returns phase, locale, or borrow errors.
    pub fn set_local_locale(&self, locale: &str) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let changed = {
            let locales = runtime
                .locale
                .as_mut()
                .ok_or(UiContextError::LocaleUnavailable)?;
            let previous = locales.generation();
            locales.set_scope(self.component.clone(), locale)?;
            locales.generation() != previous
        };
        if changed {
            let invalidated = runtime
                .environment_dependencies
                .invalidate_locale_scope(&self.component);
            runtime.dirty.extend(invalidated);
            if let Some(window) = &self.window {
                runtime.mark_window_repaint(window.clone());
            }
        }
        runtime.traces.push(
            crate::RuntimeTraceKind::Locale,
            self.component.to_string(),
            format!("select subtree locale {locale}"),
            None,
            false,
        );
        Ok(())
    }

    /// Select a theme for the current component subtree.
    ///
    /// # Errors
    ///
    /// Returns phase, theme, or borrow errors.
    pub fn set_local_theme(&self, family: &str, variant: &str) -> Result<(), UiContextError> {
        self.set_theme_preference(
            ThemeTarget::Local,
            ThemePreference::Fixed {
                selection: ThemeSelection::new(family, variant),
            },
            format!("select subtree {family}/{variant}"),
        )
    }

    /// Follow system appearance for one application theme family.
    ///
    /// # Errors
    ///
    /// Returns phase, theme, or borrow errors.
    pub fn set_theme_system(&self, family: &str) -> Result<(), UiContextError> {
        self.set_theme_preference(
            ThemeTarget::App,
            ThemePreference::System {
                family: family.to_owned(),
            },
            format!("follow system family {family}"),
        )
    }

    /// Follow system appearance for the current window.
    ///
    /// # Errors
    ///
    /// Returns phase, missing-window, theme, or borrow errors.
    pub fn set_window_theme_system(&self, family: &str) -> Result<(), UiContextError> {
        let window = self.window.clone().ok_or(UiContextError::MissingWindow)?;
        self.set_theme_preference(
            ThemeTarget::Window(window),
            ThemePreference::System {
                family: family.to_owned(),
            },
            format!("follow window system family {family}"),
        )
    }

    /// Follow system appearance for the current component subtree.
    ///
    /// # Errors
    ///
    /// Returns phase, theme, or borrow errors.
    pub fn set_local_theme_system(&self, family: &str) -> Result<(), UiContextError> {
        self.set_theme_preference(
            ThemeTarget::Local,
            ThemePreference::System {
                family: family.to_owned(),
            },
            format!("follow subtree system family {family}"),
        )
    }

    fn set_theme_preference(
        &self,
        target: ThemeTarget,
        preference: ThemePreference,
        message: String,
    ) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let invalidated = match &target {
            ThemeTarget::App => runtime.environment_dependencies.invalidate_theme_app(),
            ThemeTarget::Window(window) => runtime
                .environment_dependencies
                .invalidate_theme_window(window),
            ThemeTarget::Local => runtime
                .environment_dependencies
                .invalidate_theme_scope(&self.component),
        };
        let app_target = matches!(&target, ThemeTarget::App);
        let theme = runtime
            .theme
            .as_mut()
            .ok_or(UiContextError::ThemeUnavailable)?;
        match target {
            ThemeTarget::App => theme.set_app(preference)?,
            ThemeTarget::Window(window) => theme.set_window(window, preference)?,
            ThemeTarget::Local => theme.set_scope(self.component.clone(), preference)?,
        }
        if app_target {
            runtime.mark_all_windows_dirty();
        } else {
            runtime.dirty.insert(self.component.clone());
        }
        runtime.dirty.extend(invalidated);
        runtime.traces.push(
            crate::RuntimeTraceKind::Theme,
            self.component.to_string(),
            message,
            None,
            false,
        );
        Ok(())
    }

    /// Change the central motion preference and settle nonessential animation
    /// immediately when reduced motion is requested.
    ///
    /// # Errors
    ///
    /// Returns phase or runtime borrow errors.
    pub fn set_reduced_motion(&self, reduced: bool) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime.motions.request_preference(if reduced {
            crate::MotionPreference::Reduced
        } else {
            crate::MotionPreference::Normal
        });
        let now = runtime.clock.now();
        runtime.motion_values = runtime.motions.snapshot(now);
        runtime.dirty.insert(self.component.clone());
        runtime.traces.push(
            crate::RuntimeTraceKind::State,
            self.component.to_string(),
            format!("reduced motion {reduced}"),
            None,
            false,
        );
        Ok(())
    }

    /// Resolve a typed timeline handle in the current view.
    ///
    /// # Errors
    ///
    /// Returns an explicit missing/duplicate timeline error.
    pub fn motion_handle(&self, name: &str) -> Result<crate::MotionHandle, UiContextError> {
        let scope = self.motion_scope();
        Ok(self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .motions
            .timeline_handle_for_owner(
                &scope,
                &self.component,
                self.incarnation,
                self.generation,
                name,
            )?)
    }

    #[must_use]
    pub fn motion_tokens(&self) -> crate::ThemeMotion {
        self.with_resolved_theme(|variant| variant.tokens.motion.clone())
            .unwrap_or_default()
    }

    /// The active theme variant metadata for this context's window/component scope.
    /// Read during render to track its theme dependency. Effects restart only
    /// when this metadata is explicitly included in their declared deps.
    /// Headless/pre-native contexts resolve System using Dark until an actual
    /// window appearance is known. Returns None for missing/unresolvable themes
    /// or an unavailable runtime borrow; it does not clone theme tokens.
    #[must_use]
    pub fn resolved_theme_variant(&self) -> Option<crate::ThemeVariantInfo> {
        self.with_resolved_theme(|variant| crate::ThemeVariantInfo {
            family: variant.family.clone(),
            name: variant.name.clone(),
            mode: variant.mode,
        })
    }

    fn with_resolved_theme<R>(&self, project: impl FnOnce(&crate::ThemeVariant) -> R) -> Option<R> {
        let Ok(mut runtime) = self.runtime.try_borrow_mut() else {
            return None;
        };
        if self.phase == ExecutionPhase::Render {
            runtime
                .environment_dependencies
                .track_theme(self.window.as_deref(), &self.read_dependency);
        }
        let appearance = self
            .window
            .as_deref()
            .and_then(|window| runtime.window_appearances.get(window).copied())
            .unwrap_or(crate::SystemAppearance::Dark);
        runtime
            .theme
            .as_ref()
            .and_then(|theme| {
                theme
                    .resolve(self.window.as_deref(), Some(&self.component), appearance)
                    .ok()
            })
            .map(|theme| project(theme.variant()))
    }

    /// Resolved identity, not the app/window/local preference selecting it.
    #[must_use]
    pub fn resolved_theme_selection(&self) -> Option<ThemeSelection> {
        self.with_resolved_theme(|variant| ThemeSelection::new(&variant.family, &variant.name))
    }

    /// Resolve a semantic motion duration.
    ///
    /// # Errors
    ///
    /// Returns an unknown-token error for an undeclared role.
    pub fn motion_duration(&self, role: &str) -> Result<u64, UiContextError> {
        self.motion_tokens()
            .durations_ms
            .get(role)
            .copied()
            .ok_or_else(|| UiContextError::UnknownMotionToken {
                category: "duration",
                role: role.to_owned(),
            })
    }

    /// Resolve a semantic motion easing.
    ///
    /// # Errors
    ///
    /// Returns an unknown-token error for an undeclared role.
    pub fn motion_easing(&self, role: &str) -> Result<crate::MotionEasing, UiContextError> {
        self.motion_tokens()
            .easings
            .get(role)
            .copied()
            .ok_or_else(|| UiContextError::UnknownMotionToken {
                category: "easing",
                role: role.to_owned(),
            })
    }

    /// Resolve a semantic spring preset.
    ///
    /// # Errors
    ///
    /// Returns an unknown-token error for an undeclared role.
    pub fn motion_spring(&self, role: &str) -> Result<crate::ThemeMotionSpring, UiContextError> {
        self.motion_tokens()
            .springs
            .get(role)
            .copied()
            .ok_or_else(|| UiContextError::UnknownMotionToken {
                category: "spring",
                role: role.to_owned(),
            })
    }

    /// Resolve a semantic motion distance.
    ///
    /// # Errors
    ///
    /// Returns an unknown-token error for an undeclared role.
    pub fn motion_distance(&self, role: &str) -> Result<f64, UiContextError> {
        self.motion_tokens()
            .distances
            .get(role)
            .copied()
            .ok_or_else(|| UiContextError::UnknownMotionToken {
                category: "distance",
                role: role.to_owned(),
            })
    }

    /// Resolve a semantic stagger interval.
    ///
    /// # Errors
    ///
    /// Returns an unknown-token error for an undeclared role.
    pub fn motion_stagger(&self, role: &str) -> Result<u64, UiContextError> {
        self.motion_tokens()
            .staggers_ms
            .get(role)
            .copied()
            .ok_or_else(|| UiContextError::UnknownMotionToken {
                category: "stagger",
                role: role.to_owned(),
            })
    }

    #[must_use]
    pub fn motion_quality(&self) -> crate::MotionQuality {
        self.runtime
            .try_borrow()
            .map_or(crate::MotionQuality::Low, |runtime| {
                runtime.motions.quality()
            })
    }

    /// Play or resume a scoped timeline.
    ///
    /// # Errors
    ///
    /// Returns phase, borrow, or stale-handle errors.
    pub fn play_motion(&self, handle: &crate::MotionHandle) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime.motions.validate_handle_owner(
            handle,
            &self.motion_scope(),
            &self.component,
            self.incarnation,
            self.generation,
        )?;
        let now = runtime.clock.now();
        runtime.motions.play_timeline(handle, now)?;
        Ok(())
    }

    /// Pause a scoped timeline.
    ///
    /// # Errors
    ///
    /// Returns phase, borrow, or stale-handle errors.
    pub fn pause_motion(&self, handle: &crate::MotionHandle) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime.motions.validate_handle_owner(
            handle,
            &self.motion_scope(),
            &self.component,
            self.incarnation,
            self.generation,
        )?;
        let now = runtime.clock.now();
        runtime.motions.pause_timeline(handle, now)?;
        Ok(())
    }

    /// Seek a scoped timeline to an absolute millisecond position.
    ///
    /// # Errors
    ///
    /// Returns phase, borrow, stale-handle, or invalid-position errors.
    pub fn seek_motion(
        &self,
        handle: &crate::MotionHandle,
        position_ms: u64,
    ) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime.motions.validate_handle_owner(
            handle,
            &self.motion_scope(),
            &self.component,
            self.incarnation,
            self.generation,
        )?;
        let now = runtime.clock.now();
        runtime.motions.seek_timeline(handle, position_ms, now)?;
        runtime.motion_values = runtime.motions.snapshot(now);
        Ok(())
    }

    /// Restart a scoped timeline from zero.
    ///
    /// # Errors
    ///
    /// Returns phase, borrow, or stale-handle errors.
    pub fn restart_motion(&self, handle: &crate::MotionHandle) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime.motions.validate_handle_owner(
            handle,
            &self.motion_scope(),
            &self.component,
            self.incarnation,
            self.generation,
        )?;
        let now = runtime.clock.now();
        runtime.motions.restart_timeline(handle, now)?;
        Ok(())
    }

    /// Cancel a scoped timeline.
    ///
    /// # Errors
    ///
    /// Returns phase, borrow, or stale-handle errors.
    pub fn cancel_motion(&self, handle: &crate::MotionHandle) -> Result<(), UiContextError> {
        self.require_mutation()?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        runtime.motions.validate_handle_owner(
            handle,
            &self.motion_scope(),
            &self.component,
            self.incarnation,
            self.generation,
        )?;
        runtime.motions.cancel_timeline(handle)?;
        Ok(())
    }

    fn motion_scope(&self) -> String {
        match (self.window.as_deref(), self.view.as_deref()) {
            (Some(window), Some(view)) => format!("window:{window}/view:{view}/root"),
            (Some(window), None) => format!("window:{window}/root"),
            (None, Some(view)) => format!("view:{view}/root"),
            (None, None) => "root".to_owned(),
        }
    }

    /// Load and cache a logical image asset.
    ///
    /// # Errors
    ///
    /// Returns phase, provider, format, or borrow errors.
    pub fn load_image(&self, asset: &AssetId) -> Result<OpaqueHandle, UiContextError> {
        self.require_mutation()?;
        Ok(self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .assets
            .load_image(asset)?
            .opaque()
            .clone())
    }

    /// Start generation-bound background raster validation/decode.
    ///
    /// # Errors
    ///
    /// Returns phase, generation, provider, spawn, or borrow errors.
    pub fn start_image_decode(
        &self,
        asset: &AssetId,
        success: FnPtr,
        error: FnPtr,
    ) -> Result<ImageDecodeHandle, UiContextError> {
        self.require_mutation()?;
        self.require_generation()?;
        let success = self.scoped_callback(success)?;
        let error = self.scoped_callback(error)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        crate::RuntimeBudgets::check(
            "image_decodes",
            runtime.assets.pending_decode_count().saturating_add(1),
            runtime.budgets.image_decodes,
        )?;
        let handle = runtime.assets.start_image_decode(
            asset,
            self.async_scope
                .clone()
                .unwrap_or_else(|| AsyncScope::Component(self.component.clone())),
            self.generation,
            success,
            error,
        )?;
        runtime.traces.push(
            crate::RuntimeTraceKind::Task,
            self.component.to_string(),
            format!("decode image {}", asset.as_str()),
            None,
            false,
        );
        Ok(handle)
    }

    /// Cancel a pending image decode owned by this runtime.
    ///
    /// # Errors
    ///
    /// Returns phase or borrow errors.
    pub fn cancel_image_decode(&self, handle: ImageDecodeHandle) -> Result<bool, UiContextError> {
        self.require_mutation()?;
        Ok(self
            .runtime
            .try_borrow()
            .map_err(|_| UiContextError::Borrowed)?
            .assets
            .cancel_image_decode(handle)?)
    }

    /// Cancel a one-shot task owned by this runtime.
    ///
    /// # Errors
    ///
    /// Returns phase or borrow errors.
    pub fn cancel_task(&self, handle: TaskHandle) -> Result<bool, UiContextError> {
        self.require_mutation()?;
        Ok(self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?
            .tasks
            .cancel(handle))
    }

    /// Cancel a continuous subscription owned by this runtime.
    ///
    /// # Errors
    ///
    /// Returns phase or borrow errors.
    pub fn cancel_subscription(&self, handle: SubscriptionHandle) -> Result<bool, UiContextError> {
        self.require_mutation()?;
        Ok(self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?
            .subscriptions
            .cancel(handle))
    }

    /// Pause a declared timer by its component-local key.
    ///
    /// # Errors
    ///
    /// Returns phase, key, or borrow errors.
    pub fn pause_timeout(&self, key: &str) -> Result<bool, UiContextError> {
        self.require_mutation()?;
        let id = crate::TimerId::new(self.component.clone(), key)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let now = runtime.clock.now();
        Ok(runtime.timers.pause(&id, now))
    }

    /// Resume a declared timer by its component-local key.
    ///
    /// # Errors
    ///
    /// Returns phase, key, or borrow errors.
    pub fn resume_timeout(&self, key: &str) -> Result<bool, UiContextError> {
        self.require_mutation()?;
        let id = crate::TimerId::new(self.component.clone(), key)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        let now = runtime.clock.now();
        Ok(runtime.timers.resume(&id, now))
    }

    /// Complete/cancel a declared timer until its signature changes or disappears.
    ///
    /// # Errors
    ///
    /// Returns phase, key, or borrow errors.
    pub fn cancel_timeout(&self, key: &str) -> Result<bool, UiContextError> {
        self.require_mutation()?;
        let id = crate::TimerId::new(self.component.clone(), key)?;
        Ok(self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?
            .timers
            .cancel(&id))
    }

    /// Start a one-shot asynchronous capability call.
    ///
    /// # Errors
    ///
    /// Returns phase, capability, schema, generation, spawn, or borrow errors.
    pub fn start_task(
        &self,
        capability: &str,
        method: &str,
        input: Dynamic,
        success: FnPtr,
        error: FnPtr,
    ) -> Result<TaskHandle, UiContextError> {
        self.require_mutation()?;
        self.require_async_start()?;
        self.require_generation()?;
        let id = CapabilityId::parse(capability)?;
        let input = UiValue::from_dynamic(input)?;
        let success = self.scoped_callback(success)?;
        let error = self.scoped_callback(error)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        crate::RuntimeBudgets::check(
            "background_tasks",
            runtime.tasks.active_count().saturating_add(1),
            runtime.budgets.background_tasks,
        )?;
        let (work, output) = runtime.capabilities.start_task(&id, method, input)?;
        let handle = runtime.tasks.spawn_cancellable(
            self.async_scope
                .clone()
                .unwrap_or_else(|| AsyncScope::Component(self.component.clone())),
            self.generation,
            success,
            error,
            output,
            move |cancellation| work.run(cancellation),
        )?;
        runtime.traces.push(
            crate::RuntimeTraceKind::Task,
            self.component.to_string(),
            format!("start {capability}.{method}"),
            None,
            true,
        );
        Ok(handle)
    }

    /// Start a continuous asynchronous capability subscription.
    ///
    /// # Errors
    ///
    /// Returns phase, capability, schema, generation, spawn, or borrow errors.
    pub fn start_subscription(
        &self,
        capability: &str,
        method: &str,
        input: Dynamic,
        success: FnPtr,
        error: FnPtr,
        options: SubscriptionOptions,
    ) -> Result<SubscriptionHandle, UiContextError> {
        self.require_mutation()?;
        self.require_async_start()?;
        self.require_generation()?;
        if !matches!(self.async_scope, Some(AsyncScope::Effect { .. })) {
            return Err(UiContextError::SubscriptionRequiresEffect);
        }
        let id = CapabilityId::parse(capability)?;
        let input = UiValue::from_dynamic(input)?;
        let success = self.scoped_callback(success)?;
        let error = self.scoped_callback(error)?;
        let mut runtime = self
            .runtime
            .try_borrow_mut()
            .map_err(|_| UiContextError::Borrowed)?;
        crate::RuntimeBudgets::check(
            "subscriptions",
            runtime.subscriptions.active_count().saturating_add(1),
            runtime.budgets.subscriptions,
        )?;
        let (work, output) = runtime
            .capabilities
            .start_subscription(&id, method, input)?;
        let registration = SubscriptionRegistration::new(
            format!("{capability}.{method}"),
            self.async_scope
                .clone()
                .unwrap_or_else(|| AsyncScope::Component(self.component.clone())),
            self.generation,
            success,
            error,
            output,
        )
        .with_options(options);
        let (handle, emitter) = runtime.subscriptions.subscribe(registration);
        let closer = emitter.clone();
        if let Err(spawn_error) = std::thread::Builder::new()
            .name("gpui-rhai-subscription".to_owned())
            .spawn(move || run_subscription_work(work, emitter, &closer))
        {
            let _ = runtime
                .subscriptions
                .cancel_with_reason(handle, SubscriptionCloseReason::StartupFailed);
            return Err(AsyncRuntimeError::Spawn(spawn_error).into());
        }
        runtime.traces.push(
            crate::RuntimeTraceKind::Subscription,
            self.component.to_string(),
            format!("start {capability}.{method}"),
            None,
            true,
        );
        Ok(handle)
    }

    fn require_mutation(&self) -> Result<(), UiContextError> {
        if self.phase.allows_mutation() {
            Ok(())
        } else {
            Err(UiContextError::MutationDuringRender)
        }
    }

    fn require_async_start(&self) -> Result<(), UiContextError> {
        if self.phase.allows_async_start() {
            Ok(())
        } else {
            Err(UiContextError::AsyncDuringSuspend)
        }
    }

    fn require_generation(&self) -> Result<(), UiContextError> {
        if self.generation == ScriptGeneration::default() {
            Err(UiContextError::MissingGeneration)
        } else {
            Ok(())
        }
    }
}

fn run_subscription_work(
    work: crate::SubscriptionWork,
    emitter: crate::SubscriptionEmitter,
    closer: &crate::SubscriptionEmitter,
) {
    work.run(emitter);
    closer.close_with_reason(SubscriptionCloseReason::WorkReturned);
}

impl CustomType for UiContext {
    fn build(mut builder: TypeBuilder<Self>) {
        builder
            .with_name("UiContext")
            .with_fn(
                "emit",
                |context: &mut Self, event: ImmutableString, payload: Dynamic| {
                    context
                        .emit(event.as_str(), payload)
                        .map_err(|error| Box::new(context_runtime_error(&error)))
                },
            )
            .with_fn(
                "component_style",
                |context: &mut Self, part: ImmutableString, base: crate::Style| {
                    context.resolve_component_style(part.as_str(), base)
                },
            )
            .with_fn(
                "call_capability",
                |context: &mut Self,
                 capability: ImmutableString,
                 method: ImmutableString,
                 input: Dynamic| {
                    context
                        .call_capability(capability.as_str(), method.as_str(), input)
                        .map(UiValue::into_dynamic)
                        .map_err(|error| Box::new(context_runtime_error(&error)))
                },
            );
        register_state_store_context_methods(&mut builder);
        register_native_collection_context_methods(&mut builder);
        register_native_document_context_methods(&mut builder);
        #[cfg(feature = "charts")]
        register_native_chart_data_context_methods(&mut builder);
        register_signal_context_methods(&mut builder);
        register_element_ref_context_methods(&mut builder);
        register_async_context_methods(&mut builder);
        register_action_context_methods(&mut builder);
        register_locale_context_methods(&mut builder);
        register_theme_context_methods(&mut builder);
        register_motion_context_methods(&mut builder);
        register_asset_context_methods(&mut builder);
        register_window_context_methods(&mut builder);
    }
}

fn register_native_collection_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder.with_fn(
        "get_native_collection",
        |context: &mut UiContext, name: ImmutableString| {
            context
                .get_native_collection(name.as_str())
                .map_err(|error| Box::new(context_runtime_error(&error)))
        },
    );
}

fn register_native_document_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder.with_fn(
        "get_native_text_document",
        |context: &mut UiContext, name: ImmutableString| {
            context
                .get_native_text_document(name.as_str())
                .map_err(|error| Box::new(context_runtime_error(&error)))
        },
    );
}

#[cfg(feature = "charts")]
fn register_native_chart_data_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder.with_fn(
        "get_native_chart_data",
        |context: &mut UiContext, name: ImmutableString| {
            context
                .get_native_chart_data(name.as_str())
                .map_err(|error| Box::new(context_runtime_error(&error)))
        },
    );
}

fn register_state_store_context_methods(builder: &mut TypeBuilder<UiContext>) {
    register_state_context_methods(builder);
    register_app_store_context_methods(builder);
    register_window_store_context_methods(builder);
}

fn register_state_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn(
            "get_state",
            |context: &mut UiContext, field: ImmutableString| {
                context
                    .get_state(field.as_str())
                    .map(UiValue::into_dynamic)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "get_state_path",
            |context: &mut UiContext, field: ImmutableString, path: Array| {
                let path = rhai_value_path(path)?;
                context
                    .get_state_path(field.as_str(), &path)
                    .map(UiValue::into_dynamic)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_state",
            |context: &mut UiContext, field: ImmutableString, value: Dynamic| {
                context
                    .set_state(field.as_str(), value)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_state_path",
            |context: &mut UiContext, field: ImmutableString, path: Array, value: Dynamic| {
                let path = rhai_value_path(path)?;
                context
                    .set_state_path(field.as_str(), &path, value)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        );
}

fn register_app_store_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn(
            "get_app_store",
            |context: &mut UiContext, store: ImmutableString, field: ImmutableString| {
                context
                    .get_app_store(store.as_str(), field.as_str())
                    .map(UiValue::into_dynamic)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "get_app_store_path",
            |context: &mut UiContext,
             store: ImmutableString,
             field: ImmutableString,
             path: Array| {
                let path = rhai_value_path(path)?;
                context
                    .get_app_store_path(store.as_str(), field.as_str(), &path)
                    .map(UiValue::into_dynamic)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_app_store",
            |context: &mut UiContext,
             store: ImmutableString,
             field: ImmutableString,
             value: Dynamic| {
                context
                    .set_app_store(store.as_str(), field.as_str(), value)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_app_store_path",
            |context: &mut UiContext,
             store: ImmutableString,
             field: ImmutableString,
             path: Array,
             value: Dynamic| {
                let path = rhai_value_path(path)?;
                context
                    .set_app_store_path(store.as_str(), field.as_str(), &path, value)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        );
}

fn register_window_store_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn(
            "get_window_store",
            |context: &mut UiContext, store: ImmutableString, field: ImmutableString| {
                context
                    .get_window_store(store.as_str(), field.as_str())
                    .map(UiValue::into_dynamic)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "get_window_store_path",
            |context: &mut UiContext,
             store: ImmutableString,
             field: ImmutableString,
             path: Array| {
                let path = rhai_value_path(path)?;
                context
                    .get_window_store_path(store.as_str(), field.as_str(), &path)
                    .map(UiValue::into_dynamic)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_window_store",
            |context: &mut UiContext,
             store: ImmutableString,
             field: ImmutableString,
             value: Dynamic| {
                context
                    .set_window_store(store.as_str(), field.as_str(), value)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_window_store_path",
            |context: &mut UiContext,
             store: ImmutableString,
             field: ImmutableString,
             path: Array,
             value: Dynamic| {
                let path = rhai_value_path(path)?;
                context
                    .set_window_store_path(store.as_str(), field.as_str(), &path, value)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        );
}

fn rhai_value_path(values: Array) -> Result<UiValuePath, Box<EvalAltResult>> {
    if values.len() > 64 {
        return Err(Box::new(EvalAltResult::ErrorRuntime(
            "value path must have at most 64 segments".into(),
            Position::NONE,
        )));
    }
    let segments = values
        .into_iter()
        .enumerate()
        .map(|(index, value)| {
            let actual = value.type_name().to_owned();
            if value.is::<ImmutableString>() {
                return Ok(UiValuePathSegment::Key(
                    value.cast::<ImmutableString>().to_string(),
                ));
            }
            if value.is::<INT>() {
                let index_value = value.cast::<INT>();
                return usize::try_from(index_value)
                    .map(UiValuePathSegment::Index)
                    .map_err(|_| {
                        Box::new(EvalAltResult::ErrorRuntime(
                            format!("value path segment {index} must be a non-negative integer")
                                .into(),
                            Position::NONE,
                        ))
                    });
            }
            if let Some(mut selector) = value.try_cast::<Map>() {
                let by = selector
                    .remove("by")
                    .and_then(Dynamic::try_cast::<ImmutableString>);
                let key = selector
                    .remove("key")
                    .and_then(Dynamic::try_cast::<ImmutableString>);
                if selector.is_empty()
                    && let (Some(by), Some(key)) = (by, key)
                {
                    return Ok(UiValuePathSegment::Item {
                        key_field: by.to_string(),
                        key: key.to_string(),
                    });
                }
                return Err(Box::new(EvalAltResult::ErrorRuntime(
                    format!(
                        "value path segment {index} keyed selector must be exactly #{{ by: string, key: string }}"
                    )
                    .into(),
                    Position::NONE,
                )));
            }
            Err(Box::new(EvalAltResult::ErrorRuntime(
                format!(
                    "value path segment {index} must be a string, non-negative integer, or keyed selector map; got {actual}"
                )
                .into(),
                Position::NONE,
            )))
        })
        .collect::<Result<Vec<_>, _>>()?;
    UiValuePath::new(segments).map_err(|error| {
        Box::new(EvalAltResult::ErrorRuntime(
            error.to_string().into(),
            Position::NONE,
        ))
    })
}

fn register_signal_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn(
            "get_signal",
            |context: &mut UiContext, signal: crate::NativeSignal| {
                context
                    .get_signal(&signal)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "get_signal",
            |context: &mut UiContext, key: ImmutableString| {
                context
                    .get_signal_by_key(key.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_signal",
            |context: &mut UiContext, signal: crate::NativeSignal, value: Dynamic| {
                context
                    .set_signal(&signal, value)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_signal",
            |context: &mut UiContext, key: ImmutableString, value: Dynamic| {
                context
                    .set_signal_by_key(key.as_str(), value)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        );
}

fn register_element_ref_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn(
            "element_bounds",
            |context: &mut UiContext, reference: crate::ElementRef| {
                context
                    .element_bounds(&reference)
                    .map(UiValue::into_dynamic)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "element_bounds",
            |context: &mut UiContext, key: ImmutableString| {
                context
                    .element_bounds_by_key(key.as_str())
                    .map(UiValue::into_dynamic)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn("event_target_bounds", |context: &mut UiContext| {
            context
                .event_target_bounds()
                .map(UiValue::into_dynamic)
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn(
            "focus",
            |context: &mut UiContext, reference: crate::ElementRef| {
                context
                    .focus_element(&reference)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn("focus", |context: &mut UiContext, key: ImmutableString| {
            context
                .focus_element_by_key(key.as_str())
                .map_err(|error| Box::new(context_runtime_error(&error)))
        });
}

fn geometry_bounds_value(bounds: crate::GeometryBounds) -> UiValue {
    bounds.into_value()
}

fn register_action_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn(
            "dispatch_action",
            |context: &mut UiContext, action: ImmutableString, payload: Dynamic| {
                context
                    .dispatch_action(action.as_str(), payload)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "register_action",
            |call: NativeCallContext<'_>,
             context: &mut UiContext,
             action: ImmutableString,
             callback: FnPtr| {
                context_at_call(context, &call)
                    .register_action(action.as_str(), callback)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_action_enabled",
            |context: &mut UiContext, action: ImmutableString, enabled: bool| {
                context
                    .set_action_enabled(action.as_str(), enabled)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "scroll_to",
            |context: &mut UiContext, reference: crate::ElementRef, x: FLOAT, y: FLOAT| {
                context
                    .scroll_element_to(&reference, x, y)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "scroll_to",
            |context: &mut UiContext, key: ImmutableString, x: FLOAT, y: FLOAT| {
                context
                    .scroll_element_to_by_key(key.as_str(), x, y)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "scroll_into_view",
            |context: &mut UiContext, reference: crate::ElementRef| {
                context
                    .scroll_element_into_view(&reference)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "scroll_into_view",
            |context: &mut UiContext, key: ImmutableString| {
                context
                    .scroll_element_into_view_by_key(key.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        );
}

fn register_async_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn(
            "start_task",
            |call: NativeCallContext<'_>,
             context: &mut UiContext,
             capability: ImmutableString,
             method: ImmutableString,
             input: Dynamic,
             success: FnPtr,
             error: FnPtr| {
                context_at_call(context, &call)
                    .start_task(capability.as_str(), method.as_str(), input, success, error)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "start_subscription",
            |call: NativeCallContext<'_>,
             context: &mut UiContext,
             capability: ImmutableString,
             method: ImmutableString,
             input: Dynamic,
             success: FnPtr,
             error: FnPtr,
             options: Map| {
                let options = subscription_options(options)?;
                context_at_call(context, &call)
                    .start_subscription(
                        capability.as_str(),
                        method.as_str(),
                        input,
                        success,
                        error,
                        options,
                    )
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "cancel_task",
            |context: &mut UiContext, handle: TaskHandle| {
                context
                    .cancel_task(handle)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "cancel_subscription",
            |context: &mut UiContext, handle: SubscriptionHandle| {
                context
                    .cancel_subscription(handle)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "pause_timeout",
            |context: &mut UiContext, key: ImmutableString| {
                context
                    .pause_timeout(key.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "resume_timeout",
            |context: &mut UiContext, key: ImmutableString| {
                context
                    .resume_timeout(key.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "cancel_timeout",
            |context: &mut UiContext, key: ImmutableString| {
                context
                    .cancel_timeout(key.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        );
}

fn subscription_options(mut options: Map) -> Result<SubscriptionOptions, Box<EvalAltResult>> {
    let defaults = SubscriptionOptions::default();
    let delivery = options.remove("delivery").map_or(
        Ok(defaults.delivery()),
        |value| -> Result<_, Box<EvalAltResult>> {
            let value = value.try_cast::<ImmutableString>().ok_or_else(|| {
                Box::new(EvalAltResult::ErrorRuntime(
                    "subscription delivery must be `all` or `latest`".into(),
                    Position::NONE,
                ))
            })?;
            match value.as_str() {
                "all" => Ok(SubscriptionDeliveryPolicy::All),
                "latest" => Ok(SubscriptionDeliveryPolicy::Latest),
                _ => Err(Box::new(EvalAltResult::ErrorRuntime(
                    "subscription delivery must be `all` or `latest`".into(),
                    Position::NONE,
                ))),
            }
        },
    )?;
    let capacity = options.remove("capacity").map_or(
        Ok(defaults.capacity()),
        |value| -> Result<_, Box<EvalAltResult>> {
            value
                .try_cast::<INT>()
                .and_then(|value| usize::try_from(value).ok())
                .ok_or_else(|| {
                    Box::new(EvalAltResult::ErrorRuntime(
                        "subscription capacity must be a positive integer".into(),
                        Position::NONE,
                    ))
                })
        },
    )?;
    let throttle = options.remove("throttle_ms").map_or(
        Ok(defaults.throttle()),
        |value| -> Result<_, Box<EvalAltResult>> {
            value
                .try_cast::<INT>()
                .and_then(|value| u64::try_from(value).ok())
                .map(Duration::from_millis)
                .ok_or_else(|| {
                    Box::new(EvalAltResult::ErrorRuntime(
                        "subscription throttle_ms must be a non-negative integer".into(),
                        Position::NONE,
                    ))
                })
        },
    )?;
    if let Some(name) = options.keys().next() {
        return Err(Box::new(EvalAltResult::ErrorRuntime(
            format!("unknown subscription option `{name}`").into(),
            Position::NONE,
        )));
    }
    SubscriptionOptions::new(delivery, capacity, throttle).map_err(|error| {
        Box::new(EvalAltResult::ErrorRuntime(
            error.to_string().into(),
            Position::NONE,
        ))
    })
}

fn register_locale_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn("t", |context: &mut UiContext, key: ImmutableString| {
            context
                .text(key.as_str())
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn(
            "set_locale",
            |context: &mut UiContext, locale: ImmutableString| {
                context
                    .set_locale(locale.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn("text_direction", |context: &mut UiContext| {
            context
                .text_direction()
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn("today", |context: &mut UiContext| {
            context
                .today()
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn(
            "format_date",
            |context: &mut UiContext, date: ImmutableString, style: ImmutableString| {
                context
                    .format_date(date.as_str(), style.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "format_month_year",
            |context: &mut UiContext, date: ImmutableString| {
                context
                    .format_month_year(date.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn("calendar", |context: &mut UiContext| {
            context
                .calendar_metadata()
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn("number", |context: &mut UiContext| {
            context
                .number_metadata()
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn("format_number", |context: &mut UiContext, value: INT| {
            context
                .format_integer(value, NumberFormatOptions::default())
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn("format_number", |context: &mut UiContext, value: FLOAT| {
            context
                .format_number(value, NumberFormatOptions::default())
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn(
            "format_number",
            |context: &mut UiContext,
             value: INT,
             options: Map|
             -> Result<String, Box<EvalAltResult>> {
                let options = number_format_options(options)?;
                context
                    .format_integer(value, options)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "format_number",
            |context: &mut UiContext,
             value: FLOAT,
             options: Map|
             -> Result<String, Box<EvalAltResult>> {
                let options = number_format_options(options)?;
                context
                    .format_number(value, options)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        );
}

fn number_format_options(mut options: Map) -> Result<NumberFormatOptions, Box<EvalAltResult>> {
    let mut parsed = NumberFormatOptions::default();
    if let Some(value) = options.remove("min_fraction_digits") {
        let value = value.try_cast::<INT>().ok_or_else(|| {
            Box::new(EvalAltResult::ErrorRuntime(
                "min_fraction_digits must be an integer".into(),
                Position::NONE,
            ))
        })?;
        parsed.min_fraction_digits = u8::try_from(value).map_err(|_| {
            Box::new(EvalAltResult::ErrorRuntime(
                "min_fraction_digits must be between 0 and 12".into(),
                Position::NONE,
            ))
        })?;
    }
    if let Some(value) = options.remove("max_fraction_digits") {
        let value = value.try_cast::<INT>().ok_or_else(|| {
            Box::new(EvalAltResult::ErrorRuntime(
                "max_fraction_digits must be an integer".into(),
                Position::NONE,
            ))
        })?;
        parsed.max_fraction_digits = u8::try_from(value).map_err(|_| {
            Box::new(EvalAltResult::ErrorRuntime(
                "max_fraction_digits must be between 0 and 12".into(),
                Position::NONE,
            ))
        })?;
    }
    if let Some(value) = options.remove("grouping") {
        parsed.grouping = value.try_cast::<bool>().ok_or_else(|| {
            Box::new(EvalAltResult::ErrorRuntime(
                "grouping must be a bool".into(),
                Position::NONE,
            ))
        })?;
    }
    if let Some((unknown, _)) = options.into_iter().next() {
        return Err(Box::new(EvalAltResult::ErrorRuntime(
            format!("unknown number format option `{unknown}`").into(),
            Position::NONE,
        )));
    }
    parsed.validate().map_err(|error| {
        Box::new(EvalAltResult::ErrorRuntime(
            error.to_string().into(),
            Position::NONE,
        ))
    })?;
    Ok(parsed)
}

fn register_theme_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn(
            "theme_variant",
            |context: &mut UiContext| -> Result<Dynamic, Box<EvalAltResult>> {
                let Some(variant) = context.resolved_theme_variant() else {
                    return Ok(Dynamic::UNIT);
                };
                let mut map = rhai::Map::new();
                map.insert("family".into(), Dynamic::from(variant.family.clone()));
                map.insert("name".into(), Dynamic::from(variant.name.clone()));
                map.insert(
                    "mode".into(),
                    Dynamic::from(match variant.mode {
                        crate::ThemeMode::Light => "light",
                        crate::ThemeMode::Dark => "dark",
                    }),
                );
                Ok(Dynamic::from(map))
            },
        )
        .with_fn(
            "set_theme",
            |context: &mut UiContext, family: ImmutableString, variant: ImmutableString| {
                context
                    .set_theme(family.as_str(), variant.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_window_theme",
            |context: &mut UiContext, family: ImmutableString, variant: ImmutableString| {
                context
                    .set_window_theme(family.as_str(), variant.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_local_theme",
            |context: &mut UiContext, family: ImmutableString, variant: ImmutableString| {
                context
                    .set_local_theme(family.as_str(), variant.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_theme_system",
            |context: &mut UiContext, family: ImmutableString| {
                context
                    .set_theme_system(family.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_window_theme_system",
            |context: &mut UiContext, family: ImmutableString| {
                context
                    .set_window_theme_system(family.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_local_theme_system",
            |context: &mut UiContext, family: ImmutableString| {
                context
                    .set_local_theme_system(family.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        );
}

#[allow(clippy::too_many_lines)]
fn register_motion_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn(
            "set_reduced_motion",
            |context: &mut UiContext, reduced: bool| {
                context
                    .set_reduced_motion(reduced)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "motion_handle",
            |context: &mut UiContext, name: ImmutableString| {
                context
                    .motion_handle(name.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "motion_duration",
            |context: &mut UiContext, role: ImmutableString| {
                context
                    .motion_duration(role.as_str())
                    .map(|value| INT::try_from(value).unwrap_or(INT::MAX))
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "motion_easing",
            |context: &mut UiContext, role: ImmutableString| {
                context
                    .motion_easing(role.as_str())
                    .map(|value| match value {
                        crate::MotionEasing::Linear => "linear",
                        crate::MotionEasing::EaseIn => "ease_in",
                        crate::MotionEasing::EaseOut => "ease_out",
                        crate::MotionEasing::EaseInOut => "ease_in_out",
                    })
                    .map(ImmutableString::from)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "motion_spring",
            |context: &mut UiContext, role: ImmutableString| {
                context
                    .motion_spring(role.as_str())
                    .map(|spring| {
                        Map::from_iter([
                            ("stiffness".into(), Dynamic::from_float(spring.stiffness)),
                            ("damping".into(), Dynamic::from_float(spring.damping)),
                            ("mass".into(), Dynamic::from_float(spring.mass)),
                        ])
                    })
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "motion_distance",
            |context: &mut UiContext, role: ImmutableString| {
                context
                    .motion_distance(role.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "motion_stagger",
            |context: &mut UiContext, role: ImmutableString| {
                context
                    .motion_stagger(role.as_str())
                    .map(|value| INT::try_from(value).unwrap_or(INT::MAX))
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn("motion_quality", |context: &mut UiContext| {
            match context.motion_quality() {
                crate::MotionQuality::Low => "low",
                crate::MotionQuality::Medium => "medium",
                crate::MotionQuality::High => "high",
            }
        })
        .with_fn(
            "play_motion",
            |context: &mut UiContext, handle: crate::MotionHandle| {
                context
                    .play_motion(&handle)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "resume_motion",
            |context: &mut UiContext, handle: crate::MotionHandle| {
                context
                    .play_motion(&handle)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "pause_motion",
            |context: &mut UiContext, handle: crate::MotionHandle| {
                context
                    .pause_motion(&handle)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "seek_motion",
            |context: &mut UiContext, handle: crate::MotionHandle, position_ms: INT| {
                let position_ms = u64::try_from(position_ms).map_err(|_| {
                    Box::new(context_runtime_error(&UiContextError::Motion(
                        crate::MotionError::InvalidTimeline(
                            "seek position must be non-negative".to_owned(),
                        ),
                    )))
                })?;
                context
                    .seek_motion(&handle, position_ms)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "restart_motion",
            |context: &mut UiContext, handle: crate::MotionHandle| {
                context
                    .restart_motion(&handle)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "cancel_motion",
            |context: &mut UiContext, handle: crate::MotionHandle| {
                context
                    .cancel_motion(&handle)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        );
}

fn register_asset_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn("load_image", |context: &mut UiContext, asset: AssetId| {
            context
                .load_image(&asset)
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn(
            "start_image_decode",
            |call: NativeCallContext<'_>,
             context: &mut UiContext,
             asset: AssetId,
             success: FnPtr,
             error: FnPtr| {
                context_at_call(context, &call)
                    .start_image_decode(&asset, success, error)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "cancel_image_decode",
            |context: &mut UiContext, handle: ImageDecodeHandle| {
                context
                    .cancel_image_decode(handle)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        );
}

fn register_window_context_methods(builder: &mut TypeBuilder<UiContext>) {
    builder
        .with_fn("window_id", |context: &mut UiContext| {
            context
                .window_id()
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn("view_id", |context: &mut UiContext| {
            context
                .view_id()
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn("viewport_class", |context: &mut UiContext| {
            context
                .viewport_class()
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn(
            "open_window",
            |context: &mut UiContext,
             id: ImmutableString,
             title: ImmutableString,
             width: rhai::INT,
             height: rhai::INT,
             focus: bool| {
                context
                    .open_window(ScriptWindowSpec {
                        id: id.to_string(),
                        title: title.to_string(),
                        width: width.to_string().parse::<f64>().unwrap_or(f64::INFINITY),
                        height: height.to_string().parse::<f64>().unwrap_or(f64::INFINITY),
                        focus,
                    })
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "focus_window",
            |context: &mut UiContext, id: ImmutableString| {
                context
                    .focus_window(id.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "close_window",
            |context: &mut UiContext, id: ImmutableString| {
                context
                    .close_window(id.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_close_handler",
            |call: NativeCallContext<'_>, context: &mut UiContext, callback: FnPtr| {
                context_at_call(context, &call)
                    .set_close_handler(callback)
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn("clear_close_handler", |context: &mut UiContext| {
            context
                .clear_close_handler()
                .map_err(|error| Box::new(context_runtime_error(&error)))
        })
        .with_fn(
            "set_window_locale",
            |context: &mut UiContext, locale: ImmutableString| {
                context
                    .set_window_locale(locale.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        )
        .with_fn(
            "set_local_locale",
            |context: &mut UiContext, locale: ImmutableString| {
                context
                    .set_local_locale(locale.as_str())
                    .map_err(|error| Box::new(context_runtime_error(&error)))
            },
        );
}

fn context_at_call(context: &UiContext, call: &NativeCallContext<'_>) -> UiContext {
    context.clone().with_native_context(Some(
        crate::invocation::ScriptInvocationContext::capture_retained(call),
    ))
}

pub(crate) fn register_ui_context_api(engine: &mut Engine) {
    engine.build_type::<UiContext>();
}

fn context_runtime_error(error: &UiContextError) -> EvalAltResult {
    EvalAltResult::ErrorRuntime(error.to_string().into(), Position::NONE)
}

#[derive(Debug, Error)]
pub enum UiContextError {
    #[error("UI runtime state is already mutably borrowed by another callback")]
    Borrowed,
    #[error("state mutation and effects are forbidden during view rendering")]
    MutationDuringRender,
    #[error("new async work is forbidden while a view is suspending")]
    AsyncDuringSuspend,
    #[error("subscriptions must be started by a declarative component effect")]
    SubscriptionRequiresEffect,
    #[error("event target geometry is available only during event callbacks")]
    EventTargetOutsideEvent,
    #[error("async work requires a bound script generation")]
    MissingGeneration,
    #[error("no locale manager is configured for this application")]
    LocaleUnavailable,
    #[error("no theme manager is configured for this application")]
    ThemeUnavailable,
    #[cfg(feature = "charts")]
    #[error("native chart data name `{0}` must be a safe identifier")]
    InvalidChartDataName(String),
    #[cfg(feature = "charts")]
    #[error("native chart data `{0}` is not registered")]
    UnknownChartData(String),
    #[error("unknown theme motion {category} token `{role}`")]
    UnknownMotionToken {
        category: &'static str,
        role: String,
    },
    #[error("component `{component}` has no state field `{field}`")]
    UnknownState {
        component: ComponentInstancePath,
        field: String,
    },
    #[error("event `{0}` is not declared by this component")]
    UnknownEvent(String),
    #[error("event payload is invalid: {0}")]
    InvalidEvent(crate::SchemaValidationError),
    #[error("this UI context is not associated with a window")]
    MissingWindow,
    #[error("this UI context is not associated with a mounted script view")]
    MissingView,
    #[error(transparent)]
    Window(#[from] WindowCommandError),
    #[error(transparent)]
    Responsive(#[from] ResponsiveError),
    #[error(transparent)]
    State(#[from] StateError),
    #[error(transparent)]
    Store(#[from] StoreError),
    #[error(transparent)]
    NativeCollection(#[from] crate::NativeCollectionError),
    #[error(transparent)]
    Document(#[from] crate::DocumentError),
    #[error(transparent)]
    Action(#[from] ActionError),
    #[error(transparent)]
    Capability(#[from] CapabilityError),
    #[error(transparent)]
    Async(#[from] AsyncRuntimeError),
    #[error(transparent)]
    Locale(#[from] LocaleError),
    #[error(transparent)]
    Theme(#[from] ThemeError),
    #[error(transparent)]
    Asset(#[from] AssetError),
    #[error(transparent)]
    Value(#[from] UiValueError),
    #[error(transparent)]
    ValuePath(#[from] UiValuePathError),
    #[error(transparent)]
    Signal(#[from] crate::SignalError),
    #[error(transparent)]
    ElementRef(#[from] crate::ElementRefError),
    #[error(transparent)]
    Geometry(#[from] crate::GeometryError),
    #[error("scroll offset must be finite and non-negative, got ({x}, {y})")]
    InvalidScrollOffset { x: f64, y: f64 },
    #[error(transparent)]
    Callback(#[from] crate::ScriptCallbackDefinitionError),
    #[error(transparent)]
    Timer(#[from] crate::TimerError),
    #[error(transparent)]
    Motion(#[from] crate::MotionError),
    #[error(transparent)]
    Budget(#[from] crate::RuntimeBudgetError),
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{ComponentStateSchema, RuntimeEngine, StateField, SubscriptionWork, ValueSchema};

    fn mounted_context(phase: ExecutionPhase) -> UiContext {
        let path = ComponentInstancePath::root("Counter", "counter");
        let schema = ComponentStateSchema::new(BTreeMap::from([
            (
                "count".to_owned(),
                StateField::new(ValueSchema::integer(), UiValue::Integer(0)),
            ),
            (
                "profile".to_owned(),
                StateField::new(
                    ValueSchema::UiValue,
                    UiValue::Map(BTreeMap::from([(
                        "name".to_owned(),
                        UiValue::String("Ada".to_owned()),
                    )])),
                ),
            ),
        ]))
        .unwrap();
        let mut state = UiRuntimeState::new();
        let mut render = state.component_state.begin_render();
        render.mount(path.clone(), &schema).unwrap();
        state.component_state.commit_render(render);
        UiContext::new(
            Rc::new(RefCell::new(state)),
            path,
            Some("main".to_owned()),
            phase,
            BTreeMap::from([(
                "change".to_owned(),
                EventSchema {
                    payload: ValueSchema::integer(),
                },
            )]),
        )
    }

    #[test]
    fn theme_variant_reads_the_resolved_selection() {
        let context = mounted_context(ExecutionPhase::Event);
        // No theme manager installed: the read is (), not an error.
        assert!(context.resolved_theme_variant().is_none());
        assert_eq!(context.resolved_theme_selection(), None);

        let engine = RuntimeEngine::new();
        let dark = crate::load_theme_source(
            engine.engine(),
            "default_dark.rhai",
            include_str!("../../../registry/themes/default_dark.rhai"),
        )
        .unwrap();
        let mut light = dark.clone();
        light.name = "Light".to_owned();
        light.mode = crate::ThemeMode::Light;
        let manager = crate::ThemeManager::from_variants(
            [dark, light],
            crate::ThemeSelection::new("Default".to_owned(), "Dark".to_owned()),
        )
        .unwrap();
        context.runtime.borrow_mut().theme = Some(manager);

        let variant = context.resolved_theme_variant().expect("resolves");
        assert_eq!(variant.mode, crate::ThemeMode::Dark);
        assert_eq!(
            context.resolved_theme_selection(),
            Some(ThemeSelection::new("Default", "Dark"))
        );
    }

    #[test]
    fn first_native_appearance_replaces_dark_fallback_and_invalidates_render_readers_once() {
        let context = mounted_context(ExecutionPhase::Render);
        let engine = RuntimeEngine::new();
        let dark = crate::load_theme_source(
            engine.engine(),
            "dark",
            include_str!("../../../registry/themes/default_dark.rhai"),
        )
        .unwrap();
        let light = crate::load_theme_source(
            engine.engine(),
            "light",
            include_str!("../../../registry/themes/default_light.rhai"),
        )
        .unwrap();
        let mut manager = crate::ThemeManager::from_variants(
            [dark, light],
            ThemeSelection::new("Default", "Dark"),
        )
        .unwrap();
        manager
            .set_app(ThemePreference::System {
                family: "Default".into(),
            })
            .unwrap();
        context.runtime.borrow_mut().theme = Some(manager);
        assert_eq!(
            context.resolved_theme_variant().unwrap().mode,
            crate::ThemeMode::Dark
        );
        {
            let mut runtime = context.runtime.borrow_mut();
            runtime.dirty.clear();
            assert!(runtime.update_window_appearance("main", crate::SystemAppearance::Light));
            assert_eq!(
                runtime.dirty,
                BTreeSet::from([context.component_path().clone()])
            );
            runtime.dirty.clear();
            assert!(!runtime.update_window_appearance("main", crate::SystemAppearance::Light));
            assert!(runtime.dirty.is_empty());
        }
        assert_eq!(
            context.resolved_theme_variant().unwrap().mode,
            crate::ThemeMode::Light
        );
        context
            .runtime
            .borrow_mut()
            .update_window_appearance("main", crate::SystemAppearance::Dark);
        assert_eq!(
            context.resolved_theme_variant().unwrap().mode,
            crate::ThemeMode::Dark
        );
    }

    #[test]
    fn render_signal_reads_disable_component_reuse() {
        let context = mounted_context(ExecutionPhase::Render);
        let signal = crate::NativeSignal::new(
            crate::SignalId::new(
                context.component_path().clone(),
                "hot",
                crate::SignalKind::Float,
            )
            .unwrap(),
        );
        assert!(context.get_signal(&signal).is_err());
        assert!(!context.component_render_is_reusable());
    }

    #[test]
    fn render_context_rejects_mutation() {
        let context = mounted_context(ExecutionPhase::Render);
        assert!(matches!(
            context.set_state("count", Dynamic::from(1_i64)),
            Err(UiContextError::MutationDuringRender)
        ));
    }

    #[test]
    fn event_target_bounds_are_untracked_and_event_only() {
        let context = mounted_context(ExecutionPhase::Event).with_event_target(Some(
            crate::GeometryBounds::new(13.0, 24.0, 90.0, 40.0).unwrap(),
        ));
        assert_eq!(
            context.event_target_bounds().unwrap(),
            crate::GeometryBounds::new(13.0, 24.0, 90.0, 40.0)
                .unwrap()
                .into_value()
        );
        assert!(context.runtime().borrow().geometry.take_dirty().is_empty());

        assert!(matches!(
            mounted_context(ExecutionPhase::Render).event_target_bounds(),
            Err(UiContextError::EventTargetOutsideEvent)
        ));
        assert_eq!(
            mounted_context(ExecutionPhase::Event)
                .event_target_bounds()
                .unwrap(),
            UiValue::Null
        );
    }

    #[test]
    fn viewport_class_is_window_scoped_and_script_readable() {
        let context = mounted_context(ExecutionPhase::Render);
        context
            .runtime()
            .borrow_mut()
            .responsive
            .update_window("main", 480.0)
            .unwrap();
        assert_eq!(context.viewport_class().unwrap(), "compact");
    }

    #[test]
    fn locale_and_viewport_reads_register_exact_component_dependencies() {
        let engine = Engine::new();
        let en = crate::load_locale_source(
            &engine,
            "en.rhai",
            include_str!("../../../registry/locales/en.rhai"),
        )
        .unwrap();
        let zh = crate::load_locale_source(
            &engine,
            "zh_cn.rhai",
            include_str!("../../../registry/locales/zh_cn.rhai"),
        )
        .unwrap();
        let mut state = UiRuntimeState::new();
        state.locale = Some(LocaleManager::new([en, zh], "en", "en").unwrap());
        state.responsive.update_window("main", 480.0).unwrap();
        state.windows.register_open("main").unwrap();
        let runtime = Rc::new(RefCell::new(state));
        let reader = ComponentInstancePath::root("View", "main").child("Reader", "reader");
        let unrelated = ComponentInstancePath::root("View", "main").child("Static", "static");
        let render_context = UiContext::new(
            Rc::clone(&runtime),
            reader.clone(),
            Some("main".to_owned()),
            ExecutionPhase::Render,
            BTreeMap::new(),
        );
        assert!(!render_context.text("common.loading").unwrap().is_empty());
        assert_eq!(render_context.viewport_class().unwrap(), "compact");
        let event = UiContext::new(
            Rc::clone(&runtime),
            unrelated,
            Some("main".to_owned()),
            ExecutionPhase::Event,
            BTreeMap::new(),
        );
        event.set_locale("zh-CN").unwrap();

        assert_eq!(
            runtime.borrow_mut().drain_batch().dirty,
            BTreeSet::from([reader.clone()])
        );
        assert_eq!(
            runtime
                .borrow()
                .environment_dependencies
                .invalidate_viewport("main"),
            BTreeSet::from([reader])
        );
        assert!(runtime.borrow_mut().take_window_repaint("main"));
    }

    #[test]
    fn event_mutations_are_batched() {
        let context = mounted_context(ExecutionPhase::Event);
        context.set_state("count", Dynamic::from(1_i64)).unwrap();
        context.set_state("count", Dynamic::from(2_i64)).unwrap();
        context.emit("change", Dynamic::from(2_i64)).unwrap();

        let mut runtime = context.runtime().borrow_mut();
        let batch = runtime.drain_batch();
        assert_eq!(batch.dirty.len(), 1);
        assert_eq!(batch.events.len(), 1);
        assert_eq!(
            runtime
                .component_state
                .get(&ComponentInstancePath::root("Counter", "counter"), "count",),
            Some(&UiValue::Integer(2))
        );
    }

    #[test]
    fn semantic_event_and_action_traces_never_retain_payload_values() {
        let secret = "AUDIT_ONLY_SYNTHETIC_TOKEN";
        let path = ComponentInstancePath::root("SecretInput", "audit");
        let schema = ComponentStateSchema::new(BTreeMap::from([(
            "token".to_owned(),
            StateField::new(ValueSchema::string(), UiValue::String(secret.to_owned()))
                .sensitive(true),
        )]))
        .unwrap();
        let mut state = UiRuntimeState::new();
        let mut render = state.component_state.begin_render();
        render.mount(path.clone(), &schema).unwrap();
        state.component_state.commit_render(render);

        let mut engine = RuntimeEngine::new();
        let compiled = engine
            .compile("fn view() { text(\"trace\") } fn receive(ctx, payload) {}")
            .unwrap();
        state.actions.register_or_replace(
            crate::ActionId::parse("audit.receive").unwrap(),
            engine.callback(&compiled, "receive").unwrap(),
        );
        let runtime = Rc::new(RefCell::new(state));
        let context = UiContext::new(
            Rc::clone(&runtime),
            path,
            Some("main".to_owned()),
            ExecutionPhase::Event,
            BTreeMap::from([(
                "change".to_owned(),
                EventSchema {
                    payload: ValueSchema::string(),
                },
            )]),
        );

        let event_value = context.get_state("token").unwrap().into_dynamic();
        context.emit("change", event_value).unwrap();
        let action_value = context.get_state("token").unwrap().into_dynamic();
        context
            .dispatch_action("audit.receive", action_value)
            .unwrap();

        let traces = runtime.borrow().traces.snapshot();
        let semantic = traces
            .iter()
            .filter(|trace| {
                matches!(
                    trace.kind,
                    crate::RuntimeTraceKind::Event | crate::RuntimeTraceKind::Action
                )
            })
            .collect::<Vec<_>>();
        assert_eq!(semantic.len(), 2);
        assert!(
            semantic
                .iter()
                .all(|trace| trace.sensitive && trace.payload.is_none())
        );
        assert!(!format!("{traces:?}").contains(secret));
    }

    #[test]
    fn scripts_receive_restricted_context_without_gpui_types() {
        let context = mounted_context(ExecutionPhase::Event);
        let mut runtime = RuntimeEngine::new();
        let compiled = runtime
            .compile(
                r#"
                    fn view() { text("context") }
                    fn increment(ctx) {
                        ctx.set_state("count", ctx.get_state("count") + 1);
                    }
                "#,
            )
            .unwrap();
        runtime.render(&compiled).unwrap();
        let callback = runtime.callback(&compiled, "increment").unwrap();
        let _ = runtime
            .invoke_callback(&compiled, &callback, (context.clone(),))
            .unwrap();
        assert_eq!(context.get_state("count").unwrap(), UiValue::Integer(1));
    }

    #[test]
    fn structural_store_paths_invalidate_executable_owner_not_synthetic_scope() {
        for window_store in [false, true] {
            let runtime = Rc::new(RefCell::new(UiRuntimeState::new()));
            let owner = ComponentInstancePath::root("Panel", "paths");
            let store = if window_store {
                StoreId::window("main", "data")
            } else {
                StoreId::app("data")
            };
            runtime
                .borrow_mut()
                .stores
                .declare(
                    store,
                    ComponentStateSchema::new(BTreeMap::from([(
                        "model".into(),
                        StateField::new(
                            ValueSchema::UiValue,
                            UiValue::Map(BTreeMap::from([
                                ("label".into(), UiValue::String("before".into())),
                                ("sibling".into(), UiValue::String("untouched".into())),
                            ])),
                        ),
                    )]))
                    .unwrap(),
                )
                .unwrap();
            let render = UiContext::new(
                Rc::clone(&runtime),
                owner.clone(),
                Some("main".into()),
                ExecutionPhase::Render,
                BTreeMap::new(),
            );
            let structural = render
                .for_structural_scope(owner.child("VirtualCollection", "rows"), BTreeMap::new());
            let label = UiValuePath::new(vec![UiValuePathSegment::Key("label".into())]).unwrap();
            let sibling =
                UiValuePath::new(vec![UiValuePathSegment::Key("sibling".into())]).unwrap();
            let value = if window_store {
                structural.get_window_store_path("data", "model", &label)
            } else {
                structural.get_app_store_path("data", "model", &label)
            }
            .unwrap();
            assert_eq!(value, UiValue::String("before".into()));
            let mut event = render.clone();
            event.phase = ExecutionPhase::Event;
            let write = |path: &UiValuePath| {
                if window_store {
                    event.set_window_store_path("data", "model", path, Dynamic::from("after"))
                } else {
                    event.set_app_store_path("data", "model", path, Dynamic::from("after"))
                }
                .unwrap();
            };
            write(&sibling);
            assert!(runtime.borrow().dirty.is_empty());
            write(&label);
            assert_eq!(runtime.borrow().dirty, BTreeSet::from([owner]));
        }
    }

    #[test]
    fn scripts_use_bounded_nested_and_keyed_store_paths() {
        let context = mounted_context(ExecutionPhase::Event);
        let row = |id: &str, label: &str| {
            UiValue::Map(BTreeMap::from([
                ("id".to_owned(), UiValue::String(id.to_owned())),
                ("label".to_owned(), UiValue::String(label.to_owned())),
            ]))
        };
        context
            .runtime()
            .borrow_mut()
            .stores
            .declare(
                StoreId::app("model"),
                ComponentStateSchema::new(BTreeMap::from([(
                    "data".to_owned(),
                    StateField::new(
                        ValueSchema::UiValue,
                        UiValue::Map(BTreeMap::from([(
                            "rows".to_owned(),
                            UiValue::Array(vec![row("alpha", "Alpha"), row("beta", "Beta")]),
                        )])),
                    ),
                )]))
                .unwrap(),
            )
            .unwrap();
        let mut runtime = RuntimeEngine::new();
        let compiled = runtime
            .compile(
                r#"
                    fn view() { text("paths") }
                    fn update(ctx) {
                        let name = ctx.get_state_path("profile", ["name"]);
                        ctx.set_state_path("profile", ["name"], name + " Lovelace");
                        let label = ctx.get_app_store_path(
                            "model",
                            "data",
                            ["rows", #{ by: "id", key: "beta" }, "label"]
                        );
                        ctx.set_app_store_path(
                            "model",
                            "data",
                            ["rows", #{ by: "id", key: "beta" }, "label"],
                            label + "!"
                        );
                    }
                "#,
            )
            .unwrap();
        runtime.render(&compiled).unwrap();
        let callback = runtime.callback(&compiled, "update").unwrap();
        let _: Dynamic = runtime
            .invoke_callback(&compiled, &callback, (context.clone(),))
            .unwrap();

        let profile = context.get_state("profile").unwrap();
        assert_eq!(
            profile
                .get_path(
                    &UiValuePath::new(vec![UiValuePathSegment::Key("name".to_owned())]).unwrap()
                )
                .unwrap(),
            &UiValue::String("Ada Lovelace".to_owned())
        );
        let row_path = UiValuePath::new(vec![
            UiValuePathSegment::Key("rows".to_owned()),
            UiValuePathSegment::Item {
                key_field: "id".to_owned(),
                key: "beta".to_owned(),
            },
            UiValuePathSegment::Key("label".to_owned()),
        ])
        .unwrap();
        assert_eq!(
            context
                .runtime()
                .borrow_mut()
                .stores
                .read_path_tracked(
                    &ComponentInstancePath::root("Test", "reader"),
                    &StoreId::app("model"),
                    "data",
                    &row_path,
                )
                .unwrap(),
            UiValue::String("Beta!".to_owned())
        );
        assert!(rhai_value_path(vec![Dynamic::from(-1_i64)]).is_err());
    }

    #[test]
    fn script_theme_switch_preserves_component_state_and_ast_generation() {
        let context = mounted_context(ExecutionPhase::Event);
        context.set_state("count", Dynamic::from(7_i64)).unwrap();
        let mut runtime = RuntimeEngine::new();
        let dark = crate::load_theme_source(
            runtime.engine(),
            "default_dark.rhai",
            include_str!("../../../registry/themes/default_dark.rhai"),
        )
        .unwrap();
        let mocha = crate::load_theme_source(
            runtime.engine(),
            "catppuccin_mocha.rhai",
            include_str!("../../../registry/themes/catppuccin_mocha.rhai"),
        )
        .unwrap();
        context.runtime().borrow_mut().theme = Some(
            ThemeManager::from_variants([dark, mocha], ThemeSelection::new("Default", "Dark"))
                .unwrap(),
        );
        let compiled = runtime
            .compile(
                r#"
                    fn view() { text("theme") }
                    fn switch_theme(ctx) { ctx.set_theme("Catppuccin", "Mocha"); }
                "#,
            )
            .unwrap();
        runtime.render(&compiled).unwrap();
        let generation = compiled.generation();
        let callback = runtime.callback(&compiled, "switch_theme").unwrap();
        let _ = runtime
            .invoke_callback(&compiled, &callback, (context.clone(),))
            .unwrap();

        assert_eq!(context.get_state("count").unwrap(), UiValue::Integer(7));
        assert_eq!(compiled.generation(), generation);
        let state = context.runtime().borrow();
        let theme = state
            .theme
            .as_ref()
            .unwrap()
            .resolve(Some("main"), None, crate::SystemAppearance::Dark)
            .unwrap();
        assert_eq!(theme.variant().family, "Catppuccin");
        assert_eq!(theme.variant().name, "Mocha");
        drop(state);
        context.set_theme_system("Default").unwrap();
        let state = context.runtime().borrow();
        assert!(matches!(
            state.theme.as_ref().unwrap().app_preference(),
            ThemePreference::System { family } if family == "Default"
        ));
    }

    #[test]
    fn script_reads_fixed_today_calendar_and_locale_formatters() {
        let mut engine = Engine::new();
        register_ui_context_api(&mut engine);
        let bundle = crate::load_locale_source(
            &engine,
            "en.rhai",
            include_str!("../../../registry/locales/en.rhai"),
        )
        .unwrap();
        let mut state = UiRuntimeState::new();
        state.locale = Some(LocaleManager::new([bundle], "en", "en").unwrap());
        state.calendar_clock =
            crate::CalendarClock::fixed(crate::GregorianDate::parse_iso("2026-08-29").unwrap());
        let context = UiContext::new(
            Rc::new(RefCell::new(state)),
            ComponentInstancePath::root("App", "root"),
            Some("main".to_owned()),
            ExecutionPhase::Render,
            BTreeMap::new(),
        );
        let mut scope = rhai::Scope::new();
        scope.push("ctx", context);
        let values = engine
            .eval_with_scope::<rhai::Array>(
                &mut scope,
                r#"[
                    ctx.today(),
                    ctx.format_date("2024-02-29", "long"),
                    ctx.format_number(12345, #{ min_fraction_digits: 0, max_fraction_digits: 0 }),
                    ctx.calendar().first_weekday,
                ]"#,
            )
            .unwrap();
        assert_eq!(values[0].clone_cast::<String>(), "2026-08-29");
        assert_eq!(
            values[1].clone_cast::<String>(),
            "Thursday, February 29, 2024"
        );
        assert_eq!(values[2].clone_cast::<String>(), "12,345");
        assert_eq!(values[3].clone_cast::<String>(), "sunday");
    }

    #[test]
    fn returning_subscription_work_closes_external_emitters_with_reason() {
        let mut engine = RuntimeEngine::new();
        let compiled = engine
            .compile(
                r#"
                    fn view() { text("subscription") }
                    fn success(ctx, value) { value }
                    fn failure(ctx, error) { error }
                "#,
            )
            .unwrap();
        let generation = compiled.generation();
        let success = engine.callback(&compiled, "success").unwrap();
        let failure = engine.callback(&compiled, "failure").unwrap();
        let mut state = UiRuntimeState::new();
        let registration = SubscriptionRegistration::new(
            "app.stream.watch",
            AsyncScope::App,
            generation,
            success,
            failure,
            ValueSchema::integer(),
        );
        let (_, emitter) = state.subscriptions.subscribe(registration);
        let external = emitter.clone();
        run_subscription_work(SubscriptionWork::new(|_| {}), emitter.clone(), &emitter);

        assert!(matches!(
            external.emit(UiValue::Integer(1)),
            Err(AsyncRuntimeError::Closed {
                reason: SubscriptionCloseReason::WorkReturned
            })
        ));
        let _ = state.subscriptions.drain(generation);
        assert_eq!(
            state.subscriptions.take_closures()[0].reason,
            SubscriptionCloseReason::WorkReturned
        );
        let registration = SubscriptionRegistration::new(
            "app.stream.trace",
            AsyncScope::App,
            generation,
            engine.callback(&compiled, "success").unwrap(),
            engine.callback(&compiled, "failure").unwrap(),
            ValueSchema::integer(),
        );
        let (_, emitter) = state.subscriptions.subscribe(registration);
        emitter.close_with_reason(SubscriptionCloseReason::WorkReturned);
        let _ = state.subscriptions.drain(generation);
        state.trace_subscription_closures();
        let traces = state.traces.snapshot();
        assert!(traces.iter().any(|trace| {
            trace.kind == crate::RuntimeTraceKind::Subscription
                && trace.message == "close app.stream.trace: the subscription work returned"
        }));
    }

    #[test]
    fn receiver_subscription_forwards_external_values_until_sender_drop() {
        let mut engine = RuntimeEngine::new();
        let compiled = engine
            .compile(
                r#"
                    fn view() { text("subscription") }
                    fn success(ctx, value) { value }
                    fn failure(ctx, error) { error }
                "#,
            )
            .unwrap();
        let generation = compiled.generation();
        let registration = SubscriptionRegistration::new(
            "app.stream.receiver",
            AsyncScope::App,
            generation,
            engine.callback(&compiled, "success").unwrap(),
            engine.callback(&compiled, "failure").unwrap(),
            ValueSchema::integer(),
        );
        let mut subscriptions = SubscriptionRegistry::new();
        let (_, emitter) = subscriptions.subscribe(registration);
        let external = emitter.clone();
        let closer = emitter.clone();
        let (sender, receiver) = std::sync::mpsc::channel();
        let worker = std::thread::spawn(move || {
            run_subscription_work(SubscriptionWork::from_receiver(receiver), emitter, &closer);
        });
        sender.send(UiValue::Integer(42)).unwrap();
        drop(sender);
        worker.join().unwrap();

        let deliveries = subscriptions.drain(generation);
        assert_eq!(deliveries[0].payload, UiValue::Integer(42));
        assert!(matches!(
            external.emit(UiValue::Integer(43)),
            Err(AsyncRuntimeError::Closed {
                reason: SubscriptionCloseReason::WorkReturned
            })
        ));
    }

    #[test]
    fn receiver_subscription_waits_for_lossless_capacity_without_ending_the_stream() {
        let mut engine = RuntimeEngine::new();
        let compiled = engine
            .compile(
                "fn view() { text(\"stream\") } fn success(ctx, value) {} fn failure(ctx, value) {}",
            )
            .unwrap();
        engine.render(&compiled).unwrap();
        let generation = compiled.generation();
        let registration = SubscriptionRegistration::new(
            "stream",
            AsyncScope::App,
            generation,
            engine.callback(&compiled, "success").unwrap(),
            engine.callback(&compiled, "failure").unwrap(),
            ValueSchema::integer(),
        )
        .with_capacity(1)
        .unwrap();
        let mut subscriptions = SubscriptionRegistry::new();
        let (_, emitter) = subscriptions.subscribe(registration);
        let closer = emitter.clone();
        let (sender, receiver) = std::sync::mpsc::channel();
        let worker = std::thread::spawn(move || {
            run_subscription_work(SubscriptionWork::from_receiver(receiver), emitter, &closer);
        });
        sender.send(UiValue::Integer(1)).unwrap();
        sender.send(UiValue::Integer(2)).unwrap();
        let deadline = std::time::Instant::now() + Duration::from_secs(1);
        let first = loop {
            let values = subscriptions.drain(generation);
            if !values.is_empty() {
                break values;
            }
            assert!(std::time::Instant::now() < deadline);
            std::thread::yield_now();
        };
        assert_eq!(first[0].payload, UiValue::Integer(1));
        let second = loop {
            let values = subscriptions.drain(generation);
            if !values.is_empty() {
                break values;
            }
            assert!(std::time::Instant::now() < deadline);
            std::thread::yield_now();
        };
        assert_eq!(second[0].payload, UiValue::Integer(2));
        assert_eq!(subscriptions.active_count(), 1);
        drop(sender);
        worker.join().unwrap();
    }

    #[test]
    fn runtime_transaction_rollback_restores_cancelled_subscription() {
        let mut engine = RuntimeEngine::new();
        let compiled = engine
            .compile(
                "fn view() { text(\"test\") } fn success(ctx, value) {} fn failure(ctx, value) {}",
            )
            .unwrap();
        engine.render(&compiled).unwrap();
        let success = engine.callback(&compiled, "success").unwrap();
        let error = engine.callback(&compiled, "failure").unwrap();
        let generation = compiled.generation();
        let mut state = UiRuntimeState::new();
        let (handle, emitter) = state.subscriptions.subscribe(SubscriptionRegistration::new(
            "rollback",
            AsyncScope::App,
            generation,
            success,
            error,
            ValueSchema::integer(),
        ));
        let checkpoint = state.begin_transaction().unwrap();
        assert!(state.subscriptions.cancel(handle));
        assert_eq!(emitter.close_reason(), None);
        state.rollback_transaction(checkpoint).unwrap();
        assert_eq!(state.subscriptions.active_count(), 1);
        emitter.emit(UiValue::Integer(7)).unwrap();
        assert_eq!(state.subscriptions.drain(generation).len(), 1);
    }

    #[test]
    fn transaction_tokens_cannot_cross_runtime_or_commit_unbalanced() {
        let mut first = UiRuntimeState::new();
        let mut second = UiRuntimeState::new();
        let checkpoint = first.begin_transaction().unwrap();
        assert!(matches!(
            second.rollback_transaction(checkpoint.clone()),
            Err(UiTransactionError::ForeignSnapshot)
        ));
        assert!(matches!(
            second.commit_transaction(),
            Err(UiTransactionError::Unbalanced { .. })
        ));
        first.rollback_transaction(checkpoint).unwrap();
    }

    #[test]
    fn presentation_geometry_and_capture_are_isolated_per_view() {
        let mut first = crate::RetainedUiTree::new();
        first.reconcile(crate::UiNode::text("first")).unwrap();
        let mut second = crate::RetainedUiTree::new();
        second.reconcile(crate::UiNode::text("second")).unwrap();
        let first_node = first.root_id().unwrap();
        let second_node = second.root_id().unwrap();
        assert_eq!(
            first_node, second_node,
            "tree-local IDs intentionally overlap"
        );

        let mut state = UiRuntimeState::new();
        state.ensure_presentation("first");
        state.ensure_presentation("second");
        let first_geometry = state.geometry_for(Some("first"));
        let second_geometry = state.geometry_for(Some("second"));
        let bounds = |width| crate::ElementGeometry {
            layout: crate::GeometryBounds::new(0.0, 0.0, width, 20.0).unwrap(),
            visual: crate::GeometryBounds::new(0.0, 0.0, width, 20.0).unwrap(),
            clip: None,
        };
        first_geometry.update(first_node, bounds(100.0));
        second_geometry.update(second_node, bounds(300.0));
        second_geometry.begin_frame();
        assert!(
            (first_geometry.get(first_node).unwrap().visual.width - 100.0).abs() < f64::EPSILON
        );
        assert!(first_geometry.is_presented(first_node));

        let first_capture = state.pointer_capture_for(Some("first"));
        let second_capture = state.pointer_capture_for(Some("second"));
        first_capture.capture(0, first_node);
        second_capture.capture(0, second_node);
        assert_eq!(first_capture.captured(0), Some(first_node));
        assert_eq!(second_capture.captured(0), Some(second_node));
    }

    #[test]
    fn window_release_uses_segment_boundaries_and_clears_suspend_tombstones() {
        let now = std::time::Instant::now();
        let transition = || {
            let mut spec =
                crate::MotionTransition::new(crate::MotionProperty::Opacity, 0.0, 1.0, 1_000);
            spec.easing = crate::MotionEasing::Linear;
            crate::MotionSource::Transition(spec)
        };
        let mut state = UiRuntimeState::new();
        let ghost_path = "window:w2/view:v2/root/ghost:1";
        state
            .motions
            .start_exit(
                ComponentInstancePath::root("UiNode", ghost_path),
                transition(),
                now,
            )
            .unwrap();
        state.motion_ghosts.push(crate::motion::MotionGhost {
            id: "1".to_owned(),
            node: crate::UiNode::text("ghost"),
            bounds: crate::GeometryBounds::new(0.0, 0.0, 10.0, 10.0).unwrap(),
            path: ghost_path.to_owned(),
            domain: "window:w2/view:v2/root".to_owned(),
        });
        state
            .release_window("w", &ComponentInstancePath::root("View", "v"))
            .unwrap();
        assert_eq!(state.motion_ghosts.len(), 1);
        assert_eq!(state.motions.resource_usage().active, 1);

        let mut reopened = UiRuntimeState::new();
        let scope = "window:w/view:v/root";
        reopened
            .motions
            .start(
                ComponentInstancePath::root("UiNode", format!("{scope}/node:1")),
                transition(),
                now,
            )
            .unwrap();
        reopened
            .motions
            .suspend_node_scope(scope, now + Duration::from_millis(200));
        reopened
            .release_window("w", &ComponentInstancePath::root("View", "v"))
            .unwrap();
        let key = reopened
            .motions
            .start(
                ComponentInstancePath::root("UiNode", format!("{scope}/node:2")),
                transition(),
                now + Duration::from_millis(200),
            )
            .unwrap();
        let frame = reopened.motions.tick(now + Duration::from_millis(400));
        assert!(frame.needs_frame);
        assert!((frame.values[&key] - 0.2).abs() < 0.01);
    }

    #[test]
    fn timeline_handles_cannot_cross_view_contexts() {
        let runtime = Rc::new(RefCell::new(UiRuntimeState::new()));
        let now = std::time::Instant::now();
        let mut transition =
            crate::MotionTransition::new(crate::MotionProperty::Opacity, 0.0, 1.0, 1_000);
        transition.easing = crate::MotionEasing::Linear;
        let handle = runtime
            .borrow_mut()
            .motions
            .start_timeline(
                ComponentInstancePath::root("UiNode", "window:a/view:a/root"),
                crate::MotionTimeline::new(
                    "foreign",
                    crate::MotionTimelineStep::Track(crate::MotionTrack {
                        target: ".".to_owned(),
                        source: crate::MotionSource::Transition(transition),
                    }),
                ),
                now,
            )
            .unwrap();
        let foreign = UiContext::new(
            Rc::clone(&runtime),
            ComponentInstancePath::root("View", "b"),
            Some("b".to_owned()),
            ExecutionPhase::Event,
            BTreeMap::new(),
        )
        .with_view_id("b");

        assert!(matches!(
            foreign.cancel_motion(&handle),
            Err(UiContextError::Motion(
                crate::MotionError::ForeignTimelineHandle(_)
            ))
        ));
        assert_eq!(
            runtime.borrow().motions.timeline_state(&handle),
            Some(crate::MotionPlaybackState::Playing)
        );
    }

    #[test]
    fn focus_by_ref_key_queues_a_window_scoped_retained_command() {
        let context = mounted_context(ExecutionPhase::Event);
        let mut tree = crate::RetainedUiTree::new();
        tree.reconcile(crate::UiNode::text("field")).unwrap();
        let reference = crate::ElementRef::new(
            crate::ElementRefId::new(context.component_path().clone(), "field").unwrap(),
        );
        context.runtime().borrow_mut().element_refs.reconcile(
            context.component_path(),
            BTreeMap::from([(reference.id().clone(), tree.root_id().unwrap())]),
        );
        let node = tree.root_id().unwrap();
        context
            .runtime()
            .borrow()
            .geometry_for(Some("main"))
            .update(
                node,
                crate::ElementGeometry {
                    layout: crate::GeometryBounds::new(1.0, 2.0, 120.0, 24.0).unwrap(),
                    visual: crate::GeometryBounds::new(3.0, 4.0, 120.0, 24.0).unwrap(),
                    clip: None,
                },
            );
        assert!(matches!(
            context.element_bounds_by_key("field").unwrap(),
            UiValue::Map(bounds)
                if matches!(bounds.get("visual"), Some(UiValue::Map(visual))
                    if visual.get("width") == Some(&UiValue::Float(120.0)))
        ));
        context.focus_element_by_key("field").unwrap();
        context
            .scroll_element_to_by_key("field", 12.0, 24.0)
            .unwrap();
        context.scroll_element_into_view_by_key("field").unwrap();
        let commands = context
            .runtime()
            .borrow_mut()
            .take_window_element_commands("main");
        assert!(matches!(
            commands.as_slice(),
            [crate::element_ref::ElementCommand::Focus { node, .. },
             crate::element_ref::ElementCommand::ScrollTo { node: scroll_node, x, y, .. },
             crate::element_ref::ElementCommand::ScrollIntoView { node: reveal_node, .. }]
                if *node == tree.root_id().unwrap()
                    && scroll_node == node
                    && reveal_node == node
                    && (*x - 12.0).abs() < f64::EPSILON
                    && (*y - 24.0).abs() < f64::EPSILON
        ));
    }

    #[test]
    fn host_motion_preference_changes_without_replacing_runtime_state() {
        let mut runtime = UiRuntimeState::new();
        runtime.motions = crate::MotionRuntime::new(crate::MotionPreference::Normal);
        runtime.responsive.update_window("main", 480.0).unwrap();

        assert!(!runtime.set_motion_preference_from_host(crate::MotionPreference::Normal));
        assert!(runtime.set_motion_preference_from_host(crate::MotionPreference::Reduced));
        assert_eq!(
            runtime.motions.preference(),
            crate::MotionPreference::Reduced
        );
        assert_eq!(
            runtime.responsive.class("main"),
            crate::ViewportClass::Compact
        );
        assert!(runtime.set_motion_preference_from_host(crate::MotionPreference::None));
        assert_eq!(runtime.motions.preference(), crate::MotionPreference::None);
    }

    #[test]
    fn host_can_register_a_new_native_collection_after_mount() {
        let mut runtime = UiRuntimeState::new();
        let root = ComponentInstancePath::root("View", "live");
        assert!(
            runtime
                .native_collections
                .read_tracked(&root, "live_rows")
                .is_err()
        );
        let collection = crate::NativeCollection::new(
            "id",
            [BTreeMap::from([(
                "id".to_owned(),
                UiValue::String("row-1".to_owned()),
            )])],
        )
        .unwrap();
        runtime
            .register_native_collection_from_host(&root, "live_rows", collection)
            .unwrap();
        assert!(runtime.has_window_dirty(&root));
        assert!(matches!(
            runtime.register_native_collection_from_host(
                &root,
                "live_rows",
                crate::NativeCollection::new("id", std::iter::empty::<BTreeMap<String, UiValue>>())
                    .unwrap(),
            ),
            Err(crate::NativeCollectionError::DuplicateCollection(_))
        ));
    }
}