cli-engine 0.9.3

use std::{
    borrow::Cow,
    collections::{BTreeMap, BTreeSet, HashMap},
    fmt,
    io::IsTerminal,
    sync::{Arc, OnceLock, RwLock},
};

use serde_json::Value;

use super::{Envelope, NextAction, NextActionParam, PaginationMeta};

/// Column text alignment for the human table view.
///
/// Only affects the array/table rendering path (`render_array_with_columns`
/// via `render_table`) — property-bag rendering (`render_object_with_columns`)
/// prints `header: value` with no column widths to align, so alignment is a
/// no-op there.
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
pub enum Alignment {
    /// Left-aligned (the default) — appropriate for text-like columns.
    #[default]
    Left,
    /// Right-aligned — use for numeric/price columns so values line up on
    /// their least-significant digit.
    Right,
}

/// Column definition for registered human table views.
///
/// Column order is a priority order, most important first: table rendering
/// keeps this order on screen, and when the terminal is too narrow to show
/// every column, the lowest-priority (trailing) columns are hidden first. Put
/// the column a reader most needs — usually an id or name — first.
///
/// This declared order is only the *fallback* — whenever a `--fields`/
/// `default_fields` selection is given, its order wins instead (see
/// [`crate::output::render_human_with_registry_selected`]), for both display
/// and hide-priority. Declared order only governs output when no selection is
/// given at all.
///
/// Construct with [`TableColumn::new`], then chain builder methods like
/// [`no_truncate`](TableColumn::no_truncate)/[`nested`](TableColumn::nested)
/// — never as a struct literal. No known consumer constructs `TableColumn`
/// via struct literal, so marking it `#[non_exhaustive]` carries no real
/// breaking impact today; going forward it means the engine can add fields
/// (as it did for `nested`) without that becoming a breaking release either.
#[derive(Clone, Debug, Eq, PartialEq)]
#[non_exhaustive]
pub struct TableColumn {
    /// JSON field path. Supports simple dotted paths to reach a value nested
    /// under intermediate objects, so a column can point through a wrapper
    /// shape (a pagination envelope, a `Summary<T>`, etc.). A literal field
    /// name containing a `.` is not supported — this mirrors the dotted-path
    /// convention `crate::output::fields` already uses for `--fields`
    /// projection.
    pub field: String,
    /// Display header.
    pub header: String,
    /// When true, this column's values are never shrunk to fit the terminal
    /// (still capped at `NO_TRUNCATE_MAX_WIDTH` to bound pathologically long
    /// values). Use this for values that are useless when cut short, such as
    /// URLs.
    pub no_truncate: bool,
    /// When set, and the resolved value is list-of-objects or object shaped,
    /// this column renders as an indented child table or child property bag
    /// instead of a one-line dump — see [`TableColumn::nested`]. `None` (the
    /// default from [`TableColumn::new`]) is a complete no-op: rendering is
    /// identical to a column with no opinion about nesting.
    pub nested: Option<Vec<TableColumn>>,
    /// Header and cell text alignment — see [`TableColumn::align`].
    pub align: Alignment,
}

impl TableColumn {
    /// Creates a table column from a JSON field path and display header.
    #[must_use]
    pub fn new(field: impl Into<String>, header: impl Into<String>) -> Self {
        Self {
            field: field.into(),
            header: header.into(),
            no_truncate: false,
            nested: None,
            align: Alignment::Left,
        }
    }

    /// Opts this column out of terminal-width-driven shrinking. Values are
    /// still capped at `NO_TRUNCATE_MAX_WIDTH`.
    #[must_use]
    pub fn no_truncate(mut self, value: bool) -> Self {
        self.no_truncate = value;
        self
    }

    /// Sets this column's header and cell alignment. Defaults to
    /// `Alignment::Left`; use `Alignment::Right` for numeric or price
    /// columns so decimal points and digits line up instead of looking
    /// ragged on the left.
    #[must_use]
    pub fn align(mut self, alignment: Alignment) -> Self {
        self.align = alignment;
        self
    }

    /// Opts this column into rendering a nested list/object value as an
    /// indented child table or property bag, using `columns` as that child's
    /// own column definitions (which may themselves set `.nested(...)`).
    ///
    /// Nesting is only consulted when this column is rendered inside an
    /// object property bag (top-level, or itself a nested property bag) — a
    /// row cell inside an array-of-objects table always renders as a single
    /// flat value, ignoring `nested`, because a table row is one monospace
    /// line and can't itself contain a rendered sub-block without breaking
    /// column alignment. Recursion is otherwise unbounded through the object
    /// chain: a nested column's own child columns may set `.nested(...)`
    /// again for a grandchild table or property bag.
    #[must_use]
    pub fn nested(mut self, columns: impl Into<Vec<TableColumn>>) -> Self {
        self.nested = Some(columns.into());
        self
    }
}

/// Human view definition keyed by schema id.
///
/// `columns` order is a priority order — see [`TableColumn`].
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct HumanViewDef {
    /// Schema id, usually the command path.
    pub schema_id: String,
    /// Columns rendered for matching object or list data, most important
    /// first.
    pub columns: Vec<TableColumn>,
}

impl HumanViewDef {
    /// Creates a column-based human view for a schema id or command path.
    #[must_use]
    pub fn new(schema_id: impl Into<String>, columns: impl Into<Vec<TableColumn>>) -> Self {
        Self {
            schema_id: schema_id.into(),
            columns: columns.into(),
        }
    }
}

/// Function used to render custom human output for a JSON value.
pub type HumanViewFn = Arc<dyn Fn(&Value) -> String + Send + Sync>;

/// Custom human renderer wrapper.
#[derive(Clone)]
pub struct HumanViewRenderer {
    render: HumanViewFn,
}

impl HumanViewRenderer {
    /// Creates a custom renderer.
    #[must_use]
    pub fn new(render: impl Fn(&Value) -> String + Send + Sync + 'static) -> Self {
        Self {
            render: Arc::new(render),
        }
    }

    /// Renders data with the custom renderer.
    #[must_use]
    pub fn render(&self, data: &Value) -> String {
        (self.render)(data)
    }
}

impl fmt::Debug for HumanViewRenderer {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter
            .debug_struct("HumanViewRenderer")
            .finish_non_exhaustive()
    }
}

/// Registry of human column and custom-renderer views.
#[derive(Clone, Debug, Default)]
pub struct HumanViewRegistry {
    by_schema_id: BTreeMap<String, Vec<TableColumn>>,
    custom_by_schema_id: BTreeMap<String, HumanViewRenderer>,
}

impl HumanViewRegistry {
    /// Creates an empty registry.
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    /// Registers a column-based human view.
    pub fn register(&mut self, view: HumanViewDef) {
        self.by_schema_id.insert(view.schema_id, view.columns);
    }

    /// Registers a custom renderer for a schema id.
    pub fn register_func(
        &mut self,
        schema_id: impl Into<String>,
        render: impl Fn(&Value) -> String + Send + Sync + 'static,
    ) {
        self.custom_by_schema_id
            .insert(schema_id.into(), HumanViewRenderer::new(render));
    }

    /// Merges another registry into this one.
    pub fn merge(&mut self, other: &Self) {
        self.by_schema_id.extend(other.by_schema_id.clone());
        self.custom_by_schema_id
            .extend(other.custom_by_schema_id.clone());
    }

    /// Returns column definitions for a schema id.
    #[must_use]
    pub fn columns(&self, schema_id: &str) -> Option<&[TableColumn]> {
        self.by_schema_id.get(schema_id).map(Vec::as_slice)
    }

    /// Returns the custom renderer for a schema id.
    #[must_use]
    pub fn custom(&self, schema_id: &str) -> Option<&HumanViewRenderer> {
        self.custom_by_schema_id.get(schema_id)
    }

    /// Whether any human view (column-based or custom) is registered for a
    /// schema id. Such a view selects its own columns from the full payload, so
    /// callers must not pre-project the data before handing it to the renderer.
    #[must_use]
    pub fn has_view(&self, schema_id: &str) -> bool {
        self.by_schema_id.contains_key(schema_id)
            || self.custom_by_schema_id.contains_key(schema_id)
    }
}

static GLOBAL_HUMAN_VIEW_REGISTRY: OnceLock<RwLock<HumanViewRegistry>> = OnceLock::new();

fn global_human_view_registry() -> &'static RwLock<HumanViewRegistry> {
    GLOBAL_HUMAN_VIEW_REGISTRY.get_or_init(|| RwLock::new(HumanViewRegistry::new()))
}

/// Registers a process-global column view.
pub fn register_global_human_view(view: HumanViewDef) {
    let mut registry = global_human_view_registry()
        .write()
        .unwrap_or_else(|poisoned| poisoned.into_inner());
    registry.register(view);
}

/// Registers a process-global custom human renderer.
pub fn register_global_human_view_func(
    schema_id: impl Into<String>,
    render: impl Fn(&Value) -> String + Send + Sync + 'static,
) {
    let mut registry = global_human_view_registry()
        .write()
        .unwrap_or_else(|poisoned| poisoned.into_inner());
    registry.register_func(schema_id, render);
}

/// Looks up global columns for a schema id.
#[must_use]
pub fn lookup_global_human_view_columns(schema_id: &str) -> Option<Vec<TableColumn>> {
    global_human_view_registry()
        .read()
        .unwrap_or_else(|poisoned| poisoned.into_inner())
        .columns(schema_id)
        .map(<[TableColumn]>::to_vec)
}

/// Looks up a global custom renderer for a schema id.
#[must_use]
pub fn lookup_global_human_view_func(schema_id: &str) -> Option<HumanViewRenderer> {
    global_human_view_registry()
        .read()
        .unwrap_or_else(|poisoned| poisoned.into_inner())
        .custom(schema_id)
        .cloned()
}

/// Returns a snapshot of the process-global human view registry.
#[must_use]
pub fn global_human_view_registry_snapshot() -> HumanViewRegistry {
    global_human_view_registry()
        .read()
        .unwrap_or_else(|poisoned| poisoned.into_inner())
        .clone()
}

/// Renders an envelope using generic human output.
///
/// There's no field-selection concept at this entry point, so a no-view
/// array/object falls back to alphabetical key order — use
/// [`render_human_with_registry_selected`] when a `--fields`/`default_fields`
/// value is available, so its order can drive column order too.
#[must_use]
pub fn render_human(envelope: &Envelope) -> String {
    render_human_with_view(envelope, None, "")
}

/// Renders an envelope using a human view registry.
#[must_use]
pub fn render_human_with_registry(envelope: &Envelope, registry: &HumanViewRegistry) -> String {
    let system = envelope
        .metadata
        .as_ref()
        .map(|metadata| metadata.system.as_str())
        .unwrap_or_default();
    render_human_with_registry_for_schema(envelope, registry, system)
}

/// Renders an envelope using registry entries for a specific schema id.
///
/// Shows every column of the registered view. Use
/// [`render_human_with_registry_selected`] to narrow the columns to a field
/// selection.
#[must_use]
pub fn render_human_with_registry_for_schema(
    envelope: &Envelope,
    registry: &HumanViewRegistry,
    schema_id: &str,
) -> String {
    render_human_with_registry_selected(envelope, registry, schema_id, "")
}

/// Renders an envelope using a registered view, narrowed to `fields`.
///
/// `fields` uses the same comma-separated syntax as `--fields`: an empty
/// string, `all`, or `*` keeps every column; otherwise only the view columns
/// whose `field` is listed are shown. A custom view renderer receives the full
/// data and ignores `fields`.
#[must_use]
pub fn render_human_with_registry_selected(
    envelope: &Envelope,
    registry: &HumanViewRegistry,
    schema_id: &str,
    fields: &str,
) -> String {
    if let Some(error) = &envelope.error {
        return format!("Error: {}\n", error.message);
    }
    if let Some(data) = &envelope.data
        && let Some(custom) = registry.custom(schema_id)
    {
        return custom.render(data);
    }
    match registry.columns(schema_id) {
        Some(columns) => {
            let selected = select_columns(columns, fields);
            render_human_with_view(envelope, Some(&selected), fields)
        }
        None => render_human_with_view(envelope, None, fields),
    }
}

/// Narrows and reorders view columns to a `--fields`-style selection. An
/// empty string, `all`, or `*` keeps every column in its declared order;
/// otherwise columns are chosen and ordered by the comma-separated list
/// (deduplicated, first occurrence wins) — a name with no matching column is
/// silently skipped, so a view still only ever shows its own declared
/// fields.
fn select_columns(columns: &[TableColumn], fields: &str) -> Vec<TableColumn> {
    let fields = fields.trim();
    if fields.is_empty() || fields == "all" || fields == "*" {
        return columns.to_vec();
    }
    let mut seen = BTreeSet::new();
    fields
        .split(',')
        .map(str::trim)
        .filter(|part| !part.is_empty() && seen.insert(*part))
        .filter_map(|name| columns.iter().find(|column| column.field == name).cloned())
        .collect()
}

/// Renders an envelope using explicit table columns.
///
/// `columns`, when `Some`, is expected to already be `--fields`-selected and
/// ordered (applied by callers such as
/// [`render_human_with_registry_selected`] before this function runs) — this
/// function does not re-apply `fields` to it. `fields` is only read here when
/// `columns` is `None`, to give the dynamically-derived, no-view column
/// catalog the same field selection and order a view would have gotten. Pass
/// `""` when no field-selection value is available.
#[must_use]
pub fn render_human_with_view(
    envelope: &Envelope,
    columns: Option<&[TableColumn]>,
    fields: &str,
) -> String {
    // Errors render on their own; success output gets the data body plus, when
    // present, a "Next steps:" footer built from the envelope's next_actions
    // (these otherwise appear only in JSON/TOON).
    if let Some(error) = &envelope.error {
        let mut out = format!("Error: {}\n", error.message);
        if let Some(fix) = &envelope.fix {
            out.push_str("Fix: ");
            out.push_str(fix);
            out.push('\n');
        }
        return out;
    }
    let available_width = terminal_width();
    let (mut body, notes) = match &envelope.data {
        None => ("(no data)\n".to_owned(), RenderNotes::default()),
        Some(data) => render_data_body(
            data,
            columns,
            fields,
            available_width,
            envelope.pagination.as_ref(),
        ),
    };
    // Footers are appended in place: the common no-footer path leaves `body`
    // untouched (no realloc/copy), and non-empty content is written directly
    // into it (no per-footer temporaries).
    append_render_notes(&mut body, &notes);
    if !notes.pagination_shown {
        // `envelope.data` already reflects the fully piped result (filter ->
        // paginate -> expr -> fields), so its length is what this non-table
        // path actually rendered — unlike `pagination.count`, which is only
        // the pre-`--expr` slice size and can go stale once `--expr` reshapes
        // the array (mirrors the same fix in `render_table`).
        let shown = envelope
            .data
            .as_ref()
            .and_then(Value::as_array)
            .and_then(|items| i64::try_from(items.len()).ok());
        append_pagination_summary(&mut body, envelope.pagination.as_ref(), shown);
    }
    append_next_actions(&mut body, &envelope.next_actions);
    body
}

/// Render just the data portion of a success envelope (no next-steps footer).
fn render_data_body(
    data: &Value,
    columns: Option<&[TableColumn]>,
    fields: &str,
    available_width: usize,
    pagination: Option<&PaginationMeta>,
) -> (String, RenderNotes) {
    if let Some(columns) = columns {
        return match data {
            Value::Array(items) => {
                render_array_with_columns(items, columns, available_width, pagination)
            }
            Value::Object(map) => render_object_with_columns(map, columns, available_width),
            Value::Null | Value::Bool(_) | Value::Number(_) | Value::String(_) => {
                (format!("{}\n", format_value(data)), RenderNotes::default())
            }
        };
    }
    match data {
        Value::Array(items) => render_array(items, fields, available_width, pagination),
        Value::Object(map) => {
            let columns = dynamic_columns(fields, || map.keys().cloned().collect());
            render_object_with_columns(map, &columns, available_width)
        }
        other => (
            format!("{}\n", format_plain_value(other)),
            RenderNotes::default(),
        ),
    }
}

/// Builds the column catalog for data with no registered view: when `fields`
/// names specific fields (not empty/`all`/`*`), columns are derived from that
/// list, in the order given (deduplicated) — the same order source a
/// registered view's `--fields` selection uses (see [`select_columns`]).
/// Otherwise falls back to `natural_keys()` sorted alphabetically, since a
/// bare JSON object has no other order signal to offer.
fn dynamic_columns(fields: &str, natural_keys: impl FnOnce() -> Vec<String>) -> Vec<TableColumn> {
    let fields = fields.trim();
    if fields.is_empty() || fields == "all" || fields == "*" {
        let mut keys = natural_keys();
        keys.sort();
        return keys
            .into_iter()
            .map(|key| TableColumn::new(key.clone(), key))
            .collect();
    }
    let mut seen = BTreeSet::new();
    fields
        .split(',')
        .map(str::trim)
        .filter(|part| !part.is_empty() && seen.insert(*part))
        .map(|field| TableColumn::new(field, field))
        .collect()
}

/// True when at least one item has a JSON number at `field`, and no item
/// with a present, non-null value at `field` holds anything else.
fn column_is_all_numeric(items: &[Value], field: &str) -> bool {
    let mut saw_number = false;
    for item in items {
        match item
            .as_object()
            .and_then(|map| resolve_field_path(map, field))
        {
            Some(Value::Number(_)) => saw_number = true,
            Some(Value::Null) | None => {}
            Some(_) => return false,
        }
    }
    saw_number
}

/// Appends footer hints for truncated cells and/or hidden columns to `out`
/// (a no-op when neither happened). Mirrors `append_next_actions`: writes
/// directly into `out` rather than building a separate string.
fn append_render_notes(out: &mut String, notes: &RenderNotes) {
    // `--fields` only ever selects among top-level declared columns: it can
    // drop a `TableColumn::nested` column entirely, but can't narrow what
    // shows *inside* one. Suggesting it as a fix once any of the reported
    // narrowing happened inside a nested block would be wrong — there's no
    // flag that reaches that fine-grained, so `--json` is the only real
    // remedy in that case.
    let fields_helps = !notes.nested_narrowing;
    if notes.truncated {
        if fields_helps {
            out.push_str(
                "\nOutput truncated to fit the display width — use --fields to show fewer columns, or --json for full values.\n",
            );
        } else {
            out.push_str(
                "\nOutput truncated to fit the display width — use --json for full values.\n",
            );
        }
    }
    if !notes.hidden_columns.is_empty() {
        let suggestion = if fields_helps {
            "use --fields to choose columns, or --json for full output"
        } else {
            "use --json for full output"
        };
        out.push_str(&format!(
            "\n{} column{} hidden to fit the display width ({}) — {suggestion}.\n",
            notes.hidden_columns.len(),
            if notes.hidden_columns.len() == 1 {
                ""
            } else {
                "s"
            },
            notes.hidden_columns.join(", "),
        ));
    }
}

/// Appends a one-line pagination summary to `out` (a no-op when the response
/// wasn't paginated). Unlike `next_actions`, this always shows the underlying
/// facts even on the last page, where there's no follow-up command to
/// suggest.
///
/// Only a fallback: when the data rendered as a table, `render_table` already
/// merged these same facts into its `(N of M rows, ...)` footer
/// (`RenderNotes::pagination_shown` signals that to
/// [`render_human_with_view`]), so this only actually prints anything for a
/// paginated response that *didn't* render as a table (e.g. a bare array of
/// scalars) — otherwise the two would repeat the same count/offset/limit on
/// consecutive lines.
///
/// `shown` is the caller's actual rendered item count (from `envelope.data`,
/// post-pipeline), used in place of `pagination.count` — which is only the
/// pre-`--expr` slice size and can go stale once `--expr` reshapes the array
/// after pagination ran (mirrors the same fix in `render_table`). `None`
/// means `--expr` reshaped the data into something that's no longer even an
/// array (e.g. `length(@)` turning it into a number) — pagination still ran,
/// but there's no rendered row count left to describe, so this falls back to
/// a more neutral line instead of a "Showing N of M" claim that would no
/// longer match what's actually displayed above it.
fn append_pagination_summary(
    out: &mut String,
    pagination: Option<&PaginationMeta>,
    shown: Option<i64>,
) {
    let Some(pagination) = pagination else {
        return;
    };
    match shown {
        Some(count) => out.push_str(&format!(
            "\nShowing {count} of {} (offset {}, limit {})\n",
            pagination.total, pagination.offset, pagination.limit
        )),
        None => out.push_str(&format!(
            "\n(pagination: {} total, offset {}, limit {})\n",
            pagination.total, pagination.offset, pagination.limit
        )),
    }
}

/// Append a "Next steps:" footer listing suggested follow-up commands to `out`
/// (a no-op when there are none). Each action shows its command template with
/// any known param values substituted into their `<placeholder>` (params
/// without a known value, e.g. required-only hints, are shown as-is), followed
/// by the description beneath it. Writes directly into `out` to avoid
/// per-action temporaries.
fn append_next_actions(out: &mut String, actions: &[NextAction]) {
    if actions.is_empty() {
        return;
    }
    out.push_str("\nNext steps:\n");
    for action in actions {
        out.push_str("  ");
        out.push_str(&substitute_known_params(&action.command, &action.params));
        out.push_str("\n      ");
        out.push_str(&action.description);
        out.push('\n');
    }
}

/// Fills a `NextAction` command template with any params that carry a known
/// concrete `value` — e.g. `"domain quote <domain>"` with
/// `params["domain"].value == Some("example.com")` becomes
/// `"domain quote example.com"`. A param's placeholder is its key wrapped in
/// angle brackets (`<domain>`); params without a known value (required-only
/// hints) are left as literal placeholder text for the user to fill in.
/// Borrows `command` as-is (no allocation) when nothing has a known value.
fn substitute_known_params<'cmd>(
    command: &'cmd str,
    params: &HashMap<String, NextActionParam>,
) -> Cow<'cmd, str> {
    let mut command = Cow::Borrowed(command);
    for (key, param) in params {
        if let Some(value) = &param.value {
            let placeholder = format!("<{key}>");
            if command.contains(&placeholder) {
                command = Cow::Owned(command.replace(&placeholder, value));
            }
        }
    }
    command
}

/// Upper bound on a `no_truncate` column's width, even though it otherwise
/// skips the normal 40-char cap. Prevents a pathologically long field value
/// (not expected in practice, but not guaranteed by any schema) from padding
/// every row and the separator line out to an unusable or memory-heavy width.
///
/// This bounds runtime *values*, not the column *header*: width is always
/// widened back up to `column.header.len()` after the cap is applied, so a
/// header can never be truncated or misaligned even in the (unrealistic)
/// case where it exceeds `NO_TRUNCATE_MAX_WIDTH` itself. Headers are static,
/// developer-authored labels, not the pathological runtime data this cap
/// guards against.
const NO_TRUNCATE_MAX_WIDTH: usize = 4096;

/// Space between adjacent rendered columns. Must match the gutter
/// `render_table` actually writes, since width-fitting math (how much room
/// is left for column content) has to agree with what gets printed.
const COLUMN_GUTTER: usize = 2;

/// Indent applied to a nested table/property-bag block under a parent
/// object's field. Matches the two-space depth-step the TOON encoder already
/// uses (`crate::output::toon`'s `push_line`), for a consistent look across
/// human and TOON nested rendering.
const NESTED_INDENT: &str = "  ";

/// Detects how wide to render human-output tables and guides.
///
/// An interactive terminal gets its live width (via `termimad`); anything
/// else (pipes, files, CI) gets a fixed `80` so non-interactive `--human`
/// output stays deterministic. Floored at `20` in case a terminal reports an
/// unusably small or zero width.
#[must_use]
pub(crate) fn terminal_width() -> usize {
    if std::io::stdout().is_terminal() {
        usize::from(termimad::terminal_size().0).max(20)
    } else {
        80
    }
}

/// Signals produced while rendering a table body, used to build human-output
/// footer hints. `Default` means nothing was hidden or shortened.
#[derive(Default)]
struct RenderNotes {
    /// Whether any cell was shortened to fit the terminal.
    truncated: bool,
    /// Headers of columns dropped entirely because there wasn't room for
    /// them, in their original declared/requested order (the order they
    /// would have appeared in the table, had they fit) — not reverse
    /// priority order.
    hidden_columns: Vec<String>,
    /// Whether any of the truncation/hiding captured above happened inside a
    /// nested child block (a `TableColumn::nested` column's own table or
    /// property bag) rather than at this level's own top-level columns.
    /// `--fields` only ever selects among top-level declared columns — it
    /// can drop a nested column entirely, but can't narrow what's shown
    /// *inside* one — so [`append_render_notes`] must not suggest `--fields`
    /// as a fix when this is set, even though `hidden_columns`/`truncated`
    /// are otherwise reported identically either way.
    nested_narrowing: bool,
    /// Whether the table footer already merged in the pagination summary
    /// (`render_table`'s `(N of M rows, offset O, limit L)` line) — so
    /// [`render_human_with_view`] doesn't also append the standalone
    /// `append_pagination_summary` line and duplicate the same facts.
    pagination_shown: bool,
}

/// Chooses how many leading columns (priority order, most important first),
/// each contributing at least `min_widths[i]`, fit in `available_width` — so
/// lower-priority trailing columns can be dropped when the terminal is too
/// narrow for all of them. `min_widths[i]` should be the column's header
/// length for a column that can still shrink, or its full natural width for
/// one that can't (e.g. `no_truncate`) — using a shrinkable column's header
/// length here lets it still be counted as fitting even though its eventual
/// rendered width may be larger. Always keeps at least one column, even if
/// it alone exceeds `available_width`.
fn columns_fitting_width(min_widths: &[usize], available_width: usize) -> usize {
    let mut used = 0_usize;
    let mut kept = 0_usize;
    for (index, &min_width) in min_widths.iter().enumerate() {
        let gutter = if index == 0 { 0 } else { COLUMN_GUTTER };
        let next_used = used + gutter + min_width;
        if next_used > available_width && kept > 0 {
            break;
        }
        used = next_used;
        kept += 1;
    }
    kept
}

/// Fits `natural` (fully-untruncated) column widths into `available_width`.
///
/// `no_truncate` columns are never shrunk (they keep their natural width
/// unconditionally — that's the whole point of the flag) and their width is
/// reserved out of the budget up front. The remaining columns are never
/// shrunk below their header length, and share whatever budget is left
/// beyond that, smallest-need-first, so a column that wants only a little
/// gets exactly that instead of an equal-but-wasteful split.
///
/// Returns the fitted widths and whether any truncatable column ended up
/// narrower than its natural width (i.e. some cell will actually be cut).
fn fit_column_widths(
    headers: &[usize],
    natural: &[usize],
    no_truncate: &[bool],
    available_width: usize,
) -> (Vec<usize>, bool) {
    let mut widths = natural.to_vec();
    let truncatable: Vec<usize> = (0..no_truncate.len())
        .filter(|&index| !no_truncate[index])
        .collect();
    if truncatable.is_empty() {
        return (widths, false);
    }
    let gutters = COLUMN_GUTTER * headers.len().saturating_sub(1);
    let reserved: usize = (0..no_truncate.len())
        .filter(|&index| no_truncate[index])
        .map(|index| natural[index])
        .sum();
    let budget = available_width
        .saturating_sub(gutters)
        .saturating_sub(reserved);
    let header_floor: usize = truncatable.iter().map(|&index| headers[index]).sum();
    for &index in &truncatable {
        widths[index] = headers[index];
    }
    let mut leftover = budget.saturating_sub(header_floor);
    let mut needy: Vec<usize> = truncatable
        .iter()
        .copied()
        .filter(|&index| natural[index] > headers[index])
        .collect();
    needy.sort_by_key(|&index| natural[index] - headers[index]);
    // Smallest-need-first, take exactly what's wanted or whatever's left,
    // whichever is less. Deliberately not an even split of `leftover` across
    // the remaining columns: dividing first and taking `min(wants, share)`
    // can floor a small want to zero when `leftover < remaining columns`,
    // denying it entirely while a later, greedier column absorbs the
    // remainder — worse than just letting small wants claim what they need
    // outright before anyone larger gets a turn.
    for &index in &needy {
        let wants = natural[index] - headers[index];
        let take = wants.min(leftover);
        widths[index] += take;
        leftover -= take;
    }
    let truncated = truncatable
        .iter()
        .any(|&index| widths[index] < natural[index]);
    (widths, truncated)
}

fn render_array_with_columns(
    items: &[Value],
    columns: &[TableColumn],
    available_width: usize,
    pagination: Option<&PaginationMeta>,
) -> (String, RenderNotes) {
    if items.is_empty() || columns.is_empty() {
        // Empty columns happens when every item is `{}` (the no-view
        // dynamic catalog has no keys to show) or a view's `--fields`
        // filtered out every declared column — either way there's nothing
        // to build a table from, so fall back to the same message used for
        // no items at all rather than rendering a blank header/rows table.
        return ("(no results)\n".to_owned(), RenderNotes::default());
    }
    if !items.iter().all(Value::is_object) {
        return (render_array_lines(items), RenderNotes::default());
    }
    // Natural widths (and rows) are computed for every original column
    // before deciding what to hide: a `no_truncate` column never shrinks
    // below its natural width, so the hiding decision has to know that real
    // requirement — using just its header length here could keep a
    // low-priority trailing column that would never have fit anyway,
    // producing an overflow that hiding it would have avoided.
    let header_lens: Vec<usize> = columns.iter().map(|column| column.header.len()).collect();
    let no_truncate_all: Vec<bool> = columns.iter().map(|column| column.no_truncate).collect();
    let mut natural = header_lens.clone();
    let rows: Vec<Vec<String>> = items
        .iter()
        .map(|item| {
            columns
                .iter()
                .enumerate()
                .map(|(index, column)| {
                    let value = item
                        .as_object()
                        .and_then(|map| resolve_field_path(map, &column.field))
                        .map_or_else(String::new, format_value);
                    let cap = if column.no_truncate {
                        NO_TRUNCATE_MAX_WIDTH
                    } else {
                        usize::MAX
                    };
                    natural[index] = natural[index].max(value.len().min(cap));
                    value
                })
                .collect::<Vec<_>>()
        })
        .collect();

    let min_widths: Vec<usize> = (0..columns.len())
        .map(|index| {
            if no_truncate_all[index] {
                natural[index]
            } else {
                header_lens[index]
            }
        })
        .collect();
    let mut kept = columns_fitting_width(&min_widths, available_width);

    // Hiding a column is preferred over truncating a cell: if the survivors
    // still don't fit their natural width, keep dropping the lowest-priority
    // one and re-fitting, until either everyone remaining fits in full or
    // only one column is left (which always stays, however it fits).
    let (fitted, truncated) = loop {
        let (fitted, truncated) = fit_column_widths(
            &header_lens[..kept],
            &natural[..kept],
            &no_truncate_all[..kept],
            available_width,
        );
        if !truncated || kept <= 1 {
            break (fitted, truncated);
        }
        kept -= 1;
    };

    let hidden_columns = columns[kept..]
        .iter()
        .map(|column| column.header.clone())
        .collect::<Vec<_>>();
    let columns = &columns[..kept];
    let rows: Vec<Vec<String>> = rows
        .into_iter()
        .map(|row| row.into_iter().take(kept).collect())
        .collect();

    let table = render_table(
        &columns
            .iter()
            .map(|column| column.header.clone())
            .collect::<Vec<_>>(),
        &fitted,
        &columns
            .iter()
            .map(|column| column.align)
            .collect::<Vec<_>>(),
        &rows,
        pagination,
    );
    (
        table,
        RenderNotes {
            truncated,
            hidden_columns,
            nested_narrowing: false,
            pagination_shown: pagination.is_some(),
        },
    )
}

fn render_object_with_columns(
    map: &serde_json::Map<String, Value>,
    columns: &[TableColumn],
    available_width: usize,
) -> (String, RenderNotes) {
    if map.is_empty() || columns.is_empty() {
        // Empty columns happens the same way it does in
        // `render_array_with_columns`: a view's `--fields` filtered out
        // every declared column. Nothing to render either way, so this
        // reports the same "(no data)" a genuinely empty object gets,
        // rather than an unlabeled blank line.
        return ("(no data)\n".to_owned(), RenderNotes::default());
    }
    let mut out = String::new();
    let mut notes = RenderNotes::default();
    for column in columns {
        let value = resolve_field_path(map, &column.field);
        match (&column.nested, value) {
            (Some(nested_columns), Some(value)) if is_nestable(value) => {
                out.push_str(&format!("{}:\n", column.header));
                let child_width = available_width.saturating_sub(NESTED_INDENT.len());
                let nested_pagination = match value {
                    Value::Array(_) => {
                        resolve_field_parent(map, &column.field).and_then(resolve_nested_pagination)
                    }
                    _ => None,
                };
                let (block, child_notes) = render_nested_value(
                    value,
                    nested_columns,
                    child_width,
                    nested_pagination.as_ref(),
                );
                out.push_str(&indent_block(&block, NESTED_INDENT));
                if child_notes.truncated
                    || !child_notes.hidden_columns.is_empty()
                    || child_notes.nested_narrowing
                {
                    notes.nested_narrowing = true;
                }
                notes.truncated |= child_notes.truncated;
                notes.hidden_columns.extend(
                    child_notes
                        .hidden_columns
                        .into_iter()
                        .map(|hidden| format!("{} > {hidden}", column.header)),
                );
            }
            (_, value) => {
                let value_str = value.map_or_else(String::new, format_value);
                out.push_str(&format!("{}: {value_str}\n", column.header));
            }
        }
    }
    (out, notes)
}

fn render_array(
    items: &[Value],
    fields: &str,
    available_width: usize,
    pagination: Option<&PaginationMeta>,
) -> (String, RenderNotes) {
    if items.is_empty() {
        return ("(no results)\n".to_owned(), RenderNotes::default());
    }
    let Some(Value::Object(first_map)) = items.first() else {
        return (render_array_lines(items), RenderNotes::default());
    };
    if !items.iter().all(Value::is_object) {
        return (render_array_lines(items), RenderNotes::default());
    }
    let columns: Vec<TableColumn> = dynamic_columns(fields, || first_map.keys().cloned().collect())
        .into_iter()
        .map(|column| {
            if column_is_all_numeric(items, &column.field) {
                column.align(Alignment::Right)
            } else {
                column
            }
        })
        .collect();
    render_array_with_columns(items, &columns, available_width, pagination)
}

fn render_array_lines(items: &[Value]) -> String {
    let mut out = String::new();
    for item in items {
        out.push_str(&format!("{}\n", format_plain_value(item)));
    }
    out
}

/// Pads `text` to `width`, on the left for `Alignment::Right` and on the
/// right otherwise — matching how the header row is padded so a column's
/// header and cells share the same alignment.
fn pad_column(text: &str, width: usize, alignment: Alignment) -> String {
    match alignment {
        Alignment::Left => format!("{text:<width$}"),
        Alignment::Right => format!("{text:>width$}"),
    }
}

fn render_table(
    headers: &[String],
    widths: &[usize],
    alignments: &[Alignment],
    rows: &[Vec<String>],
    pagination: Option<&PaginationMeta>,
) -> String {
    let mut out = String::new();
    for (index, header) in headers.iter().enumerate() {
        if index > 0 {
            out.push_str("  ");
        }
        out.push_str(&pad_column(
            &header.to_uppercase(),
            widths[index],
            alignments[index],
        ));
    }
    out.push('\n');
    for (index, width) in widths.iter().enumerate() {
        if index > 0 {
            out.push_str("  ");
        }
        out.push_str(&"-".repeat(*width));
    }
    out.push('\n');
    for row in rows {
        for (index, value) in row.iter().enumerate() {
            if index > 0 {
                out.push_str("  ");
            }
            out.push_str(&pad_column(
                &truncate(value, widths[index]),
                widths[index],
                alignments[index],
            ));
        }
        out.push('\n');
    }
    // Merge the pagination facts into this footer rather than letting
    // `append_pagination_summary` print a second, redundant line right below
    // it — both would otherwise state the same shown/total count. The shown
    // count comes from `rows.len()`, not `pagination.count`: a later
    // pipeline step (`--expr`) can still reshape `envelope.data` after
    // pagination ran, so `rows.len()` is what's actually rendered above,
    // while `total`/`offset`/`limit` stay pagination's own facts.
    match pagination {
        Some(pagination) => out.push_str(&format!(
            "\n({} of {} rows, offset {}, limit {})\n",
            rows.len(),
            pagination.total,
            pagination.offset,
            pagination.limit
        )),
        None => out.push_str(&format!("\n({} rows)\n", rows.len())),
    }
    out
}

/// Resolves a column's (possibly dotted) field path against an object,
/// walking down through nested objects one segment at a time — e.g.
/// `"parameters.items"` reaches `map["parameters"]["items"]`.
///
/// Returns `None` when: `field` is empty; any segment (including a
/// leading/trailing/doubled `.`) is empty; an intermediate or leaf segment is
/// missing; or an intermediate segment's value is not an object. The leaf
/// segment's value is returned as-is whatever its `Value` variant is —
/// callers decide what to do with that.
fn resolve_field_path<'value>(
    map: &'value serde_json::Map<String, Value>,
    field: &str,
) -> Option<&'value Value> {
    let mut segments = field.split('.');
    let first = segments.next()?;
    if first.is_empty() {
        return None;
    }
    let mut current = map.get(first)?;
    for segment in segments {
        if segment.is_empty() {
            return None;
        }
        current = current.as_object()?.get(segment)?;
    }
    Some(current)
}

/// Resolves the object that directly contains `field`'s leaf segment — e.g.
/// for `"parameters.items"`, the object at `"parameters"` (the one whose keys
/// include `"items"` as a direct child). A field with no `.` has `map` itself
/// as its parent, since the leaf is already one of `map`'s direct keys.
///
/// Used to reach a nested array's `pagination` sibling (see
/// [`resolve_nested_pagination`]) that `resolve_field_path` alone can't see,
/// since that function only ever returns the leaf.
fn resolve_field_parent<'value>(
    map: &'value serde_json::Map<String, Value>,
    field: &str,
) -> Option<&'value serde_json::Map<String, Value>> {
    match field.rsplit_once('.') {
        None => Some(map),
        Some((parent_path, _leaf)) => resolve_field_path(map, parent_path)?.as_object(),
    }
}

/// Resolves a `pagination` field on `parent` — the same object that directly
/// contains a [`TableColumn::nested`] column's array — as a [`PaginationMeta`],
/// so nested tables get the exact same `"(N of M rows, offset O, limit L)"`
/// footer a top-level paginated array gets.
fn resolve_nested_pagination(parent: &serde_json::Map<String, Value>) -> Option<PaginationMeta> {
    serde_json::from_value(parent.get("pagination")?.clone()).ok()
}

/// Prefixes every non-empty line of `block` with `indent`, leaving blank
/// lines (e.g. the blank line before a table's `(N rows)` footer) bare so no
/// line ever carries trailing-whitespace-only indent. Round-trips a block's
/// existing single-trailing-newline convention.
fn indent_block(block: &str, indent: &str) -> String {
    block
        .lines()
        .map(|line| {
            if line.is_empty() {
                line.to_owned()
            } else {
                format!("{indent}{line}")
            }
        })
        .collect::<Vec<_>>()
        .join("\n")
        + "\n"
}

/// Whether `value` is a shape [`TableColumn::nested`] can render as a child
/// block: a single object, or an array whose items are all objects (an empty
/// array trivially qualifies, rendering as an indented "no results"). Gates
/// entry into nested rendering in [`render_object_with_columns`] so a column
/// with `.nested(...)` set is a true no-op — the exact same single-line
/// `format_value` rendering an un-opted-in column would have produced —
/// whenever the runtime value doesn't actually have this shape (a scalar, or
/// an array mixing objects with non-objects).
fn is_nestable(value: &Value) -> bool {
    matches!(value, Value::Object(_))
        || matches!(value, Value::Array(items) if items.iter().all(Value::is_object))
}

/// Renders a nested column's resolved value as a child block, reusing the
/// same renderers a top-level array/object would use, just at a narrowed
/// width. Only called once [`is_nestable`] has confirmed `value`'s shape, so
/// the array/object arms below are the only ones a real caller reaches; the
/// scalar fallback keeps this function total on its own.
fn render_nested_value(
    value: &Value,
    nested_columns: &[TableColumn],
    available_width: usize,
    pagination: Option<&PaginationMeta>,
) -> (String, RenderNotes) {
    match value {
        Value::Array(items) => {
            render_array_with_columns(items, nested_columns, available_width, pagination)
        }
        Value::Object(map) => render_object_with_columns(map, nested_columns, available_width),
        other => (format!("{}\n", format_value(other)), RenderNotes::default()),
    }
}

fn format_value(value: &Value) -> String {
    match value {
        Value::Null => String::new(),
        Value::Bool(true) => "yes".to_owned(),
        Value::Bool(false) => "no".to_owned(),
        Value::Number(number) => format_number(number),
        Value::String(value) => value.clone(),
        Value::Array(items) => items
            .iter()
            .map(format_value)
            .collect::<Vec<_>>()
            .join(", "),
        Value::Object(_) => serde_json::to_string(value).unwrap_or_else(|_| "{}".to_owned()),
    }
}

fn format_plain_value(value: &Value) -> String {
    match value {
        Value::Null => "<nil>".to_owned(),
        Value::Bool(value) => value.to_string(),
        Value::Number(number) => format_number(number),
        Value::String(value) => value.clone(),
        Value::Array(items) => {
            let values = items
                .iter()
                .map(format_plain_value)
                .collect::<Vec<_>>()
                .join(" ");
            format!("[{values}]")
        }
        Value::Object(object) => {
            let mut pairs = object
                .iter()
                .map(|(key, value)| (key.clone(), value.clone()))
                .collect::<Vec<_>>();
            pairs.sort_by(|left, right| left.0.cmp(&right.0));
            let object = pairs
                .into_iter()
                .collect::<serde_json::Map<String, Value>>();
            serde_json::to_string(&Value::Object(object)).unwrap_or_else(|_| "{}".to_owned())
        }
    }
}

fn truncate(value: &str, width: usize) -> String {
    if value.len() <= width {
        return value.to_owned();
    }
    if width <= 3 {
        return value.chars().take(width).collect();
    }
    let mut out = value.chars().take(width - 3).collect::<String>();
    out.push_str("...");
    out
}

fn format_number(number: &serde_json::Number) -> String {
    number.to_string()
}

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

    #[test]
    fn format_plain_value_round_trips_a_bare_string_verbatim() {
        // No quoting/escaping — the exact convention `raw_output` bypass
        // relies on to render a `CommandResult` string byte-for-byte.
        assert_eq!(
            format_plain_value(&Value::String("some\nverbatim\ntext".to_owned())),
            "some\nverbatim\ntext"
        );
    }

    #[test]
    fn human_output_appends_next_steps_footer() {
        let envelope = Envelope::success(json!({ "domain": "example.com" }), "domain")
            .with_next_actions(vec![NextAction::new(
                "domain purchase --quote-token <token> --agree --confirm",
                "Register at the quoted price",
            )]);
        let out = render_human(&envelope);
        // Data still renders as before…
        assert!(out.contains("domain: example.com"), "{out}");
        // …followed by a Next steps footer with the command and its description.
        assert!(out.contains("\nNext steps:\n"), "{out}");
        assert!(
            out.contains("domain purchase --quote-token <token> --agree --confirm"),
            "{out}"
        );
        assert!(out.contains("Register at the quoted price"), "{out}");
    }

    #[test]
    fn human_output_substitutes_known_next_action_params() {
        let envelope = Envelope::success(json!({ "domain": "example.com" }), "domain")
            .with_next_actions(vec![
                NextAction::new(
                    "domain purchase --quote-token <quote-token> --agree --confirm",
                    "Register at the quoted price",
                )
                .with_param("quote-token", NextActionParam::value("abc-123")),
            ]);
        let out = render_human(&envelope);
        assert!(
            out.contains("domain purchase --quote-token abc-123 --agree --confirm"),
            "{out}"
        );
        assert!(!out.contains("<quote-token>"), "{out}");
    }

    #[test]
    fn human_output_leaves_placeholder_without_a_known_value() {
        let envelope = Envelope::success(json!({ "domain": "example.com" }), "domain")
            .with_next_actions(vec![
                NextAction::new("domain quote <domain>", "Price a registration")
                    .with_param("domain", NextActionParam::required()),
            ]);
        let out = render_human(&envelope);
        assert!(out.contains("domain quote <domain>"), "{out}");
    }

    #[test]
    fn human_output_has_no_footer_without_next_actions() {
        let envelope = Envelope::success(json!({ "domain": "example.com" }), "domain");
        let out = render_human(&envelope);
        assert!(out.contains("domain: example.com"), "{out}");
        assert!(
            !out.contains("Next steps"),
            "no footer when there are no actions: {out}"
        );
    }

    #[test]
    fn error_output_has_no_next_steps_footer() {
        // An error envelope carries no next_actions and must render only the error.
        let envelope = Envelope::error("ERROR", "boom", "domain");
        let out = render_human(&envelope);
        assert!(out.starts_with("Error:"), "{out}");
        assert!(!out.contains("Next steps"), "{out}");
        assert!(!out.contains("Fix:"), "{out}");
    }

    #[test]
    fn error_output_appends_fix_line() {
        let envelope =
            Envelope::error("AUTH_REQUIRED", "not logged in", "auth").with_fix("Run auth login");
        let out = render_human(&envelope);
        assert_eq!(out, "Error: not logged in\nFix: Run auth login\n");
    }

    #[test]
    fn no_truncate_column_keeps_long_values_intact() {
        let long_url = "https://example.com/legal/agreements/registration-agreement-v2";
        assert!(long_url.len() > 40, "fixture must exceed the default cap");
        let items = vec![json!({ "title": long_url, "url": long_url })];
        let columns = vec![
            // Declared first (higher priority) so it survives hide-before-
            // truncate rather than the lower-priority title column
            // absorbing truncation instead — with only two columns, any
            // truncation now cascades to hiding the lower-priority one.
            TableColumn::new("url", "URL").no_truncate(true),
            TableColumn::new("title", "Title"),
        ];

        let (out, notes) = render_array_with_columns(&items, &columns, 80, None);

        assert!(
            out.contains(long_url),
            "no_truncate column must keep the full value: {out}"
        );
        assert!(
            !out.contains("..."),
            "hiding the lower-priority column avoided any truncation: {out}"
        );
        assert_eq!(
            notes.hidden_columns,
            vec!["Title".to_owned()],
            "the lower-priority truncatable column is hidden rather than shown truncated: {out}"
        );
    }

    #[test]
    fn no_truncate_column_still_caps_pathologically_long_values() {
        let huge_value = "x".repeat(NO_TRUNCATE_MAX_WIDTH * 2);
        let items = vec![json!({ "url": huge_value })];
        let columns = vec![TableColumn::new("url", "URL").no_truncate(true)];

        let (out, _notes) = render_array_with_columns(&items, &columns, 80, None);

        assert!(
            out.contains("..."),
            "values far beyond the no_truncate cap should still be truncated: {out}"
        );
        assert!(
            !out.contains(&huge_value),
            "the full pathological value should not be rendered verbatim: {out}"
        );
    }

    #[test]
    fn right_aligned_column_pads_header_and_cells_on_the_left() {
        let items = vec![
            json!({ "period": "1 year", "price": "71.99" }),
            json!({ "period": "2 years", "price": "143.99" }),
        ];
        let columns = vec![
            TableColumn::new("period", "Period"),
            TableColumn::new("price", "Price").align(Alignment::Right),
        ];

        let (out, _notes) = render_array_with_columns(&items, &columns, 80, None);
        let mut lines = out.lines();
        let header_line = lines.next().expect("header line");
        let row_lines: Vec<&str> = lines.skip(1).take(2).collect();

        // "PRICE" (5 chars) right-aligned in a 6-wide column ("143.99")
        // leaves one leading space and no trailing space.
        assert!(header_line.ends_with(" PRICE"), "{header_line}");
        assert!(row_lines[0].ends_with(" 71.99"), "{}", row_lines[0]);
        assert!(row_lines[1].ends_with("143.99"), "{}", row_lines[1]);
        // The unaligned leading column is untouched (still left-aligned).
        assert!(header_line.starts_with("PERIOD "), "{header_line}");
    }

    #[test]
    fn column_alignment_defaults_to_left() {
        let items = vec![json!({ "name": "a" }), json!({ "name": "bb" })];
        let columns = vec![TableColumn::new("name", "Name")];

        let (out, _notes) = render_array_with_columns(&items, &columns, 80, None);
        let mut lines = out.lines();
        let header_line = lines.next().expect("header line");

        assert!(
            header_line.starts_with("NAME"),
            "Alignment::Left is the default: {header_line}"
        );
    }

    #[test]
    fn column_width_never_shrinks_below_a_long_header() {
        let long_header = "A Very Long Header That Exceeds The Default Width Cap";
        let items = vec![json!({ "field": "short" })];
        let columns = vec![TableColumn::new("field", long_header)];

        // Deliberately far narrower than the header: the header must still
        // render in full even though the row ends up wider than the terminal.
        let (out, _notes) = render_array_with_columns(&items, &columns, 10, None);
        let header_line = out.lines().next().expect("header line");
        let separator_line = out.lines().nth(1).expect("separator line");

        assert_eq!(
            header_line.len(),
            separator_line.len(),
            "header and separator must stay aligned even when the header alone exceeds the terminal: {out}"
        );
        assert!(
            header_line.len() >= long_header.len(),
            "header must not be cut short: {out}"
        );
    }

    #[test]
    fn wide_terminal_shows_full_values_without_truncation() {
        let description = "a description that is well past the old forty-character cap";
        assert!(description.len() > 40, "fixture must exceed the old cap");
        let items = vec![json!({ "id": "1", "description": description })];
        let columns = vec![
            TableColumn::new("id", "ID"),
            TableColumn::new("description", "Description"),
        ];

        let (out, notes) = render_array_with_columns(&items, &columns, 200, None);

        assert!(
            !notes.truncated,
            "plenty of room, nothing to shorten: {out}"
        );
        assert!(notes.hidden_columns.is_empty(), "{out}");
        assert!(out.contains(description), "{out}");
        assert!(!out.contains("..."), "{out}");
    }

    #[test]
    fn narrow_terminal_truncates_and_reports_it() {
        // A single column whose value is far longer than the terminal
        // allows: there's nothing else to hide (hide-before-truncate has no
        // lower-priority column to drop), so truncation is the only option
        // and it must still be reported.
        let description = "a description that is well past the old forty-character cap";
        let items = vec![json!({ "description": description })];
        let columns = vec![TableColumn::new("description", "Description")];

        let (out, notes) = render_array_with_columns(&items, &columns, 20, None);

        assert!(
            notes.truncated,
            "narrow terminal must shorten a cell: {out}"
        );
        assert!(
            notes.hidden_columns.is_empty(),
            "only one column exists to begin with: {out}"
        );
        assert!(out.contains("..."), "{out}");
    }

    #[test]
    fn narrow_terminal_hides_columns_before_truncating_any_of_the_survivors() {
        // Three equally-competing columns: at this width, showing all three
        // (or even two) would require truncating every survivor a little.
        // Hide-before-truncate should instead cascade down to the single
        // highest-priority column and show it in full.
        let items = vec![json!({ "a": "x".repeat(5), "b": "x".repeat(5), "c": "x".repeat(5) })];
        let columns = vec![
            TableColumn::new("a", "A"),
            TableColumn::new("b", "B"),
            TableColumn::new("c", "C"),
        ];

        let (out, notes) = render_array_with_columns(&items, &columns, 10, None);

        assert!(
            !notes.truncated,
            "hiding B and C should leave A fully shown, untruncated: {out}"
        );
        assert_eq!(
            notes.hidden_columns,
            vec!["B".to_owned(), "C".to_owned()],
            "should cascade down to the single highest-priority column: {out}"
        );
        assert!(!out.contains("..."), "{out}");
    }

    #[test]
    fn overflow_hides_lowest_priority_columns_first() {
        let items = vec![json!({
            "id": "1",
            "name": "acme",
            "status": "active",
            "created_at": "2026-01-01",
        })];
        let columns = vec![
            TableColumn::new("id", "ID"),
            TableColumn::new("name", "Name"),
            TableColumn::new("status", "Status"),
            TableColumn::new("created_at", "Created At"),
        ];

        let (out, notes) = render_array_with_columns(&items, &columns, 10, None);

        assert_eq!(
            notes.hidden_columns,
            vec!["Status".to_owned(), "Created At".to_owned()],
            "lowest-priority (trailing) columns are dropped first: {out}"
        );
        let header_line = out.lines().next().expect("header line");
        assert!(header_line.contains("ID"), "{out}");
        assert!(header_line.contains("NAME"), "{out}");
        assert!(!header_line.contains("STATUS"), "{out}");
        assert!(!header_line.contains("CREATED"), "{out}");
    }

    #[test]
    fn render_human_with_view_reports_hidden_columns_in_footer() {
        let envelope = Envelope::success(
            json!([{
                "id": "1",
                "name": "acme",
                "status": "active",
                "region": "us-west",
                "created_at": "2026-01-01",
                "updated_at": "2026-01-02",
                "notes": "irrelevant, lowest priority",
            }]),
            "resource",
        );
        let columns = vec![
            TableColumn::new("id", "ID"),
            TableColumn::new("name", "Name"),
            TableColumn::new("status", "Status"),
            TableColumn::new("region", "Region"),
            TableColumn::new("created_at", "Created At"),
            TableColumn::new("updated_at", "Updated At"),
            // Deliberately long enough that, combined with the columns above,
            // it can't fit alongside them at the fallback 80-column width.
            TableColumn::new("notes", "This Is An Extremely Long Trailing Column Header"),
        ];

        // In test runs stdout is not a TTY, so `terminal_width()` deterministically
        // falls back to 80 — these headers don't all fit at that width.
        let out = render_human_with_view(&envelope, Some(&columns), "");

        assert!(out.contains("hidden to fit the display width"), "{out}");
        assert!(
            out.contains("This Is An Extremely Long Trailing Column Header"),
            "{out}"
        );
        assert!(out.contains("--fields"), "{out}");
        assert!(out.contains("--json"), "{out}");
    }

    #[test]
    fn select_columns_orders_by_requested_fields_not_declared_order() {
        let columns = vec![
            TableColumn::new("id", "ID"),
            TableColumn::new("name", "Name"),
            TableColumn::new("status", "Status"),
        ];

        let selected = select_columns(&columns, "status,id");

        assert_eq!(
            selected
                .iter()
                .map(|c| c.field.as_str())
                .collect::<Vec<_>>(),
            vec!["status", "id"],
            "order should follow the requested fields, not declaration order"
        );
    }

    #[test]
    fn select_columns_dedupes_and_skips_unknown_fields() {
        let columns = vec![
            TableColumn::new("id", "ID"),
            TableColumn::new("name", "Name"),
            TableColumn::new("status", "Status"),
        ];

        let selected = select_columns(&columns, "status,bogus,status,id");

        assert_eq!(
            selected
                .iter()
                .map(|c| c.field.as_str())
                .collect::<Vec<_>>(),
            vec!["status", "id"],
            "duplicates collapse to first occurrence; unknown fields are dropped"
        );
    }

    #[test]
    fn dynamic_columns_orders_by_requested_fields() {
        let columns = dynamic_columns("price1Year,domain", || {
            vec![
                "domain".to_owned(),
                "currency".to_owned(),
                "price1Year".to_owned(),
            ]
        });

        assert_eq!(
            columns.iter().map(|c| c.field.as_str()).collect::<Vec<_>>(),
            vec!["price1Year", "domain"]
        );
    }

    #[test]
    fn dynamic_columns_falls_back_to_alphabetical_without_fields() {
        let columns = dynamic_columns("", || vec!["currency".to_owned(), "domain".to_owned()]);

        assert_eq!(
            columns.iter().map(|c| c.field.as_str()).collect::<Vec<_>>(),
            vec!["currency", "domain"],
            "no fields signal at all: alphabetical is the only order available"
        );
    }

    #[test]
    fn no_view_array_rendering_right_aligns_a_column_that_is_numeric_on_every_row() {
        let items = vec![
            json!({ "name": "small", "count": 3 }),
            json!({ "name": "bigger", "count": 42 }),
        ];

        let (out, _notes) = render_array(&items, "name,count", 80, None);
        let mut lines = out.lines();
        let header_line = lines.next().expect("header line");
        let row_lines: Vec<&str> = lines.skip(1).take(2).collect();

        assert!(header_line.ends_with(" COUNT"), "{header_line}");
        assert!(row_lines[0].ends_with("   3"), "{}", row_lines[0]);
        assert!(row_lines[1].ends_with("  42"), "{}", row_lines[1]);
        assert!(header_line.starts_with("NAME "), "{header_line}");
    }

    #[test]
    fn no_view_array_rendering_keeps_a_mixed_type_column_left_aligned() {
        // Same field is a number on one row and a string on another — a
        // single non-number value anywhere disqualifies the whole column,
        // matching how right-aligning it would look ragged next to text.
        let items = vec![json!({ "code": 1 }), json!({ "code": "default" })];

        let (out, _notes) = render_array(&items, "", 80, None);
        let header_line = out.lines().next().expect("header line");

        assert!(header_line.starts_with("CODE"), "{header_line}");
    }

    #[test]
    fn no_view_array_rendering_keeps_an_all_null_column_left_aligned() {
        // No row ever has a number at this field, so there's no positive
        // signal to right-align on.
        let items = vec![json!({ "note": null }), json!({ "note": null })];

        let (out, _notes) = render_array(&items, "", 80, None);
        let header_line = out.lines().next().expect("header line");

        assert!(header_line.starts_with("NOTE"), "{header_line}");
    }

    #[test]
    fn no_view_array_rendering_follows_requested_field_order() {
        // Reproduces the real-world `domain suggest` symptom: a command with
        // no registered view whose default_fields lists `domain` first must
        // not silently reorder it after `currency` just because "c" < "d".
        let envelope = Envelope::success(
            json!([{ "domain": "example.com", "currency": "USD", "price1Year": "12.99" }]),
            "domain:suggest",
        );
        let registry = HumanViewRegistry::new();

        let rendered = render_human_with_registry_selected(
            &envelope,
            &registry,
            "domain:suggest",
            "domain,price1Year,currency",
        );

        let header_line = rendered.lines().next().expect("header line");
        assert!(header_line.contains("DOMAIN"), "{rendered}");
        let domain_pos = header_line.find("DOMAIN").expect("domain header");
        let price_pos = header_line.find("PRICE1YEAR").expect("price1Year header");
        let currency_pos = header_line.find("CURRENCY").expect("currency header");
        assert!(
            domain_pos < price_pos && price_pos < currency_pos,
            "expected DOMAIN, PRICE1YEAR, CURRENCY in that order: {header_line}"
        );
    }

    #[test]
    fn registered_view_rendering_follows_requested_field_order() {
        let mut registry = HumanViewRegistry::new();
        registry.register(HumanViewDef::new(
            "things",
            vec![
                TableColumn::new("id", "ID"),
                TableColumn::new("name", "Name"),
                TableColumn::new("status", "Status"),
            ],
        ));
        let envelope = Envelope::success(
            json!([{ "id": "1", "name": "acme", "status": "active" }]),
            "things",
        );

        let rendered =
            render_human_with_registry_selected(&envelope, &registry, "things", "status,id");

        let header_line = rendered.lines().next().expect("header line");
        assert!(!header_line.contains("NAME"), "{rendered}");
        let status_pos = header_line.find("STATUS").expect("status header");
        let id_pos = header_line.find("ID").expect("id header");
        assert!(
            status_pos < id_pos,
            "expected STATUS before ID per the requested field order: {header_line}"
        );
    }

    #[test]
    fn fit_column_widths_gives_small_wants_priority_over_larger_ones() {
        // Regression: a naive `leftover / remaining` split can floor a small
        // want to zero (denying a column that needed only 1 more char)
        // while a much larger want absorbs that same unit and stays
        // truncated anyway — net truncation is identical, but a column that
        // could have been fully satisfied wasn't.
        let headers = [1, 1, 1];
        let natural = [2, 2, 6]; // wants: 1, 1, 5
        let no_truncate = [false, false, false];

        let (widths, truncated) = fit_column_widths(&headers, &natural, &no_truncate, 8);

        assert_eq!(
            widths[0], natural[0],
            "a column that only wanted 1 more char should get it in full: {widths:?}"
        );
        assert!(truncated, "budget is still too small overall: {widths:?}");
    }

    #[test]
    fn overflow_hiding_accounts_for_no_truncate_columns_true_width() {
        // Regression: deciding what to hide from header length alone
        // under-counts a `no_truncate` column (it never shrinks below its
        // natural width), which could keep a short-header trailing column
        // that would never have fit anyway — overflowing when hiding it
        // would have let the row fit.
        let url = "x".repeat(40);
        let items = vec![json!({ "url": url, "notes": "irrelevant, lowest priority" })];
        let columns = vec![
            TableColumn::new("url", "URL").no_truncate(true),
            TableColumn::new("notes", "X"),
        ];

        // Exactly enough room for the URL alone (40 chars), not enough for
        // the URL plus even a 1-char trailing column and its gutter (43).
        let (out, notes) = render_array_with_columns(&items, &columns, 42, None);

        assert_eq!(
            notes.hidden_columns,
            vec!["X".to_owned()],
            "the trailing column must be hidden so the no_truncate URL column fits: {out}"
        );
        let header_line = out.lines().next().expect("header line");
        assert!(
            header_line.len() <= 42,
            "must not overflow once the trailing column is hidden: {out}"
        );
    }

    #[test]
    fn render_array_with_columns_handles_no_columns_gracefully() {
        // A view's `--fields` filtered out every declared column: nothing to
        // build a table from, so this must report "no results" rather than
        // a blank header/rows table.
        let items = vec![json!({ "a": "1" })];
        let (out, notes) = render_array_with_columns(&items, &[], 80, None);

        assert_eq!(out, "(no results)\n");
        assert!(!notes.truncated, "{out}");
        assert!(notes.hidden_columns.is_empty(), "{out}");
    }

    #[test]
    fn render_object_with_columns_handles_no_columns_gracefully() {
        // Sibling of the array-path test above (Copilot/human review caught
        // this asymmetry): a view's `--fields` filtered out every declared
        // column on an object-shaped response must report "(no data)"
        // rather than silently rendering an empty string.
        let map = json!({ "a": "1" });
        let (out, notes) =
            render_object_with_columns(map.as_object().expect("object fixture"), &[], 80);

        assert_eq!(out, "(no data)\n");
        assert!(!notes.truncated, "{out}");
        assert!(notes.hidden_columns.is_empty(), "{out}");
    }

    #[test]
    fn no_view_array_of_empty_objects_reports_no_results() {
        // Every item is `{}`, so the dynamic (no-view) column catalog has no
        // keys to derive columns from — same "no columns" case as above,
        // reached through the no-view path instead.
        let items = vec![json!({}), json!({})];
        let (out, notes) = render_array(&items, "", 80, None);

        assert_eq!(out, "(no results)\n");
        assert!(notes.hidden_columns.is_empty(), "{out}");
    }

    #[test]
    fn resolve_field_path_walks_dotted_wrapper_and_reports_missing_or_wrong_shape() {
        let map = json!({
            "parameters": { "items": [{"name": "limit"}], "total": 1 },
            "owner": "not-an-object",
        });
        let map = map.as_object().expect("object fixture");

        assert_eq!(
            resolve_field_path(map, "parameters.items"),
            map.get("parameters").and_then(|value| value.get("items"))
        );
        assert_eq!(resolve_field_path(map, "parameters.missing"), None);
        assert_eq!(
            resolve_field_path(map, "owner.name"),
            None,
            "intermediate value is a string, not an object"
        );
        assert_eq!(resolve_field_path(map, "missing"), None);
        assert_eq!(resolve_field_path(map, ""), None, "empty field");
        assert_eq!(resolve_field_path(map, ".parameters"), None, "leading dot");
        assert_eq!(resolve_field_path(map, "parameters."), None, "trailing dot");
        assert_eq!(
            resolve_field_path(map, "parameters..items"),
            None,
            "doubled dot"
        );
    }

    #[test]
    fn resolve_field_parent_returns_parent_object_for_dotted_and_bare_fields() {
        let map = json!({
            "parameters": { "items": [], "total": 2 },
            "owner": "not-an-object",
        });
        let map = map.as_object().expect("object fixture");

        assert_eq!(
            resolve_field_parent(map, "parameters.items"),
            map.get("parameters").and_then(Value::as_object)
        );
        assert_eq!(
            resolve_field_parent(map, "items"),
            Some(map),
            "a field with no dot has the object being rendered as its own parent"
        );
        assert_eq!(
            resolve_field_parent(map, "owner.name"),
            None,
            "intermediate value is a string, not an object"
        );
        assert_eq!(resolve_field_parent(map, "missing.items"), None);
    }

    #[test]
    fn resolve_nested_pagination_deserializes_a_pagination_meta_shaped_sibling() {
        let parent = json!({
            "pagination": { "total": 26, "offset": 0, "limit": 2, "count": 2, "has_more": true },
        });
        let parent = parent.as_object().expect("object fixture");

        let meta = resolve_nested_pagination(parent).expect("pagination sibling present");
        assert_eq!(
            meta,
            PaginationMeta {
                total: 26,
                offset: 0,
                limit: 2,
                count: 2,
                has_more: true,
            }
        );
    }

    #[test]
    fn resolve_nested_pagination_is_none_when_the_sibling_is_absent_or_malformed() {
        let no_sibling = json!({ "items": [] });
        assert_eq!(
            resolve_nested_pagination(no_sibling.as_object().expect("object fixture")),
            None,
            "no pagination field at all"
        );

        let wrong_shape = json!({ "pagination": { "total": 26 } });
        assert_eq!(
            resolve_nested_pagination(wrong_shape.as_object().expect("object fixture")),
            None,
            "missing required PaginationMeta fields fails to deserialize"
        );

        let not_an_object = json!({ "pagination": "26 total" });
        assert_eq!(
            resolve_nested_pagination(not_an_object.as_object().expect("object fixture")),
            None,
            "pagination field present but not object-shaped"
        );
    }

    #[test]
    fn nested_array_of_objects_renders_as_indented_child_table() {
        let map = json!({
            "name": "getPets",
            "parameters": {
                "items": [
                    {"name": "limit", "in": "query"},
                    {"name": "id", "in": "path"},
                ],
            },
        });
        let columns = vec![
            TableColumn::new("name", "Name"),
            TableColumn::new("parameters.items", "Parameters").nested(vec![
                TableColumn::new("name", "Name"),
                TableColumn::new("in", "In"),
            ]),
        ];

        let (out, notes) =
            render_object_with_columns(map.as_object().expect("object fixture"), &columns, 80);

        assert!(out.starts_with("Name: getPets\nParameters:\n"), "{out}");
        assert!(
            out.contains("  NAME"),
            "child header must be indented: {out}"
        );
        assert!(out.contains("  limit"), "child row must be indented: {out}");
        assert!(
            !out.contains('{'),
            "no raw JSON should leak into output: {out}"
        );
        assert!(!notes.truncated, "{out}");
        assert!(
            out.contains("(2 rows)"),
            "no pagination sibling means the plain row-count footer, unchanged: {out}"
        );
    }

    #[test]
    fn nested_array_with_pagination_sibling_renders_pagination_style_footer() {
        let map = json!({
            "name": "getPets",
            "parameters": {
                "items": [
                    {"name": "limit", "in": "query"},
                    {"name": "id", "in": "path"},
                ],
                "pagination": { "total": 26, "offset": 0, "limit": 2, "count": 2, "has_more": true },
            },
        });
        let columns = vec![
            TableColumn::new("name", "Name"),
            TableColumn::new("parameters.items", "Parameters").nested(vec![
                TableColumn::new("name", "Name"),
                TableColumn::new("in", "In"),
            ]),
        ];

        let (out, _notes) =
            render_object_with_columns(map.as_object().expect("object fixture"), &columns, 80);

        assert!(
            out.contains("(2 of 26 rows, offset 0, limit 2)"),
            "nested table should reuse the pagination sibling's PaginationMeta facts: {out}"
        );
    }

    #[test]
    fn nested_array_without_pagination_sibling_keeps_the_plain_row_count_footer() {
        let map = json!({ "items": [{"name": "limit"}] });
        let columns =
            vec![TableColumn::new("items", "Items").nested(vec![TableColumn::new("name", "Name")])];

        let (out, _notes) =
            render_object_with_columns(map.as_object().expect("object fixture"), &columns, 80);

        assert!(
            out.contains("(1 rows)"),
            "no pagination sibling means no opt-in — behavior is unchanged: {out}"
        );
    }

    #[test]
    fn nested_array_with_malformed_pagination_sibling_keeps_the_plain_row_count_footer() {
        let map =
            json!({ "items": [{"name": "limit"}], "pagination": { "total": "not-a-number" } });
        let columns =
            vec![TableColumn::new("items", "Items").nested(vec![TableColumn::new("name", "Name")])];

        let (out, _notes) =
            render_object_with_columns(map.as_object().expect("object fixture"), &columns, 80);

        assert!(
            out.contains("(1 rows)"),
            "a pagination sibling that fails to deserialize degrades to the plain footer: {out}"
        );
    }

    #[test]
    fn nested_child_table_narrows_and_reports_via_merged_render_notes() {
        let map = json!({
            "items": [
                {"a": "x".repeat(5), "b": "x".repeat(5), "c": "x".repeat(5)},
            ],
        });
        let columns = vec![TableColumn::new("items", "Items").nested(vec![
            TableColumn::new("a", "A"),
            TableColumn::new("b", "B"),
            TableColumn::new("c", "C"),
        ])];

        // Narrow enough to force the child table's own hide-before-truncate
        // cascade (mirrors `narrow_terminal_hides_columns_before_truncating_any_of_the_survivors`).
        let (out, notes) =
            render_object_with_columns(map.as_object().expect("object fixture"), &columns, 12);

        assert_eq!(
            notes.hidden_columns,
            vec!["Items > B".to_owned(), "Items > C".to_owned()],
            "hidden columns bubble up prefixed with the parent header: {out}"
        );
        assert!(
            notes.nested_narrowing,
            "narrowing happened inside the nested child, not at this level's own columns: {out}"
        );
    }

    #[test]
    fn footer_does_not_suggest_fields_for_narrowing_inside_a_nested_column() {
        // `--fields` only selects among top-level declared columns — it
        // cannot narrow what shows *inside* a `TableColumn::nested` column.
        // When a nested child's own columns get hidden, the footer must not
        // claim `--fields` fixes it (regression: it used to say so
        // unconditionally, misleading users into trying a flag that does
        // nothing for this case — see PR review discussion). Same fixture
        // shape as `render_human_with_view_reports_hidden_columns_in_footer`
        // (proven to overflow the fallback 80-column width), just nested
        // one level under an "items" field instead of being the top-level
        // view directly.
        let envelope = Envelope::success(
            json!({
                "items": [{
                    "id": "1",
                    "name": "acme",
                    "status": "active",
                    "region": "us-west",
                    "created_at": "2026-01-01",
                    "updated_at": "2026-01-02",
                    "notes": "irrelevant, lowest priority",
                }],
            }),
            "thing",
        );
        let columns = vec![TableColumn::new("items", "Items").nested(vec![
            TableColumn::new("id", "ID"),
            TableColumn::new("name", "Name"),
            TableColumn::new("status", "Status"),
            TableColumn::new("region", "Region"),
            TableColumn::new("created_at", "Created At"),
            TableColumn::new("updated_at", "Updated At"),
            TableColumn::new("notes", "This Is An Extremely Long Trailing Column Header"),
        ])];

        let out = render_human_with_view(&envelope, Some(&columns), "");

        assert!(out.contains("hidden to fit the display width"), "{out}");
        assert!(
            out.contains("Items > This Is An Extremely Long Trailing Column Header"),
            "{out}"
        );
        assert!(
            !out.contains("use --fields"),
            "must not suggest --fields as a fix when the narrowing is inside a nested column \
             (mentioning it to explain why it won't help is fine): {out}"
        );
        assert!(
            out.contains("--json"),
            "must still point at --json as the real remedy: {out}"
        );
    }

    #[test]
    fn empty_nested_array_renders_no_results_indented() {
        let map = json!({ "items": [] });
        let columns = vec![
            TableColumn::new("items", "Parameters").nested(vec![TableColumn::new("name", "Name")]),
        ];

        let (out, _notes) =
            render_object_with_columns(map.as_object().expect("object fixture"), &columns, 80);

        assert_eq!(out, "Parameters:\n  (no results)\n");
    }

    #[test]
    fn nested_object_field_renders_as_indented_property_bag() {
        let map = json!({ "owner": {"name": "Ada", "email": "ada@example.test"} });
        let columns = vec![TableColumn::new("owner", "Owner").nested(vec![
            TableColumn::new("name", "Name"),
            TableColumn::new("email", "Email"),
        ])];

        let (out, _notes) =
            render_object_with_columns(map.as_object().expect("object fixture"), &columns, 80);

        assert_eq!(out, "Owner:\n  Name: Ada\n  Email: ada@example.test\n");
    }

    #[test]
    fn unopted_in_nested_value_still_renders_as_raw_json_line() {
        // A column with no `.nested(...)` is a strict no-op even when the
        // runtime value happens to be list/object shaped — locks in the
        // "opt-in, never automatic" guarantee.
        let map = json!({
            "parameters": {"items": [{"name": "limit"}], "total": 1},
        });
        let columns = vec![TableColumn::new("parameters", "Parameters")];

        let (out, _notes) =
            render_object_with_columns(map.as_object().expect("object fixture"), &columns, 80);

        assert_eq!(
            out,
            format!(
                "Parameters: {}\n",
                format_value(map.get("parameters").expect("parameters"))
            )
        );
        assert!(out.contains('{'), "unchanged raw-JSON fallback: {out}");
    }

    #[test]
    fn nested_column_is_a_no_op_when_the_value_is_not_actually_nestable() {
        // A column can opt into `.nested(...)` while still receiving a
        // scalar or a mixed (non-uniform) array at runtime — e.g. a field
        // that's usually a list of objects but is empty/absent for this row,
        // or simply the wrong shape. Rendering must stay the same flat
        // `header: value` line a column with `nested: None` would have
        // produced, not a `header:\n  value` block — regression guard for a
        // shape-drift bug where the header line alone changed to multi-line
        // even though the value itself fell back to `format_value`.
        let map = json!({
            "scalar": "just a string",
            "mixed": ["a", {"b": 1}],
        });
        let nested_columns = vec![TableColumn::new("x", "X")];
        let columns = vec![
            TableColumn::new("scalar", "Scalar").nested(nested_columns.clone()),
            TableColumn::new("mixed", "Mixed").nested(nested_columns),
        ];
        let unnested_columns = vec![
            TableColumn::new("scalar", "Scalar"),
            TableColumn::new("mixed", "Mixed"),
        ];

        let (nested_out, _) =
            render_object_with_columns(map.as_object().expect("object fixture"), &columns, 80);
        let (unnested_out, _) = render_object_with_columns(
            map.as_object().expect("object fixture"),
            &unnested_columns,
            80,
        );

        assert_eq!(
            nested_out, unnested_out,
            "an opted-in column must render identically to an unopted-in one \
             when the runtime value isn't list-of-objects or object shaped"
        );
        assert_eq!(nested_out, "Scalar: just a string\nMixed: a, {\"b\":1}\n");
    }
}