//! Lua bridge for the extension UI event system (plan §7.6).
//!
//! This module bridges the native event machinery in `tui_event.zig` to
//! Lua: it lets a Lua `panto.ext.on(name, handler)` callback participate in
//! the SAME `EventBus` the native side fires, receive a bridged `event`
//! object (`get_component`/`set_component` + payload fields), and either
//! pass through a native default component, wrap it, or install a
//! brand-new component DEFINED IN LUA.
//!
//! It is owned by the long-lived `LuaRuntime` (one `lua_State` for the
//! whole session) and shares that state. It never opens its own state.
//!
//! ## Synchronous rendering (NOT the coroutine scheduler)
//!
//! A Lua-defined component's `render(width)` is on the engine's hot path:
//! the differential renderer calls it and needs the produced lines back
//! IMMEDIATELY. So the bridged vtable calls into Lua **synchronously** via
//! `lua_pcallk` (the same model as `LuaRuntime.runCommand`), NOT through
//! the libuv coroutine scheduler used for async tool batches. A render
//! callback may not yield; if a Lua component blocks, that is a bug in the
//! extension, and we surface a safe fallback line rather than hanging or
//! corrupting the frame.
//!
//! ## Cache-derived `firstLineChanged`
//!
//! Each bridged component owns a native `RenderCache` (the same one native
//! components use). The Lua side only returns an array of line strings per
//! `render`; the bridge calls `cache.store(lines)` and derives
//! `firstLineChanged` from the cache diff exactly like a native component.
//! This keeps the cache-derived dirty-model invariant (§3.3) and frees Lua
//! authors from implementing `firstLineChanged` correctly. A Lua-provided
//! `firstLineChanged` override could be added later; cache-derived is the
//! correct, safe default.
//!
//! ## Lifetime / ownership (§6, §7.4)
//!
//! Bridged components and Lua handlers reference Lua functions/tables that
//! must survive as long as the engine borrows them. Both are `luaL_ref`'d
//! into the registry; the refs are owned by this bridge and released at
//! runtime teardown. A bridged component (its `luaL_ref` + `RenderCache`)
//! is heap-allocated and tracked in `components`, freed on `invalidate`
//! and at teardown. There is no "active component": each `emit` that
//! produces a Lua component mints a fresh instance keyed by that
//! boundary's own event, exactly like native components.

const std = @import("std");
const lua_bridge = @import("lua_bridge.zig");
const ui_event = @import("tui_event.zig");
const component = @import("tui_component.zig");
const components = @import("tui_components.zig");
const theme = @import("tui_theme.zig");
const engine = @import("tui_engine.zig");

const c = lua_bridge.c;
const Component = component.Component;
const RenderCache = component.RenderCache;
const Event = ui_event.Event;
const Payload = ui_event.Payload;
const EventBus = ui_event.EventBus;
const Handler = ui_event.Handler;

// Metatable names (registered via `luaL_newmetatable`, looked up by
// `luaL_checkudata`/`luaL_testudata`). The `event` userdata identifies a
// bridged event object; the `component` userdata is a native-component
// passthrough handle.
const eventMtName = "panto.event";
const nativeCompMtName = "panto.component";

/// A component DEFINED IN LUA, bridged to the native `Component` vtable.
///
/// `table_ref` is a `luaL_ref` to the Lua table implementing
/// `render(self, width) -> {strings}` plus optional `firstLineChanged` /
/// `handleInput` / `invalidate` methods. The bridge owns a `RenderCache`
/// and derives the dirty signal from it.
pub const BridgedComponent = struct {
    bridge: *EventBridge,
    /// `luaL_ref` to the Lua component table.
    table_ref: c_int,
    cache: RenderCache,
    /// True once freed, to make double-free / use-after-free a no-op.
    dead: bool = false,

    fn renderImpl(ptr: *anyopaque, width: usize, alloc: std.mem.Allocator) anyerror![]const []const u8 {
        _ = alloc;
        const self: *BridgedComponent = @ptrCast(@alignCast(ptr));
        return self.bridge.renderBridged(self, width);
    }

    fn firstLineChangedImpl(ptr: *anyopaque) ?usize {
        const self: *BridgedComponent = @ptrCast(@alignCast(ptr));
        return self.cache.firstLineChanged();
    }

    fn invalidateImpl(ptr: *anyopaque) void {
        const self: *BridgedComponent = @ptrCast(@alignCast(ptr));
        self.cache.invalidate();
    }

    fn handleInputImpl(ptr: *anyopaque, data: []const u8) void {
        const self: *BridgedComponent = @ptrCast(@alignCast(ptr));
        self.bridge.handleInputBridged(self, data);
    }

    /// The shared vtable for every Lua-backed component. Its ADDRESS is the
    /// discriminator used by `EventBridge.releaseOverride` to recognize a
    /// `Component` as bridged: a `Component` whose `vtable` pointer equals
    /// `&BridgedComponent.vtable` is known to have `ptr == *BridgedComponent`.
    /// Native (non-Lua) components carry a different vtable address, so the
    /// release hook can safely leave them alone. `pub` so the discriminator is
    /// addressable from the release path (and tests).
    pub const vtable = Component.VTable{
        .render = renderImpl,
        .firstLineChanged = firstLineChangedImpl,
        .invalidate = invalidateImpl,
        .handleInput = handleInputImpl,
    };

    pub fn comp(self: *BridgedComponent) Component {
        return .{ .ptr = self, .vtable = &vtable };
    }
};

/// A registered Lua `on` handler, bridged to a native `Handler`.
///
/// `fn_ref` is a `luaL_ref` to the Lua handler function. The native
/// `Handler.ctx` points at this struct; `Handler.callback` is
/// `nativeHandlerCallback`, which builds the bridged `event` object, calls
/// the Lua function, and reads back any component it set.
pub const LuaHandler = struct {
    bridge: *EventBridge,
    fn_ref: c_int,
    /// Bridge-owned copy of the event name this handler subscribed to.
    event_name: []const u8,
};

/// The bridge: owns the Lua-side event wiring and the bridged
/// components/handlers. Lives inside the `LuaRuntime`.
pub const EventBridge = struct {
    alloc: std.mem.Allocator,
    L: *c.lua_State,
    /// The native bus a Lua `emit` drives, and that fires Lua handlers.
    /// Set once the App is constructed (`attachBus`); null before then, in
    /// which case a Lua `emit` is a no-op (nothing to fire into yet).
    bus: ?*EventBus = null,

    /// Owned Lua handler bridges (one per `panto.ext.on` registration).
    handlers: std.ArrayListUnmanaged(*LuaHandler) = .empty,
    /// Owned bridged components, tracked so their refs + caches are freed
    /// at teardown. Each is heap-allocated; an `invalidate` frees it.
    components: std.ArrayListUnmanaged(*BridgedComponent) = .empty,

    /// During a native `emit`, the event currently being presented to a
    /// Lua handler. The bridged `event` userdata's methods read/write
    /// through this. Single-threaded; valid only for the duration of one
    /// handler call. `null` outside a handler.
    active_event: ?*Event = null,

    pub fn init(alloc: std.mem.Allocator, L: *c.lua_State) EventBridge {
        return .{ .alloc = alloc, .L = L };
    }

    pub fn deinit(self: *EventBridge) void {
        for (self.handlers.items) |h| {
            c.luaL_unref(self.L, lua_bridge.LUA_REGISTRYINDEX, h.fn_ref);
            self.alloc.free(h.event_name);
            self.alloc.destroy(h);
        }
        self.handlers.deinit(self.alloc);
        for (self.components.items) |comp| self.freeComponentInner(comp);
        self.components.deinit(self.alloc);
    }

    /// Bind the native `EventBus` this bridge fires into / drives via
    /// `emit`. Called once during startup wiring, after the App's bus
    /// exists. Also registers every harvested Lua `on` handler into the
    /// bus, in registration order.
    pub fn attachBus(self: *EventBridge, bus: *EventBus) !void {
        self.bus = bus;
        for (self.handlers.items) |h| {
            try bus.on(eventNameOf(h), .{ .ctx = h, .callback = nativeHandlerCallback });
        }
    }

    /// The event name a handler subscribed to is stored alongside its ref
    /// at registration time. We keep it on the LuaHandler via a parallel
    /// slice; but to avoid a second allocation we look it up lazily. (Set
    /// in `registerOnHandler`.)
    fn eventNameOf(h: *LuaHandler) []const u8 {
        return h.event_name;
    }

    /// Record a Lua `on` handler: `luaL_ref` the function at stack index
    /// `fn_idx` and remember the event name. Registration into the bus
    /// happens later in `attachBus` (the bus may not exist yet at harvest
    /// time). Order of calls here is the registration order (§7.3).
    pub fn registerOnHandler(self: *EventBridge, event_name: []const u8, fn_idx: c_int) !void {
        // Dupe the event name into bridge-owned storage.
        const name_copy = try self.alloc.dupe(u8, event_name);
        errdefer self.alloc.free(name_copy);

        // luaL_ref pops the top of stack, so push a copy of the function.
        c.lua_pushvalue(self.L, fn_idx);
        const ref = c.luaL_ref(self.L, lua_bridge.LUA_REGISTRYINDEX);
        errdefer c.luaL_unref(self.L, lua_bridge.LUA_REGISTRYINDEX, ref);

        const h = try self.alloc.create(LuaHandler);
        h.* = .{ .bridge = self, .fn_ref = ref, .event_name = name_copy };
        try self.handlers.append(self.alloc, h);
    }

    /// Number of registered Lua `on` handlers (diagnostic/test helper).
    pub fn handlerCount(self: *const EventBridge) usize {
        return self.handlers.items.len;
    }

    // -- bridged component construction ------------------------------------

    /// Build a native `Component` backed by the Lua component table at
    /// stack index `table_idx`. `luaL_ref`s the table, allocates a tracked
    /// `BridgedComponent`, and returns its `comp()`. The component lives
    /// until `invalidate` (which frees it) or runtime teardown.
    ///
    /// No "active component": each call mints a fresh instance.
    fn makeBridgedComponent(self: *EventBridge, table_idx: c_int) !Component {
        c.lua_pushvalue(self.L, table_idx);
        const ref = c.luaL_ref(self.L, lua_bridge.LUA_REGISTRYINDEX);
        errdefer c.luaL_unref(self.L, lua_bridge.LUA_REGISTRYINDEX, ref);

        const bc = try self.alloc.create(BridgedComponent);
        errdefer self.alloc.destroy(bc);
        bc.* = .{ .bridge = self, .table_ref = ref, .cache = RenderCache.init(self.alloc) };
        try self.components.append(self.alloc, bc);
        return bc.comp();
    }

    /// Free a bridged component's Lua ref + cache and destroy it. Idempotent
    /// via the `dead` flag, BUT note it does NOT remove `bc` from
    /// `self.components` and it `destroy`s the allocation — so it must only be
    /// used in one of two safe ways:
    ///   - at teardown (`deinit`), iterating the whole list once; or
    ///   - via `releaseOverride`, which removes `bc` from `self.components`
    ///     BEFORE calling this, so teardown never revisits a destroyed pointer.
    fn freeComponentInner(self: *EventBridge, bc: *BridgedComponent) void {
        if (bc.dead) return;
        bc.dead = true;
        c.luaL_unref(self.L, lua_bridge.LUA_REGISTRYINDEX, bc.table_ref);
        bc.cache.deinit();
        self.alloc.destroy(bc);
    }

    /// Release a superseded override component handed back by the App's
    /// mid-stream swap (`App.override_release_fn`). This is the leak-prevention
    /// point: when a `tool_details` (or any lifecycle) handler swaps a NEW
    /// component over a PRIOR Lua-backed override, the prior one must drop its
    /// `luaL_ref` + `RenderCache`, or it leaks for the life of the runtime
    /// (one leak per swapped tool call).
    ///
    /// Discriminator: a `Component` is Lua-backed iff its `vtable` pointer is
    /// `&BridgedComponent.vtable` (the single shared vtable address; see
    /// `BridgedComponent.vtable`). For such a component `ptr` is a
    /// `*BridgedComponent` we own and track in `self.components`. Any other
    /// vtable belongs to a NATIVE component the App owns; we must NOT touch it
    /// (it is not ours to free), so the hook is a no-op for it.
    ///
    /// Ownership: we remove `bc` from `self.components` first, then free it, so
    /// teardown's `deinit` loop never revisits the destroyed pointer.
    pub fn releaseOverride(self: *EventBridge, old: Component) void {
        if (old.vtable != &BridgedComponent.vtable) return; // native: not ours
        const bc: *BridgedComponent = @ptrCast(@alignCast(old.ptr));
        // Remove from the tracked list before freeing (swap-remove is fine;
        // order does not matter for teardown).
        for (self.components.items, 0..) |item, i| {
            if (item == bc) {
                _ = self.components.swapRemove(i);
                break;
            }
        }
        self.freeComponentInner(bc);
    }

    /// The `*anyopaque`-typed release callback the App invokes via
    /// `override_release_fn`. `ctx` is the `*EventBridge`.
    pub fn releaseOverrideThunk(ctx: *anyopaque, old: Component) void {
        const self: *EventBridge = @ptrCast(@alignCast(ctx));
        self.releaseOverride(old);
    }

    // -- bridged render / input (SYNCHRONOUS pcall) ------------------------

    /// Render a Lua-defined component synchronously: push its table +
    /// `render` method + width, `lua_pcallk`, marshal the returned
    /// array-of-strings into the component's `RenderCache`, and return the
    /// cached lines. On ANY Lua error or bad return, return a single dim
    /// error line instead of crashing the render loop (the frame must
    /// always complete). Every returned line is truncated to `width` so
    /// the engine's width contract (§3.1) is never violated.
    fn renderBridged(self: *EventBridge, bc: *BridgedComponent, width: usize) anyerror![]const []const u8 {
        const L = self.L;
        if (bc.dead) return &.{};

        const base = c.lua_gettop(L);
        defer c.lua_settop(L, base); // restore stack no matter what

        // Push the component table, then its `render` method.
        _ = c.lua_rawgeti(L, lua_bridge.LUA_REGISTRYINDEX, @intCast(bc.table_ref));
        if (c.lua_type(L, -1) != lua_bridge.T_TABLE) return self.fallbackLines(bc, width, "component is not a table");
        _ = c.lua_getfield(L, -1, "render");
        if (c.lua_type(L, -1) != lua_bridge.T_FUNCTION) {
            return self.fallbackLines(bc, width, "component has no render()");
        }
        // Stack: ..., table, render. Call render(table, width) -> lines.
        c.lua_pushvalue(L, -2); // self (the table)
        c.lua_pushinteger(L, @intCast(width));
        if (c.lua_pcallk(L, 2, 1, 0, 0, null) != 0) {
            return self.fallbackLines(bc, width, luaErrText(L));
        }
        // Stack top: the returned lines table.
        const raw = lua_bridge.readLinesArray(L, -1, self.alloc) catch {
            return self.fallbackLines(bc, width, "render() must return an array of strings");
        };
        defer {
            for (raw) |ln| self.alloc.free(ln);
            self.alloc.free(raw);
        }
        // Enforce the width contract: truncate every line to `width`
        // columns. Build a transient view of truncated borrows for the
        // cache to dupe.
        var view: std.ArrayListUnmanaged([]const u8) = .empty;
        defer view.deinit(self.alloc);
        for (raw) |ln| {
            const vis = components.truncateToCols(ln, width);
            try view.append(self.alloc, vis);
        }
        try bc.cache.store(view.items);
        return cacheLines(&bc.cache);
    }

    /// Build the cache's single dim fallback line for a render failure and
    /// return it. Keeps the render loop alive on a misbehaving extension.
    ///
    /// The composed line MUST satisfy the engine's width contract (§3.1):
    /// visible width <= `width`, or the engine rejects it with
    /// `Error.LineOverflow` and crashes the very frame the fallback exists to
    /// save. The dim escapes are zero visible width, so we build the PLAIN
    /// error text, truncate THAT to `width` columns (codepoint-safe), and only
    /// then wrap it in the dim style.
    fn fallbackLines(self: *EventBridge, bc: *BridgedComponent, width: usize, why: []const u8) anyerror![]const []const u8 {
        _ = self;
        const dim = theme.default.fg(.dim);
        // Plain (escape-free) error text first, into a scratch buffer.
        var plain_buf: [256]u8 = undefined;
        const plain = std.fmt.bufPrint(&plain_buf, "[lua component error: {s}]", .{why}) catch "[lua component error]";
        // Truncate the visible text to the width contract (codepoint-safe).
        const vis = components.truncateToCols(plain, width);
        // Compose the styled line; if even the styled form overflows the
        // compose buffer, fall back to the bare truncated plain text (which
        // already satisfies the width contract).
        var styled_buf: [512]u8 = undefined;
        const styled = std.fmt.bufPrint(&styled_buf, "{s}{s}{s}", .{ dim.open(), vis, dim.close() }) catch vis;
        const one = [_][]const u8{styled};
        try bc.cache.store(&one);
        return cacheLines(&bc.cache);
    }

    /// Feed input to a Lua component's optional `handleInput(self, data)`
    /// method, synchronously. Errors are swallowed (input handling must
    /// never crash the loop); a component without the method ignores input.
    fn handleInputBridged(self: *EventBridge, bc: *BridgedComponent, data: []const u8) void {
        const L = self.L;
        if (bc.dead) return;
        const base = c.lua_gettop(L);
        defer c.lua_settop(L, base);

        _ = c.lua_rawgeti(L, lua_bridge.LUA_REGISTRYINDEX, @intCast(bc.table_ref));
        if (c.lua_type(L, -1) != lua_bridge.T_TABLE) return;
        _ = c.lua_getfield(L, -1, "handleInput");
        if (c.lua_type(L, -1) != lua_bridge.T_FUNCTION) return;
        c.lua_pushvalue(L, -2); // self
        _ = c.lua_pushlstring(L, data.ptr, data.len);
        // Any error: ignore (best-effort input).
        _ = c.lua_pcallk(L, 2, 0, 0, 0, null);

        // Mark the cache dirty after input. The engine reads
        // `firstLineChanged()` BEFORE calling `render`, so a clean cache means
        // the component is SKIPPED and the Lua-side mutation would never reach
        // the screen. Native components dirty on every input mutation (see
        // InputBox.applyKey -> markDirty); the bridge must do the same on the
        // component's behalf. We can't know what changed inside Lua, so we
        // re-dirty from 0; the post-render diff in `store` then recovers the
        // true lowest-changed line (preserving the streaming-tail property for
        // append-style edits). Dirty unconditionally even on a Lua error: the
        // handler may have partially mutated state before throwing.
        bc.cache.markDirty();
    }
};

// ===========================================================================
// Native handler callback: native EventBus -> Lua `on` handler
// ===========================================================================

/// The native `Handler.callback` for a bridged Lua handler. Builds the
/// `event` userdata, calls the Lua function with it (synchronously, under
/// a traceback errfunc), and lets the Lua side read/replace the component
/// via `event:get_component()` / `event:set_component()`. Errors in the Lua
/// handler are logged and swallowed — a broken handler must not abort the
/// event dispatch or the render loop.
fn nativeHandlerCallback(ctx: *anyopaque, event: *Event) void {
    const h: *LuaHandler = @ptrCast(@alignCast(ctx));
    const self = h.bridge;
    const L = self.L;

    // Make this event the active one so the userdata methods read/write it.
    const prev = self.active_event;
    self.active_event = event;
    defer self.active_event = prev;

    const base = c.lua_gettop(L);
    defer c.lua_settop(L, base);

    // Traceback errfunc beneath the call.
    _ = c.lua_getglobal(L, "debug");
    _ = c.lua_getfield(L, -1, "traceback");
    c.lua_copy(L, -1, -2);
    c.lua_settop(L, c.lua_gettop(L) - 1); // pop `debug` table
    const errfunc_idx = c.lua_gettop(L);

    _ = c.lua_rawgeti(L, lua_bridge.LUA_REGISTRYINDEX, @intCast(h.fn_ref));
    pushEventObject(self) catch {
        c.lua_settop(L, base);
        return;
    };
    if (c.lua_pcallk(L, 1, 0, errfunc_idx, 0, null) != 0) {
        var len: usize = 0;
        const msg = c.lua_tolstring(L, -1, &len);
        if (msg != null) {
            std.log.err("lua event handler '{s}' failed: {s}", .{ h.event_name, msg[0..len] });
        }
    }
}

// ===========================================================================
// The bridged `event` object (userdata + metatable)
// ===========================================================================

/// Push an `event` userdata onto the stack, carrying a pointer to the
/// bridge (which reaches the active `*Event`). Its metatable exposes
/// `get_component`, `set_component`, and read-only payload fields via
/// `__index`.
fn pushEventObject(bridge: *EventBridge) !void {
    const L = bridge.L;
    const ud: **EventBridge = @ptrCast(@alignCast(c.lua_newuserdatauv(L, @sizeOf(*EventBridge), 0).?));
    ud.* = bridge;
    ensureEventMetatable(L);
    _ = c.lua_setmetatable(L, -2);
}

/// Lazily create the `event` userdata metatable (by name, so
/// `luaL_checkudata` recognizes it) and leave it on the stack. Its
/// `__index` is a function resolving `get_component`/`set_component` and
/// payload fields.
fn ensureEventMetatable(L: *c.lua_State) void {
    // luaL_newmetatable pushes the metatable; returns 1 if freshly created.
    if (c.luaL_newmetatable(L, eventMtName) != 0) {
        c.lua_pushcclosure(L, eventIndexThunk, 0);
        c.lua_setfield(L, -2, "__index");
    }
}

/// `__index(event_ud, key)`: dispatch method names and payload fields.
fn eventIndexThunk(L_opt: ?*c.lua_State) callconv(.c) c_int {
    const L = L_opt.?;
    const ud: **EventBridge = @ptrCast(@alignCast(c.luaL_checkudata(L, 1, eventMtName) orelse return 0));
    const bridge = ud.*;
    var klen: usize = 0;
    const kptr = c.lua_tolstring(L, 2, &klen);
    if (kptr == null) return 0;
    const key = kptr[0..klen];

    if (std.mem.eql(u8, key, "get_component")) {
        c.lua_pushcclosure(L, eventGetComponentThunk, 0);
        return 1;
    }
    if (std.mem.eql(u8, key, "set_component")) {
        c.lua_pushcclosure(L, eventSetComponentThunk, 0);
        return 1;
    }
    // Payload fields + the event name.
    const ev = bridge.active_event orelse {
        c.lua_pushnil(L);
        return 1;
    };
    if (std.mem.eql(u8, key, "name")) {
        _ = c.lua_pushlstring(L, ev.name.ptr, ev.name.len);
        return 1;
    }
    pushPayloadField(L, ev, key);
    return 1;
}

/// Push the payload field named `key` for `ev`, or nil if absent. Marshals
/// the tagged-union variant's fields onto simple Lua values (§7.2).
/// Push a string field as a Lua string, or `nil` when the slice is empty.
/// Empty lifecycle fields (e.g. `delta` at a non-delta boundary, `tool_name`
/// before `tool_details`) read as nil on the Lua side, so handlers can branch
/// on presence (`if event.tool_name then ...`).
fn pushStringOrNil(L: *c.lua_State, s: []const u8) void {
    if (s.len == 0) {
        c.lua_pushnil(L);
    } else {
        _ = c.lua_pushlstring(L, s.ptr, s.len);
    }
}

fn pushPayloadField(L: *c.lua_State, ev: *Event, key: []const u8) void {
    switch (ev.payload) {
        .tool => |t| {
            // index/tool_name plus the lifecycle fields: `id` (resolved
            // call id), `delta` (this args chunk on tool_delta), `input`
            // (accumulated/final args), `output` (the result text on
            // tool_result). String fields return nil when empty/absent so a
            // handler can test `if event.delta then ...`.
            if (std.mem.eql(u8, key, "index")) {
                c.lua_pushinteger(L, @intCast(t.index));
                return;
            }
            if (std.mem.eql(u8, key, "tool_name")) return pushStringOrNil(L, t.tool_name);
            if (std.mem.eql(u8, key, "id")) return pushStringOrNil(L, t.id);
            if (std.mem.eql(u8, key, "delta")) return pushStringOrNil(L, t.delta);
            if (std.mem.eql(u8, key, "input")) return pushStringOrNil(L, t.input);
            if (std.mem.eql(u8, key, "output")) return pushStringOrNil(L, t.output);
        },
        .thinking => |t| {
            // index plus `delta` (this chunk on *_delta) and `text` (the
            // accumulated/final buffer). Empty -> nil.
            if (std.mem.eql(u8, key, "index")) {
                c.lua_pushinteger(L, @intCast(t.index));
                return;
            }
            if (std.mem.eql(u8, key, "delta")) return pushStringOrNil(L, t.delta);
            if (std.mem.eql(u8, key, "text")) return pushStringOrNil(L, t.text);
        },
        .assistant_text => |t| {
            // Same lifecycle fields as thinking.
            if (std.mem.eql(u8, key, "index")) {
                c.lua_pushinteger(L, @intCast(t.index));
                return;
            }
            if (std.mem.eql(u8, key, "delta")) return pushStringOrNil(L, t.delta);
            if (std.mem.eql(u8, key, "text")) return pushStringOrNil(L, t.text);
        },
        .user_message => |m| {
            if (std.mem.eql(u8, key, "text")) {
                _ = c.lua_pushlstring(L, m.text.ptr, m.text.len);
                return;
            }
        },
        .session_start => |s| {
            if (std.mem.eql(u8, key, "version")) {
                _ = c.lua_pushlstring(L, s.version.ptr, s.version.len);
                return;
            }
            if (std.mem.eql(u8, key, "cwd")) {
                _ = c.lua_pushlstring(L, s.cwd.ptr, s.cwd.len);
                return;
            }
            if (std.mem.eql(u8, key, "model")) {
                _ = c.lua_pushlstring(L, s.model.ptr, s.model.len);
                return;
            }
        },
        .compaction => |cm| {
            if (std.mem.eql(u8, key, "summary")) {
                _ = c.lua_pushlstring(L, cm.summary.ptr, cm.summary.len);
                return;
            }
        },
        .custom => {},
    }
    c.lua_pushnil(L);
}

/// `event:get_component()` -> the current component as a native-passthrough
/// userdata (or nil). The userdata wraps the `Component` (vtable+ptr) so
/// Lua can pass it straight back to `set_component` unchanged (§7.5 wrap
/// pattern: the inner is opaque to Lua but re-settable / wrappable).
fn eventGetComponentThunk(L_opt: ?*c.lua_State) callconv(.c) c_int {
    const L = L_opt.?;
    // arg 1 is the event userdata (method call `event:get_component()`).
    const ud: **EventBridge = @ptrCast(@alignCast(c.luaL_checkudata(L, 1, eventMtName) orelse return 0));
    const bridge = ud.*;
    const ev = bridge.active_event orelse {
        c.lua_pushnil(L);
        return 1;
    };
    if (ev.getComponent()) |comp| {
        pushNativeComponent(L, comp);
    } else {
        c.lua_pushnil(L);
    }
    return 1;
}

/// `event:set_component(c)` where `c` is EITHER a native-passthrough
/// userdata (from `get_component`) OR a Lua component table. A table is
/// bridged into a native `Component` (§7.6); a userdata passes the native
/// component straight through.
fn eventSetComponentThunk(L_opt: ?*c.lua_State) callconv(.c) c_int {
    const L = L_opt.?;
    const ud: **EventBridge = @ptrCast(@alignCast(c.luaL_checkudata(L, 1, eventMtName) orelse return 0));
    const bridge = ud.*;
    const ev = bridge.active_event orelse return 0;

    const ty = c.lua_type(L, 2);
    if (ty == lua_bridge.T_USERDATA) {
        // Native passthrough: recover the Component from the userdata.
        if (c.luaL_testudata(L, 2, nativeCompMtName)) |raw| {
            const cud: *Component = @ptrCast(@alignCast(raw));
            ev.setComponent(cud.*);
            return 0;
        }
        return c.luaL_error(L, "set_component: unknown userdata (expected a component)");
    }
    if (ty == lua_bridge.T_TABLE) {
        const comp = bridge.makeBridgedComponent(2) catch {
            return c.luaL_error(L, "set_component: failed to bridge Lua component");
        };
        ev.setComponent(comp);
        return 0;
    }
    return c.luaL_error(L, "set_component: argument must be a component (table or native handle)");
}

/// Push a native `Component` as a passthrough userdata with the
/// native-component metatable (so `set_component` can recover it).
fn pushNativeComponent(L: *c.lua_State, comp: Component) void {
    const ud: *Component = @ptrCast(@alignCast(c.lua_newuserdatauv(L, @sizeOf(Component), 0).?));
    ud.* = comp;
    ensureNativeCompMetatable(L);
    _ = c.lua_setmetatable(L, -2);
}

fn ensureNativeCompMetatable(L: *c.lua_State) void {
    // A bare named metatable (no methods); identity-only so
    // `luaL_testudata` can recognize the passthrough handle.
    _ = c.luaL_newmetatable(L, nativeCompMtName);
}

/// Read the top-of-stack Lua error as text (after a failed pcall).
fn luaErrText(L: *c.lua_State) []const u8 {
    var len: usize = 0;
    const ptr = c.lua_tolstring(L, -1, &len);
    if (ptr == null) return "lua error";
    return ptr[0..len];
}

/// Re-type the cache's owned lines as `[]const []const u8` for the vtable
/// return (mirrors the native components' `cacheLines`).
fn cacheLines(cache: *RenderCache) []const []const u8 {
    const owned = cache.lines orelse return &.{};
    return @ptrCast(owned);
}

// ===========================================================================
// emit: Lua `panto.ext.emit(name, data)` -> native EventBus
// ===========================================================================

/// C thunk installed as `panto.ext.emit` by the runtime (`installEmit`),
/// carrying the `*EventBridge` as a light-userdata upvalue. Fires a custom
/// event on the native bus so native AND Lua handlers run. The `data`
/// argument is currently surfaced to handlers only as a `.custom` payload
/// (opaque); structured custom-data marshalling can be added later. The
/// chosen component (if any handler set one) is NOT auto-mounted here —
/// imperative mounting from a bare `emit` is a future refinement; for now
/// `emit` drives handler side effects and component selection for events
/// the app fires at real component-creation boundaries.
pub fn emitThunk(L_opt: ?*c.lua_State) callconv(.c) c_int {
    const L = L_opt.?;
    const self_ptr = c.lua_touserdata(L, c.lua_upvalueindex(1));
    if (self_ptr == null) return 0;
    const bridge: *EventBridge = @ptrCast(@alignCast(self_ptr.?));
    const bus = bridge.bus orelse return 0; // no bus yet: no-op

    var nlen: usize = 0;
    const nptr = c.lua_tolstring(L, 1, &nlen);
    if (nptr == null) return c.luaL_error(L, "emit: first argument must be an event name string");
    const name = nptr[0..nlen];

    var ev = Event.init(name, null, .{ .custom = .{} });
    _ = bus.emit(&ev);
    return 0;
}

// ===========================================================================
// Tests
// ===========================================================================

const testing = std.testing;

/// Test helper: harvest every `panto.ext.on` registration currently in the
/// state's on-registrations table into `bridge`, in order. Mirrors what
/// `LuaRuntime.harvestAndStoreOnHandlers` does, without the full runtime.
fn harvestOnInto(bridge: *EventBridge) !void {
    const L = bridge.L;
    _ = c.lua_rawgetp(L, lua_bridge.LUA_REGISTRYINDEX, &lua_bridge.on_registrations_key);
    defer c.lua_settop(L, c.lua_gettop(L) - 1);
    const n: usize = @intCast(c.lua_rawlen(L, -1));
    var i: usize = 1;
    while (i <= n) : (i += 1) {
        _ = c.lua_rawgeti(L, -1, @intCast(i));
        defer c.lua_settop(L, c.lua_gettop(L) - 1);
        _ = c.lua_getfield(L, -1, "event");
        var elen: usize = 0;
        const eptr = c.lua_tolstring(L, -1, &elen);
        const name = if (eptr != null) eptr[0..elen] else "";
        c.lua_settop(L, c.lua_gettop(L) - 1);
        _ = c.lua_getfield(L, -1, "handler");
        try bridge.registerOnHandler(name, -1);
        c.lua_settop(L, c.lua_gettop(L) - 1);
    }
}

fn runScript(L: *c.lua_State, src: [:0]const u8) !void {
    // `panto` is not a global; extensions reach it via `require('panto')`.
    // Prepend the require so these bridge tests can keep using `panto.ext`
    // without each script repeating the boilerplate.
    var buf: [8192]u8 = undefined;
    const wrapped = std.fmt.bufPrintZ(&buf, "local panto = require(\"panto\")\n{s}", .{src}) catch return error.LuaScriptFailed;
    if (c.luaL_loadstring(L, wrapped.ptr) != 0 or c.lua_pcallk(L, 0, 0, 0, 0, null) != 0) {
        var len: usize = 0;
        const msg = c.lua_tolstring(L, -1, &len);
        std.debug.print("lua error: {s}\n", .{msg[0..len]});
        return error.LuaScriptFailed;
    }
}

test "Lua on-handler fires through the native bus into Lua" {
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();

    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    // A handler that records the tool_name it saw into a global.
    try runScript(L,
        \\seen = nil
        \\panto.ext.on("tool", function(e) seen = e.tool_name end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);
    try testing.expectEqual(@as(usize, 1), bridge.handlerCount());

    // Fire a native tool event; the Lua handler should observe tool_name.
    _ = bus.fire("tool", null, .{ .tool = .{ .index = 3, .tool_name = "skill" } });

    _ = c.lua_getglobal(L, "seen");
    var len: usize = 0;
    const ptr = c.lua_tolstring(L, -1, &len);
    try testing.expect(ptr != null);
    try testing.expectEqualStrings("skill", ptr[0..len]);
    c.lua_settop(L, c.lua_gettop(L) - 1);
}

test "Lua-defined component renders lines through the bridged vtable" {
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    // A handler that sets a Lua component whose render returns two lines.
    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({
        \\    render = function(self, width) return { "hello", "world" } end,
        \\  })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    const chosen = bus.fire("tool", null, .{ .tool = .{ .index = 0, .tool_name = "x" } });
    try testing.expect(chosen != null);

    // Render the bridged component at width 80.
    const lines = try chosen.?.render(80, testing.allocator);
    try testing.expectEqual(@as(usize, 2), lines.len);
    try testing.expectEqualStrings("hello", lines[0]);
    try testing.expectEqualStrings("world", lines[1]);
    // firstLineChanged is cache-derived and is the LIVE signal: after a render
    // the cache is clean, so it reports null (the first-render diff index 0 is
    // retained internally as bookkeeping only).
    try testing.expectEqual(@as(?usize, null), chosen.?.firstLineChanged());
    // A second identical render still reports no change.
    _ = try chosen.?.render(80, testing.allocator);
    try testing.expectEqual(@as(?usize, null), chosen.?.firstLineChanged());
}

test "bridged component render truncates to the width contract" {
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({
        \\    render = function(self, width) return { "abcdefghij" } end,
        \\  })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    const chosen = bus.fire("tool", null, .{ .tool = .{} }).?;
    const lines = try chosen.render(4, testing.allocator);
    try testing.expectEqual(@as(usize, 1), lines.len);
    // Truncated to 4 columns.
    try testing.expectEqualStrings("abcd", lines[0]);
}

test "bridged component render error yields a safe fallback line, not a crash" {
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({
        \\    render = function(self, width) error("boom") end,
        \\  })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    const chosen = bus.fire("tool", null, .{ .tool = .{} }).?;
    const lines = try chosen.render(80, testing.allocator);
    try testing.expectEqual(@as(usize, 1), lines.len);
    try testing.expect(std.mem.indexOf(u8, lines[0], "lua component error") != null);
}

test "wrap pattern: Lua reads the native default, wraps it, and renders through it" {
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    // The native default: a component rendering one line "DEFAULT".
    const NativeDefault = struct {
        cache: RenderCache,
        fn renderImpl(ptr: *anyopaque, width: usize, alloc: std.mem.Allocator) anyerror![]const []const u8 {
            _ = width;
            _ = alloc;
            const self: *@This() = @ptrCast(@alignCast(ptr));
            const one = [_][]const u8{"DEFAULT"};
            try self.cache.store(&one);
            const owned = self.cache.lines orelse return &.{};
            return @ptrCast(owned);
        }
        fn fcImpl(ptr: *anyopaque) ?usize {
            const self: *@This() = @ptrCast(@alignCast(ptr));
            return self.cache.firstLineChanged();
        }
        fn invImpl(ptr: *anyopaque) void {
            const self: *@This() = @ptrCast(@alignCast(ptr));
            self.cache.invalidate();
        }
        const vt = Component.VTable{ .render = renderImpl, .firstLineChanged = fcImpl, .invalidate = invImpl };
        fn comp(self: *@This()) Component {
            return .{ .ptr = self, .vtable = &vt };
        }
    };
    var nd = NativeDefault{ .cache = RenderCache.init(testing.allocator) };
    defer nd.cache.deinit();

    // Handler: read the native default via get_component, store it, set a Lua
    // component that renders "[" .. inner_first_line .. "]".
    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  local inner = e:get_component()        -- native passthrough handle
        \\  e:set_component({
        \\    inner = inner,
        \\    render = function(self, width)
        \\      -- We cannot call the native inner's render from Lua (it has no
        \\      -- Lua method); the wrap here decorates around it. Prove we held
        \\      -- the handle by setting it back is exercised by passthrough test.
        \\      return { "wrapped" }
        \\    end,
        \\  })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    const chosen = bus.fire("tool", nd.comp(), .{ .tool = .{} }).?;
    // The chosen component is the Lua wrapper, not the native default.
    try testing.expect(chosen.ptr != nd.comp().ptr);
    const lines = try chosen.render(80, testing.allocator);
    try testing.expectEqual(@as(usize, 1), lines.len);
    try testing.expectEqualStrings("wrapped", lines[0]);
}

test "skills-style claim-by-name (§7.5) works end-to-end through the Lua bridge" {
    // The canonical extension pattern: a Lua handler subscribes to `tool`,
    // returns early UNLESS event.tool_name matches its tool, and otherwise
    // set_component's a Lua-defined component. We fire two tool events through
    // the NATIVE bus and assert only the matching name is claimed (its Lua
    // component renders), while a non-matching name keeps the native default.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    // NOTE: the `event` object is only valid DURING the handler call; a
    // component must capture any payload it needs into its own state at handler
    // time, NOT close over `e` and read it at render time. Here we snapshot the
    // name into a local that the render closure captures.
    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  if e.tool_name ~= "skill" then return end   -- claim-by-name
        \\  local name = e.tool_name                    -- snapshot at handler time
        \\  e:set_component({
        \\    render = function(self, width) return { "SKILL:" .. name } end,
        \\  })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    // A native default the handler may or may not replace.
    const Native = struct {
        cache: RenderCache,
        fn renderImpl(ptr: *anyopaque, width: usize, alloc: std.mem.Allocator) anyerror![]const []const u8 {
            _ = width;
            _ = alloc;
            const self: *@This() = @ptrCast(@alignCast(ptr));
            const one = [_][]const u8{"NATIVE-DEFAULT"};
            try self.cache.store(&one);
            const owned = self.cache.lines orelse return &.{};
            return @ptrCast(owned);
        }
        fn fcImpl(ptr: *anyopaque) ?usize {
            const self: *@This() = @ptrCast(@alignCast(ptr));
            return self.cache.firstLineChanged();
        }
        fn invImpl(ptr: *anyopaque) void {
            const self: *@This() = @ptrCast(@alignCast(ptr));
            self.cache.invalidate();
        }
        const vt = Component.VTable{ .render = renderImpl, .firstLineChanged = fcImpl, .invalidate = invImpl };
        fn comp(self: *@This()) Component {
            return .{ .ptr = self, .vtable = &vt };
        }
    };

    // Non-matching name ("read"): the handler returns early, the default stays.
    {
        var nd = Native{ .cache = RenderCache.init(testing.allocator) };
        defer nd.cache.deinit();
        const chosen = bus.fire("tool", nd.comp(), .{ .tool = .{ .index = 0, .tool_name = "read" } }).?;
        try testing.expectEqual(@as(*anyopaque, nd.comp().ptr), chosen.ptr); // unchanged
        const lines = try chosen.render(80, testing.allocator);
        try testing.expectEqualStrings("NATIVE-DEFAULT", lines[0]);
    }

    // Matching name ("skill"): the handler claims it with a Lua component.
    {
        var nd = Native{ .cache = RenderCache.init(testing.allocator) };
        defer nd.cache.deinit();
        const chosen = bus.fire("tool", nd.comp(), .{ .tool = .{ .index = 1, .tool_name = "skill" } }).?;
        try testing.expect(chosen.ptr != nd.comp().ptr); // replaced by the Lua component
        const lines = try chosen.render(80, testing.allocator);
        try testing.expectEqual(@as(usize, 1), lines.len);
        try testing.expectEqualStrings("SKILL:skill", lines[0]);
    }
}

test "native-passthrough get/set round-trip: set_component(get_component()) keeps the native default" {
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    const Native = struct {
        line_storage: [1][]const u8 = undefined,
        fn renderImpl(ptr: *anyopaque, width: usize, alloc: std.mem.Allocator) anyerror![]const []const u8 {
            _ = width;
            _ = alloc;
            const self: *@This() = @ptrCast(@alignCast(ptr));
            self.line_storage[0] = "N";
            return self.line_storage[0..];
        }
        fn fcImpl(ptr: *anyopaque) ?usize {
            _ = ptr;
            return 0;
        }
        fn invImpl(ptr: *anyopaque) void {
            _ = ptr;
        }
        const vt = Component.VTable{ .render = renderImpl, .firstLineChanged = fcImpl, .invalidate = invImpl };
        fn comp(self: *@This()) Component {
            return .{ .ptr = self, .vtable = &vt };
        }
    };
    var native = Native{};

    // Handler passes the native default straight back through.
    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  e:set_component(e:get_component())
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    const chosen = bus.fire("tool", native.comp(), .{ .tool = .{} }).?;
    // Round-trip preserved the SAME native component pointer.
    try testing.expectEqual(@as(*anyopaque, native.comp().ptr), chosen.ptr);
}

test "Lua emit drives the native bus (custom event reaches a native handler)" {
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    // Install the real emit (carrying the bridge) so Lua emit reaches the bus.
    lua_bridge.installEmit(L, @ptrCast(&bridge), emitThunk);
    try bridge.attachBus(&bus);

    // A NATIVE handler that flips a flag when "custom-thing" fires.
    const Flag = struct {
        hit: bool = false,
        fn cb(ctx: *anyopaque, ev: *Event) void {
            _ = ev;
            const self: *@This() = @ptrCast(@alignCast(ctx));
            self.hit = true;
        }
    };
    var flag = Flag{};
    try bus.on("custom-thing", .{ .ctx = &flag, .callback = Flag.cb });

    // Fire it from Lua.
    try runScript(L, "panto.ext.emit(\"custom-thing\", {})");
    try testing.expect(flag.hit);
}

test "bridged render: a long error on a NARROW width still satisfies the width contract" {
    // Regression: the safe fallback line must itself obey the engine's width
    // contract (visible width <= width). Otherwise the engine rejects it with
    // LineOverflow and crashes the exact frame the fallback exists to save.
    // We render a crashing component at a width far narrower than the error
    // text and assert the produced line's visible width fits.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({
        \\    render = function(self, width) error("a very long error message that definitely exceeds a narrow terminal width") end,
        \\  })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    const chosen = bus.fire("tool", null, .{ .tool = .{} }).?;
    const width: usize = 10;
    const lines = try chosen.render(width, testing.allocator);
    try testing.expectEqual(@as(usize, 1), lines.len);
    // The crux: visible width must fit, even though the raw error is long.
    try testing.expect(engine.visibleWidth(lines[0]) <= width);
}

test "bridged render: non-array / nil / non-string returns each yield a safe fallback" {
    // render() must return an array of strings. A table-with-non-strings, a
    // bare nil, and a non-table scalar each route to the fallback line rather
    // than crashing or leaking.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    // Three components, each returning a malformed render value.
    try runScript(L,
        \\components = {
        \\  function(self, width) return { {} } end,   -- array of a table (non-string)
        \\  function(self, width) return nil end,       -- nil
        \\  function(self, width) return 42 end,        -- non-table scalar
        \\}
        \\idx = 0
        \\panto.ext.on("tool", function(e)
        \\  idx = idx + 1
        \\  e:set_component({ render = components[idx] })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    inline for (0..3) |_| {
        const chosen = bus.fire("tool", null, .{ .tool = .{} }).?;
        const lines = try chosen.render(80, testing.allocator);
        try testing.expectEqual(@as(usize, 1), lines.len);
        try testing.expect(std.mem.indexOf(u8, lines[0], "lua component error") != null);
    }
}

test "bridged render: empty array renders zero lines (no fallback)" {
    // An empty table is a VALID render result (zero lines), distinct from a
    // malformed return. It must produce no lines and no error.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({ render = function(self, width) return {} end })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    const chosen = bus.fire("tool", null, .{ .tool = .{} }).?;
    const lines = try chosen.render(80, testing.allocator);
    try testing.expectEqual(@as(usize, 0), lines.len);
}

test "bridged render: UTF-8 line truncates on codepoint boundaries to the width" {
    // The width contract counts visible columns as codepoints. A multibyte
    // line must truncate on a codepoint boundary, never mid-sequence, and the
    // result's visible width must fit.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    // "ééééé" is 5 codepoints, 10 bytes. Truncating to 3 columns must yield
    // exactly 3 codepoints (6 bytes), not split a 2-byte sequence.
    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({ render = function(self, width) return { "\195\169\195\169\195\169\195\169\195\169" } end })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    const chosen = bus.fire("tool", null, .{ .tool = .{} }).?;
    const lines = try chosen.render(3, testing.allocator);
    try testing.expectEqual(@as(usize, 1), lines.len);
    try testing.expectEqual(@as(usize, 3), engine.visibleWidth(lines[0]));
    // 3 codepoints * 2 bytes each = 6 bytes, intact.
    try testing.expectEqual(@as(usize, 6), lines[0].len);
}

test "bridged firstLineChanged is cache-derived: append stays near the tail" {
    // The bridge owns a native RenderCache, so a streaming component that
    // appends a line reports firstLineChanged near the TAIL (the append
    // boundary), not 0 — the same streaming-tail property native components
    // get. We drive a Lua component whose render output grows by one line.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    // `n` lines on each render, controlled by a global the test bumps.
    try runScript(L,
        \\n = 2
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({
        \\    render = function(self, width)
        \\      local t = {}
        \\      for i = 1, n do t[i] = "line" .. i end
        \\      return t
        \\    end,
        \\  })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);
    const chosen = bus.fire("tool", null, .{ .tool = .{} }).?;

    // First render: 2 lines. After the render the cache is clean, so the live
    // signal is null (the first-render diff index 0 is internal bookkeeping).
    _ = try chosen.render(80, testing.allocator);
    try testing.expectEqual(@as(?usize, null), chosen.firstLineChanged());
    // No change: still null.
    _ = try chosen.render(80, testing.allocator);
    try testing.expectEqual(@as(?usize, null), chosen.firstLineChanged());

    // Append a 3rd line: the cache diff reports the boundary (index 2), NOT 0.
    try runScript(L, "n = 3");
    chosen.invalidate(); // re-dirty so render recomputes
    _ = try chosen.render(80, testing.allocator);
    // invalidate() drops to a full re-dirty (from 0), so this proves the cache
    // path is wired; the precise tail-index is covered by native RenderCache
    // tests. Re-render once more with no change to confirm it settles to null.
    _ = try chosen.render(80, testing.allocator);
    try testing.expectEqual(@as(?usize, null), chosen.firstLineChanged());
}

test "bridged firstLineChanged: a mid-line replace reports the changed line, shrink reports the boundary" {
    // Cache-derived diff on REPLACE and SHRINK, mirroring native RenderCache
    // expectations through the bridge.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    try runScript(L,
        \\lines = { "a", "b", "c" }
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({ render = function(self, width) return lines end })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);
    const chosen = bus.fire("tool", null, .{ .tool = .{} }).?;

    _ = try chosen.render(80, testing.allocator); // dirty from 0
    _ = try chosen.render(80, testing.allocator); // null
    try testing.expectEqual(@as(?usize, null), chosen.firstLineChanged());

    // Replace the MIDDLE line. Diff must report index 1.
    try runScript(L, "lines = { \"a\", \"B\", \"c\" }");
    chosen.invalidate();
    _ = try chosen.render(80, testing.allocator);
    // After invalidate the first render dirties from 0; settle, then mutate
    // WITHOUT invalidate to exercise the pure diff path is not possible here
    // (the bridge re-dirties only via invalidate/markDirty). The diff index on
    // a settled-then-changed render is covered natively; here we confirm a
    // shrink settles cleanly.
    _ = try chosen.render(80, testing.allocator);

    // Shrink to 1 line.
    try runScript(L, "lines = { \"a\" }");
    chosen.invalidate();
    _ = try chosen.render(80, testing.allocator);
    const shrunk = try chosen.render(80, testing.allocator);
    try testing.expectEqual(@as(usize, 1), shrunk.len);
    try testing.expectEqualStrings("a", shrunk[0]);
}

test "bridged handleInput round-trips: a Lua method mutates state the next render reflects" {
    // handleInput(self, data) is bridged synchronously. A component that
    // accumulates input bytes must show them on the subsequent render.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({
        \\    buf = "",
        \\    handleInput = function(self, data) self.buf = self.buf .. data end,
        \\    render = function(self, width) return { self.buf } end,
        \\  })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);
    const chosen = bus.fire("tool", null, .{ .tool = .{} }).?;

    // Render once and settle the cache to clean (firstLineChanged == null).
    _ = try chosen.render(80, testing.allocator);
    _ = try chosen.render(80, testing.allocator);
    try testing.expectEqual(@as(?usize, null), chosen.firstLineChanged());

    // After input, the cache MUST be dirty so the engine (which reads
    // firstLineChanged BEFORE render) actually re-renders the component.
    chosen.handleInput("he");
    try testing.expect(chosen.firstLineChanged() != null);
    chosen.handleInput("llo");
    try testing.expect(chosen.firstLineChanged() != null);

    const lines = try chosen.render(80, testing.allocator);
    try testing.expectEqual(@as(usize, 1), lines.len);
    try testing.expectEqualStrings("hello", lines[0]);
}

test "bridged component: invalidate frees the ref+cache eagerly; teardown is leak-free" {
    // invalidate() on the COMPONENT vtable maps to cache.invalidate (re-dirty),
    // NOT a free — freeing happens at teardown for all tracked components. This
    // test sets several Lua components, renders them, and relies on the leak-
    // checked test allocator: if any ref or cache leaks, the allocator reports
    // it at deinit and the test fails.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit(); // frees all tracked BridgedComponents
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({ render = function(self, width) return { "x", "y" } end })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    // Create several distinct bridged components (each fire makes a new one).
    var i: usize = 0;
    while (i < 5) : (i += 1) {
        const chosen = bus.fire("tool", null, .{ .tool = .{} }).?;
        _ = try chosen.render(40, testing.allocator);
        chosen.invalidate(); // re-dirty; must not leak the cache on next render
        _ = try chosen.render(40, testing.allocator);
    }
    // bridge.deinit() (deferred) frees every tracked component's ref + cache;
    // the leak-checked allocator asserts no leaks.
}

test "lifecycle payload fields marshal to Lua: tool id/delta/input/output, thinking/assistant delta/text" {
    // Every new lifecycle field must be readable from a Lua handler, and an
    // empty field must read as nil so handlers can branch on presence.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    // Handlers stash what they saw into Lua globals we then assert on.
    try runScript(L,
        \\seen = {}
        \\panto.ext.on("tool_delta", function(e)
        \\  seen.delta = e.delta; seen.tn = e.tool_name; seen.idx = e.index
        \\end)
        \\panto.ext.on("tool_call_complete", function(e)
        \\  seen.input = e.input; seen.id = e.id
        \\end)
        \\panto.ext.on("tool_result", function(e)
        \\  seen.output = e.output; seen.rid = e.id
        \\end)
        \\panto.ext.on("thinking_delta", function(e)
        \\  seen.t_delta = e.delta; seen.t_text = e.text
        \\end)
        \\panto.ext.on("assistant_text_complete", function(e)
        \\  seen.a_text = e.text; seen.a_delta = e.delta  -- delta empty -> nil
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    _ = bus.fire("tool_delta", null, .{ .tool = .{ .index = 7, .tool_name = "read", .delta = "{\"p" } });
    _ = bus.fire("tool_call_complete", null, .{ .tool = .{ .index = 7, .tool_name = "read", .id = "call_1", .input = "{\"path\":\"x\"}" } });
    _ = bus.fire("tool_result", null, .{ .tool = .{ .index = 7, .id = "call_1", .output = "file contents" } });
    _ = bus.fire("thinking_delta", null, .{ .thinking = .{ .index = 2, .delta = "hm", .text = "hm" } });
    _ = bus.fire("assistant_text_complete", null, .{ .assistant_text = .{ .index = 0, .text = "done" } });

    // Assert via Lua, surfacing failures as a thrown Lua error.
    try runScript(L,
        \\assert(seen.delta == "{\"p", "tool_delta.delta")
        \\assert(seen.tn == "read", "tool_delta.tool_name")
        \\assert(seen.idx == 7, "tool_delta.index")
        \\assert(seen.input == "{\"path\":\"x\"}", "tool_call_complete.input")
        \\assert(seen.id == "call_1", "tool_call_complete.id")
        \\assert(seen.output == "file contents", "tool_result.output")
        \\assert(seen.rid == "call_1", "tool_result.id")
        \\assert(seen.t_delta == "hm" and seen.t_text == "hm", "thinking_delta")
        \\assert(seen.a_text == "done", "assistant_text_complete.text")
        \\assert(seen.a_delta == nil, "empty delta must be nil")
    );
}

test "lifecycle handlers fire for every new event name" {
    // Confirm dispatch is purely by event-name string: a handler on each new
    // lifecycle event name actually runs. No new dispatch machinery exists;
    // this guards that the names are routed.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    try runScript(L,
        \\fired = {}
        \\for _, name in ipairs({
        \\  "tool", "tool_details", "tool_delta", "tool_call_complete", "tool_result",
        \\  "thinking", "thinking_delta", "thinking_complete",
        \\  "assistant_text", "assistant_text_delta", "assistant_text_complete",
        \\}) do
        \\  panto.ext.on(name, function(e) fired[name] = (fired[name] or 0) + 1 end)
        \\end
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    _ = bus.fire("tool", null, .{ .tool = .{} });
    _ = bus.fire("tool_details", null, .{ .tool = .{ .tool_name = "x", .id = "c" } });
    _ = bus.fire("tool_delta", null, .{ .tool = .{ .delta = "a" } });
    _ = bus.fire("tool_call_complete", null, .{ .tool = .{ .input = "{}" } });
    _ = bus.fire("tool_result", null, .{ .tool = .{ .output = "r" } });
    _ = bus.fire("thinking", null, .{ .thinking = .{} });
    _ = bus.fire("thinking_delta", null, .{ .thinking = .{ .delta = "t" } });
    _ = bus.fire("thinking_complete", null, .{ .thinking = .{ .text = "t" } });
    _ = bus.fire("assistant_text", null, .{ .assistant_text = .{} });
    _ = bus.fire("assistant_text_delta", null, .{ .assistant_text = .{ .delta = "a" } });
    _ = bus.fire("assistant_text_complete", null, .{ .assistant_text = .{ .text = "a" } });

    try runScript(L,
        \\for _, name in ipairs({
        \\  "tool", "tool_details", "tool_delta", "tool_call_complete", "tool_result",
        \\  "thinking", "thinking_delta", "thinking_complete",
        \\  "assistant_text", "assistant_text_delta", "assistant_text_complete",
        \\}) do
        \\  assert(fired[name] == 1, "handler did not fire exactly once for " .. name)
        \\end
    );
}

test "claim-by-name at tool_details swaps over the start default; releasing the prior override is leak-free" {
    // The revised lifecycle: `tool` fires at block_start (name unknown), a Lua
    // handler may set a placeholder; then `tool_details` fires with the name
    // and a handler claims the call by name and swaps a NEW Lua component over
    // the prior one. The superseded override is handed to releaseOverride,
    // which must drop its luaL_ref + cache (the leak-prevention path). The
    // leak-checked test allocator asserts no leak across the swap.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    try runScript(L,
        \\-- At block_start the name is unknown; set a placeholder Lua component.
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({ render = function(self, w) return { "tool (?)" } end })
        \\end)
        \\-- At tool_details, claim by name and swap in the real component.
        \\panto.ext.on("tool_details", function(e)
        \\  if e.tool_name ~= "skill" then return end
        \\  e:set_component({ render = function(self, w) return { "SKILL" } end })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    // block_start: handler sets the placeholder Lua component.
    const start = bus.fire("tool", null, .{ .tool = .{ .index = 0 } }).?;
    {
        const lines = try start.render(40, testing.allocator);
        try testing.expectEqual(@as(usize, 1), lines.len);
        try testing.expectEqualStrings("tool (?)", lines[0]);
    }
    // Two distinct Lua components were created so far would leak if not freed;
    // track the count before the swap.
    try testing.expectEqual(@as(usize, 1), bridge.components.items.len);

    // tool_details: seed the event with the CURRENT override (the placeholder),
    // mirroring how the App seeds get_component with the current component. The
    // handler claims "skill" and swaps in "SKILL".
    const details = bus.fire("tool_details", start, .{ .tool = .{ .index = 0, .tool_name = "skill", .id = "c0" } }).?;
    try testing.expect(details.ptr != start.ptr); // a NEW component
    {
        const lines = try details.render(40, testing.allocator);
        try testing.expectEqualStrings("SKILL", lines[0]);
    }
    // Now two bridged components are tracked (placeholder + skill).
    try testing.expectEqual(@as(usize, 2), bridge.components.items.len);

    // The App's mid-stream swap hands the SUPERSEDED override (the placeholder
    // `start`) back to the release hook. Exercise it directly.
    bridge.releaseOverride(start);
    // The placeholder is freed and untracked; only the skill component remains.
    try testing.expectEqual(@as(usize, 1), bridge.components.items.len);

    // The surviving component still renders correctly after the release.
    const lines = try details.render(40, testing.allocator);
    try testing.expectEqualStrings("SKILL", lines[0]);

    // releaseOverride on a NATIVE component is a no-op (different vtable).
    const Native = struct {
        cache: RenderCache,
        fn r(ptr: *anyopaque, w: usize, a: std.mem.Allocator) anyerror![]const []const u8 {
            _ = w;
            _ = a;
            const s: *@This() = @ptrCast(@alignCast(ptr));
            const one = [_][]const u8{"N"};
            try s.cache.store(&one);
            return @ptrCast(s.cache.lines orelse return &.{});
        }
        fn fc(ptr: *anyopaque) ?usize {
            const s: *@This() = @ptrCast(@alignCast(ptr));
            return s.cache.firstLineChanged();
        }
        fn inv(ptr: *anyopaque) void {
            const s: *@This() = @ptrCast(@alignCast(ptr));
            s.cache.invalidate();
        }
        const vt = Component.VTable{ .render = r, .firstLineChanged = fc, .invalidate = inv };
        fn comp(s: *@This()) Component {
            return .{ .ptr = s, .vtable = &vt };
        }
    };
    var native = Native{ .cache = RenderCache.init(testing.allocator) };
    defer native.cache.deinit();
    bridge.releaseOverride(native.comp()); // must NOT touch our tracked list
    try testing.expectEqual(@as(usize, 1), bridge.components.items.len);
    // bridge.deinit() frees the remaining skill component; allocator asserts no leak.
}

test "intra-emit clobber: two handlers each mint a Lua component in ONE emit; both are tracked and freed at teardown (no true leak)" {
    // §7.3 "last-wins-blind": when two handlers for the SAME event each call
    // set_component within a single emit, the bus keeps only the last as
    // `current`. The App records only that last one as the entry's override,
    // so the FIRST handler's freshly-minted Lua component is never handed to
    // `releaseOverride` (the App never sees it). It is therefore NOT released
    // mid-stream — it lingers in `bridge.components` until teardown.
    //
    // This test pins that behavior precisely:
    //   - it is NOT a true leak: `bridge.deinit` frees every tracked component
    //     (the leak-checked allocator below would fail otherwise);
    //   - but it IS per-emit accumulation: a clobbering handler chain grows
    //     `bridge.components` by one orphan per clobber for the runtime's life.
    //
    // The documented mitigation is the §7.3 wrap pattern (get_component ->
    // wrap -> set_component), under which no component is orphaned because each
    // handler decorates the current one instead of minting a rival. A handler
    // that clobbers blind is at fault per the plan; the resource is still
    // reclaimed at teardown, so correctness (no UAF / no true leak) holds.
    const L = c.luaL_newstate() orelse return error.LuaInitFailed;
    defer c.lua_close(L);
    c.luaL_openlibs(L);
    lua_bridge.install(L);
    lua_bridge.installTestPantoTable(L);

    var bridge = EventBridge.init(testing.allocator, L);
    defer bridge.deinit();
    var bus = EventBus.init(testing.allocator);
    defer bus.deinit();

    // Two blind-clobber handlers for the same event: each mints its own Lua
    // component, ignoring the current one.
    try runScript(L,
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({ render = function(self, w) return { "FIRST" } end })
        \\end)
        \\panto.ext.on("tool", function(e)
        \\  e:set_component({ render = function(self, w) return { "SECOND" } end })
        \\end)
    );
    try harvestOnInto(&bridge);
    try bridge.attachBus(&bus);

    const chosen = bus.fire("tool", null, .{ .tool = .{ .index = 0 } }).?;
    // The LAST handler won.
    {
        const lines = try chosen.render(40, testing.allocator);
        try testing.expectEqualStrings("SECOND", lines[0]);
    }
    // BOTH components were minted and tracked: the first is now an orphan that
    // the App can never release (it only saw `chosen`). It is reclaimed only
    // at teardown.
    try testing.expectEqual(@as(usize, 2), bridge.components.items.len);

    // bridge.deinit() (deferred) frees BOTH — the leak-checked allocator proves
    // there is no TRUE leak even though the orphan was never released mid-stream.
}