cmms-embed: ai-bridge apply — carry newly-placed symbols' (lib_symbols) defs

The cmms-ai-editor-apply handler diffed the proposed sheet with docDelta and
pushed the item delta through applyDeltaToY. docDelta only diffs uuid-bearing
items; a (lib_symbols ...) definition has no uuid, so an AI proposal that
places a part the sheet has never carried landed the instance with no library
definition — KiCad drew an instance pointing at an undefined symbol (nothing).

applyToActiveBuffer now upserts the proposal's lib defs into kdoc_libsymbols
(upsert by lib id, never deletes — the CMMS's kicad_splice_elements always
splices into the existing block, so the proposal is existing ∪ additions) before
the item delta, mirroring kicad-binding.ts's own DOWN path
(upsertLibSymbolsToY(doc, defs, ORIGIN)). Deliberately not syncLayoutToY, which
would also LWW-reconcile non-item layout heads (root uuid, sheet_instances,
paper) from the proposal.

New ai-bridge.test.ts covers it (fails without the upsert: the placed symbol's
definition never reaches kdoc_libsymbols).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/standalone/src/App.tsx

@@ -1,5 +1,6 @@
 import { useEffect } from "react";
 import { Route, Routes, useLocation } from "react-router-dom";
+import { CmmsAiWidget } from "@/components/CmmsAiWidget";
 import { VersionBadge } from "@/components/VersionBadge";
 import { useChromeHidden } from "@/lib/chrome-visibility";
 import { APP_URL } from "@/lib/config";
@@ -34,6 +35,9 @@ export default function App() {
       {/* Version + source link, bottom-right on every route (home + editor).
           Keys off the Figma-like hide-UI toggle (hidden is the mobile default). */}
       {!chromeHidden && <VersionBadge />}
+      {/* No-op (fetches config, renders nothing) unless the CMMS embed's
+          ai_assistant module is on for this tenant — see CmmsAiWidget. */}
+      <CmmsAiWidget />
     </>
   );
 }

web/standalone/src/components/CmmsAiWidget.tsx

@@ -0,0 +1,139 @@
+// cmms-embed / PCBJam Part 2: floating AI-assistant launcher + panel, for the
+// CMMS embed only. Inert (renders nothing) unless `/api/cmms-config` answers
+// `aiEnabled: true` — a plain pcbjam.io deploy or a CMMS tenant with the
+// module off never fetches or renders anything here beyond the one config
+// call. Visual language (position, colors, toggle/panel shape) mirrors
+// `render_ai_assistant_editor_embed()` (TT-DB `src/ai_assistant_widget.php`)
+// so it reads as the same widget as every other embedded editor; the
+// draggable/resizable geometry system that PHP version has is CMMS-side
+// static JS this bundle can't import, so this is fixed-position (bottom
+// right) — a reasonable v1 given the panel is small relative to the board
+// canvas.
+import * as React from "react";
+import { fetchCmmsConfig, type CmmsConfig } from "@/lib/cmms-config";
+import { getActiveFilePath, installAiBridge } from "@/wasm/collab/ai-bridge";
+import { setTheme } from "@/lib/theme";
+
+export function CmmsAiWidget(): React.ReactElement | null {
+  const [config, setConfig] = React.useState<CmmsConfig | null>(null);
+  const [open, setOpen] = React.useState(false);
+
+  React.useEffect(() => {
+    let cancelled = false;
+    // fetchCmmsConfig() never rejects (its own internal .catch() falls back
+    // to NO_WIDGET) — this .catch() guards the callback body itself instead
+    // (setConfig/installAiBridge/setTheme), so a mistake here becomes a
+    // logged no-op, not a silent unhandled rejection with nothing to say why
+    // the widget didn't appear.
+    fetchCmmsConfig()
+      .then((c) => {
+        if (cancelled) return;
+        setConfig(c);
+        if (c.aiEnabled) installAiBridge();
+        // Belt-and-braces alongside the `?theme=` hand-off (lib/theme.ts) —
+        // that param already wins whenever edit.php sets it, so this only
+        // matters if it's ever absent. Skip if the URL param already ran;
+        // setTheme is otherwise idempotent (persists + toggles `.dark`).
+        if (c.dark && !new URLSearchParams(window.location.search).get("theme")) {
+          setTheme("dark");
+        }
+      })
+      .catch((err: unknown) => {
+        console.error("[cmms-ai-widget] boot failed:", err);
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, []);
+
+  if (!config?.aiEnabled) return null;
+
+  // Computed at render time (not memoized) so re-opening the panel after
+  // switching sheets sends the file that's actually open now — a context
+  // hint only; get-buffer carries the real content regardless.
+  const params = new URLSearchParams({
+    editor: "kicad",
+    editor_entity_type: config.entityType,
+    editor_entity_id: config.entityId,
+    editor_filename: getActiveFilePath() ?? "",
+    page_context: "PCBJam (KiCad editor)",
+  });
+  const src = `/modules/ai_assistant/widget-frame.php?${params.toString()}`;
+
+  return (
+    <div id="cmms-ai-widget">
+      <button
+        type="button"
+        aria-label="AI Assistant"
+        title="AI Assistant"
+        onClick={() => setOpen((v) => !v)}
+        style={{
+          position: "fixed",
+          right: 16,
+          bottom: 16,
+          zIndex: 2147483000,
+          width: 48,
+          height: 48,
+          borderRadius: "50%",
+          border: "1px solid rgba(0,0,0,0.15)",
+          display: "flex",
+          alignItems: "center",
+          justifyContent: "center",
+          background: "#ffffff",
+          color: "#1e293b",
+          cursor: "pointer",
+          padding: 0,
+          boxShadow: "0 2px 12px rgba(0,0,0,0.3)",
+        }}
+      >
+        <svg viewBox="0 0 24 24" width="24" height="24" fill="none" stroke="currentColor" strokeWidth={2} aria-hidden="true">
+          <path d="M4 4h16v12H8l-4 4V4z" strokeLinejoin="round" strokeLinecap="round" />
+        </svg>
+      </button>
+      {open && (
+        <div
+          style={{
+            position: "fixed",
+            right: 16,
+            bottom: 76,
+            zIndex: 2147483000,
+            width: 380,
+            height: 560,
+            border: "1px solid rgba(0,0,0,0.15)",
+            borderRadius: 8,
+            overflow: "hidden",
+            boxShadow: "0 6px 32px rgba(0,0,0,0.35)",
+            background: "#ffffff",
+            display: "flex",
+            flexDirection: "column",
+          }}
+        >
+          <div
+            style={{
+              flex: "none",
+              display: "flex",
+              alignItems: "center",
+              justifyContent: "space-between",
+              padding: "6px 10px",
+              background: "#f1f5f9",
+              color: "#1e293b",
+              font: "600 13px system-ui, sans-serif",
+            }}
+          >
+            <span>AI Assistant</span>
+            <button
+              type="button"
+              aria-label="Close"
+              title="Close"
+              onClick={() => setOpen(false)}
+              style={{ background: "none", border: "none", color: "inherit", cursor: "pointer", fontSize: 16, padding: "2px 6px" }}
+            >
+              &times;
+            </button>
+          </div>
+          <iframe title="AI Assistant" src={src} style={{ flex: 1, width: "100%", border: 0, display: "block", minHeight: 0 }} />
+        </div>
+      )}
+    </div>
+  );
+}

web/standalone/src/components/WasmTool.tsx

@@ -47,6 +47,7 @@ import { startFilesWatch, type FilesWatchHandle } from "@/wasm/collab/files-watc
 import { dump as dumpTrace, mark } from "@/wasm/load-trace";
 import { errorMessage, isTerminalError } from "@/wasm/terminal-error";
 import { registerSaveHook, type SaveBlock, type SaveBytes } from "@/wasm/save-flow";
+import { registerActiveCollabDoc } from "@/wasm/collab/ai-bridge";
 import type {
   KicadCollabHandle,
   KicadDocSession,
@@ -420,6 +421,7 @@ export function WasmTool({
     localSelectionRef.current?.destroy();
     localSelectionRef.current = null;
     setPanelDoc(null);
+    registerActiveCollabDoc(null);
     commentsRef.current?.destroy();
     commentsRef.current = null;
     followRef.current?.destroy();
@@ -1219,6 +1221,7 @@ export function WasmTool({
                 startPresence(activeRoom?.provider, activeRoom?.sheetPath, activeRoom?.doc);
                 startComments(activeRoom?.doc);
                 setPanelDoc(activeRoom?.doc ?? null);
+                registerActiveCollabDoc(activeRoom?.doc ?? null, activeRoom?.sheetPath);
                 if (activeRoom && !readOnly) {
                   driftRef.current = startDriftDetection({
                     doc: activeRoom.doc,
@@ -1273,6 +1276,7 @@ export function WasmTool({
           startPresence(collabHandle?.provider, undefined, collabHandle?.doc);
           startComments(collabHandle?.doc);
           setPanelDoc(collabHandle?.doc ?? null);
+          registerActiveCollabDoc(collabHandle?.doc ?? null, targetPath);
           // Live sibling mirror (project-sync 0001 bug 3): keep the schematic
           // files a PCB session syncs from fresh in MEMFS, instead of the
           // one-shot boot snapshot. Same opt-out as the room collab; read-only

web/standalone/src/lib/cmms-config.ts

@@ -0,0 +1,70 @@
+// cmms-embed / PCBJam Part 2: fetch the AI-widget config the CMMS side
+// exposes at boot. Mirrors the existing `/api/me` identity call (same-origin,
+// `credentials: "include"` for the session cookie) — see lib/api.ts.
+//
+// Absent route, non-2xx, or malformed JSON all mean "no AI widget" (a plain
+// pcbjam.io deploy, or a CMMS build where the module is off) — never throws,
+// never blocks boot.
+import { API_BASE_URL } from "@/lib/config";
+export interface CmmsConfig {
+  dark: boolean;
+  aiEnabled: boolean;
+  aiEditorKind: "kicad";
+  csrfToken: string;
+  entityType: string;
+  entityId: string;
+}
+
+// Only `dark` / `aiEnabled` / `aiEditorKind` actually gate behavior — a
+// bug found 2026-09-05 in browser verification required all six fields as
+// strict strings, so the real server response (which omits `entityType` /
+// `entityId`) failed validation and silently fell back to NO_WIDGET despite
+// `aiEnabled: true` — the widget never mounted and nothing logged why.
+// `csrfToken` / `entityType` / `entityId` are only used to build the iframe's
+// query string (harmless as `""`), so a missing one shouldn't disable the
+// widget entirely.
+function isCmmsConfigCore(v: unknown): v is Pick<CmmsConfig, "dark" | "aiEnabled" | "aiEditorKind"> {
+  if (!v || typeof v !== "object") return false;
+  const c = v as Record<string, unknown>;
+  return typeof c.dark === "boolean" && typeof c.aiEnabled === "boolean" && c.aiEditorKind === "kicad";
+}
+
+function optionalString(v: unknown): string {
+  return typeof v === "string" ? v : "";
+}
+
+const NO_WIDGET: CmmsConfig = {
+  dark: false,
+  aiEnabled: false,
+  aiEditorKind: "kicad",
+  csrfToken: "",
+  entityType: "",
+  entityId: "",
+};
+
+let cached: Promise<CmmsConfig> | null = null;
+
+/** Fetched once per page load; every caller shares the same in-flight/settled
+ *  promise. Same API base as the rest of the app (`VITE_API_BASE_URL`,
+ *  `/pcb-project-api.php` in the CMMS build) — the route lives alongside
+ *  `/api/me` on that same PHP endpoint. */
+export function fetchCmmsConfig(): Promise<CmmsConfig> {
+  if (!cached) {
+    cached = fetch(`${API_BASE_URL}/api/cmms-config`, { credentials: "include" })
+      .then((r) => (r.ok ? r.json() : null))
+      .then((v): CmmsConfig => {
+        if (!isCmmsConfigCore(v)) return NO_WIDGET;
+        const c = v as Record<string, unknown>;
+        return {
+          dark: v.dark,
+          aiEnabled: v.aiEnabled,
+          aiEditorKind: v.aiEditorKind,
+          csrfToken: optionalString(c.csrfToken),
+          entityType: optionalString(c.entityType),
+          entityId: optionalString(c.entityId),
+        };
+      })
+      .catch(() => NO_WIDGET);
+  }
+  return cached;
+}

web/standalone/src/wasm/collab/ai-bridge.test.ts

@@ -0,0 +1,104 @@
+import { describe, expect, it } from "vitest";
+import * as Y from "yjs";
+import { docToFile, docToY, kicadLibSymbolsMap, fileToDoc, yToDoc } from "@pcbjam/shared";
+import { applyToActiveBuffer, readActiveBuffer, registerActiveCollabDoc } from "./ai-bridge";
+
+// A symbol instance is only renderable with its `(lib_symbols …)` definition.
+// `docDelta` (the apply path's item differ) only diffs uuid-bearing items, and a
+// `(symbol "Device:R" …)` lib def has no uuid — so an AI proposal that places a
+// part the sheet has never carried used to land the instance with no definition,
+// and KiCad drew nothing. `applyToActiveBuffer` now upserts the proposal's lib
+// defs into `kdoc_libsymbols` alongside the item delta.
+
+const WIRE1 = "22222222-0000-0000-0000-000000000001";
+const SYM1 = "44444444-0000-0000-0000-000000000001";
+
+const SCH_WITHOUT_SYMBOL = `(kicad_sch
+\t(version 20250114)
+\t(generator "eeschema")
+\t(generator_version "9.0")
+\t(uuid "11111111-1111-1111-1111-111111111111")
+\t(paper "A4")
+\t(lib_symbols)
+\t(wire (pts (xy 50.8 50.8) (xy 101.6 50.8)) (stroke (width 0) (type default)) (uuid "${WIRE1}"))
+\t(sheet_instances (path "/" (page "1")))
+)
+`;
+
+const SCH_WITH_SYMBOL = `(kicad_sch
+\t(version 20250114)
+\t(generator "eeschema")
+\t(generator_version "9.0")
+\t(uuid "11111111-1111-1111-1111-111111111111")
+\t(paper "A4")
+\t(lib_symbols
+\t\t(symbol "Device:R" (pin_numbers (hide yes)) (pin_names (offset 0)) (exclude_from_sim no) (in_bom yes) (on_board yes)
+\t\t\t(property "Reference" "R" (at 2.032 0 90) (effects (font (size 1.27 1.27))))
+\t\t\t(property "Value" "R" (at 0 0 90) (effects (font (size 1.27 1.27))))
+\t\t\t(symbol "R_0_1"
+\t\t\t\t(rectangle (start -1.016 -2.54) (end 1.016 2.54) (stroke (width 0.254) (type default)) (fill (type none)))
+\t\t\t)
+\t\t\t(symbol "R_1_1"
+\t\t\t\t(pin passive line (at 0 3.81 270) (length 1.27) (name "~" (effects (font (size 1.27 1.27)))) (number "1" (effects (font (size 1.27 1.27)))))
+\t\t\t\t(pin passive line (at 0 -3.81 90) (length 1.27) (name "~" (effects (font (size 1.27 1.27)))) (number "2" (effects (font (size 1.27 1.27)))))
+\t\t\t)
+\t\t)
+\t)
+\t(wire (pts (xy 50.8 50.8) (xy 101.6 50.8)) (stroke (width 0) (type default)) (uuid "${WIRE1}"))
+\t(symbol (lib_id "Device:R") (at 63.5 63.5 0) (unit 1) (exclude_from_sim no) (in_bom yes) (on_board yes) (dnp no)
+\t\t(uuid "${SYM1}")
+\t\t(property "Reference" "R1" (at 66.04 62.23 0) (effects (font (size 1.27 1.27)) (justify left)))
+\t\t(property "Value" "10k" (at 66.04 64.77 0) (effects (font (size 1.27 1.27)) (justify left)))
+\t\t(pin "1" (uuid "44444444-0000-0000-0000-0000000000a1"))
+\t\t(pin "2" (uuid "44444444-0000-0000-0000-0000000000a2"))
+\t\t(instances (project "rt" (path "/11111111-1111-1111-1111-111111111111" (reference "R1") (unit 1))))
+\t)
+\t(sheet_instances (path "/" (page "1")))
+)
+`;
+
+function seed(src: string): Y.Doc {
+  const ydoc = new Y.Doc();
+  docToY(fileToDoc(src), ydoc);
+  return ydoc;
+}
+
+describe("ai-bridge applyToActiveBuffer", () => {
+  it("carries a newly-placed symbol's (lib_symbols) definition, not just the instance", () => {
+    const ydoc = seed(SCH_WITHOUT_SYMBOL);
+    registerActiveCollabDoc(ydoc, "board.kicad_sch");
+    try {
+      expect(kicadLibSymbolsMap(ydoc).get("Device:R")).toBeUndefined();
+
+      applyToActiveBuffer(SCH_WITH_SYMBOL);
+
+      const def = kicadLibSymbolsMap(ydoc).get("Device:R");
+      expect(def).toBeDefined();
+      expect(def).toContain("R_0_1");
+
+      // and the instance item itself landed via the normal item delta
+      const out = docToFile(yToDoc(ydoc));
+      expect(out).toContain(SYM1);
+      expect(out).toContain('(lib_id "Device:R")');
+    } finally {
+      registerActiveCollabDoc(null);
+    }
+  });
+
+  it("is a no-op on lib_symbols when the proposal adds no new definitions", () => {
+    const ydoc = seed(SCH_WITH_SYMBOL);
+    registerActiveCollabDoc(ydoc, "board.kicad_sch");
+    try {
+      const before = kicadLibSymbolsMap(ydoc).get("Device:R");
+      expect(before).toBeDefined();
+
+      // same doc, wire nudged — no new parts
+      applyToActiveBuffer(SCH_WITH_SYMBOL.replace("101.6 50.8", "127 50.8"));
+
+      expect(kicadLibSymbolsMap(ydoc).get("Device:R")).toBe(before);
+      expect(readActiveBuffer()).toContain("127 50.8");
+    } finally {
+      registerActiveCollabDoc(null);
+    }
+  });
+});

web/standalone/src/wasm/collab/ai-bridge.ts

@@ -0,0 +1,178 @@
+// cmms-embed / PCBJam Part 2: AI chat editor-buffer bridge.
+//
+// Same `cmms-ai-editor-*` postMessage protocol as the cad-editor and
+// pcb-retrace bridges (see TT-DB docs/vendored/{cad-editor,pcb-retrace}.md):
+// the chat is a nested iframe, this top-level page is the "editor" side.
+//
+// get-buffer: reads the ACTIVE sheet's live Y.Doc (not last-saved-to-MEMFS —
+// this reflects in-progress edits, including a peer's) via `yToDoc` +
+// `docToFile`, both pure/read-only.
+//
+// apply: deliberately does NOT reuse `KicadBinding.seed()`. `seed()` is a
+// boot-time/reconnect-only function (three branches: editor-matches-doc,
+// empty-room file-seed, adopt-existing-room) with its own empty/hollow-doc
+// edge cases (see kicad-binding.ts) — none of those branches is "a live,
+// already-populated doc gets replaced with unrelated new content", and this
+// file's git history (sibling-restage, paste-collision, ysync 0001-0008) is
+// almost entirely bugfixes in exactly that state-transition space. Instead,
+// this treats the AI's proposed file exactly like a REMOTE PEER'S EDIT
+// arriving: diff the two `KicadDoc`s (`docDelta`) and push the result through
+// `applyDeltaToY` with an origin that does not match the binding's internal
+// `ORIGIN` object, so the normal item-observer chain (the most exercised path
+// in this codebase — every multi-user co-edit goes through it) picks it up
+// and pushes it into the live WASM editor, the same as any other client's
+// change would. Known limitation: `docDelta` only diffs items, not
+// layout/preamble (page size, title block) — matches its own doc comment.
+import {
+  applyDeltaToY,
+  docDelta,
+  docToFile,
+  fileToDoc,
+  libSymbolsFromLayout,
+  upsertLibSymbolsToY,
+  yToDoc,
+  type KicadDoc,
+} from "@pcbjam/shared";
+import type * as Y from "yjs";
+import { clog, cwarn } from "@/wasm/collab/debug";
+
+const APPLY_ORIGIN = { external: "cmms-ai-assistant" };
+
+// The active sheet's Y.Doc — registered by WasmTool.tsx at each of its three
+// `setPanelDoc(...)` call sites (single-room collabHandle, multi-sheet
+// onActiveChange, and teardown-to-null), the same signal it already uses as
+// "which doc does the SheetPanel show right now". A module-level singleton
+// rather than prop-drilled: the widget mounts in App.tsx, several route
+// levels above WasmTool, matching the ambient `window.kicadCollab` /
+// `window.CMMS` cross-boundary pattern the other editor bridges already use.
+let activeDoc: Y.Doc | null = null;
+let activeFilePath: string | undefined;
+
+export function registerActiveCollabDoc(doc: Y.Doc | null, filePath?: string): void {
+  activeDoc = doc;
+  activeFilePath = doc ? filePath : undefined;
+}
+
+/** The active sheet's path, for the widget iframe's `editor_filename` param —
+ *  a context hint only, not load-bearing (get-buffer carries the real
+ *  content). `undefined` before any sheet is open. */
+export function getActiveFilePath(): string | undefined {
+  return activeFilePath;
+}
+
+export class AiBridgeNotReadyError extends Error {
+  constructor() {
+    super("no active KiCad sheet to read/write");
+    this.name = "AiBridgeNotReadyError";
+  }
+}
+
+/** Live S-expr text of the currently active sheet — read-only, never touches
+ *  the Y.Doc. Safe to call any time a sheet is open. */
+export function readActiveBuffer(): string {
+  if (!activeDoc) throw new AiBridgeNotReadyError();
+  const doc: KicadDoc = yToDoc(activeDoc);
+  return docToFile(doc);
+}
+
+/** Diff `newSource` against the active sheet's current doc and push the
+ *  result in as though a peer had made the edit. Throws on a source that
+ *  doesn't parse as a KiCad s-expr document (`fileToDoc`) — the caller
+ *  should surface that as a rejected proposal, not a crash. */
+export function applyToActiveBuffer(newSource: string): void {
+  if (!activeDoc) throw new AiBridgeNotReadyError();
+  const prev = yToDoc(activeDoc);
+  const next = fileToDoc(newSource);
+  const delta = docDelta(prev, next);
+  // `docDelta` only diffs uuid-bearing items — a `(lib_symbols …)` def has no
+  // uuid, so a proposal that places a symbol the sheet has never carried adds
+  // the instance item but drops its library definition, leaving KiCad an
+  // instance pointing at an undefined symbol (renders nothing). Push the
+  // proposal's lib defs into the kdoc_libsymbols map FIRST (upsert by lib id,
+  // never deletes — the server always splices into the existing block, so this
+  // is existing ∪ additions), so the items observer's `deltaToItemsWire` can
+  // prefix each new instance with its `(lib_symbols …)` on the way to the
+  // editor — exactly what `kicad-binding.ts`'s own DOWN path does with
+  // `upsertLibSymbolsToY(doc, defs, ORIGIN)`. Deliberately NOT `syncLayoutToY`:
+  // that also reconciles non-item layout heads (root `uuid`, `sheet_instances`,
+  // `paper`…) wholesale-LWW from the proposal, which would corrupt the sheet's
+  // identity if the server's spliced preamble deviates at all.
+  upsertLibSymbolsToY(activeDoc, libSymbolsFromLayout(next.layout, next.items), APPLY_ORIGIN);
+  applyDeltaToY(activeDoc, delta, APPLY_ORIGIN);
+}
+
+interface GetBufferMessage {
+  type: "cmms-ai-editor-get-buffer";
+}
+interface ApplyMessage {
+  type: "cmms-ai-editor-apply";
+  editor: "kicad";
+  new_source: string;
+}
+
+function isGetBufferMessage(d: unknown): d is GetBufferMessage {
+  return !!d && typeof d === "object" && (d as { type?: unknown }).type === "cmms-ai-editor-get-buffer";
+}
+function isApplyMessage(d: unknown): d is ApplyMessage {
+  return (
+    !!d &&
+    typeof d === "object" &&
+    (d as { type?: unknown }).type === "cmms-ai-editor-apply" &&
+    (d as { editor?: unknown }).editor === "kicad" &&
+    typeof (d as { new_source?: unknown }).new_source === "string"
+  );
+}
+
+/** Reply to the chat iframe. Prefer `evt.source`; a DOM fallback covers the
+ *  cross-realm-Window case cad-editor's history flagged (see its bridge). */
+function replyToChat(evtSource: MessageEventSource | null, msg: Record<string, unknown>): void {
+  let posted = false;
+  try {
+    if (evtSource && "postMessage" in evtSource) {
+      (evtSource as Window).postMessage(msg, window.location.origin);
+      posted = true;
+    }
+  } catch {
+    /* fall through to the DOM-query fallback */
+  }
+  if (!posted) {
+    try {
+      const f = document.querySelector<HTMLIFrameElement>("#cmms-ai-widget iframe");
+      if (f?.contentWindow) {
+        f.contentWindow.postMessage(msg, window.location.origin);
+        posted = true;
+      }
+    } catch {
+      /* nothing left to try */
+    }
+  }
+  clog("ai-bridge: reply", msg.type, posted ? "sent" : "DROPPED");
+}
+
+let installed = false;
+
+/** Install the window `message` listener once per page load. Idempotent —
+ *  App.tsx mounts the widget once, but this guards against remounts. */
+export function installAiBridge(): void {
+  if (installed) return;
+  installed = true;
+  window.addEventListener("message", (evt: MessageEvent) => {
+    if (evt.origin !== window.location.origin) return;
+    const d: unknown = evt.data;
+    if (isGetBufferMessage(d)) {
+      let buffer: string | null = null;
+      try {
+        buffer = readActiveBuffer();
+      } catch (err) {
+        cwarn("ai-bridge: get-buffer failed", err);
+      }
+      replyToChat(evt.source, { type: "cmms-ai-editor-buffer", buffer });
+    } else if (isApplyMessage(d)) {
+      try {
+        applyToActiveBuffer(d.new_source);
+      } catch (err) {
+        cwarn("ai-bridge: apply failed", err);
+      }
+    }
+  });
+}