15 changed files with 535 additions and 66 deletions
@@ -46,6 +46,13 @@ export function AudioMenu({ editor }: EditorMenuProps) {
        return null;
      }

+      // #343 PART 1: skip getAttributes unless an audio node is active. The menu
+      // only shows for an active audio node (shouldShow), so the null state while
+      // inactive is never rendered — behavior unchanged.
+      if (!ctx.editor.isActive("audio")) {
+        return null;
+      }
+
      const audioAttrs = ctx.editor.getAttributes("audio");

      return {
@@ -43,8 +43,15 @@ export function CalloutMenu({ editor }: EditorMenuProps) {
        return null;
      }

+      // #343 PART 1: skip the per-type isActive() probes unless a callout is
+      // active. The menu only shows for an active callout (shouldShow), so the
+      // null state while inactive is never rendered — behavior unchanged.
+      if (!ctx.editor.isActive("callout")) {
+        return null;
+      }
+
      return {
-        isCallout: ctx.editor.isActive("callout"),
+        isCallout: true,
        isInfo: ctx.editor.isActive("callout", { type: "info" }),
        isNote: ctx.editor.isActive("callout", { type: "note" }),
        isSuccess: ctx.editor.isActive("callout", { type: "success" }),
@@ -22,6 +22,12 @@ export default function CodeBlockView(props: NodeViewProps) {
  const [isSelected, setIsSelected] = useState(false);

  useEffect(() => {
+    // #343 PART 6: `isSelected` only drives the mermaid source's visibility (the
+    // `hidden` prop below). For every non-mermaid code block it is never read,
+    // so skip the per-block `selectionUpdate` listener entirely — otherwise N
+    // code blocks each add a global listener + a setState on every caret move.
+    if (language !== "mermaid") return;
+
    const updateSelection = () => {
      const { state } = editor;
      const { from, to } = state.selection;
@@ -32,11 +38,14 @@ export default function CodeBlockView(props: NodeViewProps) {
      setIsSelected(isNodeSelected);
    };

+    // Initialize on attach so switching a block's language to "mermaid" reflects
+    // the current selection immediately (the listener was not running before).
+    updateSelection();
    editor.on("selectionUpdate", updateSelection);
    return () => {
      editor.off("selectionUpdate", updateSelection);
    };
-  }, [editor, getPos(), node.nodeSize]);
+  }, [editor, getPos(), node.nodeSize, language]);

  function changeLanguage(language: string) {
    setLanguageValue(language);
@@ -1,5 +1,7 @@
 import type { Editor } from "@tiptap/react";
 import { useEditorState } from "@tiptap/react";
+import { undoDepth, redoDepth } from "@tiptap/pm/history";
+import { yUndoPluginKey } from "@tiptap/y-tiptap";

 export interface ToolbarState {
  isBold: boolean;
@@ -16,14 +18,45 @@ export interface ToolbarState {
  canRedo: boolean;
 }

-// Undo/redo come from either StarterKit's history or the Yjs collaboration
-// history extension. During the brief moment a page is rendered with the
-// static editor (mainExtensions only, undoRedo disabled), neither is loaded
-// and editor.can().undo/redo is undefined.
-function safeCan(editor: Editor, command: "undo" | "redo"): boolean {
-  const can = editor.can() as Record<string, unknown>;
-  const fn = can[command];
-  return typeof fn === "function" ? (fn as () => boolean)() : false;
+// Undo/redo availability, computed WITHOUT `editor.can().undo()/.redo()`.
+//
+// `editor.can()` runs the command as a dry-run (building a throwaway state +
+// transaction) — the most expensive work in this selector, and it ran on every
+// keystroke (and every REMOTE keystroke under collaboration). Instead we read
+// the history stack depth directly, which is a cheap plugin-state lookup and
+// mirrors exactly what the undo/redo commands themselves check:
+//
+//  - Collaboration (Yjs): the yjs UndoManager's undo/redo stack lengths — the
+//    same `undoStack.length === 0` / `redoStack.length === 0` guard the
+//    Collaboration extension's undo/redo commands use.
+//  - Plain history (templates / non-collab): prosemirror-history's undoDepth /
+//    redoDepth, which back the UndoRedo extension.
+//
+// When neither history backend is installed (the pre-sync static editor —
+// mainExtensions only, undoRedo disabled), both fall through to 0 -> false,
+// matching the previous `safeCan` behavior.
+function historyAvailability(editor: Editor): {
+  canUndo: boolean;
+  canRedo: boolean;
+} {
+  const state = editor.state;
+
+  // Collaboration history (Yjs) takes precedence when present.
+  const yState = yUndoPluginKey.getState(state) as
+    | { undoManager?: { undoStack: unknown[]; redoStack: unknown[] } }
+    | undefined;
+  if (yState?.undoManager) {
+    return {
+      canUndo: yState.undoManager.undoStack.length > 0,
+      canRedo: yState.undoManager.redoStack.length > 0,
+    };
+  }
+
+  // Plain prosemirror-history (returns 0 when the history plugin is absent).
+  return {
+    canUndo: undoDepth(state) > 0,
+    canRedo: redoDepth(state) > 0,
+  };
 }

 export function useToolbarState(editor: Editor | null): ToolbarState | null {
@@ -31,6 +64,7 @@ export function useToolbarState(editor: Editor | null): ToolbarState | null {
    editor,
    selector: (ctx) => {
      if (!ctx.editor) return null;
+      const { canUndo, canRedo } = historyAvailability(ctx.editor);
      return {
        isBold: ctx.editor.isActive("bold"),
        isItalic: ctx.editor.isActive("italic"),
@@ -42,8 +76,8 @@ export function useToolbarState(editor: Editor | null): ToolbarState | null {
        isBulletList: ctx.editor.isActive("bulletList"),
        isOrderedList: ctx.editor.isActive("orderedList"),
        isTaskList: ctx.editor.isActive("taskList"),
-        canUndo: safeCan(ctx.editor, "undo"),
-        canRedo: safeCan(ctx.editor, "redo"),
+        canUndo,
+        canRedo,
      };
    },
  });
@@ -38,6 +38,14 @@ export function ImageMenu({ editor }: EditorMenuProps) {
        return null;
      }

+      // #343 PART 1: skip the expensive per-keystroke work (getAttributes + the
+      // alignment isActive() probes) unless an image is actually active. The
+      // menu is only shown when an image is active (see shouldShow), so a null
+      // state while inactive is never rendered — behavior is unchanged.
+      if (!ctx.editor.isActive("image")) {
+        return null;
+      }
+
      const imageAttrs = ctx.editor.getAttributes("image");

      return {
@@ -25,6 +25,13 @@ export function PdfMenu({ editor }: EditorMenuProps) {
        return null;
      }

+      // #343 PART 1: skip getAttributes unless a pdf node is active. The menu
+      // only shows for an active pdf node (shouldShow), so the null state while
+      // inactive is never rendered — behavior unchanged.
+      if (!ctx.editor.isActive("pdf")) {
+        return null;
+      }
+
      const pdfAttrs = ctx.editor.getAttributes("pdf");

      return {
@@ -70,7 +70,14 @@ export const SubpagesMenu = React.memo(
    // toggle without re-rendering on every keystroke.
    const isRecursive = useEditorState({
      editor,
-      selector: (ctx) => ctx.editor?.getAttributes("subpages")?.recursive ?? false,
+      // #343 PART 1: skip getAttributes unless a subpages node is active. The
+      // menu only shows for an active subpages node (shouldShow), so the value
+      // is only read then; getAttributes on an inactive node returns the default
+      // (recursive === false) anyway, so this is behavior-preserving.
+      selector: (ctx) =>
+        ctx.editor?.isActive("subpages")
+          ? (ctx.editor.getAttributes("subpages")?.recursive ?? false)
+          : false,
    });

    return (
@@ -4,6 +4,7 @@ import React, { FC, useEffect, useRef, useState } from "react";
 import classes from "./table-of-contents.module.css";
 import clsx from "clsx";
 import { Box, Text, Title } from "@mantine/core";
+import { useDebouncedCallback } from "@mantine/hooks";
 import { useTranslation } from "react-i18next";

 type TableOfContentsProps = {
@@ -79,13 +80,21 @@ export const TableOfContents: FC<TableOfContentsProps> = (props) => {
    setHeadingDOMNodes(result.nodes);
  };

+  // Debounce the update-driven rescan: `$nodes("heading")` scans every heading
+  // in the document, and it previously ran on EVERY keystroke while the TOC
+  // panel was open. The panel is derived UI, so recomputing ~300ms after typing
+  // settles keeps it correct without doing an all-headings scan per keystroke
+  // (#343, PART 7). `useDebouncedCallback` returns a stable reference and always
+  // invokes the latest `handleUpdate`.
+  const debouncedHandleUpdate = useDebouncedCallback(handleUpdate, 300);
+
  useEffect(() => {
-    props.editor?.on("update", handleUpdate);
+    props.editor?.on("update", debouncedHandleUpdate);

    return () => {
-      props.editor?.off("update", handleUpdate);
+      props.editor?.off("update", debouncedHandleUpdate);
    };
-  }, [props.editor]);
+  }, [props.editor, debouncedHandleUpdate]);

  useEffect(
    () => {
@@ -31,6 +31,13 @@ export function VideoMenu({ editor }: EditorMenuProps) {
        return null;
      }

+      // #343 PART 1: skip getAttributes + alignment isActive() probes unless a
+      // video is active. The menu only shows for an active video (shouldShow),
+      // so the null state while inactive is never rendered — behavior unchanged.
+      if (!ctx.editor.isActive("video")) {
+        return null;
+      }
+
      const videoAttrs = ctx.editor.getAttributes("video");

      return {
@@ -6,6 +6,23 @@ import getSuggestionItems from '@/features/editor/components/slash-menu/menu-ite

 export const slashMenuPluginKey = new PluginKey('slash-command');

+// getSuggestionItems fuzzy-matches EVERY command against the query (plus its
+// wrong-keyboard-layout remaps) and, while the slash menu is open, is invoked
+// TWICE per keystroke: once by the synchronous `allow` gate below and once by
+// the popup's `items` builder. A synchronous gating predicate can't be
+// debounced without breaking the suggestion decoration/activation, so instead we
+// memoize the LAST query's result: the two same-query calls in one keystroke
+// build the list only once, and the cache invalidates the moment the query
+// changes — so there is no stale-state risk (#343, PART 7).
+let lastQuery: string | null = null;
+let lastResult: ReturnType<typeof getSuggestionItems> | null = null;
+function suggestionItemsForQuery(query: string) {
+  if (query === lastQuery && lastResult) return lastResult;
+  lastQuery = query;
+  lastResult = getSuggestionItems({ query });
+  return lastResult;
+}
+
 // @ts-ignore
 const Command = Extension.create({
  name: 'slash-command',
@@ -38,7 +55,7 @@ const Command = Extension.create({
          // non-matching queries while keeping multi-word matches (e.g.
          // "/Heading 1") working.
          const query = state.doc.textBetween(range.from + 1, range.to);
-          const groups = getSuggestionItems({ query });
+          const groups = suggestionItemsForQuery(query);
          const hasMatches = Object.values(groups).some(
            (items) => items.length > 0,
          );
@@ -61,7 +78,9 @@ const Command = Extension.create({

 const SlashCommand = Command.configure({
  suggestion: {
-    items: getSuggestionItems,
+    // Share the per-query memo with `allow` so the pair of same-query calls in a
+    // single keystroke rebuilds the list once (#343, PART 7).
+    items: ({ query }: { query: string }) => suggestionItemsForQuery(query),
    render: renderItems,
  },
 });
@@ -0,0 +1,100 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { renderHook, act } from "@testing-library/react";
+import type { MutableRefObject } from "react";
+import type { Editor } from "@tiptap/react";
+
+// Mock the app entry so importing the hook doesn't boot the whole app; the hook
+// only needs queryClient's cache read/write, which we stub here. Declared via
+// vi.hoisted so the spies exist before the hoisted vi.mock factory runs.
+const { getQueryData, setQueryData } = vi.hoisted(() => ({
+  getQueryData: vi.fn(() => undefined as unknown),
+  setQueryData: vi.fn(),
+}));
+vi.mock("@/main.tsx", () => ({
+  queryClient: { getQueryData, setQueryData },
+}));
+
+import { usePageContentCache } from "./use-page-content-cache";
+
+const SNAPSHOT = { type: "doc", content: [] };
+
+function makeFakeEditor(overrides: Partial<Editor> = {}): Editor {
+  return {
+    isEmpty: false,
+    isDestroyed: false,
+    getJSON: vi.fn(() => SNAPSHOT),
+    ...overrides,
+  } as unknown as Editor;
+}
+
+describe("usePageContentCache (#343 PART 3) — getJSON off the keystroke path", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.clearAllMocks();
+    // A cached page exists so the write path runs.
+    getQueryData.mockReturnValue({ id: "p1", content: {} });
+  });
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it("onUpdate (calling the debounced fn) does NOT call getJSON synchronously", () => {
+    const editor = makeFakeEditor();
+    const editorRef = { current: editor } as MutableRefObject<Editor | null>;
+
+    const { result } = renderHook(() =>
+      usePageContentCache(editorRef, "slug-1", 3000),
+    );
+
+    // Simulate a keystroke's onUpdate -> only schedules the debounce.
+    act(() => {
+      result.current();
+      result.current();
+      result.current();
+    });
+
+    // The whole-doc serialization must NOT have happened yet.
+    expect(editor.getJSON).not.toHaveBeenCalled();
+    expect(setQueryData).not.toHaveBeenCalled();
+
+    // Once the debounce window elapses, getJSON runs exactly once (not per call).
+    act(() => vi.advanceTimersByTime(3000));
+    expect(editor.getJSON).toHaveBeenCalledTimes(1);
+    expect(setQueryData).toHaveBeenCalledWith(["pages", "slug-1"], {
+      id: "p1",
+      content: SNAPSHOT,
+    });
+  });
+
+  it("flushes the pending snapshot on unmount so the last edit isn't lost", () => {
+    const editor = makeFakeEditor();
+    const editorRef = { current: editor } as MutableRefObject<Editor | null>;
+
+    const { result, unmount } = renderHook(() =>
+      usePageContentCache(editorRef, "slug-1", 3000),
+    );
+
+    act(() => result.current());
+    expect(editor.getJSON).not.toHaveBeenCalled();
+
+    // Navigation/unmount must flush (not drop) the pending write.
+    act(() => unmount());
+    expect(editor.getJSON).toHaveBeenCalledTimes(1);
+    expect(setQueryData).toHaveBeenCalledTimes(1);
+  });
+
+  it("skips the write when the editor is destroyed (flush racing teardown)", () => {
+    const editor = makeFakeEditor({ isDestroyed: true });
+    const editorRef = { current: editor } as MutableRefObject<Editor | null>;
+
+    const { result } = renderHook(() =>
+      usePageContentCache(editorRef, "slug-1", 3000),
+    );
+
+    act(() => result.current());
+    act(() => vi.advanceTimersByTime(3000));
+
+    expect(editor.getJSON).not.toHaveBeenCalled();
+    expect(setQueryData).not.toHaveBeenCalled();
+  });
+});
@@ -0,0 +1,50 @@
+import type { MutableRefObject } from "react";
+import { useDebouncedCallback } from "@mantine/hooks";
+import type { Editor } from "@tiptap/react";
+import { queryClient } from "@/main.tsx";
+import { IPage } from "@/features/page/types/page.types.ts";
+
+/**
+ * Off-keystroke local page-cache updater (issue #343, PART 3).
+ *
+ * The editor's `onUpdate` fires on every keystroke — and, under collaboration,
+ * on every REMOTE keystroke too. Serializing the WHOLE document with
+ * `editor.getJSON()` on that hot path is expensive, and the previous 3s debounce
+ * only guarded the cache WRITE, not the serialization: `getJSON()` still ran per
+ * keystroke.
+ *
+ * This hook moves the serialization INSIDE the debounced callback, so the
+ * full-doc traversal happens at most once per `delay`, not per keystroke. Call
+ * the returned function from `onUpdate` (it only schedules the debounce); the
+ * `getJSON()` snapshot is taken when the debounce fires.
+ *
+ * On unmount/navigation the pending snapshot is FLUSHED (via `flushOnUnmount`)
+ * so the last edits within the debounce window aren't lost from the local cache.
+ * The source of truth is collab/Yjs, but the cache must not go stale.
+ *
+ * IMPORTANT: call this hook BEFORE `useEditor`. React runs effect cleanups in
+ * declaration order on unmount, so the debounce's flush cleanup must be declared
+ * before `useEditor`'s teardown to run while the editor is still alive; the
+ * `isDestroyed` guard keeps a flush that still races teardown safe (it skips).
+ */
+export function usePageContentCache(
+  editorRef: MutableRefObject<Editor | null>,
+  slugId: string | undefined,
+  delay = 3000,
+) {
+  return useDebouncedCallback(
+    () => {
+      const e = editorRef.current;
+      if (!e || e.isDestroyed || e.isEmpty) return;
+      const pageData = queryClient.getQueryData<IPage>(["pages", slugId]);
+      if (pageData) {
+        // getJSON() (full-doc serialization) runs HERE, off the keystroke path.
+        queryClient.setQueryData(["pages", slugId], {
+          ...pageData,
+          content: e.getJSON(),
+        });
+      }
+    },
+    { delay, flushOnUnmount: true },
+  );
+}
@@ -62,7 +62,7 @@ import ExcalidrawMenu from "./components/excalidraw/excalidraw-menu-lazy";
 import DrawioMenu from "./components/drawio/drawio-menu";
 import { useCollabToken } from "@/features/auth/queries/auth-query.tsx";
 import SearchAndReplaceDialog from "@/features/editor/components/search-and-replace/search-and-replace-dialog.tsx";
-import { useDebouncedCallback, useDocumentVisibility } from "@mantine/hooks";
+import { useDocumentVisibility } from "@mantine/hooks";
 import { useIdle } from "@/hooks/use-idle.ts";
 import { queryClient } from "@/main.tsx";
 import { IPage } from "@/features/page/types/page.types.ts";
@@ -79,6 +79,7 @@ import { PageEditMode } from "@/features/user/types/user.types.ts";
 import { jwtDecode } from "jwt-decode";
 import { searchSpotlight } from "@/features/search/constants.ts";
 import { useEditorScroll } from "./hooks/use-editor-scroll";
+import { usePageContentCache } from "./hooks/use-page-content-cache";
 import { useScrollRestoreOnSwap } from "./hooks/use-scroll-position";
 import { useSwapHeightReservation } from "./hooks/use-swap-height-reservation";
 import { EditorLinkMenu } from "@/features/editor/components/link/link-menu";
@@ -267,8 +268,13 @@ export default function PageEditor({
    }
  }, [isIdle, documentState, providersReady, resetIdle]);

-  // Attach here, to make sure the connection gets properly established
-  providersRef.current?.remote.attach();
+  // Attach the remote provider once it's ready (and again after a pageId swap
+  // recreates it) to make sure the connection gets properly established. This
+  // used to run in the render body — a side effect during render (#343, PART 7).
+  // `attach()` is idempotent, so re-running it on these deps is safe.
+  useEffect(() => {
+    providersRef.current?.remote.attach();
+  }, [providersReady, pageId]);

  const extensions = useMemo(() => {
    if (!providersReady || !providersRef.current || !currentUser?.user) {
@@ -283,6 +289,12 @@ export default function PageEditor({
    ];
  }, [providersReady, currentUser?.user]);

+  // getJSON() serialization + cache write live in the hook, off the keystroke
+  // path, and flush on unmount so the last snapshot survives navigation (#343).
+  // MUST be declared before useEditor: React runs effect cleanups in declaration
+  // order on unmount, so the flush must run before the editor is torn down.
+  const debouncedUpdateContent = usePageContentCache(editorRef, slugId);
+
  const editor = useEditor(
    {
      extensions,
@@ -353,11 +365,11 @@ export default function PageEditor({
          editorRef.current = editor;
        }
      },
-      onUpdate({ editor }) {
-        if (editor.isEmpty) return;
-        const editorJson = editor.getJSON();
-        //update local page cache to reduce flickers
-        debouncedUpdateContent(editorJson);
+      onUpdate() {
+        // Only schedule the debounce here — the whole-doc getJSON() serialization
+        // happens INSIDE the debounced callback (see usePageContentCache), so it
+        // no longer runs synchronously on every (local or remote) keystroke.
+        debouncedUpdateContent();
      },
    },
    [pageId, editable, extensions],
@@ -403,17 +415,6 @@ export default function PageEditor({
    };
  }, [editor, pageId, editorIsEditable]);

-  const debouncedUpdateContent = useDebouncedCallback((newContent: any) => {
-    const pageData = queryClient.getQueryData<IPage>(["pages", slugId]);
-
-    if (pageData) {
-      queryClient.setQueryData(["pages", slugId], {
-        ...pageData,
-        content: newContent,
-      });
-    }
-  }, 3000);
-
  const handleActiveCommentEvent = (event) => {
    const { commentId, resolved } = event.detail;

@@ -0,0 +1,134 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { getSchema } from '@tiptap/core';
+import { Document } from '@tiptap/extension-document';
+import { Paragraph } from '@tiptap/extension-paragraph';
+import { Text } from '@tiptap/extension-text';
+import { EditorState } from '@tiptap/pm/state';
+import { Node as PMNode } from '@tiptap/pm/model';
+import { FootnoteReference } from './footnote-reference';
+import { FootnotesList } from './footnotes-list';
+import { FootnoteDefinition } from './footnote-definition';
+import {
+  footnoteNumberingPlugin,
+  footnoteNumberingPluginKey,
+  getFootnoteNumber,
+} from './footnote-numbering';
+import {
+  FOOTNOTE_REFERENCE_NAME,
+  FOOTNOTES_LIST_NAME,
+  FOOTNOTE_DEFINITION_NAME,
+} from './footnote-util';
+
+const extensions = [
+  Document,
+  Paragraph,
+  Text,
+  FootnoteReference,
+  FootnotesList,
+  FootnoteDefinition,
+];
+
+const schema = getSchema(extensions);
+
+function makeState(docJson: any): EditorState {
+  return EditorState.create({
+    doc: PMNode.fromJSON(schema, docJson),
+    plugins: [footnoteNumberingPlugin()],
+  });
+}
+
+const withTwoFootnotes = {
+  type: 'doc',
+  content: [
+    {
+      type: 'paragraph',
+      content: [
+        { type: 'text', text: 'a' },
+        { type: FOOTNOTE_REFERENCE_NAME, attrs: { id: 'x' } },
+        { type: 'text', text: 'b' },
+        { type: FOOTNOTE_REFERENCE_NAME, attrs: { id: 'y' } },
+      ],
+    },
+    {
+      type: FOOTNOTES_LIST_NAME,
+      content: [
+        {
+          type: FOOTNOTE_DEFINITION_NAME,
+          attrs: { id: 'x' },
+          content: [{ type: 'paragraph' }],
+        },
+        {
+          type: FOOTNOTE_DEFINITION_NAME,
+          attrs: { id: 'y' },
+          content: [{ type: 'paragraph' }],
+        },
+      ],
+    },
+  ],
+};
+
+describe('footnote numbering plugin — short-circuit (#343 PART 5)', () => {
+  afterEach(() => vi.restoreAllMocks());
+
+  it('does ZERO document traversals on a docChanged transaction when the doc has no footnotes', () => {
+    const state = makeState({
+      type: 'doc',
+      content: [{ type: 'paragraph', content: [{ type: 'text', text: 'hi' }] }],
+    });
+
+    // Only count traversals caused by the transaction, not the initial build.
+    const descendantsSpy = vi.spyOn(PMNode.prototype, 'descendants');
+
+    const before = footnoteNumberingPluginKey.getState(state);
+    // A real content edit (docChanged) that introduces no footnote node.
+    const next = state.apply(state.tr.insertText('!', 3));
+    const after = footnoteNumberingPluginKey.getState(next);
+
+    // The plugin never walked the document...
+    expect(descendantsSpy).not.toHaveBeenCalled();
+    // ...and reused the exact same (empty) state object — proof it short-circuited.
+    expect(after).toBe(before);
+    expect(after?.hasFootnotes).toBe(false);
+  });
+
+  it('rebuilds (numbering appears) the first time a footnote is inserted into a footnote-free doc', () => {
+    const state = makeState({
+      type: 'doc',
+      content: [{ type: 'paragraph', content: [{ type: 'text', text: 'hi' }] }],
+    });
+    expect(footnoteNumberingPluginKey.getState(state)?.hasFootnotes).toBe(false);
+
+    const ref = schema.nodes[FOOTNOTE_REFERENCE_NAME].create({ id: 'x' });
+    const next = state.apply(state.tr.insert(3, ref));
+
+    const after = footnoteNumberingPluginKey.getState(next);
+    expect(after?.hasFootnotes).toBe(true);
+    expect(getFootnoteNumber(next, 'x')).toBe(1);
+  });
+});
+
+describe('footnote numbering plugin — numbering unchanged with footnotes (#343 PART 5)', () => {
+  it('numbers references in document order via the single merged walk', () => {
+    const state = makeState(withTwoFootnotes);
+    expect(getFootnoteNumber(state, 'x')).toBe(1);
+    expect(getFootnoteNumber(state, 'y')).toBe(2);
+  });
+
+  it('produces a decoration for every reference and matching definition', () => {
+    const state = makeState(withTwoFootnotes);
+    const decos = footnoteNumberingPluginKey.getState(state)?.decorations;
+    // 2 references + 2 definitions = 4 number decorations.
+    expect(decos?.find().length).toBe(4);
+  });
+
+  it('keeps numbering current after an edit while footnotes exist', () => {
+    const state = makeState(withTwoFootnotes);
+    // Insert a NEW reference (id "z") before the others: it must become #1 and
+    // shift x -> #2, y -> #3 (deterministic document-order numbering).
+    const ref = schema.nodes[FOOTNOTE_REFERENCE_NAME].create({ id: 'z' });
+    const next = state.apply(state.tr.insert(1, ref));
+    expect(getFootnoteNumber(next, 'z')).toBe(1);
+    expect(getFootnoteNumber(next, 'x')).toBe(2);
+    expect(getFootnoteNumber(next, 'y')).toBe(3);
+  });
+});
@@ -1,11 +1,9 @@
-import { EditorState, Plugin, PluginKey } from '@tiptap/pm/state';
+import { EditorState, Plugin, PluginKey, Transaction } from '@tiptap/pm/state';
 import { Decoration, DecorationSet } from '@tiptap/pm/view';
-import { Node as ProseMirrorNode } from '@tiptap/pm/model';
+import { Node as ProseMirrorNode, Slice } from '@tiptap/pm/model';
 import {
  FOOTNOTE_DEFINITION_NAME,
  FOOTNOTE_REFERENCE_NAME,
-  computeFootnoteNumbers,
-  computeFootnoteRefCounts,
 } from './footnote-util';

 export const footnoteNumberingPluginKey = new PluginKey<FootnoteNumberingState>(
@@ -27,8 +25,22 @@ interface FootnoteNumberingState {
  refCounts: Map<string, number>;
  /** Decorations rendering those numbers (refs + definitions). */
  decorations: DecorationSet;
+  /** Whether the document contains ANY footnote reference/definition node.
+   *  Cached so `apply` can skip the whole-doc walk on every keystroke in the
+   *  common case (documents with no footnotes), recomputing only once a
+   *  transaction actually inserts a footnote node (#343, PART 5). */
+  hasFootnotes: boolean;
 }

+/** Reusable empty state for footnote-free documents — avoids reallocating an
+ *  empty map/decoration set on every keystroke while there are no footnotes. */
+const EMPTY_STATE: FootnoteNumberingState = {
+  numbers: new Map(),
+  refCounts: new Map(),
+  decorations: DecorationSet.empty,
+  hasFootnotes: false,
+};
+
 /**
 * Build the decoration set for footnote numbers. Pure function of the document:
 * walk references in document order, assign 1-based numbers, then attach a
@@ -41,50 +53,101 @@ export function buildFootnoteDecorations(doc: ProseMirrorNode): DecorationSet {
  return buildFootnoteNumberingState(doc).decorations;
 }

+function numberDecoration(pos: number, nodeSize: number, num: number): Decoration {
+  return Decoration.node(pos, pos + nodeSize, {
+    'data-footnote-number': String(num),
+    style: `--footnote-number: "${num}";`,
+  });
+}
+
 /**
- * Compute both the number map AND the decorations for `doc` in a single walk.
- * The plugin caches the result so NodeViews can read numbers without
- * recomputing.
+ * Compute the number map, reference counts AND the decorations for `doc` in a
+ * SINGLE document walk (previously three separate O(n) traversals per
+ * docChanged — computeFootnoteNumbers + computeFootnoteRefCounts + a decoration
+ * pass, #343 PART 5). The plugin caches the result so NodeViews can read numbers
+ * without recomputing.
+ *
+ * References are numbered and decorated as they are encountered (document
+ * order). Definition positions are collected during the same walk and decorated
+ * afterwards from the completed number map — so a definition that appears before
+ * its reference in document order still resolves to the correct number, and the
+ * output is identical to the previous three-pass implementation. (Decoration
+ * insertion order does not matter: DecorationSet.create indexes by position.)
 */
 function buildFootnoteNumberingState(
  doc: ProseMirrorNode,
 ): FootnoteNumberingState {
-  const numbers = computeFootnoteNumbers(doc);
-  const refCounts = computeFootnoteRefCounts(doc);
+  const numbers = new Map<string, number>();
+  const refCounts = new Map<string, number>();
  const decorations: Decoration[] = [];
+  const definitions: { id: string; pos: number; nodeSize: number }[] = [];
+  let n = 0;
+  let hasFootnotes = false;

  doc.descendants((node, pos) => {
-    if (node.type.name === FOOTNOTE_REFERENCE_NAME) {
-      const num = numbers.get(node.attrs.id);
-      if (num != null) {
-        decorations.push(
-          Decoration.node(pos, pos + node.nodeSize, {
-            'data-footnote-number': String(num),
-            style: `--footnote-number: "${num}";`,
-          }),
-        );
-      }
-    }
-    if (node.type.name === FOOTNOTE_DEFINITION_NAME) {
-      const num = numbers.get(node.attrs.id);
-      if (num != null) {
-        decorations.push(
-          Decoration.node(pos, pos + node.nodeSize, {
-            'data-footnote-number': String(num),
-            style: `--footnote-number: "${num}";`,
-          }),
-        );
+    const typeName = node.type.name;
+    if (typeName === FOOTNOTE_REFERENCE_NAME) {
+      hasFootnotes = true;
+      const id = node.attrs.id;
+      if (id) {
+        if (!numbers.has(id)) numbers.set(id, ++n);
+        refCounts.set(id, (refCounts.get(id) ?? 0) + 1);
+        decorations.push(numberDecoration(pos, node.nodeSize, numbers.get(id)!));
      }
+    } else if (typeName === FOOTNOTE_DEFINITION_NAME) {
+      hasFootnotes = true;
+      const id = node.attrs.id;
+      if (id != null) definitions.push({ id, pos, nodeSize: node.nodeSize });
    }
  });

+  if (!hasFootnotes) return EMPTY_STATE;
+
+  for (const def of definitions) {
+    const num = numbers.get(def.id);
+    if (num != null) {
+      decorations.push(numberDecoration(def.pos, def.nodeSize, num));
+    }
+  }
+
  return {
    numbers,
    refCounts,
    decorations: DecorationSet.create(doc, decorations),
+    hasFootnotes: true,
  };
 }

+/**
+ * Cheap check: does any of a transaction's inserted content contain a footnote
+ * reference/definition node? Footnote nodes can only ENTER the document through
+ * replace steps (ReplaceStep / ReplaceAroundStep both expose a `.slice`), so
+ * scanning only the inserted slices — O(change size), not O(doc) — is sufficient
+ * to detect a newly-added footnote. Mark/attr steps never introduce nodes.
+ * Lets `apply` keep skipping the whole-doc walk until a footnote first appears.
+ */
+function transactionInsertsFootnote(tr: Transaction): boolean {
+  for (const step of tr.steps) {
+    const slice = (step as unknown as { slice?: Slice }).slice;
+    if (!slice || slice.content.size === 0) continue;
+    let found = false;
+    slice.content.descendants((node) => {
+      if (found) return false;
+      const typeName = node.type.name;
+      if (
+        typeName === FOOTNOTE_REFERENCE_NAME ||
+        typeName === FOOTNOTE_DEFINITION_NAME
+      ) {
+        found = true;
+        return false;
+      }
+      return true;
+    });
+    if (found) return true;
+  }
+  return false;
+}
+
 /**
 * Read the cached footnote number for `id` from the numbering plugin's state.
 * This is the source NodeViews should use instead of calling
@@ -126,6 +189,13 @@ export function footnoteNumberingPlugin(): Plugin {
        // the number map NodeViews read stays current on every edit while
        // non-doc transactions (selection, etc.) reuse the cache for free.
        if (!tr.docChanged) return old;
+        // Short-circuit the whole-doc walk while the document has no footnotes:
+        // if there were none and this transaction did not INSERT one, there is
+        // still nothing to number, so reuse the empty state (#343, PART 5). Once
+        // a footnote exists we always rebuild (covers renumbering/deletion).
+        if (!old.hasFootnotes && !transactionInsertsFootnote(tr)) {
+          return old;
+        }
        return buildFootnoteNumberingState(tr.doc);
      },
    },