feat(ai): generate page title from content (#199)

Add an AI button in the page byline that generates a note's title from the
live editor content (including unsaved edits) and applies it immediately.

Server: one-shot, non-streaming POST /ai-chat/generate-page-title mirroring
the chat generateTitle path — gated by settings.ai.generative, throttled via
AI_CHAT_THROTTLER, resolves the workspace chat model and returns { title }.
The endpoint never touches the page; the client applies the title through the
existing /pages/update route (which enforces edit permission).

Client: ai-chat-service.generatePageTitle, a useGeneratePageTitle hook that
converts the editor HTML to markdown, calls the endpoint, applies the title
via updateTitle + updatePageData, reflects it in the unfocused title editor,
and broadcasts the UpdateEvent (mirroring TitleEditor.saveTitle). A sparkles
button (GenerateTitleGroup) renders next to dictation, edit-mode + flag gated.

Tests: pure cleanGeneratedTitle helper + controller gate/delegation/error-map.
i18n: en-US + ru-RU strings.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/client/public/locales/en-US/translation.json

@@ -1328,5 +1328,13 @@
   "The address \"{{alias}}\" currently points to \"{{title}}\". Move it to this page?": "The address \"{{alias}}\" currently points to \"{{title}}\". Move it to this page?",
   "The address \"{{alias}}\" is already in use. Move it to this page?": "The address \"{{alias}}\" is already in use. Move it to this page?",
   "Failed to set custom address": "Failed to set custom address",
-  "Failed to remove custom address": "Failed to remove custom address"
+  "Failed to remove custom address": "Failed to remove custom address",
+  "Generate title with AI": "Generate title with AI",
+  "Title generated": "Title generated",
+  "Failed to generate title": "Failed to generate title",
+  "The note is empty": "The note is empty",
+  "Could not generate a title": "Could not generate a title",
+  "AI title generation is disabled": "AI title generation is disabled",
+  "AI is not configured": "AI is not configured",
+  "Too many requests, please try again later": "Too many requests, please try again later"
 }

apps/client/public/locales/ru-RU/translation.json

@@ -1185,5 +1185,13 @@
   "The address \"{{alias}}\" currently points to \"{{title}}\". Move it to this page?": "Адрес «{{alias}}» сейчас указывает на «{{title}}». Переместить его на эту страницу?",
   "The address \"{{alias}}\" is already in use. Move it to this page?": "Адрес «{{alias}}» уже используется. Переместить его на эту страницу?",
   "Failed to set custom address": "Не удалось задать пользовательский адрес",
-  "Failed to remove custom address": "Не удалось удалить пользовательский адрес"
+  "Failed to remove custom address": "Не удалось удалить пользовательский адрес",
+  "Generate title with AI": "Сгенерировать название через AI",
+  "Title generated": "Название сгенерировано",
+  "Failed to generate title": "Не удалось сгенерировать название",
+  "The note is empty": "Заметка пустая",
+  "Could not generate a title": "Не удалось придумать название",
+  "AI title generation is disabled": "Генерация названий через AI отключена",
+  "AI is not configured": "AI не настроен",
+  "Too many requests, please try again later": "Слишком много запросов, попробуйте позже"
 }

apps/client/src/features/ai-chat/services/ai-chat-service.ts

@@ -68,6 +68,19 @@ export async function exportAiChat(
   return req.data.markdown;
 }
 
+/**
+ * Generate a page title from note content (markdown). One-shot, non-streaming
+ * (#199): the server only summarizes the supplied text and returns a suggestion;
+ * it never writes the page. The caller applies the title via /pages/update.
+ */
+export async function generatePageTitle(content: string): Promise<string> {
+  const req = await api.post<{ title: string }>(
+    "/ai-chat/generate-page-title",
+    { content },
+  );
+  return req.data.title;
+}
+
 /**
  * Agent roles API (`/ai-chat/roles`). `list` is available to any workspace
  * member (for the chat-creation picker); create/update/delete are admin-only

apps/client/src/features/editor/components/fixed-toolbar/groups/generate-title-group.tsx

@@ -0,0 +1,39 @@
+import { FC } from "react";
+import { ActionIcon, Tooltip } from "@mantine/core";
+import { IconSparkles } from "@tabler/icons-react";
+import { useTranslation } from "react-i18next";
+import { useGeneratePageTitle } from "@/features/editor/hooks/use-generate-page-title.ts";
+
+interface Props {
+  pageId: string;
+  color?: string;
+  iconSize?: number;
+}
+
+/**
+ * AI "generate title" button (#199). Reads the live editor content and applies a
+ * model-suggested title immediately. Rendered in the page byline, only in edit
+ * mode and when the workspace's generative AI flag is on.
+ */
+export const GenerateTitleGroup: FC<Props> = ({
+  pageId,
+  color = "gray",
+  iconSize = 20,
+}) => {
+  const { t } = useTranslation();
+  const gen = useGeneratePageTitle(pageId);
+
+  return (
+    <Tooltip label={t("Generate title with AI")} withArrow openDelay={250}>
+      <ActionIcon
+        variant="subtle"
+        color={color}
+        aria-label={t("Generate title with AI")}
+        loading={gen.isPending}
+        onClick={() => gen.mutate()}
+      >
+        <IconSparkles size={iconSize} stroke={1.5} />
+      </ActionIcon>
+    </Tooltip>
+  );
+};

apps/client/src/features/editor/full-editor.tsx

@@ -32,6 +32,7 @@ import {
   pageEditorAtom,
 } from "@/features/editor/atoms/editor-atoms.ts";
 import { DictationGroup } from "@/features/editor/components/fixed-toolbar/groups/dictation-group";
+import { GenerateTitleGroup } from "@/features/editor/components/fixed-toolbar/groups/generate-title-group";
 
 const MemoizedTitleEditor = React.memo(TitleEditor);
 const MemoizedPageEditor = React.memo(PageEditor);
@@ -74,6 +75,9 @@ export function FullEditor({
   const [user] = useAtom(userAtom);
   const workspace = useAtomValue(workspaceAtom);
   const isDictationEnabled = workspace?.settings?.ai?.dictation === true;
+  // AI title generation reuses the generative AI flag (same gate as the on-page
+  // generative menu); the server enforces it too (#199).
+  const isTitleGenEnabled = workspace?.settings?.ai?.generative === true;
   const fullPageWidth = user.settings?.preferences?.fullPageWidth;
   const editorToolbarEnabled =
     user.settings?.preferences?.editorToolbar ?? false;
@@ -111,11 +115,13 @@ export function FullEditor({
         editable={editable}
       />
       <PageByline
+        pageId={pageId}
         creator={creator}
         contributors={contributors}
         editable={editable}
         isEditMode={isEditMode}
         isDictationEnabled={isDictationEnabled}
+        isTitleGenEnabled={isTitleGenEnabled}
       />
       <MemoizedPageEditor
         pageId={pageId}
@@ -128,19 +134,23 @@ export function FullEditor({
 }
 
 type PageBylineProps = {
+  pageId: string;
   creator?: PageUser;
   contributors?: IContributor[];
   editable?: boolean;
   isEditMode?: boolean;
   isDictationEnabled?: boolean;
+  isTitleGenEnabled?: boolean;
 };
 
 function PageByline({
+  pageId,
   creator,
   contributors,
   editable,
   isEditMode,
   isDictationEnabled,
+  isTitleGenEnabled,
 }: PageBylineProps) {
   const { t } = useTranslation();
   const detailsTriggerProps = useAsideTriggerProps("details");
@@ -148,6 +158,9 @@ function PageByline({
   const showDictation = Boolean(
     isDictationEnabled && editable && isEditMode && editor,
   );
+  const showTitleGen = Boolean(
+    isTitleGenEnabled && editable && isEditMode && editor,
+  );
 
   const otherContributors = (contributors ?? []).filter(
     (c) => c.id !== creator?.id,
@@ -238,6 +251,11 @@ function PageByline({
         {showDictation && editor && (
           <DictationGroup editor={editor} color="gray" iconSize={20} />
         )}
+        {/* Shown only in edit mode when the workspace's generative AI flag is on,
+            so AI title generation stays reachable from the byline (#199). */}
+        {showTitleGen && (
+          <GenerateTitleGroup pageId={pageId} color="gray" iconSize={20} />
+        )}
       </Group>
     </Group>
   );

apps/client/src/features/editor/hooks/use-generate-page-title.ts

@@ -0,0 +1,104 @@
+import { useMutation } from "@tanstack/react-query";
+import { useAtomValue } from "jotai";
+import { notifications } from "@mantine/notifications";
+import { useTranslation } from "react-i18next";
+import { htmlToMarkdown } from "@docmost/editor-ext";
+import {
+  pageEditorAtom,
+  titleEditorAtom,
+} from "@/features/editor/atoms/editor-atoms.ts";
+import {
+  updatePageData,
+  useUpdateTitlePageMutation,
+} from "@/features/page/queries/page-query.ts";
+import { generatePageTitle } from "@/features/ai-chat/services/ai-chat-service.ts";
+import { useQueryEmit } from "@/features/websocket/use-query-emit.ts";
+import { UpdateEvent } from "@/features/websocket/types";
+import localEmitter from "@/lib/local-emitter.ts";
+
+// Maximum length we send to the model. The server truncates again; this is a
+// cheap client-side bound so we never ship a huge body over the wire.
+const MAX_CONTENT_CHARS = 20000;
+
+/**
+ * Generate a title for the given page from the LIVE editor content (#199),
+ * including unsaved edits, then apply it IMMEDIATELY (per product decision). The
+ * server endpoint only summarizes the supplied markdown — it never writes the
+ * page; the actual title write goes through the existing /pages/update mutation
+ * (which enforces edit permission), and is mirrored to the title field + other
+ * clients exactly like TitleEditor.saveTitle. Returns a mutation-like API so the
+ * button can show a loading state via `isPending`.
+ */
+export function useGeneratePageTitle(pageId: string) {
+  const { t } = useTranslation();
+  const pageEditor = useAtomValue(pageEditorAtom);
+  const titleEditor = useAtomValue(titleEditorAtom);
+  const { mutateAsync: updateTitle } = useUpdateTitlePageMutation();
+  const emit = useQueryEmit();
+
+  return useMutation<void, Error, void>({
+    mutationFn: async () => {
+      if (!pageEditor || pageEditor.isDestroyed) return;
+
+      const markdown = htmlToMarkdown(pageEditor.getHTML()).trim();
+      if (!markdown) {
+        notifications.show({ message: t("The note is empty"), color: "yellow" });
+        return;
+      }
+
+      const title = (
+        await generatePageTitle(markdown.slice(0, MAX_CONTENT_CHARS))
+      ).trim();
+      if (!title) {
+        // The model returned nothing usable — keep the existing title untouched.
+        notifications.show({
+          message: t("Could not generate a title"),
+          color: "yellow",
+        });
+        return;
+      }
+
+      const page = await updateTitle({ pageId, title }); // POST /pages/update
+      updatePageData(page); // refresh the react-query cache
+
+      // Reflect the new title in the field immediately. The button lives in the
+      // byline, so the title editor is not focused — setContent is safe and stays
+      // undoable through its History extension (Ctrl/Cmd+Z reverts the change).
+      if (titleEditor && !titleEditor.isDestroyed && !titleEditor.isFocused) {
+        titleEditor.commands.setContent(page.title);
+      }
+
+      // Broadcast to other clients, mirroring TitleEditor.saveTitle's event shape.
+      const event: UpdateEvent = {
+        operation: "updateOne",
+        spaceId: page.spaceId,
+        entity: ["pages"],
+        id: page.id,
+        payload: {
+          title: page.title,
+          slugId: page.slugId,
+          parentPageId: page.parentPageId,
+          icon: page.icon,
+        },
+      };
+      localEmitter.emit("message", event);
+      emit(event);
+
+      notifications.show({ message: t("Title generated") });
+    },
+    onError: (err) => {
+      // Map known HTTP statuses to friendly messages, falling back to generic.
+      const status = (err as { response?: { status?: number } })?.response
+        ?.status;
+      const message =
+        status === 403
+          ? t("AI title generation is disabled")
+          : status === 503
+            ? t("AI is not configured")
+            : status === 429
+              ? t("Too many requests, please try again later")
+              : t("Failed to generate title");
+      notifications.show({ message, color: "red" });
+    },
+  });
+}