feat(ai-chat): auto-open last chat bound to the document (#191)

On opening the floating AI-chat window from the header on a document page,
auto-open the LAST chat bound to that document. Binding reuses the existing
ai_chats.page_id (no migration): the bound chat is the requesting user's
most-recent non-deleted chat created on that page, so a new chat on the page
becomes the bound one for free. Resolution happens only on a genuine
closed -> open transition; the provenance badge deep-link is untouched.

Server: AiChatRepo.findLatestByPage + POST /ai-chat/bound-chat (BoundChatDto),
both read-only and owner/workspace-scoped.
Client: getBoundChat service + useOpenAiChatForCurrentPage hook wired into the
app-header entry point (fail-soft to a fresh chat; draft/role cleared only on a
real switch).
Tests: repo scoping/ordering, controller wiring, and hook behavior.

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

apps/server/src/core/ai-chat/ai-chat.controller.bound-chat.spec.ts

@@ -0,0 +1,44 @@
+import { AiChatController } from './ai-chat.controller';
+import type { User, Workspace } from '@docmost/db/types/entity.types';
+
+/**
+ * Wiring spec for the #191 `POST /ai-chat/bound-chat` endpoint. It must forward
+ * the requesting user + workspace + pageId to findLatestByPage and return the
+ * matched chat's id, or `{ chatId: null }` when there is none. The repo already
+ * scopes to the caller's OWN chats, so a foreign pageId simply yields no match
+ * (null) — no extra page-access check is needed. Exercised with hand-rolled
+ * mocks, no Nest graph and no DB.
+ */
+describe('AiChatController.boundChat', () => {
+  const user = { id: 'u1' } as User;
+  const workspace = { id: 'ws1' } as Workspace;
+
+  function makeController(chat: unknown) {
+    const aiChatRepo = {
+      findLatestByPage: jest.fn().mockResolvedValue(chat),
+    };
+    const controller = new AiChatController(
+      {} as never,
+      aiChatRepo as never,
+      {} as never,
+      {} as never,
+    );
+    return { controller, aiChatRepo };
+  }
+
+  it('returns the owned chat id and scopes the lookup to user + workspace + page', async () => {
+    const { controller, aiChatRepo } = makeController({
+      id: 'c1',
+      creatorId: 'u1',
+    });
+    const res = await controller.boundChat({ pageId: 'p1' }, user, workspace);
+    expect(aiChatRepo.findLatestByPage).toHaveBeenCalledWith('u1', 'ws1', 'p1');
+    expect(res).toEqual({ chatId: 'c1' });
+  });
+
+  it('returns { chatId: null } for a page with no owned chat (incl. foreign pageId)', async () => {
+    const { controller } = makeController(undefined);
+    const res = await controller.boundChat({ pageId: 'foreign' }, user, workspace);
+    expect(res).toEqual({ chatId: null });
+  });
+});

apps/server/src/core/ai-chat/ai-chat.controller.ts

@@ -30,6 +30,7 @@ import { FileInterceptor } from '../../common/interceptors/file.interceptor';
 import { AiChatService, AiChatStreamBody } from './ai-chat.service';
 import { AiTranscriptionService } from './ai-transcription.service';
 import {
+  BoundChatDto,
   ChatIdDto,
   ExportChatDto,
   GeneratePageTitleDto,
@@ -67,6 +68,28 @@ export class AiChatController {
     return this.aiChatRepo.findByCreator(user.id, workspace.id, pagination);
   }
 
+  /**
+   * Resolve the chat bound to a document for the requesting user: the most-recent
+   * non-deleted chat created on that page (ai_chats.page_id). Returns
+   * { chatId: null } when the page has no owned chat (-> a fresh chat). No page
+   * access check needed: only the caller's OWN chats are matched, so a foreign
+   * pageId reveals nothing.
+   */
+  @HttpCode(HttpStatus.OK)
+  @Post('bound-chat')
+  async boundChat(
+    @Body() dto: BoundChatDto,
+    @AuthUser() user: User,
+    @AuthWorkspace() workspace: Workspace,
+  ): Promise<{ chatId: string | null }> {
+    const chat = await this.aiChatRepo.findLatestByPage(
+      user.id,
+      workspace.id,
+      dto.pageId,
+    );
+    return { chatId: chat?.id ?? null };
+  }
+
   /** Fetch the messages of a chat (oldest first, paginated). */
   @HttpCode(HttpStatus.OK)
   @Post('messages')

apps/server/src/core/ai-chat/dto/ai-chat.dto.ts

@@ -37,6 +37,12 @@ export class GetChatMessagesDto {
   cursor?: string;
 }
 
+/** Resolve the chat bound to a document (the page's most-recent owned chat). */
+export class BoundChatDto {
+  @IsString()
+  pageId: string;
+}
+
 /** Export a chat to Markdown (#183). `lang` localizes the few fixed
  *  role/tool-action labels; defaults to English server-side. */
 export class ExportChatDto {

apps/server/src/database/repos/ai-chat/ai-chat.repo.spec.ts

@@ -0,0 +1,85 @@
+import { AiChatRepo } from './ai-chat.repo';
+import type { KyselyDB } from '../../types/kysely.types';
+
+/**
+ * Unit test for AiChatRepo.findLatestByPage — the "bound chat" resolver behind
+ * #191 (auto-open the last chat created on a document). It builds the scoping
+ * query, so we assert the EXACT predicates/ordering the spec mandates over a
+ * chainable builder mock (no live DB): user + workspace + page scope, the
+ * deletedAt filter, newest-by-createdAt with an id tiebreaker, limit 1. A
+ * live-Postgres ordering test is out of scope for this pure unit test.
+ */
+describe('AiChatRepo.findLatestByPage', () => {
+  type Recorded = {
+    table?: string;
+    wheres: Array<[string, string, unknown]>;
+    orderBys: Array<[string, string]>;
+    limit?: number;
+  };
+
+  function makeDb(result: unknown): { db: KyselyDB; rec: Recorded } {
+    const rec: Recorded = { wheres: [], orderBys: [] };
+    const builder: Record<string, unknown> = {};
+    const chain = () => builder;
+    builder.selectAll = chain;
+    builder.where = (col: string, op: string, val: unknown) => {
+      rec.wheres.push([col, op, val]);
+      return builder;
+    };
+    builder.orderBy = (col: string, dir: string) => {
+      rec.orderBys.push([col, dir]);
+      return builder;
+    };
+    builder.limit = (n: number) => {
+      rec.limit = n;
+      return builder;
+    };
+    builder.executeTakeFirst = () => Promise.resolve(result);
+    const db = {
+      selectFrom: (table: string) => {
+        rec.table = table;
+        return builder;
+      },
+    } as unknown as KyselyDB;
+    return { db, rec };
+  }
+
+  it('returns the matched chat and scopes by user + workspace + page (deletedAt null)', async () => {
+    const chat = { id: 'c1', creatorId: 'u1', workspaceId: 'ws1', pageId: 'p1' };
+    const { db, rec } = makeDb(chat);
+    const repo = new AiChatRepo(db);
+
+    const res = await repo.findLatestByPage('u1', 'ws1', 'p1');
+
+    expect(res).toBe(chat);
+    expect(rec.table).toBe('aiChats');
+    expect(rec.wheres).toEqual(
+      expect.arrayContaining([
+        ['creatorId', '=', 'u1'],
+        ['workspaceId', '=', 'ws1'],
+        ['pageId', '=', 'p1'],
+        ['deletedAt', 'is', null],
+      ]),
+    );
+  });
+
+  it('orders newest-first by createdAt then id, limit 1', async () => {
+    const { db, rec } = makeDb(undefined);
+    const repo = new AiChatRepo(db);
+
+    await repo.findLatestByPage('u1', 'ws1', 'p1');
+
+    expect(rec.orderBys).toEqual([
+      ['createdAt', 'desc'],
+      ['id', 'desc'],
+    ]);
+    expect(rec.limit).toBe(1);
+  });
+
+  it('returns undefined when the page has no owned chat', async () => {
+    const { db } = makeDb(undefined);
+    const repo = new AiChatRepo(db);
+
+    await expect(repo.findLatestByPage('u1', 'ws1', 'p1')).resolves.toBeUndefined();
+  });
+});

apps/server/src/database/repos/ai-chat/ai-chat.repo.ts

@@ -80,6 +80,32 @@ export class AiChatRepo {
     });
   }
 
+  /**
+   * The "bound chat" for a document: the requesting user's most recently
+   * created, non-deleted chat whose origin page is `pageId`. Auto-opened when
+   * the AI chat window is opened on that page. Newest-by-createdAt wins, so a
+   * chat created later on the same page supersedes earlier ones — exactly how
+   * "new chat -> becomes the bound one" falls out for free. Scoped to the user +
+   * workspace, so a foreign pageId can only ever match the caller's own chats.
+   */
+  async findLatestByPage(
+    creatorId: string,
+    workspaceId: string,
+    pageId: string,
+  ): Promise<AiChat | undefined> {
+    return this.db
+      .selectFrom('aiChats')
+      .selectAll('aiChats')
+      .where('creatorId', '=', creatorId)
+      .where('workspaceId', '=', workspaceId)
+      .where('pageId', '=', pageId)
+      .where('deletedAt', 'is', null)
+      .orderBy('createdAt', 'desc')
+      .orderBy('id', 'desc') // stable tiebreaker, mirrors findByCreator's cursor
+      .limit(1)
+      .executeTakeFirst();
+  }
+
   async insert(
     insertable: InsertableAiChat,
     trx?: KyselyTransaction,