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/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,