feat(comments): attribute MCP agent comments as AI (unspoofable provenance)

Mark comments (and, via existing page provenance, pages) created under an
is_agent service account as authored by AI, derived from the SIGNED server
identity rather than any client field, and render the existing AI badge in
the comments sidebar.

Backend (B1):
- Add additive users.is_agent boolean (default false) migration; reflect in
  the Users Kysely type, the user repo baseFields, and (via Selectable) the
  User entity.
- jwt.strategy: derive req.raw.actor from user.isAgent (an is_agent account
  stamps every write 'agent'); external MCP has no internal ai_chats row so
  aiChatId stays null. Non-spoofable: a plain user cannot obtain
  created_source='agent'.
- Loosen the provenance aiChatId type to string|null across token.service and
  the JwtPayload/JwtCollabPayload claims (type-level only; the internal AI-chat
  path still passes a real aiChatId).

Frontend (B2):
- Extend IComment with createdSource/aiChatId/resolvedSource (backend already
  returns them via selectAll).
- Extract the local AiAgentBadge from history-item into a shared
  components/ui/ai-agent-badge.tsx (clickable deep-link when aiChatId present,
  plain label when null/absent); reuse it in history-item and render it in
  comment-list-item next to the author name when createdSource==='agent'.

Tests: comment.service agent/null-aiChatId provenance, jwt.strategy provenance
derivation + anti-spoof, AiAgentBadge clickable/non-clickable branches, and
comment-list-item badge render/no-render.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/src/database/migrations/20260623T120000-user-is-agent.ts

@@ -0,0 +1,23 @@
+import { type Kysely } from 'kysely';
+
+/**
+ * Agent identity flag on users (MCP comment/page AI attribution).
+ *
+ * Additive boolean marking a service account as an AI agent. When set, the JWT
+ * strategy derives provenance ('agent') from this SIGNED server-side identity —
+ * never from a client-supplied field — so every write by the account is
+ * attributed to AI in a non-spoofable way. Defaults to false; ordinary users
+ * are unaffected. Kept as a dedicated column (not `role`, which has
+ * authorization semantics, and not buried in `settings`) for a cheap filter and
+ * explicitness.
+ */
+export async function up(db: Kysely<any>): Promise<void> {
+  await db.schema
+    .alterTable('users')
+    .addColumn('is_agent', 'boolean', (col) => col.notNull().defaultTo(false))
+    .execute();
+}
+
+export async function down(db: Kysely<any>): Promise<void> {
+  await db.schema.alterTable('users').dropColumn('is_agent').execute();
+}

apps/server/src/database/repos/user/user.repo.ts

@@ -36,6 +36,9 @@ export class UserRepo {
     'updatedAt',
     'deletedAt',
     'hasGeneratedPassword',
+    // AI agent identity flag — needed by the JWT strategy to derive a
+    // non-spoofable 'agent' provenance from the signed server-side identity.
+    'isAgent',
   ];
 
   async findById(

apps/server/src/database/types/db.d.ts

@@ -368,6 +368,7 @@ export interface Users {
   emailVerifiedAt: Timestamp | null;
   id: Generated<string>;
   invitedById: string | null;
+  isAgent: Generated<boolean>;
   lastActiveAt: Timestamp | null;
   lastLoginAt: Timestamp | null;
   locale: string | null;