v1.4-fork-header: fork from message + delete message + header polish + housekeeping

- Fork: POST /api/chats/:id/fork creates a new chat in the same session,
  copies messages up to target (status=complete) with row-offset
  clock_timestamp() for stable ordering. Client emits open_chat_in_active_pane
  event; Workspace opens it in the active pane. No maybeAutoNameChat on forks.
- Delete: DELETE /api/chats/:id/messages/:message_id with 409 if the chat is
  currently streaming. Cascading-forward delete (created_at >= target).
  MessageBubble Trash button + confirm Dialog.
- Header: Projects -> Project -> Session breadcrumb, model badge pill,
  inline session rename, active file path via new useActivePane() hook.
  Server now publishes session_renamed on PATCH /api/sessions/:id;
  client-side dup emit removed from Session.tsx.
- Housekeeping: NOW() -> clock_timestamp() in schema.sql defaults, dead
  PaneTab.tsx and panes/PaneShell.tsx removed, session_panes backfill
  INSERT removed (CREATE TABLE retained), Tailnet trust comment near
  app.listen().

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/server/src/routes/chats.ts

@@ -12,6 +12,11 @@ const PatchBody = z.object({
   name: z.string().min(1).max(200),
 });
 
+const ForkBody = z.object({
+  message_id: z.string().uuid(),
+  name: z.string().min(1).max(200).optional(),
+});
+
 export function registerChatRoutes(
   app: FastifyInstance,
   sql: Sql,
@@ -181,6 +186,78 @@ export function registerChatRoutes(
     }
   );
 
+  app.post<{ Params: { id: string } }>(
+    '/api/chats/:id/fork',
+    async (req, reply) => {
+      const parsed = ForkBody.safeParse(req.body ?? {});
+      if (!parsed.success) {
+        reply.code(400);
+        return { error: 'invalid body', details: parsed.error.flatten() };
+      }
+
+      const sourceRows = await sql<Chat[]>`
+        SELECT id, session_id, name, status, created_at, updated_at
+        FROM chats WHERE id = ${req.params.id}
+      `;
+      if (sourceRows.length === 0) {
+        reply.code(404);
+        return { error: 'chat not found' };
+      }
+      const source = sourceRows[0]!;
+
+      const targetRows = await sql<{ created_at: string; status: string }[]>`
+        SELECT created_at, status FROM messages
+        WHERE chat_id = ${source.id} AND id = ${parsed.data.message_id}
+      `;
+      if (targetRows.length === 0) {
+        reply.code(404);
+        return { error: 'message not found in chat' };
+      }
+      const target = targetRows[0]!;
+      if (target.status !== 'complete') {
+        reply.code(400);
+        return { error: 'can only fork from completed messages' };
+      }
+
+      const newName = parsed.data.name ?? `${source.name ?? 'Chat'} (fork)`;
+
+      const newChat = await sql.begin(async (tx) => {
+        const [chat] = await tx<Chat[]>`
+          INSERT INTO chats (session_id, name, status)
+          VALUES (${source.session_id}, ${newName}, 'open')
+          RETURNING id, session_id, name, status, created_at, updated_at
+        `;
+        await tx`
+          INSERT INTO messages (
+            session_id, chat_id, role, content, kind, tool_calls, tool_results,
+            status, tokens_used, ctx_used, ctx_max, started_at, finished_at,
+            created_at
+          )
+          SELECT
+            ${source.session_id}, ${chat!.id}, role, content, kind,
+            tool_calls, tool_results, status,
+            tokens_used, ctx_used, ctx_max, started_at, finished_at,
+            clock_timestamp() + (
+              ROW_NUMBER() OVER (ORDER BY created_at ASC, id ASC) * INTERVAL '1 microsecond'
+            )
+          FROM messages
+          WHERE chat_id = ${source.id}
+            AND created_at <= ${target.created_at}::timestamptz
+            AND status = 'complete'
+        `;
+        return chat!;
+      });
+
+      broker.publishUser('default', {
+        type: 'chat_created',
+        chat: newChat,
+        session_id: source.session_id,
+      });
+      reply.code(201);
+      return newChat;
+    }
+  );
+
   app.get<{ Params: { id: string } }>(
     '/api/chats/:id/messages',
     async (req, reply) => {