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/messages.ts

@@ -18,6 +18,7 @@ interface MessageHandlers {
   ) => void;
   publishMessagesDeleted: (sessionId: string, chatId: string, messageIds: string[]) => void;
   cancelInference: (sessionId: string, chatId: string) => Promise<boolean>;
+  hasActiveInference: (chatId: string) => boolean;
 }
 
 export function registerMessageRoutes(
@@ -156,6 +157,53 @@ export function registerMessageRoutes(
     }
   );
 
+  app.delete<{ Params: { id: string; message_id: string } }>(
+    '/api/chats/:id/messages/:message_id',
+    async (req, reply) => {
+      const { id: chatId, message_id: messageId } = req.params;
+
+      const chatRows = await sql<Chat[]>`
+        SELECT id, session_id FROM chats WHERE id = ${chatId}
+      `;
+      if (chatRows.length === 0) {
+        reply.code(404);
+        return { error: 'chat not found' };
+      }
+      const chat = chatRows[0]!;
+
+      if (handlers.hasActiveInference(chatId)) {
+        reply.code(409);
+        return { error: 'chat is currently streaming; stop it first' };
+      }
+
+      const deletedIds = await sql.begin(async (tx) => {
+        const deletedRows = await tx<{ id: string }[]>`
+          DELETE FROM messages
+          WHERE chat_id = ${chatId}
+            AND created_at >= (
+              SELECT created_at FROM messages
+              WHERE id = ${messageId} AND chat_id = ${chatId}
+            )
+          RETURNING id
+        `;
+        if (deletedRows.length > 0) {
+          await tx`UPDATE chats SET updated_at = clock_timestamp() WHERE id = ${chatId}`;
+        }
+        return deletedRows.map((r) => r.id);
+      });
+
+      if (deletedIds.length === 0) {
+        reply.code(404);
+        return { error: 'message not found' };
+      }
+
+      handlers.publishMessagesDeleted(chat.session_id, chatId, deletedIds);
+
+      reply.code(204);
+      return null;
+    }
+  );
+
   app.post<{ Params: { id: string } }>(
     '/api/chats/:id/compact',
     async (req, reply) => {