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/web/src/hooks/sessionEvents.ts

@@ -57,6 +57,11 @@ export interface AttachChatFileEvent {
   attachment: Omit<Attachment, 'id'>;
 }
 
+export interface OpenChatInActivePaneEvent {
+  type: 'open_chat_in_active_pane';
+  chat_id: string;
+}
+
 export interface SessionArchivedEvent {
   type: 'session_archived';
   session_id: string;
@@ -120,6 +125,7 @@ export type SessionEvent =
   | SessionLoadedEvent
   | OpenFileInBrowserEvent
   | AttachChatFileEvent
+  | OpenChatInActivePaneEvent
   | SessionArchivedEvent
   | ChatCreatedEvent
   | ChatUpdatedEvent

apps/web/src/hooks/useActivePane.ts

@@ -0,0 +1,61 @@
+import { useEffect, useState } from 'react';
+import type { WorkspacePaneKind } from '@/api/types';
+
+export interface ActivePaneSnapshot {
+  sessionId: string | null;
+  paneId: string | null;
+  kind: WorkspacePaneKind | null;
+  activeFile: string | null;
+}
+
+const EMPTY: ActivePaneSnapshot = {
+  sessionId: null,
+  paneId: null,
+  kind: null,
+  activeFile: null,
+};
+
+let current: ActivePaneSnapshot = EMPTY;
+const subs = new Set<() => void>();
+
+function notify(): void {
+  for (const sub of subs) {
+    try {
+      sub();
+    } catch {
+      // swallow — one bad listener shouldn't break others
+    }
+  }
+}
+
+function isSame(a: ActivePaneSnapshot, b: ActivePaneSnapshot): boolean {
+  return (
+    a.sessionId === b.sessionId &&
+    a.paneId === b.paneId &&
+    a.kind === b.kind &&
+    a.activeFile === b.activeFile
+  );
+}
+
+export function setActivePaneInfo(next: ActivePaneSnapshot): void {
+  if (isSame(current, next)) return;
+  current = next;
+  notify();
+}
+
+export function clearActivePane(): void {
+  setActivePaneInfo(EMPTY);
+}
+
+export function useActivePane(): ActivePaneSnapshot {
+  const [snap, setSnap] = useState<ActivePaneSnapshot>(current);
+  useEffect(() => {
+    const sub = () => setSnap(current);
+    subs.add(sub);
+    sub();
+    return () => {
+      subs.delete(sub);
+    };
+  }, []);
+  return snap;
+}

apps/web/src/hooks/useSidebar.ts

@@ -148,6 +148,9 @@ function applyEvent(prev: SidebarResponse, event: import('./sessionEvents').Sess
       return prev;
     case 'attach_chat_file':
       return prev;
+    case 'open_chat_in_active_pane':
+      // Consumed by Workspace; sidebar has no business with pane state.
+      return prev;
     case 'session_archived': {
       let changed = false;
       const projects = prev.projects.map((p) => {