feat: v2.6 follow-ups — apps/server close-hook caller + DiffPanel staging hint (3.7)

apps/server fire-and-forgets BooCoder's Phase-3 close hooks (new coder-notify.ts, reuses BOOCODER_URL, never-rejects) on session-delete + chat archive/archive-all/delete, so warm backends + worktrees tear down immediately (idle-evict/reaper was the backstop). 3.7: BooCoder DiffPanel shows a muted one-liner when the selected provider can't see another agent's unapplied worktree edits (pure derivation from per-change agent + current provider, no new state). 6 new server tests (coder-notify); 537 server tests pass; web+server tsc/build clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/server/src/routes/sessions.ts

@@ -5,6 +5,7 @@ import type { Config } from '../config.js';
 import type { Broker } from '../services/broker.js';
 import type { Session, WorktreeRiskReport } from '../types/api.js';
 import { getSetting } from './settings.js';
+import { notifyCoderClose } from '../services/coder-notify.js';
 
 const CreateBody = z.object({
   name: z.string().min(1).max(200).optional(),
@@ -513,6 +514,10 @@ export function registerSessionRoutes(
       }
       const project_id = deleted[0]!.project_id;
       broker.publishUserFrame('default', { type: 'session_deleted', session_id: id, project_id });
+      // Fire-and-forget: ask BooCoder to tear down this session's warm agent
+      // backends + worktree immediately. Best-effort — never blocks/fails the
+      // delete; the coder's idle-evict + orphan reaper backstop a missed call.
+      void notifyCoderClose('session', id, req.log);
       reply.code(204);
       return null;
     }