feat(register): auto hot-reload service after channel register/deregister

Making a channel registration live no longer depends on an operator/agent
remembering to restart. setup/register.ts and scripts/deregister-room.ts now
call signalEjclawReload() after the DB write, which sends SIGHUP to the running
service's main PID (→ runtimeState.reloadRoomBindings). Best-effort and
injectable-for-tests; no-ops when the service isn't running.

Also document the canonical rule in the committed, agent-loaded platform prompt
(prompts/claude-platform.md): prefer these paths, never fake a restart, verify
via the "Room bindings reloaded" log; a plain in-turn systemctl restart is
forbidden (it kills the agent).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

setup/register.ts

@@ -11,6 +11,7 @@ import { assignRoom, initDatabase } from '../src/db.js';
 import { isValidGroupFolder } from '../src/group-folder.js';
 import { ensurePairedWorkspaceProvisioned } from '../src/paired-workspace-manager.js';
 import { logger } from '../src/logger.js';
+import { signalEjclawReload } from '../src/runtime-reload-signal.js';
 import { emitStatus } from './status.js';
 
 interface RegisterArgs {
@@ -133,12 +134,17 @@ export async function run(args: string[]): Promise<void> {
   });
   logger.info({ folder: parsed.folder }, 'Ensured group log directory exists');
 
+  // Make the registration live immediately: signal the running service to
+  // hot-reload its room bindings (no full restart, no operator follow-up).
+  const reloaded = signalEjclawReload();
+
   emitStatus('REGISTER_CHANNEL', {
     JID: parsed.jid,
     NAME: parsed.name,
     FOLDER: parsed.folder,
     CHANNEL: parsed.channel,
     STATUS: 'success',
+    RELOADED: reloaded ? 'yes' : 'no',
     LOG: 'logs/setup.log',
   });
 }