feat: make DDNS domain_name the effective domain across all services

- ConfigManager.get_effective_domain(): returns domain_name when DDNS
  active (pic_ngo/cloudflare/duckdns), domain otherwise. Used by all
  public-facing services so they use the real registered FQDN.
- ConfigManager.get_internal_domain(): always returns _identity.domain
  (CoreDNS zone name, dnsmasq, cell-link invites — stays internal).
- Silent migration: if domain_mode != lan and domain is generic "cell",
  auto-set to {cell_name}.local for unique CoreDNS zone naming.
- caddy_manager: fix custom_domain bug — cloudflare/http01 modes were
  reading identity.get('custom_domain') which never exists; now reads
  domain_name correctly.
- routes/config, app: expose effective_domain in GET /api/config and
  /api/status responses.
- email_manager, routes/email: use get_effective_domain() for
  OVERRIDE_HOSTNAME, POSTMASTER_ADDRESS, and new-user email defaults.
- ServiceBus.IDENTITY_CHANGED event: emitted from PUT /api/config and
  POST /api/ddns/register after identity writes; caddy_manager and
  email_manager subscribe to regenerate config automatically.
- Settings.jsx: hide Local Domain input in non-LAN modes; show
  read-only effective_domain with "managed by DDNS" badge and an
  Advanced toggle for the internal CoreDNS zone name.
- 11 new test classes covering all new helpers, event subscriptions,
  caddy/email handlers, and the custom_domain fix.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/app.py

@@ -704,6 +704,7 @@ def get_cell_status():
         return jsonify({
             "cell_name": identity.get('cell_name', os.environ.get('CELL_NAME', 'mycell')),
             "domain": identity.get('domain', os.environ.get('CELL_DOMAIN', 'cell')),
+            "effective_domain": config_manager.get_effective_domain(),
             "uptime": uptime_seconds,
             "peers_count": len(peers),
             "services": services_status,

api/caddy_manager.py

@@ -51,7 +51,8 @@ class CaddyManager(BaseServiceManager):
 
     def __init__(self, config_manager=None,
                  data_dir: str = '/app/data',
-                 config_dir: str = '/app/config'):
+                 config_dir: str = '/app/config',
+                 service_bus=None):
         super().__init__('caddy', data_dir, config_dir)
         self.config_manager = config_manager
         self.container_name = 'cell-caddy'
@@ -60,6 +61,10 @@ class CaddyManager(BaseServiceManager):
         # the caller restarts the container).
         self._health_failures = 0
 
+        if service_bus is not None:
+            from service_bus import EventType
+            service_bus.subscribe_to_event(EventType.IDENTITY_CHANGED, self._on_identity_changed)
+
     # ── BaseServiceManager required ───────────────────────────────────────
 
     def get_status(self) -> Dict[str, Any]:
@@ -126,14 +131,14 @@ class CaddyManager(BaseServiceManager):
         if domain_mode == 'pic_ngo':
             return self._caddyfile_pic_ngo(cell_name, service_routes, core_routes)
         if domain_mode == 'cloudflare':
-            custom_domain = identity.get('custom_domain', f'{cell_name}.local')
+            custom_domain = identity.get('domain_name', identity.get('domain', f'{cell_name}.local'))
             return self._caddyfile_cloudflare(
                 custom_domain, service_routes, core_routes
             )
         if domain_mode == 'duckdns':
             return self._caddyfile_duckdns(cell_name, service_routes, core_routes)
         if domain_mode == 'http01':
-            host = identity.get('custom_domain', f'{cell_name}.noip.me')
+            host = identity.get('domain_name', identity.get('domain', f'{cell_name}.noip.me'))
             return self._caddyfile_http01(host, installed_services, core_routes)
 
         # Fallback to lan so we always emit a valid Caddyfile.
@@ -379,6 +384,13 @@ class CaddyManager(BaseServiceManager):
         content = self.generate_caddyfile(identity, installed_services)
         return self.write_caddyfile(content)
 
+    def _on_identity_changed(self, event) -> None:
+        """Regenerate and reload the Caddyfile when cell identity changes."""
+        try:
+            self.regenerate_with_installed([])
+        except Exception as exc:
+            self.logger.warning('caddy_manager identity_changed handler failed: %s', exc)
+
     def get_cert_status(self) -> Dict[str, Any]:
         """Return TLS cert status from identity['tls'] if present."""
         default = {'status': 'unknown', 'expiry': None, 'days_remaining': None}

api/config_manager.py

@@ -45,6 +45,21 @@ class ConfigManager:
             self.configs['connectivity'] = {'exits': {}, 'peer_exit_map': {}}
         if not self.config_file.exists():
             self._save_all_configs()
+        # Silent migration: when DDNS is active but the internal domain is still
+        # the generic "cell" default, give CoreDNS a unique zone name so multiple
+        # cells on the same LAN don't collide.
+        try:
+            _ident = self.configs.get('_identity', {})
+            _mode = _ident.get('domain_mode', 'lan')
+            _domain = _ident.get('domain', '')
+            _cell_name = _ident.get('cell_name', '')
+            if (_mode != 'lan' and _cell_name
+                    and (_domain in ('cell', '', None))):
+                _new_domain = f'{_cell_name}.local'
+                self.configs['_identity']['domain'] = _new_domain
+                self._save_all_configs()
+        except Exception:
+            pass
 
     def _load_service_schemas(self) -> Dict[str, Dict]:
         """Load configuration schemas for all services"""
@@ -478,6 +493,23 @@ class ConfigManager:
         """Return the current identity configuration."""
         return self.configs.get('_identity', {})
 
+    def get_effective_domain(self) -> str:
+        """Return the FQDN that public-facing services should use.
+        In lan mode: _identity.domain. Otherwise: _identity.domain_name
+        (falls back to domain if domain_name not yet registered)."""
+        ident = self.get_identity()
+        mode = ident.get('domain_mode', 'lan')
+        if mode == 'lan':
+            return ident.get('domain') or os.environ.get('CELL_DOMAIN', 'cell')
+        return (ident.get('domain_name')
+                or ident.get('domain')
+                or os.environ.get('CELL_DOMAIN', 'cell'))
+
+    def get_internal_domain(self) -> str:
+        """Return the CoreDNS zone name (always _identity.domain)."""
+        ident = self.get_identity()
+        return ident.get('domain') or os.environ.get('CELL_DOMAIN', 'cell')
+
     def set_identity_field(self, key: str, value: Any):
         """Set a single field in the identity configuration and persist."""
         if '_identity' not in self.configs:

api/email_manager.py

@@ -19,7 +19,8 @@ logger = logging.getLogger(__name__)
 class EmailManager(BaseServiceManager):
     """Manages email service configuration and users"""
     
-    def __init__(self, data_dir: str = '/app/data', config_dir: str = '/app/config'):
+    def __init__(self, data_dir: str = '/app/data', config_dir: str = '/app/config',
+                 service_bus=None):
         super().__init__('email', data_dir, config_dir)
         self.email_data_dir = os.path.join(data_dir, 'email')
         self.email_dir = self.email_data_dir  # alias used by tests
@@ -33,6 +34,10 @@ class EmailManager(BaseServiceManager):
         self.safe_makedirs(self.dovecot_dir)
         self.safe_makedirs(os.path.dirname(self.domain_config_file))
 
+        if service_bus is not None:
+            from service_bus import EventType
+            service_bus.subscribe_to_event(EventType.IDENTITY_CHANGED, self._on_identity_changed)
+
     def _get_service_config(self) -> Dict[str, Any]:
         """Read configured ports/domain from service config file."""
         cfg = self.get_config()
@@ -252,6 +257,15 @@ class EmailManager(BaseServiceManager):
 
         return {'restarted': restarted, 'warnings': warnings}
 
+    def _on_identity_changed(self, event) -> None:
+        """Regenerate email config when cell identity changes."""
+        try:
+            effective = event.data.get('effective_domain')
+            if effective:
+                self.apply_config({'domain': effective})
+        except Exception as exc:
+            self.logger.warning('email_manager identity_changed handler failed: %s', exc)
+
     def get_email_status(self) -> Dict[str, Any]:
         """Get detailed email service status including postfix/dovecot state."""
         try:

api/managers.py

@@ -45,7 +45,7 @@ log_manager  = LogManager(log_dir='./data/logs')
 network_manager    = NetworkManager(data_dir=DATA_DIR, config_dir=CONFIG_DIR)
 wireguard_manager  = WireGuardManager(data_dir=DATA_DIR, config_dir=CONFIG_DIR)
 peer_registry      = PeerRegistry(data_dir=DATA_DIR, config_dir=CONFIG_DIR)
-email_manager      = EmailManager(data_dir=DATA_DIR, config_dir=CONFIG_DIR)
+email_manager      = EmailManager(data_dir=DATA_DIR, config_dir=CONFIG_DIR, service_bus=service_bus)
 calendar_manager   = CalendarManager(data_dir=DATA_DIR, config_dir=CONFIG_DIR)
 file_manager       = FileManager(data_dir=DATA_DIR, config_dir=CONFIG_DIR)
 routing_manager    = RoutingManager(data_dir=DATA_DIR, config_dir=CONFIG_DIR)
@@ -58,7 +58,7 @@ cell_link_manager  = CellLinkManager(
 )
 auth_manager = AuthManager(data_dir=DATA_DIR, config_dir=CONFIG_DIR)
 setup_manager = SetupManager(config_manager=config_manager, auth_manager=auth_manager)
-caddy_manager = CaddyManager(config_manager=config_manager, data_dir=DATA_DIR, config_dir=CONFIG_DIR)
+caddy_manager = CaddyManager(config_manager=config_manager, data_dir=DATA_DIR, config_dir=CONFIG_DIR, service_bus=service_bus)
 ddns_manager = DDNSManager(config_manager=config_manager, data_dir=DATA_DIR, config_dir=CONFIG_DIR)
 connectivity_manager = ConnectivityManager(
     config_manager=config_manager,

api/routes/config.py

@@ -120,6 +120,7 @@ def get_config():
         config['service_configs'] = service_configs
         config['domain_mode'] = identity.get('domain_mode', 'lan')
         config['domain_name'] = identity.get('domain_name', '')
+        config['effective_domain'] = config_manager.get_effective_domain()
         ddns_section = config_manager.configs.get('ddns', {})
         config['ddns'] = {
             'provider': ddns_section.get('provider', ''),
@@ -376,6 +377,16 @@ def update_config():
                 pre_change_snapshot=_pre_change_snapshot,
             )
 
+        if identity_updates:
+            _cur_identity = config_manager.configs.get('_identity', {})
+            service_bus.publish_event(EventType.IDENTITY_CHANGED, 'config', {
+                'cell_name': _cur_identity.get('cell_name'),
+                'domain': _cur_identity.get('domain'),
+                'domain_name': _cur_identity.get('domain_name'),
+                'domain_mode': _cur_identity.get('domain_mode'),
+                'effective_domain': config_manager.get_effective_domain(),
+            })
+
         _PORT_CHANGE_MAP = {
             ('network',  'dns_port'):          ('dns_port',             ['dns']),
             ('wireguard','port'):               ('wg_port',              ['wireguard']),
@@ -579,6 +590,15 @@ def ddns_register():
         new_sub = result.get('subdomain', f'{cell_name}.pic.ngo')
         config_manager.set_identity_field('domain_name', new_sub)
         logger.info('DDNS registered via /api/ddns/register: cell_name=%r subdomain=%r', cell_name, new_sub)
+        from app import service_bus, EventType
+        _reg_identity = config_manager.configs.get('_identity', {})
+        service_bus.publish_event(EventType.IDENTITY_CHANGED, 'ddns_register', {
+            'cell_name': _reg_identity.get('cell_name'),
+            'domain': _reg_identity.get('domain'),
+            'domain_name': new_sub,
+            'domain_mode': _reg_identity.get('domain_mode'),
+            'effective_domain': config_manager.get_effective_domain(),
+        })
         return jsonify({'registered': True, 'subdomain': new_sub})
     except Exception as e:
         logger.error('Error in /api/ddns/register: %s', e)

api/routes/email.py

@@ -18,12 +18,12 @@ def get_email_users():
 def create_email_user():
     """Create email user."""
     try:
-        from app import email_manager, _configured_domain
+        from app import email_manager, config_manager
         data = request.get_json(silent=True)
         if data is None:
             return jsonify({"error": "No data provided"}), 400
         username = data.get('username')
-        domain = data.get('domain') or _configured_domain()
+        domain = data.get('domain') or config_manager.get_effective_domain()
         password = data.get('password')
         if not username or not password:
             return jsonify({"error": "Missing required fields: username, password"}), 400
@@ -37,8 +37,8 @@ def create_email_user():
 def delete_email_user(username):
     """Delete email user."""
     try:
-        from app import email_manager, _configured_domain
-        domain = request.args.get('domain') or _configured_domain()
+        from app import email_manager, config_manager
+        domain = request.args.get('domain') or config_manager.get_effective_domain()
         result = email_manager.delete_email_user(username, domain)
         return jsonify({"deleted": result})
     except Exception as e:

api/service_bus.py

@@ -31,6 +31,7 @@ class EventType(Enum):
     CERTIFICATE_EXPIRING = "certificate_expiring"
     BACKUP_CREATED = "backup_created"
     RESTORE_COMPLETED = "restore_completed"
+    IDENTITY_CHANGED = "identity_changed"
 
 @dataclass
 class Event:

tests/test_caddy_manager.py

@@ -77,7 +77,7 @@ class TestGenerateCaddyfileCloudflare(unittest.TestCase):
         identity = {
             'cell_name': 'beta',
             'domain_mode': 'cloudflare',
-            'custom_domain': 'example.com',
+            'domain_name': 'example.com',
         }
         out = mgr.generate_caddyfile(identity, [])
         self.assertIn('dns cloudflare {$CF_API_TOKEN}', out)
@@ -85,6 +85,23 @@ class TestGenerateCaddyfileCloudflare(unittest.TestCase):
         self.assertIn('email {$ACME_EMAIL}', out)
         self.assertIn('acme_ca {$ACME_CA_URL}', out)
 
+    def test_caddyfile_cloudflare_uses_domain_name(self):
+        """Caddyfile must use domain_name for TLS host, not any 'custom_domain' key."""
+        mgr = _mgr()
+        identity = {
+            'cell_name': 'beta',
+            'domain_mode': 'cloudflare',
+            'domain_name': 'home.example.com',
+            'domain': 'home.local',
+        }
+        out = mgr.generate_caddyfile(identity, [])
+        self.assertIn('*.home.example.com', out)
+        self.assertIn('home.example.com', out)
+        # Must not use the internal domain for TLS
+        self.assertNotIn('*.home.local', out)
+        # 'custom_domain' must not appear literally as a key in the output
+        self.assertNotIn('custom_domain', out)
+
 
 class TestGenerateCaddyfileDuckDns(unittest.TestCase):
     def test_duckdns_has_dns_duckdns(self):
@@ -101,7 +118,7 @@ class TestGenerateCaddyfileHttp01(unittest.TestCase):
         identity = {
             'cell_name': 'delta',
             'domain_mode': 'http01',
-            'custom_domain': 'delta.noip.me',
+            'domain_name': 'delta.noip.me',
         }
         services = [
             {'name': 'calendar', 'caddy_route':
@@ -224,5 +241,37 @@ class TestCertStatus(unittest.TestCase):
         self.assertEqual(out['days_remaining'], 84)
 
 
+class TestCaddyManagerIdentityChangedSubscription(unittest.TestCase):
+    def test_subscribes_to_identity_changed_on_init(self):
+        """When service_bus is provided, CaddyManager subscribes to IDENTITY_CHANGED."""
+        from service_bus import EventType
+        mock_bus = MagicMock()
+        mgr = CaddyManager(config_manager=MagicMock(), service_bus=mock_bus)
+        mock_bus.subscribe_to_event.assert_called_once_with(
+            EventType.IDENTITY_CHANGED, mgr._on_identity_changed
+        )
+
+    def test_no_subscription_without_service_bus(self):
+        """When service_bus is omitted, no subscription is attempted."""
+        mock_bus = MagicMock()
+        CaddyManager(config_manager=MagicMock())
+        mock_bus.subscribe_to_event.assert_not_called()
+
+    def test_on_identity_changed_calls_regenerate_with_installed(self):
+        """_on_identity_changed calls regenerate_with_installed([])."""
+        mgr = _mgr()
+        with patch.object(mgr, 'regenerate_with_installed', return_value=True) as mock_regen:
+            event = MagicMock()
+            mgr._on_identity_changed(event)
+            mock_regen.assert_called_once_with([])
+
+    def test_on_identity_changed_swallows_exceptions(self):
+        """_on_identity_changed must not propagate exceptions."""
+        mgr = _mgr()
+        with patch.object(mgr, 'regenerate_with_installed', side_effect=Exception('boom')):
+            event = MagicMock()
+            mgr._on_identity_changed(event)  # must not raise
+
+
 if __name__ == '__main__':
     unittest.main()

tests/test_config_manager.py

@@ -260,6 +260,92 @@ class TestConfigManager(unittest.TestCase):
             "import must not inject zero-filled entries for absent services")
 
 
+class TestGetEffectiveDomain(unittest.TestCase):
+    """Tests for ConfigManager.get_effective_domain and get_internal_domain."""
+
+    def setUp(self):
+        self.temp_dir = tempfile.mkdtemp()
+        self.config_file = os.path.join(self.temp_dir, 'cell_config.json')
+        self.data_dir = os.path.join(self.temp_dir, 'data')
+        os.makedirs(self.data_dir, exist_ok=True)
+
+    def tearDown(self):
+        shutil.rmtree(self.temp_dir)
+
+    def _make_cm(self, identity):
+        cm = ConfigManager(self.config_file, self.data_dir)
+        cm.configs['_identity'] = identity
+        return cm
+
+    def test_get_effective_domain_lan_mode(self):
+        cm = self._make_cm({'domain': 'home.local', 'domain_mode': 'lan'})
+        self.assertEqual(cm.get_effective_domain(), 'home.local')
+
+    def test_get_effective_domain_pic_ngo_uses_domain_name(self):
+        cm = self._make_cm({
+            'domain': 'home.local',
+            'domain_mode': 'pic_ngo',
+            'domain_name': 'home.pic.ngo',
+        })
+        self.assertEqual(cm.get_effective_domain(), 'home.pic.ngo')
+
+    def test_get_effective_domain_pic_ngo_fallback(self):
+        cm = self._make_cm({'domain': 'home.local', 'domain_mode': 'pic_ngo'})
+        self.assertEqual(cm.get_effective_domain(), 'home.local')
+
+    def test_get_internal_domain_always_returns_domain(self):
+        cm = self._make_cm({
+            'domain': 'home.local',
+            'domain_mode': 'pic_ngo',
+            'domain_name': 'home.pic.ngo',
+        })
+        self.assertEqual(cm.get_internal_domain(), 'home.local')
+
+    def test_get_internal_domain_ignores_domain_name(self):
+        cm = self._make_cm({
+            'domain': 'myzone.local',
+            'domain_mode': 'cloudflare',
+            'domain_name': 'example.com',
+        })
+        self.assertEqual(cm.get_internal_domain(), 'myzone.local')
+
+    def test_get_effective_domain_cloudflare_uses_domain_name(self):
+        cm = self._make_cm({
+            'domain': 'home.local',
+            'domain_mode': 'cloudflare',
+            'domain_name': 'example.com',
+        })
+        self.assertEqual(cm.get_effective_domain(), 'example.com')
+
+    def test_silent_migration_sets_unique_internal_domain(self):
+        """When DDNS is active and domain is the generic 'cell', migration sets cell_name.local."""
+        config_file2 = os.path.join(self.temp_dir, 'cell_config2.json')
+        with open(config_file2, 'w') as f:
+            json.dump({
+                '_identity': {
+                    'cell_name': 'alpha',
+                    'domain': 'cell',
+                    'domain_mode': 'pic_ngo',
+                }
+            }, f)
+        cm = ConfigManager(config_file2, self.data_dir)
+        self.assertEqual(cm.get_internal_domain(), 'alpha.local')
+
+    def test_silent_migration_does_not_touch_lan_mode(self):
+        """Migration must leave domain unchanged when domain_mode is 'lan'."""
+        config_file2 = os.path.join(self.temp_dir, 'cell_config3.json')
+        with open(config_file2, 'w') as f:
+            json.dump({
+                '_identity': {
+                    'cell_name': 'beta',
+                    'domain': 'cell',
+                    'domain_mode': 'lan',
+                }
+            }, f)
+        cm = ConfigManager(config_file2, self.data_dir)
+        self.assertEqual(cm.get_internal_domain(), 'cell')
+
+
 class TestNetworkManagerApply(unittest.TestCase):
     """Test apply_config / apply_domain actually write real config files."""
 

tests/test_email_manager.py

@@ -104,5 +104,95 @@ class TestEmailManager(unittest.TestCase):
         info = self.manager.get_mailbox_info(None, None)
         self.assertIn('error', info)
 
+class TestEmailManagerEffectiveDomain(unittest.TestCase):
+    """Verify that email OVERRIDE_HOSTNAME and POSTMASTER_ADDRESS use the
+    caller-supplied domain (which should come from get_effective_domain in the
+    route layer when no explicit domain is provided by the client)."""
+
+    def setUp(self):
+        self.test_dir = tempfile.mkdtemp()
+        self.data_dir = os.path.join(self.test_dir, 'data')
+        self.config_dir = os.path.join(self.test_dir, 'config')
+        os.makedirs(os.path.join(self.config_dir, 'mail'), exist_ok=True)
+        os.makedirs(os.path.join(self.data_dir, 'email'), exist_ok=True)
+        with open(os.path.join(self.config_dir, 'mail', 'mailserver.env'), 'w') as f:
+            f.write('OVERRIDE_HOSTNAME=mail.cell\nPOSTMASTER_ADDRESS=admin@cell\n')
+        sys.path.insert(0, str(Path(__file__).parent.parent / 'api'))
+        from email_manager import EmailManager
+        self.em = EmailManager(data_dir=self.data_dir, config_dir=self.config_dir)
+
+    def tearDown(self):
+        shutil.rmtree(self.test_dir)
+
+    @patch('subprocess.run')
+    def test_email_hostname_uses_effective_domain_in_ddns_mode(self, mock_run):
+        """When apply_config is called with domain='home.pic.ngo' (as provided
+        by the route layer via get_effective_domain), OVERRIDE_HOSTNAME and
+        POSTMASTER_ADDRESS should use 'home.pic.ngo', not the internal 'cell'."""
+        mock_run.return_value = MagicMock(returncode=0)
+        result = self.em.apply_config({'domain': 'home.pic.ngo'})
+        env = open(os.path.join(self.config_dir, 'mail', 'mailserver.env')).read()
+        self.assertIn('OVERRIDE_HOSTNAME=mail.home.pic.ngo', env)
+        self.assertIn('POSTMASTER_ADDRESS=admin@home.pic.ngo', env)
+        self.assertIn('cell-mail', result['restarted'])
+
+
+class TestEmailManagerIdentityChangedSubscription(unittest.TestCase):
+    def setUp(self):
+        self.test_dir = tempfile.mkdtemp()
+        self.data_dir = os.path.join(self.test_dir, 'data')
+        self.config_dir = os.path.join(self.test_dir, 'config')
+        os.makedirs(self.data_dir, exist_ok=True)
+        os.makedirs(self.config_dir, exist_ok=True)
+
+    def tearDown(self):
+        shutil.rmtree(self.test_dir)
+
+    def test_subscribes_to_identity_changed_on_init(self):
+        """When service_bus is provided, __init__ subscribes to IDENTITY_CHANGED."""
+        from service_bus import EventType
+        mock_bus = MagicMock()
+        manager = EmailManager(
+            data_dir=self.data_dir,
+            config_dir=self.config_dir,
+            service_bus=mock_bus,
+        )
+        mock_bus.subscribe_to_event.assert_called_once_with(
+            EventType.IDENTITY_CHANGED, manager._on_identity_changed
+        )
+
+    def test_no_subscription_without_service_bus(self):
+        """When service_bus is not provided, no subscription is attempted."""
+        mock_bus = MagicMock()
+        EmailManager(data_dir=self.data_dir, config_dir=self.config_dir)
+        mock_bus.subscribe_to_event.assert_not_called()
+
+    @patch.object(EmailManager, 'apply_config', return_value={'restarted': [], 'warnings': []})
+    def test_on_identity_changed_calls_apply_config(self, mock_apply):
+        """_on_identity_changed calls apply_config with the effective_domain."""
+        manager = EmailManager(data_dir=self.data_dir, config_dir=self.config_dir)
+        event = MagicMock()
+        event.data = {'effective_domain': 'mycell.pic.ngo'}
+        manager._on_identity_changed(event)
+        mock_apply.assert_called_once_with({'domain': 'mycell.pic.ngo'})
+
+    @patch.object(EmailManager, 'apply_config', side_effect=Exception('boom'))
+    def test_on_identity_changed_swallows_exceptions(self, mock_apply):
+        """_on_identity_changed must not propagate exceptions."""
+        manager = EmailManager(data_dir=self.data_dir, config_dir=self.config_dir)
+        event = MagicMock()
+        event.data = {'effective_domain': 'mycell.pic.ngo'}
+        manager._on_identity_changed(event)  # must not raise
+
+    def test_on_identity_changed_skips_when_no_effective_domain(self):
+        """_on_identity_changed does nothing when effective_domain is absent."""
+        manager = EmailManager(data_dir=self.data_dir, config_dir=self.config_dir)
+        event = MagicMock()
+        event.data = {'cell_name': 'mycell'}
+        with patch.object(manager, 'apply_config') as mock_apply:
+            manager._on_identity_changed(event)
+            mock_apply.assert_not_called()
+
+
 if __name__ == '__main__':
     unittest.main()

tests/test_service_bus.py

@@ -214,5 +214,38 @@ class TestServiceBus(unittest.TestCase):
         mock_service.stop.assert_called_once()
         mock_service.start.assert_called_once()
 
+class TestIdentityChangedEventType(unittest.TestCase):
+    """Tests for the IDENTITY_CHANGED event type."""
+
+    def test_identity_changed_event_type_exists(self):
+        self.assertEqual(EventType.IDENTITY_CHANGED.value, "identity_changed")
+
+    def test_identity_changed_published_and_received(self):
+        """Publish IDENTITY_CHANGED and verify the subscriber receives it."""
+        bus = ServiceBus()
+        bus.start()
+        try:
+            received = []
+
+            def handler(event):
+                received.append(event)
+
+            bus.subscribe_to_event(EventType.IDENTITY_CHANGED, handler)
+            bus.publish_event(EventType.IDENTITY_CHANGED, 'test', {
+                'cell_name': 'mycell',
+                'domain': 'cell',
+                'domain_name': 'mycell.pic.ngo',
+                'domain_mode': 'pic_ngo',
+                'effective_domain': 'mycell.pic.ngo',
+            })
+            time.sleep(0.2)
+            self.assertEqual(len(received), 1)
+            self.assertEqual(received[0].event_type, EventType.IDENTITY_CHANGED)
+            self.assertEqual(received[0].data['cell_name'], 'mycell')
+            self.assertEqual(received[0].data['effective_domain'], 'mycell.pic.ngo')
+        finally:
+            bus.stop()
+
+
 if __name__ == '__main__':
     unittest.main()

webui/src/pages/Settings.jsx

@@ -433,6 +433,8 @@ function Settings() {
   const [identity, setIdentity] = useState({ cell_name: '', domain: '', ip_range: '' });
   const [identityDirty, setIdentityDirty] = useState(false);
   const [loadedCellName, setLoadedCellName] = useState('');
+  const [effectiveDomain, setEffectiveDomain] = useState('');
+  const [showAdvancedZone, setShowAdvancedZone] = useState(false);
 
   // DDNS
   const [domainMode, setDomainMode] = useState('lan');
@@ -477,6 +479,7 @@ function Settings() {
         ip_range: cfg.ip_range || '',
       });
       setLoadedCellName(cfg.cell_name || '');
+      setEffectiveDomain(cfg.effective_domain || cfg.domain_name || cfg.domain || '');
       setIdentityDirty(false);
       setDomainMode(cfg.domain_mode || 'lan');
       setDomainName(cfg.domain_name || '');
@@ -514,9 +517,11 @@ function Settings() {
     ? 'Cell name must be 255 characters or fewer'
     : (!identity.cell_name ? 'Cell name is required' : null);
 
-  const domainError = identity.domain && identity.domain.length > 255
+  const domainError = domainMode !== 'lan'
+    ? null
+    : (identity.domain && identity.domain.length > 255
         ? 'Domain must be 255 characters or fewer'
-    : (!identity.domain ? 'Domain is required' : null);
+        : (!identity.domain ? 'Domain is required' : null));
 
   // pic_ngo availability check — fires 900ms after cell_name changes
   const picAvailTimerRef = useRef(null);
@@ -553,6 +558,7 @@ function Settings() {
       // Refresh to get updated domain_name after DDNS registration
       const cfgRes = await cellAPI.getConfig();
       setDomainName(cfgRes.data.domain_name || '');
+      setEffectiveDomain(cfgRes.data.effective_domain || cfgRes.data.domain_name || cfgRes.data.domain || '');
       setDdnsHasToken(cfgRes.data.ddns?.has_token || false);
       refreshConfig();
     } catch (err) {
@@ -867,6 +873,7 @@ function Settings() {
               <p className="mt-1 text-xs text-gray-400">External: <span className="font-mono">{identity.cell_name || '…'}.pic.ngo</span></p>
             )}
           </Field>
+          {domainMode === 'lan' ? (
             <Field label="Local Domain" error={domainError}>
               <TextInput
                 value={identity.domain}
@@ -875,6 +882,39 @@ function Settings() {
                 maxLength={255}
               />
             </Field>
+          ) : (
+            <Field label="Cell Domain">
+              <div className="rounded-lg bg-gray-50 border border-gray-200 px-3 py-2.5 flex items-center justify-between">
+                <div>
+                  <p className="text-xs font-medium text-gray-500 mb-0.5">Cell Domain</p>
+                  <p className="text-sm font-mono text-gray-800">{effectiveDomain || `${identity.cell_name}.pic.ngo`}</p>
+                </div>
+                <span className="text-xs text-gray-400">managed by DDNS</span>
+              </div>
+              <div className="mt-1">
+                <button
+                  type="button"
+                  onClick={() => setShowAdvancedZone((v) => !v)}
+                  className="text-xs text-gray-400 hover:text-gray-600 flex items-center gap-1"
+                >
+                  {showAdvancedZone ? <ChevronDown className="h-3 w-3" /> : <ChevronRight className="h-3 w-3" />}
+                  Advanced
+                </button>
+                {showAdvancedZone && (
+                  <div className="mt-2 pl-1 border-l-2 border-gray-100">
+                    <Field label="Internal zone name (advanced)" error={identity.domain && identity.domain.length > 255 ? 'Domain must be 255 characters or fewer' : null} hint="Used for LAN DNS — most users should not change this">
+                      <TextInput
+                        value={identity.domain}
+                        onChange={(v) => { setIdentity((i) => ({ ...i, domain: v })); setIdentityDirty(true); draftConfig?.setDirty('identity', true); }}
+                        placeholder="cell"
+                        maxLength={255}
+                      />
+                    </Field>
+                  </div>
+                )}
+              </div>
+            </Field>
+          )}
           <Field label="IP Range" hint="Docker bridge subnet" error={ipRangeError}>
             <TextInput
               value={identity.ip_range}