fix(namespace): executor/router/buildermgr RemoveNamespace + per-NS informer lifecycle

- Add RemoveNamespace(ctx, ns) to executortype.ExecutorType interface
- Implement RemoveNamespace in poolmgr, newdeploy, container executor types
- Add per-namespace context cancellation (nsCancels map) in all three types so
  informer factories are stopped when namespace is removed (fixes goroutine leak)
- Add PoolPodController.RemoveNamespace to clear envLister/podLister maps
- Add deregisterNamespace() in executor multitenant subscriber
- Switch executor/router/buildermgr watcher strategy from TrackOnly to DispatchRemove
  so RemoveFunc is called when fission.io/managed label is removed
- Add RemoveFunc to executor/router/buildermgr namespace subscribers
- Add RemoveNamespace to environmentWatcher and packageWatcher with per-NS cancel
- Add RemoveNamespace to HTTPTriggerSet: cancels informers, removes from maps, calls syncTriggers
- Fix ns_watcher_test.go fakeExecutorType to implement new RemoveNamespace method

Fixes:
- Executor dedup gap: re-added namespace was silently skipped (envLister/deplLister still present)
- Goroutine/FD leak: old informer factories ran forever after namespace removal
- Router stale routes: HTTPTriggers for removed namespace stayed in routing table

pkg/executor/multitenant/namespace_subscriber.go

@@ -24,6 +24,9 @@ func NewNamespaceSubscriber(
 			registerNamespace(ctx, logger, kubernetesClient, record.Name, executorTypes, mgr)
 			return nil
 		},
+		RemoveFunc: func(ctx context.Context, record utils.NamespaceRecord) error {
+			return deregisterNamespace(ctx, logger, record.Name, executorTypes)
+		},
 		ResyncFunc: func(ctx context.Context, record utils.NamespaceRecord) error {
 			registerNamespace(ctx, logger, kubernetesClient, record.Name, executorTypes, mgr)
 			return nil

pkg/executor/multitenant/ns_watcher.go

@@ -87,7 +87,9 @@ func StartNSWatcher(
 	executorTypes map[fv1.ExecutorType]executortype.ExecutorType,
 	mgr manager.Interface,
 ) {
-	_, err := utils.RunManagedNamespaceWatcher(ctx, logger, kubernetesClient, mgr, utils.NewDefaultManagedNamespaceWatcherConfig("multitenant.NSWatcher", NewNamespaceSubscriber(logger, kubernetesClient, executorTypes, mgr)))
+	config := utils.NewDefaultManagedNamespaceWatcherConfig("multitenant.NSWatcher", NewNamespaceSubscriber(logger, kubernetesClient, executorTypes, mgr))
+	config.RemovalStrategy = utils.NamespaceRemovalStrategyDispatchRemove
+	_, err := utils.RunManagedNamespaceWatcher(ctx, logger, kubernetesClient, mgr, config)
 	if err != nil {
 		logger.Error("multitenant.NSWatcher: BootstrapAndDispatch failed", zap.Error(err))
 	}
@@ -135,3 +137,26 @@ func registerExecutorTypes(
 	}
 	return joinErr
 }
+
+// deregisterNamespace calls RemoveNamespace on every executor type for the given namespace.
+// Called when a Namespace with label fission.io/managed=true is removed.
+func deregisterNamespace(
+	ctx context.Context,
+	logger *zap.Logger,
+	ns string,
+	executorTypes map[fv1.ExecutorType]executortype.ExecutorType,
+) error {
+	var joinErr error
+
+	for _, et := range executorTypes {
+		if err := et.RemoveNamespace(ctx, ns); err != nil {
+			logger.Error("multitenant.NSWatcher: RemoveNamespace failed",
+				zap.String("namespace", ns),
+				zap.Error(err),
+			)
+			joinErr = errors.Join(joinErr, err)
+		}
+	}
+	logger.Info("multitenant.NSWatcher: deregistered namespace", zap.String("namespace", ns))
+	return joinErr
+}

pkg/executor/multitenant/ns_watcher_test.go

@@ -46,6 +46,7 @@ func (f *fakeExecutorType) AddNamespace(ctx context.Context, ns string, mgr mana
 	f.lastNamespace = ns
 	return f.addErr
 }
+func (f *fakeExecutorType) RemoveNamespace(ctx context.Context, ns string) error { return nil }
 
 var _ executortype.ExecutorType = (*fakeExecutorType)(nil)