fix: skip session:patch hook clone without listeners

src/gateway/server-methods/sessions.ts

@@ -19,6 +19,7 @@ import {
   updateSessionStore,
 } from "../../config/sessions.js";
 import {
+  hasInternalHookListeners,
   triggerInternalHook,
   type SessionPatchHookContext,
   type SessionPatchHookEvent,
@@ -899,20 +900,22 @@ export const sessionsHandlers: GatewayRequestHandlers = {
       return;
     }
 
-    const hookContext: SessionPatchHookContext = structuredClone({
-      sessionEntry: applied.entry,
-      patch: p,
-      cfg,
-    });
-    const hookEvent: SessionPatchHookEvent = {
-      type: "session",
-      action: "patch",
-      sessionKey: target.canonicalKey ?? key,
-      context: hookContext,
-      timestamp: new Date(),
-      messages: [],
-    };
-    void triggerInternalHook(hookEvent);
+    if (hasInternalHookListeners("session", "patch")) {
+      const hookContext: SessionPatchHookContext = structuredClone({
+        sessionEntry: applied.entry,
+        patch: p,
+        cfg,
+      });
+      const hookEvent: SessionPatchHookEvent = {
+        type: "session",
+        action: "patch",
+        sessionKey: target.canonicalKey ?? key,
+        context: hookContext,
+        timestamp: new Date(),
+        messages: [],
+      };
+      void triggerInternalHook(hookEvent);
+    }
 
     const parsed = parseAgentSessionKey(target.canonicalKey ?? key);
     const agentId = normalizeAgentId(parsed?.agentId ?? resolveDefaultAgentId(cfg));

src/gateway/server.sessions.gateway-server-sessions-a.test.ts

@@ -34,6 +34,7 @@ const bootstrapCacheMocks = vi.hoisted(() => ({
 }));
 
 const sessionHookMocks = vi.hoisted(() => ({
+  hasInternalHookListeners: vi.fn(() => true),
   triggerInternalHook: vi.fn(async (_event: unknown) => {}),
 }));
 
@@ -96,6 +97,7 @@ vi.mock("../hooks/internal-hooks.js", async () => {
   );
   return {
     ...actual,
+    hasInternalHookListeners: sessionHookMocks.hasInternalHookListeners,
     triggerInternalHook: sessionHookMocks.triggerInternalHook,
   };
 });
@@ -260,6 +262,8 @@ describe("gateway server sessions", () => {
     sessionCleanupMocks.clearSessionQueues.mockClear();
     sessionCleanupMocks.stopSubagentsForRequester.mockClear();
     bootstrapCacheMocks.clearBootstrapSnapshot.mockReset();
+    sessionHookMocks.hasInternalHookListeners.mockReset();
+    sessionHookMocks.hasInternalHookListeners.mockReturnValue(true);
     sessionHookMocks.triggerInternalHook.mockClear();
     subagentLifecycleHookMocks.runSubagentEnded.mockClear();
     subagentLifecycleHookState.hasSubagentEndedHook = true;
@@ -1938,6 +1942,30 @@ describe("gateway server sessions", () => {
     ws.close();
   });
 
+  test("session:patch skips clone and dispatch when no hooks listen", async () => {
+    const structuredCloneSpy = vi.spyOn(globalThis, "structuredClone");
+    sessionHookMocks.hasInternalHookListeners.mockReturnValue(false);
+
+    const { ws } = await openClient();
+    const patched = await rpcReq(ws, "sessions.patch", {
+      key: "agent:main:main",
+      label: "no-hook-listener",
+    });
+
+    expect(patched.ok).toBe(true);
+    expect(structuredCloneSpy).not.toHaveBeenCalledWith(
+      expect.objectContaining({
+        cfg: expect.any(Object),
+        patch: expect.any(Object),
+        sessionEntry: expect.any(Object),
+      }),
+    );
+    expect(sessionHookMocks.triggerInternalHook).not.toHaveBeenCalled();
+
+    structuredCloneSpy.mockRestore();
+    ws.close();
+  });
+
   test("session:patch hook mutations cannot change the response path", async () => {
     await createSessionStoreDir();
     await writeSessionStore({

src/hooks/internal-hooks.ts

@@ -268,6 +268,12 @@ export function getRegisteredEventKeys(): string[] {
   return Array.from(handlers.keys());
 }
 
+export function hasInternalHookListeners(type: InternalHookEventType, action: string): boolean {
+  return (
+    (handlers.get(type)?.length ?? 0) > 0 || (handlers.get(`${type}:${action}`)?.length ?? 0) > 0
+  );
+}
+
 /**
  * Trigger a hook event
  *
@@ -281,15 +287,14 @@ export function getRegisteredEventKeys(): string[] {
  * @param event - The event to trigger
  */
 export async function triggerInternalHook(event: InternalHookEvent): Promise<void> {
-  const typeHandlers = handlers.get(event.type) ?? [];
-  const specificHandlers = handlers.get(`${event.type}:${event.action}`) ?? [];
-
-  const allHandlers = [...typeHandlers, ...specificHandlers];
-
-  if (allHandlers.length === 0) {
+  if (!hasInternalHookListeners(event.type, event.action)) {
     return;
   }
 
+  const typeHandlers = handlers.get(event.type) ?? [];
+  const specificHandlers = handlers.get(`${event.type}:${event.action}`) ?? [];
+  const allHandlers = [...typeHandlers, ...specificHandlers];
+
   for (const handler of allHandlers) {
     try {
       await handler(event);