fix: dispose codex app-server harnesses

extensions/codex/harness.ts

@@ -8,6 +8,7 @@ import type {
 } from "./src/app-server/models.js";
 import { runCodexAppServerAttempt } from "./src/app-server/run-attempt.js";
 import { clearCodexAppServerBinding } from "./src/app-server/session-binding.js";
+import { clearSharedCodexAppServerClient } from "./src/app-server/shared-client.js";
 
 const DEFAULT_CODEX_HARNESS_PROVIDER_IDS = new Set(["codex", "openai-codex"]);
 
@@ -47,5 +48,8 @@ export function createCodexAppServerAgentHarness(options?: {
         await clearCodexAppServerBinding(params.sessionFile);
       }
     },
+    dispose: () => {
+      clearSharedCodexAppServerClient();
+    },
   };
 }