fix: handle custom-agents endpoint in replay proxy for CLI 1.0.11

CLI 1.0.11 makes a GET request to /agents/*/custom-agents/* during
startup. The replay proxy had no handler for this endpoint, causing
it to call onError and hang new CLI processes. This broke the
'should resume a session using a new client' and 'should produce
deltas after session resume' E2E tests which spawn a second
CopilotClient.

Add a stub handler (returning empty agents list) matching the
existing pattern used for memory endpoints.

Author: MackinnonBuck

test/harness/replayingCapiProxy.ts

@@ -230,6 +230,19 @@ export class ReplayingCapiProxy extends CapturingHttpProxy {
           return;
         }
 
+        // Handle custom-agents endpoints - return empty list in tests
+        if (options.requestOptions.path?.match(/\/agents\/.*\/custom-agents\//)) {
+          const body = JSON.stringify({ agents: [] });
+          const headers = {
+            "content-type": "application/json",
+            ...commonResponseHeaders,
+          };
+          options.onResponseStart(200, headers);
+          options.onData(Buffer.from(body));
+          options.onResponseEnd();
+          return;
+        }
+
         // Handle /chat/completions endpoint
         if (
           state.storedData &&