Address review feedback: explicit catch and corrected comment

- TestHelper.cs: replace bare `catch { }` in the backfill-drain `finally`

  with `catch (Exception) { /* intentionally ignored: already propagated

  via tcs */ }` to make the swallow intent explicit and satisfy CodeQL.

- sdkTestHelper.ts: update the comment above `getFutureFinalResponse` to

  reflect that the live subscription is installed before the existing-

  messages RPC fires, matching the actual call ordering.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: stephentoub

dotnet/test/Harness/TestHelper.cs

@@ -78,7 +78,8 @@ void TryComplete()
         {
             // Drain the backfill before our `using` scopes (cts, subscription) dispose.
             // Any exception was already routed through tcs above, so swallow here.
-            try { await backfill.ConfigureAwait(false); } catch { }
+            try { await backfill.ConfigureAwait(false); }
+            catch (Exception) { /* intentionally ignored: already propagated via tcs */ }
         }
 
         async Task CheckExistingMessagesAsync()

nodejs/test/e2e/harness/sdkTestHelper.ts

@@ -8,8 +8,8 @@ export async function getFinalAssistantMessage(
     session: CopilotSession,
     { alreadyIdle = false }: { alreadyIdle?: boolean } = {}
 ): Promise<AssistantMessageEvent> {
-    // Start listening for the answer immediately so we don't miss any events that arrive
-    // between the existing-messages RPC starting and the subscription being installed.
+    // Install the live subscription (via getFutureFinalResponse) before issuing the
+    // existing-messages RPC so we don't miss events that arrive while that RPC is in flight.
     const futurePromise = getFutureFinalResponse(session);
     // We may end up returning from the existing-messages path; attach a noop handler so
     // the unawaited future-response rejection doesn't surface as an unhandled rejection.