Fix flaky SDK E2E tests

[stephentoub]

The Windows .NET E2E job was intermittently timing out in permission-handler coverage and reporting replay cache misses from a background-agent notification race. This makes the affected assertions deterministic and hardens the shared replay matching for semantically equivalent task-completion notification wording.

Summary

• Assert .NET permission-handler error handling by observing the replayed denied tool result instead of waiting for final assistant prose.
• Wait for background-agent completion notifications before cleanup in .NET and the matching Python E2E test.
• Normalize read_agent task-completion notification wording in the shared replay proxy and add proxy coverage.

Validation

• Repeated the affected .NET E2E tests 5 times across net8.0 and net472.
• Ran npm test -- replayingCapiProxy in test/harness.
• Ran python -m pytest e2e\test_rpc_tasks_and_handlers_e2e.py -k should_start_background_agent_and_report_task_details.
• Ran git diff --check.

[Copilot]

Pull request overview

This PR hardens the replaying CAPI proxy and E2E assertions to eliminate flakiness caused by background-agent completion notification timing and slightly varying notification wording, with a focus on stabilizing Windows .NET E2E runs.

Changes:

• Normalize background-agent completion notification wording (read_agent “unread results” → “full results”) in the replaying proxy to avoid replay cache misses.
• Make .NET and Python E2E tests deterministic by waiting for the background-agent completion notification event before teardown.
• Fix .NET permission-handler error coverage to assert against the replayed denied tool result rather than final assistant prose.

Show a summary per file

File	Description
test/harness/replayingCapiProxy.ts	Normalizes semantically equivalent read_agent completion-notification wording for stable replay matching.
test/harness/replayingCapiProxy.test.ts	Adds regression coverage to ensure the new notification normalization is applied.
python/e2e/test_rpc_tasks_and_handlers_e2e.py	Waits for the background-agent completion notification event and unsubscribes the handler during cleanup.
dotnet/test/E2E/RpcTasksAndHandlersE2ETests.cs	Waits for the background-agent completion notification event to avoid teardown races.
dotnet/test/E2E/PermissionE2ETests.cs	Asserts permission-handler failure behavior via replayed tool result content for determinism.

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 0

[github-actions]

Cross-SDK Consistency Review ✅

This PR fixes flaky E2E tests and hardens the shared replay proxy — no cross-SDK consistency concerns.

Summary of changes:

• test/harness/replayingCapiProxy.ts — shared infrastructure fix that benefits all SDK implementations equally
• dotnet/test/E2E/ and python/e2e/ — parallel, symmetric fixes applied to both SDKs: the same pattern (wait for a concrete observable event before cleanup, rather than relying on final assistant prose) was applied consistently in both .NET and Python

Parity check:
The equivalent background-agent task completion and permission-handler error tests in Go and Node.js were not modified, but since the flakiness was specific to Windows .NET CI and Python, and the shared proxy normalization fix is already universal, no further changes appear needed for consistency.

No cross-SDK inconsistencies introduced.

Generated by SDK Consistency Review Agent for issue #1418 · ● 980.6K · ◷