dotnet: Deflake session event capture

[devm33]

Problem

The runtime repository's SDK compatibility run 35719029303 failed SessionE2ETests.Should_Receive_Session_Events on Alpine with:

System.InvalidOperationException: Collection was modified; enumeration operation may not execute.

The test records startup events in a mutable List<SessionEvent> from an asynchronous event callback, then enumerates that list after observing session.start. Later event delivery can mutate the list during the assertion. The test is worthwhile because it verifies that events emitted during session creation are not dropped.

Changes

Use ConcurrentQueue<SessionEvent> for the startup-event capture. This preserves the assertion while making concurrent callback writes and test enumeration safe.

Product impact

No SDK product behavior changes. This only removes a race from the .NET E2E test.

Validation

• Reproduced by github/copilot-agent-runtime run 35719029303, Alpine .NET in-process CAPI leg.
• git diff --check
• Local .NET execution unavailable in the current environment; CI validation is required.

Validation	Run
Exact-head .NET validation 1-10 (2390cf6681e3e24b289d6ee72fa729b664c944bb)	Pending

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused test-only change correctly eliminates the identified enumeration race.

Review effort: Balanced
Findings: None

What changed in this PR

Deflakes the .NET session-event E2E test by making asynchronous event capture thread-safe.

Changes:

• Replaces List<SessionEvent> with ConcurrentQueue<SessionEvent>.
• Uses Enqueue for concurrent callback writes.

File	Description
dotnet/​test/​E2E/​SessionE2ETests.cs	Prevents concurrent modification during startup-event assertions.

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[github-actions]

SDK Consistency Review

This PR (dotnet: Deflake session event capture) only touches dotnet/test/E2E/SessionE2ETests.cs, replacing a non-thread-safe List<SessionEvent> with ConcurrentQueue<SessionEvent> (and .Add → .Enqueue) to fix a flaky test where events captured from a background OnEvent callback race with the main thread's assertions.

Assessment: No cross-SDK consistency concerns.

• This is an internal test-reliability fix, not a public SDK API change.
• No new feature, method, or behavior is being added/changed in the .NET client itself — only test-harness code.
• Other language SDKs' equivalent E2E tests are unaffected and don't need changes.

No action needed for other SDKs.

Generated by SDK Consistency Review Agent for #2745 · copilot · sonnet50 · 13.7 AIC · ⌖ 11.4 AIC · ⊞ 7.8K · ◷