Fix .NET in-process E2E transport coverage

[roji]

The .NET E2E fixture explicitly selected TCP even in the in-process matrix, so those tests never exercised the FFI transport and hid FFI-specific behavior.

This change:

• Allows resuming the same session in .NET SDK, aligning it with the other SDK's behavior (.NET specifically had a check against doing that). This was a blocker for some .NET E2E tests in inproc mode.
• selects RuntimeConnection.ForInProcess() for the in-process matrix while preserving TCP coverage in the other matrix
• restores the native host environment before each test because the shared fixture outlives per-test environment isolation
• aligns same-client session resume with the other SDKs by replacing the routed session wrapper before the resume RPC, without adding operation-wide locking or concurrent-resume rejection
• keeps TCP-only multi-client behavior intact and adds fixture policy and session lifetime coverage
• uses a checkpoint number valid for the native runtime's u32 domain

The complete .NET in-process suite passes through FFI with 672 tests passed and 3 existing skips. Targeted TCP resume coverage and all .NET target-framework builds also pass.

[Copilot]

Pull request overview

Updates .NET E2E coverage to exercise the FFI transport and supports same-client session resumption.

Changes:

• Selects in-process or TCP transport according to the test matrix.
• Restores host environment state between in-process tests.
• Adds same-client resume replacement behavior and related coverage.

Show a summary per file

File	Description
dotnet/src/Client.cs	Replaces tracked wrappers during resume.
dotnet/test/Harness/E2ETestFixture.cs	Selects matrix-appropriate transport.
dotnet/test/Harness/E2ETestContext.cs	Restores in-process environment state.
dotnet/test/Harness/E2ETestBase.cs	Prepares tests and chooses resume client.
dotnet/test/E2E/SessionE2ETests.cs	Covers same-client resume replacement.
dotnet/test/E2E/RpcWorkspaceCheckpointsE2ETests.cs	Uses a native-compatible checkpoint value.
dotnet/test/Unit/E2ETestFixtureTests.cs	Tests fixture transport selection.
dotnet/test/Unit/ClientSessionLifetimeTests.cs	Tests replacement and failure lifetimes.

Review details

• Files reviewed: 8/8 changed files
• Comments generated: 1
• Review effort level: Medium

[roji]

@SteveSandersonMS noticed this while working on other stuff, take a look - we weren't doing actual FFI in the .NET SDK, plus the .NET SDK was unique in not allowing the same session ID to be resumed with a new session object (which obstructed fixing the former).

[github-actions]

Cross-SDK Consistency Review ✅

This PR aligns .NET with the behavior of all other SDK implementations.

Key behavioral change: .NET previously threw InvalidOperationException when ResumeSessionAsync was called on the same client that already tracked the session. This PR replaces that rejection with the replace-existing semantics that every other SDK already implements:

SDK	Same-client resume behavior (before this PR)
Node.js	Replaces the tracked session (map assignment)
Go	Replaces the tracked session (c.sessions[sessionID] = session)
Python	Replaces the tracked session
Rust	Replaces the tracked session
Java	Replaces the tracked session
.NET (before)	❌ Threw InvalidOperationException
.NET (after)	✅ Replaces the tracked session — now consistent

The implementation is careful to restore the previous session on failure, which is a correctness improvement over the implicit behavior in simpler SDKs.

No other SDKs need updates. The change is a .NET-only catch-up to the already-established cross-SDK contract.

Generated by SDK Consistency Review Agent for #1986 · sonnet46 34.9 AIC · ⌖ 5.43 AIC · ⊞ 6.6K · ◷

[Copilot]

Review details

Comments suppressed due to low confidence (3)

dotnet/test/Unit/ClientSessionLifetimeTests.cs:1

• These tests manually dispose sessions at the end, but if an assertion fails mid-test the sessions may not be disposed, which can leak tracked sessions and make later tests flaky. Prefer await using var session = ... / await using var resumedSession = ... (or a try/finally) so cleanup happens even on test failure.

/*---------------------------------------------------------------------------------------------

dotnet/src/Client.cs:826

• ConcurrentDictionary.AddOrUpdate may invoke the update delegate multiple times under contention, so capturing displacedSession via a closure can yield an indeterminate replacedSession (not necessarily the instance that was ultimately replaced). Consider using a retry loop with TryGetValue + TryUpdate (or TryAdd) to deterministically capture and return the actual replaced session.

        if (replaceExisting)
        {
            CopilotSession? displacedSession = null;
            _sessions.AddOrUpdate(
                session.SessionId,
                session,
                (_, current) =>
                {
                    displacedSession = current;
                    return session;
                });
            replacedSession = displacedSession;
        }

dotnet/test/Unit/ClientSessionLifetimeTests.cs:485

• This test helper relies on reflection and a hard-coded private method name (GetSession), which is brittle and can break on refactors unrelated to behavior. If feasible, expose a minimal internal test hook (e.g., internal accessor with InternalsVisibleTo for the test assembly) so the tests verify tracking without reflection.

    private static CopilotSession? GetTrackedSession(CopilotClient client, string sessionId)
    {
        var method = typeof(CopilotClient).GetMethod("GetSession", BindingFlags.Instance | BindingFlags.NonPublic)
            ?? throw new InvalidOperationException("GetSession method was not found.");
        return (CopilotSession?)method.Invoke(client, [sessionId]);
    }

• Files reviewed: 8/8 changed files
• Comments generated: 1
• Review effort level: Low

[Copilot]

Review details

Comments suppressed due to low confidence (2)

dotnet/test/E2E/SessionE2ETests.cs:231

• This test still requires same-client resume to throw, which contradicts the new contract that replaces the tracked wrapper before session.resume. With that behavior enabled, Assert.ThrowsAsync fails and the new path remains unverified. Update this test to expect a successful resume on Client and assert that the returned session has the same ID (and receives routing intended for the replacement).

        await using var session1 = await CreateSessionAsync();

dotnet/test/Harness/E2ETestBase.cs:123

• This reflection bypasses the public same-client replacement behavior that this PR is intended to cover and makes the E2E suite depend on the private CopilotSession.RemoveFromClient implementation. Keep the suspended wrapper tracked and resume through Ctx.ResumeSessionAsync; then rename this helper and update its callers. That both exercises the real SDK contract and keeps .NET tests limited to public SDK APIs.

        var removeFromClient = typeof(CopilotSession).GetMethod(
            "RemoveFromClient",
            BindingFlags.Instance | BindingFlags.NonPublic)
            ?? throw new InvalidOperationException("CopilotSession.RemoveFromClient was not found.");
        removeFromClient.Invoke(session, null);

• Files reviewed: 9/9 changed files
• Comments generated: 0 new
• Review effort level: Medium