[JQ100]

Fixes #3045.

Before: protocol:timeout:max-total switched to fake timers, started tools/call, and advanced the clock straight away. Over SSE the request is a real HTTP POST that fake timers don't wait for, so when it landed late the 500ms per-request timeout fired before any progress was sent. The SSE variants then failed intermittently with expected 0 to be greater than or equal to 3, and when they did, the test never exercised maxTotalTimeout.

After: the tool handler resolves a promise as soon as it starts, and the test awaits it before advancing the clock. Awaiting a promise doesn't move the fake clock, unlike vi.waitFor, which advances fake timers while it polls. Test-only change, 9 lines, no changeset.

Motivation and Context

On a clean clone on macOS, pnpm test:all intermittently fails on this test, while CI on main is green. Details and the original investigation are in #3045.

One correction to that issue: it says the failure is followed by an unhandled SdkError: Request timed out. max-total attaches call.catch(() => {}), so that rejection isn't from this test. It comes from protocol:timeout:reset-on-progress (data: { timeout: 200 }), which leaves 1–2 unhandled rejections on every run on macOS, with or without this change. That's a separate problem and I've left it out of this PR; happy to open an issue for it.

How Has This Been Tested?

On macOS (Darwin 27), Node 24.16.0, from main @ 39ae8e61:

• Measured: pnpm vitest run scenarios/protocol.test.ts -t "timeout:basic|timeout:max-total" in test/e2e, repeated. Before: 5 of 20 SSE variants failed (10 runs). After: 0 of 40 (20 runs).
• Forced: a temporary patch delayed only the tools/call POST by 50ms of real time (via a setTimeout captured before vi.useFakeTimers()). Without this change both SSE variants failed on 3 of 3 runs; with it all 12 variants passed on 3 of 3 runs. The patch isn't part of this PR.
• pnpm lint:all and pnpm --filter @modelcontextprotocol/test-e2e typecheck pass. In pnpm test:all every test passes; vitest still exits 1 because of the reset-on-progress unhandled rejections described above.

[changeset-bot]

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Latest commit: 61396ea

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commit: 61396ea

[arhancanli]

Read 61396ea (not run). The reasoning holds: the client-side timers are armed while the clock is frozen, so awaiting callReceived can only let the POST land, and unlike vi.waitFor it does not advance fake time.

One failure mode: callReceived has no timeout and no reject path. If the call never reaches the handler (schema rejection of delayMs/steps, a transport bug, a session that fails to open), the test hangs on a promise that never settles with fake timers on, so it dies on the suite-level timeout with no hint of why. A cheap guard is await Promise.race([callReceived, call.then(() => { throw new Error('call settled before the handler ran'); })]), which turns that into an immediate named failure (call already has a catch attached, so use a separate handle for the race).

Question: markCallReceived is also invoked on the stdio and in-memory variants where the ordering was never a problem. Do you want to keep it unconditional so all variants share one code path (my preference), or gate it to SSE?