fix(runner): bound server scenarios with a per-scenario timeout - #454
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pcarleton merged 2 commits intoSep 6, 2026
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The client runner has had a 30s per-scenario timeout since it was written, but `runServerConformanceTest` awaited `scenario.run(ctx)` with no bound. A server under test that accepts the TCP connection and then never answers an initialize POST, a tools call, or an SSE read stalled the entire suite run, not just its own scenario. modelcontextprotocol#316 bounded the session-termination DELETEs in teardown, but that is a call-site fix: covering the rest that way needs the same treatment on every raw fetch in every scenario. Bounding at the runner makes those per-call bounds defense-in-depth instead of the only protection. `--timeout` now applies to server mode too, with the same 30s default as client mode. On expiry the scenario reports a `scenario-timeout` FAILURE naming the elapsed bound, so a wedged server reads as a failing scenario rather than a hung process. The timed-out scenario promise is left pending deliberately — a read blocked on a socket has no cancellation channel — with its rejection swallowed so a late failure can't surface against whichever scenario is running by then. Fixes modelcontextprotocol#427
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@pcarleton against #427, which you filed. No CI has run here — the workflow runs are sitting in One open question from the description, if you have a view: I left the timed-out |
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Thanks, leaving the timed-out run pending is good enough for now; we can worry about threading an AbortSignal through RunContext if we find we need that later. One nit for a follow-up: validate --timeout as a positive integer, parseInt lets 30s through as 30 ms and NaN makes every scenario time out immediately.
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September 6, 2026 19:14
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Closes #427.
The client runner has bounded each scenario since it was written. The server runner never did, so a server that accepts the TCP connection and then stops answering stalled the whole run instead of failing its own scenario.
--timeoutnow works in server mode, same 30s default as client mode. When it fires, the scenario gets ascenario-timeoutFAILURE naming the bound and the suite carries on.The one decision I'd like a second opinion on: the timed-out
scenario.runpromise is left pending rather than cancelled. A read blocked on a socket has nothing to cancel through, so there is nothing to await — I swallow its rejection so a late failure can't land on whatever scenario is running by then. Threading anAbortSignalthroughRunContextwould let scenarios actually tear down, but that touches every scenario and seemed like a separate change. Say the word and I'll do it that way instead.Tested by pointing
server-initializeat a server that completes the handshake and never writes a byte. With the runner change reverted the test hangs until vitest kills it at 30s. Full suite, typecheck and lint pass.#316's per-call bounds still earn their keep — they fail faster and attribute the failure better. They're just no longer the only thing between a wedged server and an unbounded run.