The LLM budgets bound the failure we actually hit. This is the backstop for the
ones they cannot see: a wedged plugin hook, a virtual-tool handler, an upstream
path without its own timeout.
transport.onmessage IS the whole request pipeline, and it writes to a socket
that has already been hijacked from Fastify. The SDK does not await it, so a
throw became an unhandled rejection and a hang became silence -- in both cases
the client got no response at all and waited out its own timeout. onmessage is
now structured so that reaching transport.send() is unconditional: the route
call is raced against a deadline, and the notification flush and the send each
carry their own catch, so a failure while flushing can no longer cost the client
its response.
transport.onerror was never assigned, so SDK-level transport errors were
swallowed entirely. It is now.
Shape of the answer is deliberate. A tools/call comes back as a SUCCESSFUL
result with isError and readable text naming the trace code -- the same shape
router.ts already uses for an expired _resultId, because a transport error tends
to surface as a hard failure while a tool error is something the model reads and
acts on. It also says the upstream may still be running, which is true and
matters. Other methods get a JSON-RPC error (-32001).
MCPLOCAL_TOOLCALL_DEADLINE_MS defaults to TOOLCALL_TIMEOUT_MS + 30s rather than
120s. The watchdog arms earlier in the request than mcpd's fetch does, so at
equal values it would always fire first, masking mcpd's specific
UpstreamTimeoutError with a generic message and cutting off pagination and the
rest of the post-processing. There is a test asserting the two stay ordered.
The pause queue is exempt, but not bypassed. It blocks until a human operator
releases, edits or drops a response, so the deadline SUSPENDS -- clock stopped,
then re-armed with whatever was left. A test asserts the re-arm, because an
exemption that forgot to re-arm would silently make every paused request
immortal.
End-to-end: an upstream that never settles now yields a response in under a
second carrying ⚠, the deadline, and `mcpctl trace <code>`.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GqMidYEGUJG5fxeoTELBu2
