prompt.submit is fire-and-forget — turn completion is signaled by stream /
message.complete events, not the RPC return — but it inherited the generic 30s
default RPC timeout. A turn that legitimately takes >30s to ACK (MoA presets
running references + aggregator in series, deep reasoning, large tool chains)
popped a false 'request timed out: prompt.submit' toast at 30s while the turn
was still running and streamed its real answer in 60-120s later (#55024).
Add PROMPT_SUBMIT_REQUEST_TIMEOUT_MS (1_800_000 = the backend's
agent.gateway_timeout ceiling) and pass it on all four prompt.submit call sites
(submit, resume-recovery retry, regenerate, rewind), mirroring the existing
SESSION_LIST_REQUEST_TIMEOUT_MS opt-out precedent. Widen the GatewayRequest
type (+ the inline requestGateway prop type) to carry the optional timeoutMs the
runtime impl already accepts.
Tests: use-prompt-actions/index.test.tsx 34/34 pass; tsc -b clean.
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