A reply echoes the request's message_id (and on failures its service_id,
operation and payload_schema; on chunk answers its chunk_hash). answer now
refuses any of them over MAX_ECHOED_FIELD_BYTES (256) at the door with a
transport Error that carries none, so every reply, including the largest
Deferred and ResponseTooLarge, fits the window. A deferred answer's envelope
carries the status of the answer it stands for. The retention docs name the
missing per-peer budget and that expiry runs only when a frame arrives.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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