The hold default jumped 8x in v4.2.3 to absorb slower-provider
session.error arrivals before reservation release. Update the RFC code
block, the prose default callout, and the retry-latency note so the
documented default matches src/shared/prompt-async-gate.ts.
Documents the reservation-based duplicate-injection guard introduced in v4.2.0 with accepted status, exported API signatures, release semantics, migration notes, and commit references.
Closes MEDIUM-11
YeonGyu-Kim