Write backpressure: 429 + Retry-After
OriginChainDB refuses overload with HTTP 429 and a Retry-After computed from the token bucket's refill schedule. The per-API-key limits, and retry code.
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Per-key TTL: agent memory that forgets
Per-key TTL lets each record expire on its own: a ttl in seconds on any write, invisible to reads at expiry, compacted in the background. Maximum 365 days.