WarmHubErrorDetails

WarmHubErrorDetails = NonNullable<NonNullable<BackendStreamAppendResult["results"][number]["error"]>["details"]>

Structured backend error details surfaced on data.warmhub.details. Derived from the generated wire type so it stays in lockstep with the backend’s WarmHubError.details union. Branch on details.reason to recover the structured payload type-safely — e.g. read currentVersion after an expected_version_mismatch to retry against HEAD (#3624), or leaseExpiresAt after a lease_held to back off until the lease expires (#3625).