Error codes

Code	Meaning	Sidecar action
FENCING_EPOCH_STALE	Sidecar's lease expired	Fail-closed; re-acquire (GA gate)
RESERVATION_STATE_CONFLICT	Reservation not in expected state	Adapter SHOULD re-query reservation context
RESERVATION_TTL_EXPIRED	Reservation TTL passed before commit	TTL sweeper releases automatically
PRICING_FREEZE_MISMATCH	Bundle pricing differs from claim's pricing	Operator: re-issue bundle
OVERRUN_RESERVATION	Estimated > original reserved	Adapter MUST split into separate calls
MULTI_RESERVATION_COMMIT_DEFERRED	Multi-claim ReserveSet not in POC	Use single-claim
IDEMPOTENCY_CONFLICT	Idempotency key reused with different body	Surface to caller as hard error
AUDIT_INVARIANT_VIOLATED	SP found audit chain inconsistency	Page on-call; not retriable

See services/sidecar/src/domain/error.rs and proto/spendguard/common/v1/common.proto Error.Code enum for the authoritative list.