Status and errors

Feed health states:

State	Meaning
LIVE	Feed is producing current canonical updates under policy
DEGRADED	Feed remains usable but source/freshness policy is reduced
STALE	No fresh canonical update inside policy
HALTED	Feed is not currently streamable

Common errors:

Error	Meaning
unauthorized	Missing, invalid, revoked, or unsuitable credential
feed_not_found	Unknown feed ID
invalid_request	Request shape failed validation
payment_already_consumed	x402 payment proof was already used
ohlcv_disabled	Candle service disabled in that runtime
no_canonical_update	Feed exists but has no current signed update

Consumers should fail closed when correctness is uncertain, but UI should avoid flickering for harmless duplicate or reordered transport frames.