# description
A change-notification subscription ([B2], §Y): the receiver a publisher delivers signed envelopes to, the per-(publisher,receiver) HMAC signing secret, an optional event filter, and an active flag. Provisioning is out-of-band in 0.1; this standardizes the object's shape. Human-readable mirror is spec Part II §5c.

# properties.receiverUrl.description
HTTPS endpoint the publisher POSTs signed envelopes to (https required, no http).

# properties.secret.description
The per-(publisher,receiver) HMAC signing secret (OpenOM-Signature). Exchanged out-of-band; MUST be unique per pair and MUST NOT be reused across receivers. >=16 chars.

# properties.events.description
Event filter; absent or empty = deliver all events.

# properties.active.description
Whether the publisher should currently deliver.

# properties.description.description
Human label for the subscription (optional).