Outbound webhooks: Standard Webhooks signing, durable retries, failure ladder
Subscribe HTTPS endpoints to five event types. Every delivery is Standard-Webhooks-signed, retried on a durable 9-attempt schedule, and protected by a failure ladder that warns before auto-disabling a dead endpoint.
Added
- /v1/webhook-endpoints: list, create, update, delete, and test-deliver webhook endpoints by API.
- Five event types: post.published, post.failed, channel.connected, channel.reauth_required, delivery.failed.
- Standard Webhooks signatures (webhook-id / webhook-timestamp / webhook-signature headers, `v1,` HMAC-SHA256 scheme) with show-once signing secrets and dual-signature rotation.
- Durable retries: 9 attempts over ~31.7 hours (30s → 14h backoff); warning emails at 5/10/15 consecutive failures; auto-disable at 20.
- SSRF gauntlet: delivery URLs are validated against private, loopback, link-local, and cloud-metadata address space — at creation and at every delivery.
- Webhook endpoint management UI in Settings → Webhooks.