- Adopt Standard Webhooks as the delivery signature scheme (webhook-id/timestamp/signature, v1 base64, multi-sig rotation); keep X-MCP-Subscription-Id as the one MCP-specific header
- Webhook secret is now client-supplied and REQUIRED (whsec_ + 24-64B base64, server MUST reject otherwise); server never generates one
- Subscription identity is (principal?, delivery.url, name, params); the response returns a server-derived id used only for routing, never as input
- Revert to no-mode-mandatory for delivery modes
- TLS is now MUST for delivery.url
- Allow cursor: null in any delivery for event types without replay; clarify CursorExpired always implies a possible gap
Make poll a mandatory delivery mode so every events-capable server is reachable by every client (push/webhook remain optional optimizations). Add a Webhook Delivery Profile subsection with WAF-relevant invariants (POST-only, required headers, 256 KiB body SHOULD, TLS termination) and defer User-Agent to SEP-1336 and egress-IP discovery to SEP-2127. Incorporate further fixes from adversarial review.
Resolve internal contradictions and design gaps found in review:
- Webhook cursors are now client-owned (per-event retry, no server watermark); name/params/delivery.url are immutable identity fields; unsubscribe requires delivery.url
- Unify error/terminated shape across modes; define heartbeat and terminated notifications; renumber error codes to -32011..-32016 to avoid base-spec collision
- SSRF: validate at delivery time, block fe80::/10, MUST NOT follow redirects; HMAC: X-MCP-Subscription-Id header, hex-lowercase encoding, mandatory timestamp, retry regenerates
- events/stream scoped to event notifications only (existing GET SSE retained); StreamEventsResult send rules clarified per transport
- Broadcast emit now uses author-supplied match/transform hooks with ctx; poll lease keyed on (principal, eventName, hash(params)); eventId SHOULD be upstream's stable identifier
- Qualify at-least-once for emit-only types; refresh reactivates suspended delivery; capability uses listChanged
- Add Open Questions on multi-event-name subscriptions and ownership-verification handshake
Add design-sketch-revision-deltas.md documenting all changes for implementations built against the prior revision.
