docs(extensions): register Settlement Attestation, Composite Trust Query, and RFC 9421 Message Signing extensions (AlgoVoi-authored)

docs/topics/extensions.md

@@ -50,6 +50,10 @@
 | [Hello World or Timestamp Extension](https://github.com/a2aproject/a2a-samples/tree/main/extensions/timestamp) | A simple extension demonstrating how to augment base A2A types by adding timestamps to the `metadata` field of `Message` and `Artifact` objects (v1). |
 | [Traceability Extension](https://github.com/a2aproject/a2a-samples/tree/main/samples/python/extensions/traceability) | Explore the Python implementation and basic usage of the Traceability Extension (v1). |
 | [Agent Gateway Protocol (AGP) Extension](https://github.com/a2aproject/a2a-samples/tree/main/extensions/agp) | A Core Protocol Layer or Routing Extension that introduces Autonomous Squads (ASq) and routes Intent payloads based on declared Capabilities, enhancing scalability (v1). |
+| [Compliance Gate Extension](https://docs.algovoi.co.uk/compliance-gate-v1) | An AlgoVoi-authored Method Extension adding the `compliance/gate` RPC method. Returns a categorical admission-time sanctions/KYC verdict (`ALLOW` / `REFER` / `DENY`) as a seven-field Compliance Receipt canonicalized under RFC 8785 (JCS). Companion IETF I-D: [`draft-hopley-x402-compliance-receipt`](https://datatracker.ietf.org/doc/draft-hopley-x402-compliance-receipt/) (v1). |
+| [Settlement Attestation Extension](https://docs.algovoi.co.uk/settlement-attestation-v1) | An AlgoVoi-authored Method Extension providing a categorical post-settlement record emitted by the facilitator after on-chain confirmation: `SETTLED`, `PENDING_FINALITY`, or `REVERSED`. Canonicalized under RFC 8785 (JCS) with `settled_payment_ref` binding the attestation to its Payment Mandate. Companion IETF I-D: [`draft-hopley-x402-settlement-attestation`](https://datatracker.ietf.org/doc/draft-hopley-x402-settlement-attestation/) (v1). |
+| [Composite Trust Query Extension](https://docs.algovoi.co.uk/composite-trust-query-v1) | An AlgoVoi-authored Method Extension returning a categorical composite verdict (`TRUSTED` / `PROVISIONAL` / `INSUFFICIENT_EVIDENCE` / `UNTRUSTED`) over a set of issuer attestations from independent parties. Composes admission-time compliance, settlement, and counterparty-risk evidence into a single verifiable envelope canonicalized under RFC 8785 (JCS). Companion IETF I-D: [`draft-hopley-x402-composite-trust-query`](https://datatracker.ietf.org/doc/draft-hopley-x402-composite-trust-query/) (v1). |
+| [RFC 9421 Message Signing Extension](https://docs.algovoi.co.uk/rfc9421-binding-v1) | An AlgoVoi-authored binding of RFC 9421 (HTTP Message Signatures) and RFC 9530 (Digest Fields) to A2A task envelopes and agent card exchange, providing transport-layer cryptographic signing for agent-to-agent messages with multi-hop proxy-chain survival. Reference implementation: [`algovoi-rfc9421-verifier`](https://pypi.org/project/algovoi-rfc9421-verifier/) (PyPI / npm, Apache 2.0). |
 
 ## Extension Governance