docs(extensions): register Compliance Gate Extension v1 — admission-time sanctions/KYC gate RPC method

[chopmob-cloud]

Closes #1887.

Summary

Registers the AlgoVoi-authored Compliance Gate Extension (v1) in the A2A
example extensions list.

The extension defines an RPC method compliance/gate that any
A2A-conformant agent MAY implement to expose an admission-time
compliance check endpoint. The method returns a categorical verdict
(ALLOW, REFER, DENY) bound to the request by sha256: reference
under RFC 8785 (JCS) canonicalisation.

Extension URI: https://docs.algovoi.co.uk/compliance-gate-v1

The extension specification itself is hosted at the AlgoVoi-controlled
URI and is the canonical artefact. This PR adds a single row to the
example extensions table in docs/topics/extensions.md pointing at the
URI. No code changes. No samples added to the A2A tree. No changes to
existing extension entries.

Why A2A benefits from this

A2A's Extension URI mechanism (per docs/topics/extensions.md) is
designed precisely for this shape of contribution: anyone may author,
publish, and implement an extension identified by URI. Agent-to-agent
payment authorisation flows currently have no first-class way to obtain
a regulator-recognised admission-time decision (sanctions screening,
jurisdiction filtering, KYC verification) before mandate construction.
This extension fills that gap with a minimal Method Extension that
composes cleanly with payment-mandate primitives.

The example extensions table already includes domain-specific extensions
(Secure Passport, Timestamp, Traceability, AGP). The Compliance Gate
Extension fits the same pattern as a regulator-discipline extension for
agents operating in regulated payment flows.

Production reference

The endpoint shape and verdict format are generated in production by
the AlgoVoi facilitator at
api.algovoi.co.uk/compliance/screen,
live since 2026-05-06 across eight chain families. Documentation:
docs.algovoi.co.uk/platform/compliance-engine.
Public audit verifier: docs.algovoi.co.uk/audit-verifier.

This is not a theoretical extension. The endpoint described in this
specification has been serving live admission-time gate checks for
over three weeks.

Authorship and substrate-author position

This extension is sole AlgoVoi authorship across extension URI,
endpoint shape, verdict enumeration, canonicalisation discipline, and
the composition with the AlgoVoi-authored canonicalisation pin and
Compliance Receipt format.

Companion IETF Internet-Draft:
draft-hopley-x402-compliance-receipt
(Independent Submission, Informational, on IETF datatracker).

Reference implementation, AlgoVoi-authored, Apache 2.0:

• algovoi-substrate on PyPI
• @algovoi/substrate on npm

Cross-validated 192-of-192 byte-for-byte across eight independent
language implementations (Python, TypeScript, Go, Rust, Java, PHP, .NET,
Ruby). Conformance corpus:
chopmob-cloud/algovoi-jcs-conformance-vectors.

The verdict enumeration is closed by design and may be amended only
by a normative successor extension authored by AlgoVoi or with explicit
AlgoVoi co-authorship. Re-publication of this extension under a
different URI or attribution does not constitute substrate authorship
of the elements defined here.

The extension URI is AlgoVoi-controlled
(docs.algovoi.co.uk/compliance-gate-v1). Resolution of the URI is
solely under AlgoVoi control; A2A's registration in the example
extensions list is a pointer to the canonical specification, not a
re-hosting of it.

No coalition acknowledgements. This extension does not absorb from,
depend on, or share authorship with any other party's work.

Orthogonality

This extension defines the verdict format and gate endpoint at the
admission-time sanctions and KYC screening layer. It is orthogonal
to counterparty-risk evidence endpoints, settlement-attestation
endpoints, agent identity verification, reputation scoring, trust
scoring, composable trust evidence formats, and behavioural attestation
extensions proposed elsewhere as A2A extensions. The Compliance Gate
Extension makes no claims about, and depends on no fields from, any of
the above.

A calling agent that combines a Compliance Gate verdict with other
attestation extensions does so at the calling agent's discretion; this
extension specifies nothing about the combination.

Scope

Single addition to the example extensions table in
docs/topics/extensions.md. No new files in the A2A tree. No code
changes. No samples. No changes to existing extension entries.

-- AlgoVoi (chopmob-cloud)
https://docs.algovoi.co.uk/acquisition

[gemini-code-assist]

Code Review

This pull request adds the Compliance Gate Extension to the extensions documentation. The reviewer suggested a minor spelling correction to change 'canonicalised' to 'canonicalized' to maintain consistency with the US English spelling used throughout the document.

[gemini-code-assist]

To maintain spelling consistency with the rest of the document (which uses US English spelling, e.g., 'personalization' on line 49 and 'authorization' on line 278), 'canonicalised' should be spelled as 'canonicalized'.

Suggested change

| [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 canonicalised under RFC 8785 (JCS). Companion IETF I-D: [`draft-hopley-x402-compliance-receipt`](https://datatracker.ietf.org/doc/draft-hopley-x402-compliance-receipt/) (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). |