ADR-026 Adjacent Notes¶

Purpose¶

These notes capture adjacent decisions and sequencing around protocol adapters without widening ADR-026's normative contract.

Why ACP first¶

ACP is the preferred MVP because it creates an immediate governance use case around: - checkout and intent transitions - authorization evidence - protocol payload preservation for dispute and audit analysis

ACP therefore stresses the parts of the adapter API that matter most: - deterministic translation - lossiness accounting - raw payload preservation - versioned conformance fixtures

Why A2A second¶

A2A is strategically important, but it should follow ACP for two reasons: - the protocol and ecosystem surface are still moving quickly - A2A will benefit from a proven adapter API and conformance harness instead of co-defining them

Open-core boundary¶

Protocol adapters are open core when they provide protocol-to-evidence translation infrastructure.

Out of scope for open core in this area: - hosted adapter registries - organization-specific approval middleware - managed protocol policy workflows

Attachment-writer direction¶

Raw payload persistence should live behind a host-provided attachment writer in the evidence/core layer.

This keeps adapters free of filesystem policy and reduces IO surface area.

Deferred topics¶

These topics are intentionally deferred to follow-up ADRs or later slices: - Wasm adapter transport/runtime - remote adapter registry and signing distribution - protocol-specific middleware injection into MCP or hosted gateways - enterprise control-plane features on top of adapters

Candidate follow-ups¶

Likely follow-up slices after ADR-026 Step1: - adapter API freeze implementation skeleton (assay-adapter-api) - ACP MVP adapter crate - ACP conformance fixture harness - A2A follow-up ADR or Step2 freeze