Context

A2A interoperability will benefit from shared, versioned conformance fixtures that different implementations can run in CI.

Proposal

Introduce a small conformance-fixtures/ pack (or companion repo) with protocol-level test vectors.

Starter fixture categories:

1. Agent Card validation examples (valid/invalid)
2. Capability negotiation edge cases
3. Message routing and correlation IDs
4. Error payload normalization
5. Security-related negative cases (malformed claims, unsupported transport assumptions)

Expected outcome

• Faster implementation consistency across languages
• Easier compatibility regression checks
• Clearer path for external contributors to add new edge-case vectors

If useful, I can draft an initial fixture structure and contribution pattern.