[I] [Feature] Add A2A Agent Card Registry to EventMesh (eventmesh)

["qqeasonchen (via GitHub)" <gi...@apache.org>]

qqeasonchen opened a new issue, #5247:
URL: https://github.com/apache/eventmesh/issues/5247

   ### Search before asking
   
   - [x] I had searched in the [issues](https://github.com/apache/eventmesh/issues?q=is%3Aissue) and found no similar issues.
   
   
   ### Feature Request
   
   ## Background
   
   The A2A (Agent-to-Agent) protocol is an open standard for agent interoperability. EMQX has implemented a production-grade A2A Registry (`emqx_a2a_registry`) that provides Agent Card management, discovery, and status tracking via MQTT retained messages. EventMesh's current A2A implementation only includes a JSON-RPC to CloudEvent protocol adaptor and MCP message models, missing the core Agent Card lifecycle management defined by the A2A specification.
   
   ## Current State
   
   EventMesh's existing A2A implementation has the following gaps compared to the A2A specification and EMQX's reference:
   
   | Feature | EMQX | EventMesh (Before) |
   |---------|------|---------------------|
   | Agent Card Schema & Model | Full JSON Schema + Erlang maps | None |
   | Agent Card Registry (CRUD) | `emqx_a2a_registry` with retained messages | None (stub pass-through service) |
   | Agent Discovery (Topic-based) | `$a2a/v1/discovery/{org}/{unit}/{agent}` | None |
   | Hierarchical Agent ID | `org_id / unit_id / agent_id` | None |
   | Agent Status (online/offline) | `lookup_agent_status` via MQTT client state | None |
   | Card Validation | JSON Schema validation with toggle | None |
   | Security Schemes | Full (APIKey / OAuth2 / mTLS / OpenID / HTTP) | None |
   | Agent Capabilities & Skills | Full model per A2A spec | String constants only |
   | REST API for Card Management | `/a2a/cards/*` | None |
   
   ## Proposed Changes
   
   1. **Agent Card Java Model** — Add POJOs matching the A2A Agent Card JSON Schema (`AgentCard`, `AgentInterface`, `AgentProvider`, `AgentCapabilities`, `AgentSkill`, `AgentCardSignature`, `SecurityScheme` with all OAuth flow subtypes, `SecurityRequirement`)
   
   2. **Agent Card JSON Schema** — Port `agent_card_schema.json` from EMQX as a classpath resource for validation
   
   3. **Agent Card Validator** — JSON Schema-based validation with configurable toggle (when disabled, only validates JSON object structure)
   
   4. **Agent Identity** — Hierarchical identity model (`orgId/unitId/agentId`) with discovery topic construction (`a2a/v1/discovery/{orgId}/{unitId}/{agentId}`), topic parsing, wildcard query matching, and ID format validation (`^[A-Za-z0-9._-]+$`)
   
   5. **A2A Protocol Constants** — Extend with Agent Card operations (`agent/card/register`, `agent/card/delete`, `agent/card/list`, `agent/card/update`), status constants, CloudEvent extension keys, and discovery topic components
   
   6. **Enhanced A2A Protocol Adaptor** — Add Agent Card operation routing with discovery topic resolution, card validation during registration, and status metadata extensions (`a2astatus`, `a2astatussource`)
   
   7. **A2A Publish Subscribe Service** — Replace stub with full Agent Card Registry (in-memory `ConcurrentHashMap`, CRUD operations, agent status tracking, event metadata augmentation for discovery topics)
   
   8. **A2A Card HTTP Handler** — REST API matching EMQX's pattern:
      - `GET /a2a/cards/list` — list cards with query filters
      - `GET /a2a/cards/card/{org_id}/{unit_id}/{agent_id}` — get specific card
      - `POST /a2a/cards/card/{org_id}/{unit_id}/{agent_id}` — register card
      - `DELETE /a2a/cards/card/{org_id}/{unit_id}/{agent_id}` — delete card
   
   9. **Demo & Dependencies** — Add `AgentCardDemo` example; add `json-schema-validator` dependency
   
   ## Impact Analysis
   
   - **No impact on existing EventMesh functionality.** All new code is additive — new model classes, new utilities, and new handlers. Modified files (`A2AProtocolConstants`, `EnhancedA2AProtocolAdaptor`, `A2APublishSubscribeService`) maintain backward compatibility: existing message routing paths are unchanged, and the `process()` method remains a pass-through for non-A2A-discovery events.
   - All existing tests pass (`eventmesh-runtime`, `eventmesh-protocol-a2a`, core modules).
   
   ## References
   
   - EMQX A2A Registry: `apps/emqx_a2a_registry/`
   - A2A Protocol Specification: https://a2a-protocol.org/latest/specification/
   
   ### Are you willing to submit PR?
   
   - [x] Yes I am willing to submit a PR!
   
   ### Code of Conduct
   
   - [x] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct) *


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Re: [I] [Feature] Add A2A Agent Card Registry to EventMesh (eventmesh)

["qqeasonchen (via GitHub)" <gi...@apache.org>]

qqeasonchen closed issue #5247: [Feature] Add A2A Agent Card Registry to EventMesh
URL: https://github.com/apache/eventmesh/issues/5247


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