Concepts

A2A and MCP interfaces

Protocol adapters for agent discovery, JSON-RPC tasks, and MCP tools.

The protocol layer belongs to agentic-fabric; provider implementation belongs to vendor-fabric. Both interfaces are adapters over public AgenticData and VendorData behavior, not alternate connector stacks.

A2A 1.0

The a2a extra uses the official A2A Python SDK 1.x and implements the A2A 1.0 JSON-RPC binding. create_a2a_app serves public Agent Card discovery at /.well-known/agent-card.json and the JSON-RPC path declared by the first AgentInterface. Cards advertise streaming and explicitly do not advertise push notifications.

A2AAgentSpec is the stable application boundary. Its handler receives an A2ARequest containing normalized text, data parts, metadata, and task identifiers. The executor emits the Task first, a working update, one text or data artifact, and exactly one completed or failed terminal update. Cancellation emits a canceled terminal update.

Two factory paths are included:

  • create_fabric_agent_spec sends a message and data parts to a registered or inline fabric agent through AgenticData.run_fabric_agent.
  • create_vendor_agent_spec requires a JSON object with provider, operation, and optional arguments and calls AgenticData.call(operation, provider, **arguments).

The bundled CLI is a local development server:

agentic-fabric-vendor-a2a --host 127.0.0.1 --port 8000 \
  --url https://agents.example.com/a2a

The advertised URL is part of the interoperability contract and must be the client-reachable URL, not an internal bind address. Production applications should mount the returned Starlette routes inside their own authenticated ASGI stack and replace InMemoryTaskStore when task survival matters. REST, gRPC, push notifications, card signing, and a persistent task store are deliberately not claimed by this adapter.

MCP 2026-07-28

The mcp extra requires the stable MCP Python SDK 2.x. The generic MCPToolAdapter describes a finite tool name, description, input schema, callable, and optional output schema. create_tool_server constructs the SDK's low-level server with explicit list and call handlers.

The server enforces these contracts:

  • tool names are unique;
  • every input schema and declared output schema is valid Draft 2020-12 JSON Schema;
  • every invocation is validated before its callable runs;
  • structured results conform to a declared output schema;
  • successful and failed calls return typed CallToolResult values with structured content and a serialized text fallback;
  • input or execution failures set isError; unknown tools raise an MCP invalid-parameters protocol error.

agentic-fabric-vendor-mcp enumerates only capabilities that VendorData.capabilities(include_unavailable=False) reports as available. It obtains method signatures from the public get_connector_class API to describe inputs, then invokes the route through AgenticData.call. Catalog tools use public package functions. agentic-fabric-meshy-mcp consumes the provider-owned Meshy tool definitions without moving their functions or models into this package.

Both shipped MCP commands use stdio. Callers that need Streamable HTTP should mount the returned SDK server in an application that owns authentication, authorization, rate limits, transport configuration, and audit policy.

Specifications

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