feat: add A2A protocol support to seller and buyer agents #29
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Add A2A (Agent-to-Agent) protocol as a new entry point alongside the existing HTTP/x402 mode, enabling standard agent card discovery and JSON-RPC messaging with payment-protected interactions. Seller changes: - New `poetry run agent-a2a` entry point with PaymentsA2AServer - Agent card at /.well-known/agent.json with urn:nevermined:payment extension - StrandsA2AExecutor wraps Strands agent for A2A message handling - Plain tools (no @requires_payment) since PaymentsRequestHandler handles payment at the A2A message level Buyer changes: - New `discover_agent` tool fetches and parses A2A agent cards - New `purchase_a2a` tool sends A2A messages via PaymentsClient - New `poetry run client-a2a` scripted demo for A2A flow - Updated system prompt to describe both HTTP and A2A workflows Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
- Seller: bump uvicorn to >=0.34.2 (required by strands-agents[a2a]) - Seller: require NVM_AGENT_ID for A2A mode (needed by agent card builder) - Buyer: use direct JSON-RPC+httpx instead of PaymentsClient (avoids sync/async mismatch in PaymentsClient._get_access_token) - Buyer: simplify client_a2a.py to reuse purchase_a2a_impl directly Tested e2e: seller agent-a2a -> agent card -> buyer discovery -> A2A JSON-RPC message with x402 token -> Strands agent execution -> response with credits_used=1. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Replace the manual JSON-RPC + httpx workaround in purchase_a2a.py with PaymentsClient from payments-py, which handles x402 token generation and injection automatically. Key changes: - buyer purchase_a2a.py: use PaymentsClient.send_message_stream() to collect SSE events and extract the final completed response - seller agent_a2a.py: enable streaming in agent card capabilities (required by PaymentsClient which uses message/stream) - Handle tuple-based SSE events (Task, TaskStatusUpdateEvent) returned by the a2a-sdk streaming client Requires payments-py fix: nevermined-io/payments-py#135 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Released version includes the sync/async fix for PaymentsClient._get_access_token (nevermined-io/payments-py#135). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Fix agent history accumulation bug: _calculate_credits() was scanning all messages ever sent through the shared Strands agent, causing incorrect credit counts on subsequent requests. Now snapshots the message offset before each invocation and only counts new messages. Code cleanup (code-simplifier): - Extract _error()/_success() helpers in purchase_a2a.py - Replace string-based error detection with proper exception types - Extract _now_iso(), _make_status_event() helpers in agent_a2a.py - Remove unused import json and pretty_json() in client_a2a.py - Sort imports alphabetically Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Summary
poetry run agent-a2awith standard agent card discovery at/.well-known/agent.jsonand payment-protected JSON-RPC messaging viaPaymentsA2AServerdiscover_agentandpurchase_a2atools plus a scriptedpoetry run client-a2ademoPaymentsRequestHandler(seller tools are plain@tool, no@requires_payment)Files changed
seller/pyproject.tomla2aextra to strands-agents, addagent-a2ascriptseller/src/strands_agent_plain.py@toolversions (no@requires_payment) for A2A modeseller/src/agent_a2a.pyPaymentsA2AServerseller/.env.exampleA2A_PORTbuyer/pyproject.tomla2aextra to payments-py, addclient-a2ascriptbuyer/src/tools/discover_a2a.pybuyer/src/tools/purchase_a2a.pyPaymentsClientbuyer/src/strands_agent.pydiscover_agentandpurchase_a2atools + updated system promptbuyer/src/client_a2a.pybuyer/.env.exampleSELLER_A2A_URLTest plan
cd agents/seller-simple-agent && poetry install && poetry run agent-a2astarts without errorscurl -s http://localhost:9000/.well-known/agent.jsonreturns agent card withurn:nevermined:paymentextensioncd agents/buyer-simple-agent && poetry install && poetry run client-a2adiscovers agent card and sends A2A messagepoetry run agent/poetry run client) still works unchangedpoetry run agent) has both HTTP and A2A tools available🤖 Generated with Claude Code