Skill for authoring A2A (Agent2Agent) multi-agent workflows, featuring host-agent orchestration and sub-agent communication. TRIGGER when: 'A2A workflow', 'A2A multi-agent', 'A2A host', 'A2A sub-agent', 'Agent2Agent collaboration', 'AgentCard', 'agent-card.json', 'A2ACardResolver'. DO NOT TRIGGER when: normal ADK workflows without A2A (use google-agents-cli-adk-code).
