A2A is the emerging standard for agents discovering and talking to other agents. Heidi implements A2A v1.0: every install publishes a signed agent card so peers can find her, verify who she is, and, with explicit trust, delegate work.
Where MCP connects an agent to tools, A2A connects agents to agents. Heidi's card at /.well-known/agent-card.json declares her capabilities and endpoints, signed so the publisher identity is cryptographically bound to the domain.
Trust is explicit and inbound-controlled: callers must be declared peers, and nothing sensitive works without the bearer credential the card describes.