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Ecosystem boundaries
Agent Runtime coordinates many systems. It should not absorb their ownership.
| System | Owns | Runtime relationship |
|---|---|---|
| Agent UI | Surfaces, interactions, local drafts, progressive rendering. | Consumes runtime facts and sends controlled actions. |
| Model providers | Native APIs, streaming formats, usage accounting, provider errors. | Runtime adapts provider facts into normalized lifecycle events. |
| MCP servers and connectors | Tools, resources, prompts, connector auth, external side effects. | Runtime discovers, filters, invokes, and records tool lifecycle. |
| A2A peers | Remote agent cards, capabilities, peer tasks, messages, artifacts, streaming, and push notifications. | Runtime maps peer work to local task/subagent edges, channel facts, and artifact refs while preserving A2A native ids. |
| Context stores | Memory, knowledge, search, retrieval, source ranking. | Runtime records selected refs, omissions, and compaction boundaries. |
| Policy systems | Permission rules, risk, sandbox profiles, org policy. | Runtime enforces or asks, then records decisions. |
| Artifact services | Content, versions, diff, export bytes. | Runtime emits artifact refs and lifecycle facts. |
| Evidence systems | Traces, verification, replay, review, audit verdicts. | Runtime exports and links evidence facts. |
| Host application | Workspace, account, local storage, deployment, navigation. | Runtime uses host scope and returns portable state models. |
A clean runtime boundary makes it possible to replace the UI, model provider, connector system, or evidence backend without rewriting the execution contract.
A2A boundary
A2A is the right protocol reference when one agent delegates work to another independent agent. Agent Runtime should cite and interoperate with it, but not absorb it:
| A2A concept | Runtime mapping |
|---|---|
| Agent Card | Peer capability snapshot, channel capabilities, routing input, and optional agent_card_ref. |
Task / taskId / contextId | Remote task ref linked to a local task_id, parent task, subagent, or channel. |
| Message | Channel input, task interaction, status message, or clarification; not a durable output by itself. |
| Artifact / artifact update | Artifact refs and produced_artifact / consumed_artifact task graph edges. |
| Streaming / push notification | channel.*, task.progress, task.completed, artifact.changed, cursor, ack, and snapshot repair facts. |
| In-task authorization | action.required, permission bridge events, and policy decision facts. |
The runtime boundary remains internal execution truth: attempts, tool calls, process execution, sandbox, hooks, local permission decisions, evidence, and replay are runtime facts even when the remote peer speaks A2A.