042. A task is open until the worker finishes it

Status: accepted, built 2026-10-07 — amends ADR-041 ("a task is one turn"); details in docs/a2a-tasks.md

← every decision dev notes

Context

ADR-041 made an A2A task one turn: from its message to its result. A turn is one model response, and a turn can end with the work half done — proteus ended a review with "writing the probe" and went idle, and nothing resumed it; the heartbeats that used to were switched off for burning tokens on nothing. A task that ends with its turn cannot tell finished from stopped. Jimmy proposed supervising the task instead of the session; this is that, after review.

Decision

• A task lasts until the worker says how it ended — task_update done, blocked or failed, an MCP tool every session has — or it is cancelled, or it expires after 24 hours. That is what A2A means by a task (non-terminal states across many messages, ended by the serving agent); one turn per task was our shortcut.
• "Idle with a task open" is the stall, exactly, with nothing inferred from prose. A watchdog on the worker's machine reminds the session — a reminder written by the agent, with the request and the worker's last words — on a ladder (after 2/5 min quiet, then 1, 2, 5, 10, 30), at most 6 an hour per session, never while Claude Code still runs a background command, never after the owner stopped the session; after the ladder the task is stalled and the owner is told through the apps.
• A busy session queues tasks instead of rejecting them.
• The asker's acknowledgement is bookkeeping (AckTask, a shrooms extension), not what closes a task: completed stays final, as in A2A.
• Kept on disk where the worker is, and declared in the Agent Card as an extension.

Consequences

• Cost follows open obligations, not the clock: an idle desk with no task open is never woken, and the heartbeats can stay off.
• A worker must call task_update. Every session is told so (its system-prompt note, and the header of each task); one that does not is reminded, and in the end the task is stalled and a person looks — which is the honest outcome.
• A blocking SendMessage now waits until the task is finished or needs input (at most 10 minutes), not merely until a turn ends.