0003. The hook never blocks an agent

Status: Accepted, 2026-10-04 (the rule dates from the start of the project).

Context

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The hook runs on every event of every agent. If it hangs or prints the wrong thing, the user’s work stops, and they did not ask us to be in that path.

Decision

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On any failure (app closed, slow, a bad message) the hook exits 0 with empty stdout, and the agent goes on as if we were not there. A permission request waits for the app’s acknowledgement for 800 ms at most; a human for at most the decision budget (110 s), then the agent asks in its terminal.

Consequences

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• The hook is std and serde_json only: it starts fast and has little to break.
• Features that would need the agent to wait for us (a stop, a pause) cannot be built on the hook alone. See 0011.