Pure probe reducer -- the clock seam (04 design §1b).

step(state, event) where event is {:input, bytes}, {:clock, monotonic_ms}, or :start. No time is read inside step and no process sleeps anywhere: the silence timeout is driven entirely by injected clock events, so every timing case is a table row, not a flake. The real driver wraps this with a receive/after loop feeding System.monotonic_time(:millisecond) as {:clock, now} events.

Sentinel discipline (F0 §2): the batched query ends with Primary DA (CSI c). Every VT-class terminal answers DA1, so read-to-sentinel converts "did it ignore me?" into a bounded wait -- any wanted reply that did not arrive before the sentinel is unsupported. Silence past the deadline is the failure mode, answered with a conservative default.

Deadline policy (F0 §7 step 3): ~100 ms local, ~1 s when $SSH_* is present; extended AT MOST ONCE when a first byte is seen but the sentinel is not. After the sentinel, one drain window stays open until the next clock event so reordered replies (a documented terminal bug) are still parsed; after :done, late replies are drained, never reclassified, and never leaked as keystrokes.