Module liveness 

Dead/stuck detection — the three-detector model + the EOF x pong classifier.

This is the pure heart of supervision: given timestamps and flags, decide whether a child is healthy, legitimately busy, stuck-alive, or dead. The supervisor feeds it events (on_event/on_pong/on_eof) and asks classify(now) on each reactor tick; the kill ladder (kill.rs) acts on a teardown verdict. No processes or signals here — those are spawn.rs, reap.rs, kill.rs.

The three detectors:

• A — hard deadline (always on, no child cooperation).
• B — no-progress watchdog: substantive events (loop.step, tool.call, usage) stamp last_event_at; silence past progress_timeout is suspicious.
• C — ping/pong: pongs (answered by the child’s control thread, which is separate from its agentic loop) stamp last_pong_at. Pongs continuing while events have stopped means “busy in a long legitimate tool call”; pongs also stopping means the process is wedged.

Structs

Liveness

Per-child liveness tracker. Construct at spawn with the child’s absolute deadline; feed it events as they arrive; classify(now) each tick.

LivenessConfig

Sensible default timeouts. progress_timeout is generous because a single tool/model call can legitimately take a while; pong_timeout is tight because the control thread answers a ping immediately regardless of what the loop is doing.

Enums

Health

A child’s liveness verdict on a given tick.