E84StateMachine had the full signal-level handshake but no timer
enforcement. In a real AMHS that's a deadlock: if equipment is slow to
assert L_REQ / U_REQ, or AMHS is slow to assert BUSY / COMPT, neither
side notices — the wires just sit stuck. SEMI E84 §6 mandates three
timers that bound each leg of the dance.
TA1 — armed in ValidAsserted, cancelled in Load/UnloadReady.
AMHS bounds how long equipment takes to acknowledge VALID.
TA2 — armed in Load/UnloadReady, cancelled in Transferring.
Equipment bounds how long AMHS takes to start the transfer.
TA3 — armed in Transferring, cancelled on Complete.
Equipment bounds the BUSY-phase duration.
The FSM stays I/O-free (it's the design invariant): arm/cancel are
delivered via callbacks, the application owns the asio::steady_timer,
and the application calls `fsm.on_timeout(id)` when its real clock
fires. Stale on_timeout calls (post-cancel race) are no-ops.
On expiry, the FSM transitions to a new `HandoffFault` state, records
the `E84Fault` reason, fires the optional fault_handler, and latches
the fault until `reset()`. Signal jitter on the wires cannot silently
clear a recorded handshake timeout — once you've crossed the timer,
you stop.
Defaults are all-zero, which disables arming. This is what every
existing test relies on, and what back-to-back simulation (no
wall-clock) needs. Production tools call `set_timeouts({2s, 2s, 60s})`
or whatever their port spec dictates.
12 new test cases / 59 assertions: arming per state, cancelling per
exit, expiry-to-fault for all three timers, ES cancels everything,
stale-expiry no-op, fault latching across signal jitter, and a
full-cycle arm/cancel trace.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
