A credential read at an exit lane validates the session, then opens. Adds a
'read' channel to the device bus (DeviceReadEvent: ticket/plate/qr/card);
entry stays button-driven so reads are exit/identity events.
Flow: read -> fold the SIGNED ledger for that identity -> validate open + PAID
+ within gracePeriodExitMin -> signed vehicle_exit -> pulseOpen -> close the
session cache. Unpaid / grace-expired / unknown -> signed anomaly, barrier
stays closed (a deliberate business reject, not a fail-state; 'exit fails open'
is about host/power loss). Validation reads the ledger (authoritative), not the
cache.
No payment events exist until the pay station is built, so every transient exit
currently rejects -- the correct end-state, not yet passable. Verified against
stubs: unpaid->anomaly+no-open; paid+grace->exit+open+closed; expired->anomaly;
unknown->anomaly; verifyChain ok across entry->pay->exit.
Flagged: lane_devices has no entry/exit direction model (exit door hardcoded to
1); needs a lane-direction/role model before multi-reader lanes.
julian