fix(hal): EBDS escrow stack/return latch + return-on-disable

Cash-in stalled on the batm3: a note reached escrow and was read, but the
acceptor never stacked or returned it, and the customer was never
credited. Root cause: EBDS carries the stack/return decision as bits in
the omnibus *poll* command, but the driver sent stack()/reject() as a
single one-shot frame while a free-running 100ms poller kept sending
plain polls. The lone stack frame races/collides with the poller (or its
ack desyncs), gets dropped, and the device holds the note in escrow
indefinitely.

- ebds-rs232: latch the escrow decision (`pendingAction`) into the poll
  command byte and re-assert it on every poll until the device leaves
  escrow (cleared in _process when `!escrowed`). A dropped frame is now
  simply retried on the next poll.
- hal-service: return an escrowed note on disableValidator() — disable
  alone does not release it on EBDS, so an inactivity timeout / cancel
  previously stranded the bill in the transport (observed on the batm3).
- atm store: stringify the `[ATM] Sending event` / `[ATM] State` logs —
  they were printing `[object Object]`, which blinded the cash-in trace.

Verified: hal builds, machine app typechecks. Hardware behaviour to be
confirmed on the batm3 (no unit tests exist for this serial driver).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/machine/electron/hal-service.ts

@@ -221,6 +221,15 @@ export async function initializeHal(config: HalConfig): Promise<HalInstance> {
     },
 
     disableValidator: () => {
+      // If a note is sitting in escrow when we disable (inactivity timeout,
+      // cancel, or leaving the insert screen), return it to the customer.
+      // Disabling alone does NOT release an escrowed note on EBDS — it would
+      // be stranded in the transport until the next power cycle.
+      if (escrowDenomination !== null) {
+        console.log('[HAL] Returning escrowed bill on disable:', escrowDenomination)
+        escrowDenomination = null
+        validator?.reject()
+      }
       validator?.disable()
       validator?.lightOff()
     },