feat(hal/ebds): surface accepting/stacking/returning transient states

parseStatus previously collapsed all in-motion bits into a single derived
status, hiding when the MEI was moving a bill between escrow and the
stacker/mouth. Field journals showed nothing in the window where the
BATM3 tore bills.

Surface the three transient bits between the terminal states and
escrow/standby, route them through EbdsFsm with a Date.now() timestamp,
and emit them as diagnostic events on the validator. No state machine
consumes them; they're for journalctl.

Also: warn when `returning` is observed straight out of escrow with no
host reject() — that signature is the autonomous-return failure mode we
just polled around. Surfacing it gives us field confirmation the 100ms
fix is sufficient (or evidence it isn't).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/hal/src/validators/ebds/ebds-fsm.ts

@@ -34,9 +34,17 @@ export class EbdsFsm extends EventEmitter {
     // Blank stacks happen on power up or cassette re-insertion — ignore
     if (status === 'blankStack') return
 
+    const prev = this.currentStatus
     this.currentStatus = status
+    console.log('[EBDS] %d status: %s → %s', Date.now(), prev ?? '(init)', status)
 
     switch (status) {
+      case 'accepting':
+        // Transient: bill is being read by the validator head. Diagnostic
+        // only — useful for measuring time-to-escrow under field load.
+        this.emit('accepting')
+        break
+
       case 'billsRead':
         // Bill is in escrow — verify currency and emit
         if (bill) {
@@ -51,6 +59,26 @@ export class EbdsFsm extends EventEmitter {
         }
         break
 
+      case 'stacking':
+        // Transient: bill is moving from escrow to stacker. Should follow
+        // a host stack() command — if it precedes one, MEI is moving the
+        // bill on its own and we should investigate.
+        this.emit('stacking')
+        break
+
+      case 'returning':
+        // Transient: bill is moving from escrow back to mouth. Should
+        // follow a host reject() command — if it precedes one, MEI is
+        // autonomously returning, which is the BATM3 tearing failure mode.
+        if (prev === 'billsRead') {
+          console.warn(
+            '[EBDS] returning observed straight from escrow with no host reject — ' +
+              'MEI may be autonomously returning. Watch for torn bills.'
+          )
+        }
+        this.emit('returning')
+        break
+
       case 'billsValid':
         // Bill stacked successfully — but ignore if no denomination
         // (can happen when cashbox is re-inserted)

packages/hal/src/validators/ebds/ebds-rs232.ts

@@ -186,21 +186,29 @@ function destructData(data: Buffer): DestructedData | null {
   ]
 }
 
-/** Derive high-level status string from destructed status bytes */
+/**
+ * Derive high-level status string from destructed status bytes.
+ *
+ * Terminal states (stacked / returned / cheated / rejected / jammed /
+ * stackerOpen) take priority over transient states. Transient states
+ * (`stacking`, `returning`, `accepting`) are surfaced so the FSM can
+ * time the escrow grace window and so field logs reveal when MEI moves
+ * a bill on its own (the BATM3 tearing failure mode).
+ */
 function parseStatus(data: DestructedData): string | null {
-  return data[0].stacked
-    ? 'billsValid'
-    : data[0].escrowed
-      ? 'billsRead'
-      : data[0].returned || data[1].cheated || data[1].rejected
-        ? 'billsRejected'
-        : data[1].jammed
-          ? 'jam'
-          : !data[1].cassetteAttached
-            ? 'stackerOpen'
-            : data[0].idling
-              ? 'standby'
-              : null
+  // Terminal — bill has reached a resting position
+  if (data[0].stacked) return 'billsValid'
+  if (data[0].returned || data[1].cheated || data[1].rejected) return 'billsRejected'
+  if (data[1].jammed) return 'jam'
+  if (!data[1].cassetteAttached) return 'stackerOpen'
+  // Transient — bill is in motion. Surface before `escrowed` so we observe
+  // the MEI moving the bill out of escrow autonomously.
+  if (data[0].stacking) return 'stacking'
+  if (data[0].returning) return 'returning'
+  if (data[0].escrowed) return 'billsRead'
+  if (data[0].accepting) return 'accepting'
+  if (data[0].idling) return 'standby'
+  return null
 }
 
 /** Destruct the control byte (§6.4) */

packages/hal/src/validators/ebds/index.ts

@@ -118,6 +118,13 @@ export class EbdsValidator extends EventEmitter implements BillValidator {
       this.emit('billsRejected')
     })
 
+    // Diagnostic events — surface MEI transport motion so field logs can
+    // distinguish host-driven movement from autonomous (timeout-induced)
+    // movement. No state machine consumes these; they're for journals.
+    this.fsm.on('accepting', () => this.emit('accepting'))
+    this.fsm.on('stacking', () => this.emit('stacking'))
+    this.fsm.on('returning', () => this.emit('returning'))
+
     this.fsm.on('stackerOpen', () => {
       this.emit('stackerOpen')
     })