fix: update event count retrieval logic in AchSession and MiniMateClient

bridges/ach_server.py

@@ -257,29 +257,11 @@ class AchSession:
             # Used to detect post-erase key reuse — see comment block above.
             max_seen_key: str = unit_state.get("max_downloaded_key", "00000000")
 
-            # Use the event count already read from the event index during connect().
-            # This is fast (no extra round-trips) and confirmed accurate (matches LCD).
-            # Falls back to count_events() only if connect() wasn't called.
-            if device_info is not None:
-                current_count = device_info.event_count or 0
-            else:
-                try:
-                    current_count = client.count_events()
-                except Exception as exc:
-                    log.error("  [FAIL] count_events failed: %s", exc)
-                    return
-
-            log.info("  Unit has %d stored event(s); %d key(s) previously downloaded",
-                     current_count, len(seen_keys))
-
-            if current_count == 0:
-                log.info("  [OK] No events on device -- nothing to download")
-                log.info("Session complete (no events) -> %s", session_dir)
-                return
-
-            # Fast pre-check: walk the event index (browse-mode, no 5A) to get
-            # the current key list, then bail early if everything is already seen.
-            # This avoids calling get_events() at all when there's nothing new.
+            # Walk the event index (browse-mode, no 5A) to get the actual current
+            # key list.  The SUB 08 event_count field is a lifetime "total events
+            # ever recorded" counter that does NOT decrement on erase — confirmed
+            # 2026-04-13.  list_event_keys() via the 1E/1F chain is the only
+            # reliable way to know what is actually stored on the device right now.
             log.info("  Checking device key list (browse walk, no waveform download)...")
             try:
                 device_keys = client.list_event_keys()
@@ -287,6 +269,17 @@ class AchSession:
                 log.warning("  list_event_keys failed: %s -- falling back to full download", exc)
                 device_keys = None
 
+            # Use the walk result as our authoritative current count.
+            current_count = len(device_keys) if device_keys is not None else 0
+
+            log.info("  Unit has %d stored event(s); %d key(s) previously downloaded",
+                     current_count, len(seen_keys))
+
+            if device_keys is not None and current_count == 0:
+                log.info("  [OK] No events on device -- nothing to download")
+                log.info("Session complete (no events) -> %s", session_dir)
+                return
+
             if device_keys is not None:
                 # ── Post-erase detection ──────────────────────────────────────
                 # After the device memory is erased, new events start from key
@@ -359,10 +352,14 @@ class AchSession:
                 new_key_set = None  # unknown; proceed with full download
 
             # Apply max_events cap
-            stop_idx = current_count - 1
+            # stop_idx: when we know the count from list_event_keys, use it as
+            # an upper bound.  When list_event_keys failed (device_keys is None),
+            # pass None — get_events will run until the null sentinel naturally.
+            stop_idx: Optional[int] = (current_count - 1) if device_keys is not None else None
             if self.max_events is not None:
-                stop_idx = min(stop_idx, self.max_events - 1)
-                if self.max_events < current_count:
+                cap = self.max_events - 1
+                stop_idx = cap if stop_idx is None else min(stop_idx, cap)
+                if device_keys is not None and self.max_events < current_count:
                     log.warning(
                         "  max_events=%d cap: will download events 0-%d only "
                         "(unit has %d total)",