diff --git a/recognization/code/app.py b/recognization/code/app.py
index bcbd1ff..abb1e8c 100644
--- a/recognization/code/app.py
+++ b/recognization/code/app.py
@@ -21,6 +21,7 @@ import argparse
 import asyncio
 import base64
 from contextlib import asynccontextmanager
+from dataclasses import dataclass
 import json
 import logging
 import os
@@ -29,8 +30,7 @@ import sys
 import threading
 import time
 import uuid
-from dataclasses import dataclass
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, List, Optional, Tuple
 
 # Keep the demo off the network before anything imports ultralytics.
 os.environ.setdefault("YOLO_OFFLINE", "1")
@@ -296,6 +296,9 @@ def create_app(
     recorder = FrameRecorder(settings.record_frames, every=settings.record_every) \
         if settings.record_frames else None
     samples = {item["id"]: item for item in get_available_shelf_images("add")}
+    # path -> (mtime_ns, size, width, height). Dropped when the file changes.
+    sample_dimensions: Dict[str, Tuple[int, int, int, int]] = {}
+    sample_dimensions_lock = threading.Lock()
     sessions: Dict[str, LiveSession] = {}
     sessions_lock = asyncio.Lock()
     app.state.engine = engine
@@ -371,15 +374,37 @@ def create_app(
             raise _error("NOT_FOUND", f"unknown sku '{sku_id}'", 404)
         return {"status": "success", "product": product}
 
-    def _sample_listing() -> List[Dict[str, Any]]:
-        listing = []
+    def _sample_dimensions(path: str) -> Optional[Tuple[int, int]]:
+        try:
+            stat = os.stat(path)
+        except OSError:
+            with sample_dimensions_lock:
+                sample_dimensions.pop(path, None)
+            return None
+        key = (stat.st_mtime_ns, stat.st_size)
+        with sample_dimensions_lock:
+            cached = sample_dimensions.get(path)
+            if cached is not None and cached[:2] == key:
+                return cached[2], cached[3]
         import cv2
 
+        image = cv2.imread(path)
+        if image is None:
+            with sample_dimensions_lock:
+                sample_dimensions.pop(path, None)
+            return None
+        width, height = int(image.shape[1]), int(image.shape[0])
+        with sample_dimensions_lock:
+            sample_dimensions[path] = (key[0], key[1], width, height)
+        return width, height
+
+    def _sample_listing() -> List[Dict[str, Any]]:
+        listing = []
         for item in samples.values():
             entry = {"id": item["id"], "label": item["label"], "url": f"/v1/samples/{item['id']}"}
-            image = cv2.imread(item["path"])
-            if image is not None:
-                entry["width"], entry["height"] = int(image.shape[1]), int(image.shape[0])
+            dimensions = _sample_dimensions(item["path"])
+            if dimensions is not None:
+                entry["width"], entry["height"] = dimensions
             listing.append(entry)
         return listing
 
@@ -693,7 +718,6 @@ def create_app(
             async def send(payload: Dict[str, Any]) -> None:
                 async with send_lock:
                     await websocket.send_text(json.dumps(payload))
-
             await send(
                 {
                     "type": "hello",
@@ -717,7 +741,7 @@ def create_app(
 
         async def processing_loop() -> None:
             while not session.closed:
-                pending = await loop.run_in_executor(None, session.take_pending, 0.25)
+                pending = await session.take_pending_async()
                 if pending is None:
                     continue
                 frame_id, payload = pending
diff --git a/recognization/code/engine.py b/recognization/code/engine.py
index f63e714..6a84c92 100644
--- a/recognization/code/engine.py
+++ b/recognization/code/engine.py
@@ -273,6 +273,10 @@ class RecognitionEngine:
             self.settings.image_store_max_bytes,
         )
         self._catalog_cache: Optional[Tuple[str, List[Dict[str, Any]]]] = None
+        # (version, csv mtime_ns, csv size, sorted image name:size). Version is
+        # the content digest; the rest is the cheap fingerprint that invalidates it.
+        self._catalog_version_cache: Optional[Tuple[str, int, int, Tuple[Tuple[str, int], ...]]] = None
+        self._catalog_version_lock = threading.Lock()
         self._started_at = time.time()
 
     # ------------------------------------------------------------------ lifecycle
@@ -477,6 +481,8 @@ class RecognitionEngine:
                     len(gallery.sku_ids),
                     gallery.device,
                 )
+                if gallery.head_reason != "ok":
+                    LOGGER.warning("identity head: %s (%s)", gallery.head_reason, gallery._head_path)
             else:
                 LOGGER.warning("identity gallery unavailable; gallery requests stay unrecognized")
             return gallery if loaded else None
@@ -606,24 +612,53 @@ class RecognitionEngine:
 
     # ------------------------------------------------------------------ catalog
     def catalog_version(self) -> str:
-        digest = hashlib.sha256()
+        """12-hex digest of stock.csv bytes plus template image names and sizes.
+
+        Unchanged files reuse the digest. A stock update that has not been written
+        back to the CSV still changes the digest, because the in-memory fingerprint
+        is dropped. Same-size content rewritten without a new mtime is not detected
+        until the next stock update or a real stat change.
+        """
         csv_path = os.path.join(self.settings.stock_dir, self.settings.stock_csv)
         try:
-            with open(csv_path, "rb") as handle:
-                digest.update(handle.read())
+            stat = os.stat(csv_path)
+            csv_key = (stat.st_mtime_ns, stat.st_size)
         except OSError:
-            digest.update(b"missing-csv")
+            csv_key = None
         try:
-            entries = sorted(
+            entries = tuple(sorted(
                 (name, os.path.getsize(os.path.join(self.settings.stock_dir, name)))
                 for name in os.listdir(self.settings.stock_dir)
                 if name.lower().endswith((".jpeg", ".jpg", ".png"))
-            )
+            ))
         except OSError:
-            entries = []
+            entries = ()
+        fingerprint = (
+            csv_key[0] if csv_key else -1,
+            csv_key[1] if csv_key else -1,
+            entries,
+        )
+        with self._catalog_version_lock:
+            cached = self._catalog_version_cache
+            if cached is not None and csv_key is not None and cached[1:] == fingerprint:
+                return cached[0]
+        digest = hashlib.sha256()
+        if csv_key is None:
+            digest.update(b"missing-csv")
+        else:
+            try:
+                with open(csv_path, "rb") as handle:
+                    digest.update(handle.read())
+            except OSError:
+                digest.update(b"missing-csv")
+                csv_key = None
         for name, size in entries:
             digest.update(f"{name}:{size}".encode("utf-8"))
-        return digest.hexdigest()[:12]
+        version = digest.hexdigest()[:12]
+        if csv_key is not None:
+            with self._catalog_version_lock:
+                self._catalog_version_cache = (version, csv_key[0], csv_key[1], entries)
+        return version
 
     def model_version(self) -> str:
         try:
@@ -689,6 +724,8 @@ class RecognitionEngine:
             product = self.inventory.get_product(sku_id) or {}
             payload = self._product_payload(sku_id, product)
         self._catalog_cache = None
+        with self._catalog_version_lock:
+            self._catalog_version_cache = None
         return payload
 
     def sku_count(self) -> int: