feat: record a live session so it can become data

The deep review's first recommendation was real data, because every accuracy number
so far comes from one or two photographs - the identity benchmark even takes its
gallery and its queries from the same photo. This is the mechanism for replacing
that.

`--record-frames DIR` writes each processed frame, sampled every Nth, with a JSON
line describing what the server saw in it: the boxes, the identity channels and the
tag reading. The lines are the labelling input - `labelling_candidates()` returns
the facings the tag channel named with a corroborated price, which are seeds for the
confirmation screen rather than guesses. Nothing here is a training set on its own.

Sampling keeps each frame's own number in the index, so a sampled recording says so
instead of hiding it, and `/v1/health` reports how much has been written. Measured
on a 163-frame walk: 32 frames and their lines.

`docs/DATA.md` is the runbook: what to capture (a slow walk per rail, a close pass
for the barcode, and the same shelf on a second visit), how to turn it into labels,
and how to freeze a benchmark with a cross-visit split.

167 tests pass.

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

recognization/code/app.py

@@ -72,6 +72,7 @@ from engine import (  # noqa: E402
     settings_from_env,
 )
 from demo import DemoCamera, DemoSourceError  # noqa: E402
+from record import FrameRecorder  # noqa: E402
 from live import LiveSession, LiveSettings  # noqa: E402
 
 LOGGER = logging.getLogger("dorayaki")
@@ -99,6 +100,9 @@ class ServerSettings:
     live_conf: float = 0.1
     live_tags: bool = True
     demo_walk: bool = False
+    # A live session can be recorded so it becomes data to label (record.py).
+    record_frames: Optional[str] = None
+    record_every: int = 3
     log_level: str = "info"
     ssl_certfile: Optional[str] = None
     ssl_keyfile: Optional[str] = None
@@ -278,6 +282,7 @@ def create_app(
                 "engine": getattr(engine.ocr_engine, "name", "none"),
                 "available": bool(getattr(engine.ocr_engine, "available", lambda: False)()),
             },
+            "recording": recorder.stats() if recorder is not None else None,
             "sessions_active": len(sessions),
             "uptime_s": round(engine.uptime_s(), 1),
         }
@@ -322,6 +327,8 @@ def create_app(
     # still recognition mapped into each walk frame, which is a film-making device,
     # not a perception result. Every payload it produces is marked synthetic.
     demo_recognition = None
+    recorder = FrameRecorder(settings.record_frames, every=settings.record_every) \
+        if settings.record_frames else None
 
 
 
@@ -693,6 +700,10 @@ def create_app(
                     await send({"type": "error", "code": "INTERNAL", "frame_id": frame_id,
                                 "message": "frame processing failed"})
                     continue
+                if recorder is not None:
+                    # Record what the client sent and what we saw in it, so the walk
+                    # can be labelled later instead of only measured on photographs.
+                    recorder.write(session_id, frame_id, payload, result)
                 if demo_recognition is not None and demo_sample_ids:
                     # The walk's frames are served from the shelf's full recognition,
                     # so every product is already labelled with name and price.
@@ -980,6 +991,10 @@ def main() -> None:
                         help="classifications in flight per session (demo walks want a larger budget)")
     parser.add_argument("--live-attempts", type=int, default=None,
                         help="classification attempts per track")
+    parser.add_argument("--record-frames", type=str, default=None,
+                        help="write processed frames and their results under this directory")
+    parser.add_argument("--record-every", type=int, default=None,
+                        help="record one frame in every N (default 3)")
     parser.add_argument("--demo-walk", action="store_true",
                         help="serve the demo walk's pre-recognised shelf as live tracks")
     parser.add_argument("--no-tags", action="store_true", help="disable price-tag OCR")
@@ -1017,6 +1032,10 @@ def main() -> None:
         server.log_level = args.log_level
 
     engine_settings = settings_from_env()
+    if args.record_frames is not None:
+        server.record_frames = args.record_frames
+    if args.record_every is not None:
+        server.record_every = args.record_every
     if args.live_inflight is not None:
         engine_settings.live_inflight = args.live_inflight
     if args.live_attempts is not None: