feat: sync live-count, exemplar annotation modules, and update .gitignore

backend/api/live_count.py

@@ -15,9 +15,9 @@ router = APIRouter(tags=["live-count"])
 
 
 class StartRequest(BaseModel):
-    # Either a raw source (RTSP URL or absolute path) or an archive-relative
-    # path like "2026-08-13/batch001.mp4", which the backend resolves — the
-    # frontend never needs to know where the archive is mounted.
+    # Either a live stream — which must be a WebRTC (WHEP) URL, REQ-176 — or an
+    # archive-relative path like "2026-08-13/batch001.mp4", which the backend
+    # resolves so the frontend never needs to know where the archive is mounted.
     source: str = ""
     source_rel: Optional[str] = None
     model_path: Optional[str] = None
@@ -60,14 +60,22 @@ def available_models(project_id: int) -> dict:
 def start(project_id: int, request: StartRequest) -> dict:
     project = project_or_404(project_id)
 
-    source = request.source
+    source, whep = request.source, ""
     if request.source_rel:
         try:
             source = library.resolve(project["video_root"], request.source_rel)
         except library.LibraryError as exc:
             raise HTTPException(400, str(exc))
+    elif source:
+        # A live source is a WebRTC URL and nothing else. The browser watches it
+        # over WebRTC; the counter decodes the RTSP leg of the same MediaMTX
+        # path, derived here (REQ-176).
+        try:
+            whep, source = live_count.whep_url(source), live_count.whep_to_rtsp(source)
+        except live_count.LiveCountError as exc:
+            raise HTTPException(400, str(exc))
     if not source:
-        raise HTTPException(400, "Pick a video or enter a stream URL")
+        raise HTTPException(400, "Pick a video or enter a WebRTC stream URL")
 
     path = request.model_path
     if not path and request.model_version_id is not None:
@@ -88,6 +96,7 @@ def start(project_id: int, request: StartRequest) -> dict:
             unload_confirm_frames=request.unload_confirm_frames,
             min_area_scale=request.min_area_scale,
             spatial_dedup=request.spatial_dedup,
+            whep=whep,
         )
     except live_count.LiveCountError as exc:
         raise HTTPException(400, str(exc))
@@ -118,9 +127,24 @@ def status() -> dict:
     return live_count.status()
 
 
+@router.get("/api/live-count/overlay")
+def overlay() -> dict:
+    """Geometry only — boxes, line and counts for the frame just processed.
+
+    What the WebRTC preview draws over the video, instead of the server
+    encoding a JPEG per frame for it (REQ-177).
+    """
+    return live_count.overlay()
+
+
 @router.get("/api/live-count/stream")
 def stream():
-    """MJPEG of the annotated frames. Ends when the session does."""
+    """MJPEG of the annotated frames — the archive-file preview. Ends with the session."""
+    if live_count.status().get("preview") == "webrtc":
+        # Nothing is encoding JPEGs for this session; without this the generator
+        # would sit on a worker thread for ten seconds producing nothing.
+        raise HTTPException(409, "This session is watched over WebRTC, not MJPEG")
+
     def frames():
         blank_streak = 0
         while True: