feat: skip track forward on result overlap, not class presence (REQ-189)

Frame holding the tracked class is now annotated like any other; the run's
result is dropped only when it intersects a same-class shape already there.

backend/api/review.py

@@ -38,6 +38,8 @@ class AssistRequest(BaseModel):
     box: List[float]
     class_id: int = 0
     threshold: float = 0.5
+    # Track Forward only: drop the result when it lands on an existing shape.
+    dedupe: bool = False
 
 
 class PoolExemplar(BaseModel):
@@ -116,7 +118,7 @@ def bulk_reclass(request: BulkReclassRequest) -> dict:
 def assist(frame_id: int, request: AssistRequest) -> dict:
     try:
         return review_store.assist(frame_id, request.box, request.class_id,
-                                   request.threshold)
+                                   request.threshold, dedupe=request.dedupe)
     except review_store.ReviewError as exc:
         raise HTTPException(400, str(exc))
 

backend/batches.py

@@ -137,15 +137,11 @@ def frames(batch_id: int) -> List[dict]:
     with db.cursor() as cur:
         cur.execute(
             """SELECT f.*, (SELECT COUNT(*) FROM annotations a WHERE a.frame_id = f.id)
-                        AS annotation_count,
-                        (SELECT GROUP_CONCAT(DISTINCT a.class_id) FROM annotations a
-                          WHERE a.frame_id = f.id) AS class_ids
+                        AS annotation_count
                FROM frames f WHERE f.batch_id = ? ORDER BY f.idx""",
             (batch_id,),
         )
         rows = [dict(row) for row in cur.fetchall()]
-    for row in rows:
-        row["class_ids"] = [int(v) for v in row["class_ids"].split(",")] if row["class_ids"] else []
     return rows
 
 

backend/review.py

@@ -320,7 +320,7 @@ def frames_with_auto(batch_id: int) -> set:
 
 
 def assist(frame_id: int, box: List[float], class_id: int = 0,
-           threshold: float = 0.5) -> dict:
+           threshold: float = 0.5, dedupe: bool = False) -> dict:
     """Drag a rough box, get SAM3's shape for the object inside it (REQ-043).
 
     The box is a visual exemplar rather than a crop: SAM3 may return several
@@ -378,6 +378,16 @@ def assist(frame_id: int, box: List[float], class_id: int = 0,
     finally:
         jobs.gpu_lock.release()
 
+    # Track Forward passes dedupe=True (REQ-189): the run still happens, but a
+    # result that lands on a shape already there is the same object twice, so
+    # nothing is written and the caller reports the frame as skipped. Runs after
+    # the lock is released because this part needs no GPU.
+    if dedupe:
+        landed = to_box(geometry)
+        for existing in listing(frame_id):
+            if existing["class_id"] == class_id and intersects(landed, to_box(existing["geometry"])):
+                return {"skipped": True}
+
     return add(frame_id, class_id, geometry, source="manual", score=detection.score)
 
 
@@ -397,6 +407,16 @@ def _overlap(detection_box: List[float], drawn: List[float],
     return inter / (area_box + area_drawn - inter)
 
 
+def intersects(a: List[float], b: List[float]) -> bool:
+    """Any pixel of intersection between two normalized xyxy boxes (REQ-189).
+
+    Deliberately not IoU: two trucks that merely touch are two trucks. Raising
+    this to a ratio is the upgrade path if adjacent same-class boxes ever start
+    getting dropped as duplicates.
+    """
+    return min(a[2], b[2]) > max(a[0], b[0]) and min(a[3], b[3]) > max(a[1], b[1])
+
+
 def clear_batch_class_annotations(batch_id: int, class_id: int) -> int:
     """Delete all annotations matching class_id across all frames in a batch (REQ-046)."""
     with db.cursor() as cur: