add stage2_min_updates gate to stage-2 (default=0 disabled)

- Mature-track-only stage-2: only tracks with >= N updates participate in low-conf recovery
- Neutral at N=0,1; regresses at N>=2 — ghost exclusion hurts legitimate young tracks
- Added to Optuna search space [0, 5] for future joint optimisation

---
Co-authored-by: Claude Code <noreply@anthropic.com>

Author: Borda

autotrack/default_config.json

@@ -17,7 +17,8 @@
         "max_interpolation_gap": 32,
         "p_reset_threshold": 26,
         "oru_threshold": 14,
-        "conf_cost_weight": 0.0
+        "conf_cost_weight": 0.0,
+        "stage2_min_updates": 0
     },
     "sort": {
         "lost_track_buffer": 30,

autotrack/optimize_tracking.py

@@ -186,6 +186,7 @@ def _build_tracker(params: dict, tracker_name: str):
             iou_age_weight=params["iou_age_weight"],
             high_conf_det_threshold=params["high_conf_det_threshold"],
             conf_cost_weight=params.get("conf_cost_weight", 0.0),
+            stage2_min_updates=params.get("stage2_min_updates", 0),
         )
     if tracker_name == "sort":
         from trackers import SORTTracker

autotrack/search_space.json

@@ -92,6 +92,11 @@
             "type": "float",
             "low": 0.0,
             "high": 1.0
+        },
+        "stage2_min_updates": {
+            "type": "int",
+            "low": 0,
+            "high": 5
         }
     },
     "sort": {

trackers/core/bytetrack/tracker.py

@@ -83,6 +83,7 @@ def __init__(
         iou_age_weight: float = 0.03,
         high_conf_det_threshold: float = 0.6,
         conf_cost_weight: float = 0.0,
+        stage2_min_updates: int = 0,
     ) -> None:
         # Calculate maximum frames without update based on lost_track_buffer and
         # frame_rate. This scales the buffer based on the frame rate to ensure
@@ -95,6 +96,7 @@ def __init__(
         self.track_activation_threshold = track_activation_threshold
         self.high_conf_det_threshold = high_conf_det_threshold
         self.conf_cost_weight = conf_cost_weight
+        self.stage2_min_updates = stage2_min_updates
         self.tracks: list[ByteTrackKalmanBoxTracker] = []
 
     def update(
@@ -187,7 +189,20 @@ def update(
             out_det_indices.append(int(high_indices[col]))
             out_tracker_ids.append(track.tracker_id)
 
-        remaining_tracks = [self.tracks[i] for i in unmatched_tracks]
+        # Stage-2 maturity gate: only established tracks participate in low-conf
+        # recovery.  Young tracks (number_of_successful_updates < stage2_min_updates)
+        # are excluded to prevent tentative ghost tracks from being incorrectly
+        # recovered via low-confidence detections.  When stage2_min_updates == 0
+        # (default) all unmatched tracks participate, preserving the original behaviour.
+        if self.stage2_min_updates > 0:
+            remaining_tracks = [
+                self.tracks[i]
+                for i in unmatched_tracks
+                if self.tracks[i].number_of_successful_updates
+                >= self.stage2_min_updates
+            ]
+        else:
+            remaining_tracks = [self.tracks[i] for i in unmatched_tracks]
 
         # Step 2: associate low-confidence detections to remaining tracks
         iou_matrix = get_iou_matrix(remaining_tracks, low_boxes)