Tighten cutter phase span validation

src/cv/global_scan.py

@@ -1330,7 +1330,10 @@ def estimate_usable_source_duration(
 
     warmup_scores = [score for offset, score in scores if offset <= min(1.0, beat.duration_s * 0.35)]
     baseline = max(warmup_scores) if warmup_scores else max(score for _, score in scores)
-    min_score = max(0.34, baseline * 0.48)
+    # Keep the usable span tied to the same action phase, not just the same room
+    # or actors. A loose cutoff hides "same scene, wrong moment" drift in long
+    # dialogue shots where the background remains highly correlated.
+    min_score = max(0.42, baseline * 0.62)
 
     last_good = 0.0
     bad_run = 0
@@ -1363,8 +1366,8 @@ def estimate_usable_source_duration(
             if (
                 len(tail_scores) >= 3
                 and float(np.std(tail_scores)) < 0.025
-                and float(np.mean(tail_scores)) > 0.20
-                and baseline >= 0.30
+                and float(np.mean(tail_scores)) > max(0.30, baseline * 0.58)
+                and baseline >= 0.42
             ):
                 logger.debug(
                     'Beat %d: stable plateau detected at offset %.3fs '