fix: pad delayed signal instead of trimming leading samples in apply_lag

verify_sync.py

@@ -103,12 +103,14 @@ def extract_audio_from_mkv(mkv_path: str, stream_index: int, out_wav: str, sr: i
 
 def apply_lag(a: np.ndarray, b: np.ndarray, lag_samples: int) -> tuple[np.ndarray, np.ndarray]:
     if lag_samples >= 0:
-        a_out = a[lag_samples:]
+        # B is delayed by lag_samples — pad B with silence, A stays in place
         b_out = np.concatenate([np.zeros(lag_samples, dtype=np.float32), b])
+        a_out = a
     else:
+        # A is delayed by |lag_samples| — pad A with silence, B stays in place
         pad = -lag_samples
         a_out = np.concatenate([np.zeros(pad, dtype=np.float32), a])
-        b_out = b[pad:]
+        b_out = b
     ml = min(len(a_out), len(b_out))
     return a_out[:ml], b_out[:ml]