v4: no double-kicks (5kHz split+sneak), xcorr beat align, pre-drop mix-in (structure.py)

structure.py

@@ -207,17 +207,21 @@ def find_mix_points(analysis) -> dict:
     intros = [s for s in segments if get(s, 'label') == 'intro']
     outros = [s for s in segments if get(s, 'label') == 'outro']
     
-    # Mix-in: start of the BUILDUP before the first drop.
-    # The audience hears B from here. The intro plays on headphones only.
-    # If no buildup, use 16 bars before the first drop.
-    if buildups:
-        mix_in_time = get(buildups[0], 'start')
-    elif drops:
-        # 16 bars before the first drop
+    # Mix-in: where the audience first hears this track.
+    # Prefer: buildup BEFORE the first drop (the energy ramp into the drop).
+    # If no buildup before the drop, use the last 16 bars of the intro.
+    first_drop_time = get(drops[0], 'start') if drops else duration * 0.3
+    
+    pre_drop_buildups = [s for s in buildups if get(s, 'start') < first_drop_time]
+    if pre_drop_buildups:
+        mix_in_time = get(pre_drop_buildups[-1], 'start')
+    elif intros:
+        # No buildup detected — use intro, 16 bars before the drop
         bars_16 = 16 * 4 * 60.0 / max(analysis.bpm, 60)
-        mix_in_time = max(0, get(drops[0], 'start') - bars_16)
+        mix_in_time = max(0, first_drop_time - bars_16)
     else:
-        mix_in_time = duration * 0.15
+        bars_16 = 16 * 4 * 60.0 / max(analysis.bpm, 60)
+        mix_in_time = max(0, first_drop_time - bars_16)
     
     # First drop
     if drops: