fix(sound): concert advance via body wrists

The hand-based arms-crossed gesture could never fire: hand L/R is
position-sorted (rx>=lx always), and at full-body distance MediaPipe
doesnt detect the hands at all (crossing also occludes them). Detect
the advance from the body wrists instead: new /pose/wrist OSCdef ->
~poseWrist, and detectCross fires when the right wrist swaps clearly
left of the left wrist (a clear X), performer centered, wrists at chest
height. Verified headless (wrist-cross advance 1->2).

sound_algo/control/data_feeds.scd

@@ -495,6 +495,7 @@ OSCdef(\poseLeave, { |msg|
     ~poseState.removeAt(pid);
     ~poseKin.removeAt(pid);
     ~poseCenter.removeAt(pid);
+    ~poseWrist !? { ~poseWrist.removeAt(pid) };
 }, '/pose/leave');
 
 OSCdef(\poseHands, { |msg|
@@ -509,6 +510,17 @@ OSCdef(\poseHands, { |msg|
     ~handFeat[\dist]   = msg[10];
 }, '/pose/hands');
 
+// Body wrists (skeleton, tracked even when hands are occluded/too small).
+// /pose/wrist  <pid> <l|r> <x> <y>   (anatomical L/R from MediaPipe pose)
+~poseWrist = ~poseWrist ? Dictionary.new;
+OSCdef(\poseWrist, { |msg|
+    var pid = msg[1].asInteger;
+    var e = ~poseWrist[pid] ? ();
+    if(msg[2].asString[0] == $l) { e[\lx] = msg[3]; e[\ly] = msg[4]; }
+    { e[\rx] = msg[3]; e[\ry] = msg[4]; };
+    ~poseWrist[pid] = e;
+}, '/pose/wrist');
+
 ~poseCenter = ~poseCenter ? Dictionary.new;
 OSCdef(\poseCenter, { |msg|
     var pid = msg[1].asInteger;

sound_algo/data_only/scene_concert.scd

@@ -57,13 +57,17 @@
 
 // geste bras-croises : main D a gauche de main G, a mi-hauteur, maintenu
 ~concert[\detectCross] = { |pose, now|
-    var hf = pose[\hands];
-    var ry = (hf[\ry] ? 0); var ly = (hf[\ly] ? 0);
-    var crossed = pose[\hasBody] and: {
-        ((hf[\rx] ? 0.5) < ((hf[\lx] ? 0.5) - 0.08))
-        and: { (ry >= 0.25) and: { ry <= 0.75 } }
-        and: { (ly >= 0.25) and: { ly <= 0.75 } }
-    };
+    // Detect via BODY WRISTS (skeleton), not hands: at full-body distance the
+    // hands aren't detected and crossing occludes them. Clear X cross = the
+    // right wrist swaps to the LEFT of the left wrist. Require the performer
+    // centered (not at a frame edge) + wrists at chest height.
+    var w = (~poseWrist.notNil.if({ ~poseWrist.values.detect({ |v| v.notNil }) })) ? ();
+    var lx = (w[\lx] ? 0.5); var rx = (w[\rx] ? 0.5);
+    var ly = (w[\ly] ? 0.5); var ry = (w[\ry] ? 0.5);
+    var centered = (lx > 0.15) and: { lx < 0.85 } and: { rx > 0.15 } and: { rx < 0.85 };
+    var midH = (ly > 0.2) and: { ly < 0.85 } and: { ry > 0.2 } and: { ry < 0.85 };
+    var crossed = pose[\hasBody] and: { centered } and: { midH }
+        and: { rx < (lx - 0.10) };
     if(crossed) {
         if(~concert[\crossT] <= 0) { ~concert[\crossT] = now };
         if(((now - ~concert[\crossT]) >= ~ccCrossHold)