fix: close round-3 review findings — smallest-target-first, residue test fix, extraction

Waveform overlay now resolves node/tab/marker click collisions by target area instead of check order; residue test now uses a distinguishing fixture; Gate-unavailable-while-drawn logic extracted to one pure helper shared by resolvePlay and applyControl.

src/shell/instrument/editor_controls.cpp

@@ -274,8 +274,8 @@ void ReaSamplerEditor::applyControl(int id, PlaySeconds& play, double value,
     // (above) or an enable toggle (kPitchEnvEnable/kFilterEnable), whose enabling can make an
     // already-Spline pitch/filter envelope newly active. Applying it once here, rather than at
     // each site that could cause the flip, is what keeps a future such control from reopening
-    // the same hole.
-    if (splineActive(play)) play.playMode = PlayMode::Trigger;
+    // the same hole. `resolvePlay` (sample_map.cpp) is the other caller of the shared helper.
+    enforceGateUnavailableWhileDrawn(play);
 }
 
 double ReaSamplerEditor::liveSampleRate() const {