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.

tests/test_spline_egs.cpp

@@ -344,6 +344,25 @@ static void testTwoPointContourRisingFromZeroSoundsForItsFullSpan() {
     CHECK(v.soundingNote());              // still sounding at the midpoint, rising toward 1
 }
 
+// The positive direction of the fix above: a contour whose final segment is flat at 0 (here,
+// the whole two-point span) DOES free the voice early, on its very first tick. Nothing exercises
+// this without it — a future tightening of the gate (e.g. requiring more than onFinalSegment() +
+// segmentEndValue()) could silently turn the early-free off, which is a performance regression
+// (a ringing but silent voice) rather than an audible one, so nothing else would catch it.
+static void testFlatZeroFinalSegmentStillFreesTheVoiceEarly() {
+    const VelocityCurve contour =
+        VelocityCurve::fromPoints({{kVelMin, 0.0}, {kVelMax, 0.0}}, CurveDomain::Unipolar);
+    const std::size_t frames = 1000;
+    const SampleData s = splineAmpSample(frames, contour);
+
+    Voice v;
+    v.start(60, 100, s);
+    CHECK(v.soundingNote());              // fresh note: sounding before anything is rendered
+    const double y0 = v.renderFrame();
+    CHECK(near(y0, 0.0, 1e-9));
+    CHECK(!v.soundingNote());             // a genuine permanent terminus, not a mid-contour dip
+}
+
 // --- 9. A fresh spline EG opens on the smooth y = 1 - x ----------------------
 
 static void testAFreshSplineEgDefaultsToTheSmoothDownwardSlope() {
@@ -424,6 +443,27 @@ static void testGateIsUnavailableWhileASplineEgIsActiveAndReturnsAfterwards() {
     CHECK(!deckKnobInert(DeckParam::kFilterModAmt, gates));
 }
 
+// enforceGateUnavailableWhileDrawn (play_params.h) is the ONE enforcement resolvePlay and the
+// editor's applyControl both call — resolvePlay's own coverage above only exercises it through
+// the frames mirror; pin it directly over BOTH representations it is shared between, closing the
+// coverage gap the extraction was for (applyControl has no shell test target of its own).
+static void testEnforceGateUnavailableWhileDrawnForcesTriggerOnBothRepresentations() {
+    PlaySeconds seconds;
+    seconds.playMode = PlayMode::Gate;
+    enforceGateUnavailableWhileDrawn(seconds);
+    CHECK(seconds.playMode == PlayMode::Gate);  // not splineActive -> untouched
+    seconds.ampSpline.mode = EnvMode::Spline;
+    enforceGateUnavailableWhileDrawn(seconds);
+    CHECK(seconds.playMode == PlayMode::Trigger);
+
+    PlayParams frames;
+    frames.playMode = PlayMode::Gate;
+    frames.filter.enabled = true;
+    frames.filterSpline.mode = EnvMode::Spline;
+    enforceGateUnavailableWhileDrawn(frames);
+    CHECK(frames.playMode == PlayMode::Trigger);
+}
+
 // --- 11. The velocity->amp curve is the same grammar -------------------------
 
 static void testTheVelocityAmpCurveGainsTheToggleAndKeepsItsDelete() {
@@ -491,8 +531,10 @@ int main() {
     testAV12PayloadLoadsWithoutLoss();
     testAContourReplaysProportionallyOnADifferentLengthSample();
     testTwoPointContourRisingFromZeroSoundsForItsFullSpan();
+    testFlatZeroFinalSegmentStillFreesTheVoiceEarly();
     testAFreshSplineEgDefaultsToTheSmoothDownwardSlope();
     testGateIsUnavailableWhileASplineEgIsActiveAndReturnsAfterwards();
+    testEnforceGateUnavailableWhileDrawnForcesTriggerOnBothRepresentations();
     testTheVelocityAmpCurveGainsTheToggleAndKeepsItsDelete();
     testSplineCursorBinarySearchAgreesWithTheColdReaderOnAJumpingRead();
     if (g_fail == 0) std::printf("spline_egs: all tests passed\n");