Bake window derives itself: %-knob fold, declick pad, Gate held to exhaustion, preview velocity; Hold is the one knob a loop needs

tests/test_trigger_seam.cpp

@@ -3,7 +3,8 @@
 //
 // Covers triggerPlayLength: zero play length, startFrame set, startFrame past frameCount,
 // rounding, and the Finding 1 regression (start-point set — the case that was broken before
-// this module existed).
+// this module existed); plus effectiveLengthFraction, the spline fold every consumer of the
+// span must go through.
 
 #include "../src/core/instrument/map/trigger_seam.h"
 
@@ -57,7 +58,46 @@ static void testPlayLengthRounding() {
     CHECK(triggerPlayLength(0.6, 3, 0) == 2);
 }
 
+// --- effectiveLengthFraction --------------------------------------------------
+
+// A drawn contour covers the FULL sample length, so the stored %-knob goes inert. It is not
+// cleared, though — a pre-spline value survives in the record, and every reader that takes it
+// raw plays, draws or bakes a fraction of the take.
+static void testDrawnEnvelopeFoldsTheFractionToOne() {
+    PlayParams p;
+    p.trigger.lengthFraction = 0.25;
+    CHECK(effectiveLengthFraction(p) == 0.25);   // staged: the knob is what it says
+
+    p.ampSpline.mode = EnvMode::Spline;
+    CHECK(effectiveLengthFraction(p) == 1.0);    // drawn: the whole take
+    CHECK(p.trigger.lengthFraction == 0.25);     // …and the stored value is untouched
+
+    // Flipping back restores the stored fraction, which is why the fold cannot be a write.
+    p.ampSpline.mode = EnvMode::Staged;
+    CHECK(effectiveLengthFraction(p) == 0.25);
+}
+
+// The fold reads the SAME predicate the engine's Gate refusal does, gating flags included: a
+// Spline mode on a DISABLED pitch/filter envelope binds no cursor, so it must not fold.
+static void testDisabledEnvelopesDoNotFoldTheFraction() {
+    PlayParams p;
+    p.trigger.lengthFraction = 0.5;
+
+    p.pitchSpline.mode = EnvMode::Spline;
+    CHECK(effectiveLengthFraction(p) == 0.5);    // pitchEnv.enabled is still false
+    p.pitchEnv.enabled = true;
+    CHECK(effectiveLengthFraction(p) == 1.0);
+
+    p.pitchEnv.enabled = false;
+    p.filterSpline.mode = EnvMode::Spline;
+    CHECK(effectiveLengthFraction(p) == 0.5);    // filter.enabled is still false
+    p.filter.enabled = true;
+    CHECK(effectiveLengthFraction(p) == 1.0);
+}
+
 int main() {
+    testDrawnEnvelopeFoldsTheFractionToOne();
+    testDisabledEnvelopesDoNotFoldTheFraction();
     testPlayLengthNoStartPoint();
     testPlayLengthWithStartPoint();
     testPlayLengthZeroFrameCount();