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

src/core/instrument/map/trigger_seam.h

@@ -1,19 +1,32 @@
 // trigger_seam — the shared Trigger play-span formula: how the stored %-length becomes the
-// source-frame span the voice plays and the overlay draws over. One home so the engine's
-// note-on resolve and the editor's overlay pack cannot disagree about where a Trigger note
-// ends.
+// source-frame span the voice plays, the overlay draws over, and the bake's window holds.
+// One home so those three cannot disagree about where a Trigger note ends.
 //
-// playLengthFrames = round(lengthFraction * (frameCount - startFrame))
+// playLengthFrames = round(effectiveLengthFraction * (frameCount - startFrame))
 
 #pragma once
 
 #include <cstdint>
 
+#include "core/instrument/engine/play_params.h"  // splineActive (the %-knob's inert rule)
+
 namespace reasampler::instrument::map {
 
+// The %-length the voice ACTUALLY plays. A drawn contour is a pure time function over the
+// full sample length, so any active spline EG folds the fraction to 1.0 and the stored knob
+// goes inert (splineActive, play_params.h) — but the stored value survives, so a pre-spline
+// setting is still there to be read. Every consumer of the span must fold it here or it
+// silently plays/draws/bakes a fraction of the take.
+//
+// Templated over the two parameter representations for the same reason splineActive is.
+template <class Play>
+double effectiveLengthFraction(const Play& p) {
+    return splineActive(p) ? 1.0 : p.trigger.lengthFraction;
+}
+
 // postStart = max(0, frameCount - startFrame); playLength = round(lengthFraction * postStart).
-// `startFrame` is the effective start point (0 when absent). Returns 0 when postStart == 0
-// or lengthFraction <= 0.
+// `startFrame` is the effective start point (0 when absent), `lengthFraction` the EFFECTIVE
+// one above. Returns 0 when postStart == 0 or lengthFraction <= 0.
 std::int64_t triggerPlayLength(double lengthFraction,
                                std::int64_t frameCount,
                                std::int64_t startFrame);