instrument: one staged-envelope system — per-segment curves, the sustain-less AHD, and a shared overlay for all three envelopes

Trigger's fade pair folds into the AHD (and goes live); the release anchors right;
Preserve rings its synthetic tail out instead of cutting it. Payload v10.

src/core/instrument/map/trigger_seam.h

@@ -1,8 +1,7 @@
-// trigger_seam — converts Trigger fade lengths between the engine domain (TriggerParams:
-// SOURCE FRAMES, anchored to the source-timeline read pointer) and the overlay domain
-// (AmpEnvelope: FRACTIONS in [0,1] of the played span, so the drawn shape stays invariant
-// across sample-rate changes). Owns the one shared pack/unpack formula so both directions
-// stay consistent; reasampler_editor calls these from packEnvelope/unpackEnvelope.
+// 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.
 //
 // playLengthFrames = round(lengthFraction * (frameCount - startFrame))
 
@@ -19,11 +18,4 @@ std::int64_t triggerPlayLength(double lengthFraction,
                                std::int64_t frameCount,
                                std::int64_t startFrame);
 
-// PACK direction (draw path): frames -> fraction of play span. Not clamped here — the
-// caller clamps to [0,1] when filling AmpEnvelope (envelope_edit owns that logic).
-double framesToFadeFraction(std::int64_t fadeFrames, std::int64_t playLength);
-
-// UNPACK direction (commit path): fraction -> nearest source frame.
-std::int64_t fadeFractionToFrames(double fadeFraction, std::int64_t playLength);
-
 }  // namespace reasampler::instrument::map