instrument: fix AHD node-tracking/tie-break/live-latch defects and close staged-envelope-curve test gaps

src/core/instrument/ui/envelope_overlay.h

@@ -13,10 +13,9 @@
 
 namespace reasampler::instrument::ui {
 
-// Which LAYOUT POLICY an envelope takes, decided by whether it has a sustain stage rather
-// than by which processor it modulates. A gated (AHDSR) envelope right-anchors its release so
-// the sustain plateau reads full-width; a sustain-less (AHD) one maps 1:1 onto the waveform's
-// own time axis, which only means anything for a trigger shape. The two policies coexist.
+// Which LAYOUT POLICY an envelope takes — see core/instrument/CLAUDE.md's "envelope overlay"
+// section for why (decided by sustain-stage presence, not by which processor it modulates).
+// Ahdsr right-anchors its release; Ahd maps 1:1 onto the waveform's own time axis.
 enum class EnvKind { Ahdsr, Ahd };
 
 // Gate nodes: Origin -> AttackEnd -> HoldEnd -> DecayEnd(sustain) -> ReleaseStart -> ReleaseEnd.