fix: close round-2 review findings — Critical silent-note bug plus majors/minors

Fixes the 2-point spline-EG early-free bug causing silent fade-ins, the pitch/filter enable-toggle Trigger-forcing hole, the contour-node/marker pixel shadow, missing deck-residue test coverage, and stale comments in knob_deck and spline_edit.

tests/test_component_state_io.cpp

@@ -788,6 +788,11 @@ static void testNonFiniteAhdSecondsLiftToZero() {
 // the record is disturbed. Corrupts only the AMP curve's tail; FILTER/PITCH follow at their
 // normal, byte-precise offsets, proving a mismatch on one curve does not cascade to its
 // neighbours.
+//
+// Companion, not a regression guard: this in-bounds-mismatch path was already non-wiping
+// before the r.ok fix below — it pins the documented promise, not the fix. The two tests that
+// follow (OUT-OF-BOUNDS count, and a mid-count truncation) are what actually guard it — both
+// tripped the old "reset the whole record to defaults" behavior.
 static void testV13HardFlagInBoundsMismatchDropsFlagsOnly() {
     ComponentState in;
     in.selectionId = "pad";