Modular sub-engines computed amp_val as a pure function of mod_amp (the
matrix d08_amp destination sum), so once the MLP drove the matrix cells
every joystick movement had a chance to silence the voice: matrix cells
have signed range [-1, 1], sigmoid outputs near 0.5 denormalise to 0,
and the amp gate collapsed. Additive survived in scattered regions
because it only has one kill-switch (d08_amp); subtractive and fm were
almost always dead because they also have d05_cutoff and d01_op1_level.
Two changes:
1. DSP: each sub-engine gets a base_amp hslider (default 1.0) so
amp_val = clamp(base_amp + mod_amp) * level * vel_gain. At the
default the voice is always fully open and d08_amp modulation is
purely additive decoration; drop base_amp to 0 for classic
ADSR-gated VCA behaviour.
2. ModularEngine._rebuildParamMeta: restore the _exposedMatrixCells
gate (default empty). paramCount drops from 512 to 32 (4 ADSR * 4
+ 8 LFO * 2); matrix cells are opt-in via setExposeMatrixCell.
_applyDefaultPatch no longer writes s00_d08_amp since base_amp
keeps the voice audible without routing.
Tests updated for the new 32-param baseline; matrix-cell persistence
test now calls setExposeMatrixCell(1, 5, true) before asserting the
cell lands in paramMeta. Drive-by: engine-switching test bumped from
3 to 4 engine cards (stale since the modular engine was added).
b290144670