Joystick -> MLP -> MIDI CC for an external hardware synth, using the
compile-time device templates from nisps/midi/generated. ExternalSynthMIDIMode
<const MidiDevice&, NOut> mirrors SoundAnalysisMIDIMode (NoOpEngine,
kRouteOutputsToEngine=false, pushes ControlChange events). A consteval
pick_cc_slots curates which NOut params fill the output slots (prefers musical
params over Bank Select/global). Adds six flashable variants
(MEMLNautModeExtSynth{Sub37,SubPhatty,Pro12,AnalogKeys,Hydrasynth,JD800}) wired
into mode_select.hpp + the .ino variant list + NISPS_ST guards, and a src/nisps/
midi symlink so the sketch tree can reach nisps/midi.
Host-compile-verified under C++20 (incl. via the sketch include path) and
lint-clean; full arduino-cli build + flash is on the hardware (no toolchain here.
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