contrapunk-nih-plug-skeleton

name	contrapunk-nih-plug-skeleton
description	Create or review nih-plug CLAP/VST3 plugin crates in Contrapunk, especially Elixir plugin work. Use when adding plugin/Cargo.toml crates, implementing Plugin/ClapPlugin/Vst3Plugin, handling MIDI events, or creating DAW-facing synth/effect skeletons.

Contrapunk nih-plug Skeleton

Pattern

For new DAW plugin surfaces, start with a small compiling nih_plug crate that exports both CLAP and VST3, then add full parameter/editor/preset surfaces in later commits.

Minimum Skeleton

1. Add a workspace crate with:
   • [lib] crate-type = ["cdylib", "rlib"]
   • nih_plug dependency pinned to the repo's existing git fork
   • product/core crate dependency (elixir-core, etc.)
2. Implement:
   • #[derive(Params)] parameter struct
   • plugin struct with Arc<Params> and DSP engine state
   • impl Plugin with AUDIO_IO_LAYOUTS, MIDI config, initialize, reset, process
   • impl ClapPlugin
   • impl Vst3Plugin
   • nih_export_clap! and nih_export_vst3!
3. For instrument plugins:
   • main_input_channels: None
   • mono + stereo output layouts
   • MIDI_INPUT: MidiConfig::Basic
   • ClapFeature::Instrument + ClapFeature::Synthesizer
   • VST3 subcategories Instrument + Synth

Realtime Rules

• Do not allocate in process().
• Use BufferConfig::max_buffer_size to preallocate scratch in initialize() when scratch is needed.
• For tiny mono/stereo frame rendering, prefer stack arrays ([f32; 2]) over heap scratch.
• Handle sample-accurate MIDI by iterating buffer.iter_samples().enumerate() and applying events whose event.timing() <= sample_id.
• Keep B3 small: no editor, no giant parameter matrix, no preset format. Those belong to B4/B5.

Validation

• cargo check -p <plugin-crate>
• If the crate touches shared DSP, also run the source core tests (e.g. cargo test -p elixir-core --lib).
• Check both CLAP and VST3 metadata for stable IDs before release.