Scaffold NIH-plug project: full-band gain VST3/CLAP with one-slider egui GUI

Sets up the Rust/NIH-plug build (pinned to nih-plug rev f36931f) producing
VST3 and CLAP bundles via 'cargo xtask bundle'. Implements the first landmark:
a full-band gain plugin with a single egui ParamSlider.

- Cargo workspace + xtask bundler, .cargo alias, bundler.toml
- src/lib.rs: Codename206 plugin (gain param, egui editor)
- deploy.ps1/.bat: build + install to system VST3/CLAP folders (real copy,
  not a junction, for FL Studio); -User flag for a no-admin dev loop
- LICENSE: GPL-3.0 (required by NIH-plug's VST3 bindings)
- README: corrected architecture for the 'All' aggregate channel (4th comp/lim
  stack on the summed bands; all-bands-bypassed = simple full-band comp)
- .gitignore excludes /target and the local nih-plug + _template reference clones

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib.rs

@@ -0,0 +1,148 @@
+use nih_plug::prelude::*;
+use nih_plug_egui::{create_egui_editor, egui, widgets, EguiState};
+use std::sync::Arc;
+
+/// Codename 206 — landmark build.
+///
+/// This is intentionally tiny: a single full-band gain parameter exposed through one
+/// egui slider. It is the foundation the multiband compressor/limiter (see README.md)
+/// will be built on top of. The signal path is currently just `sample *= gain`.
+struct Codename206 {
+    params: Arc<Codename206Params>,
+}
+
+#[derive(Params)]
+struct Codename206Params {
+    /// The egui editor's window state (size). Persisted with the parameter state so a
+    /// resized window is restored on reload.
+    #[persist = "editor-state"]
+    editor_state: Arc<EguiState>,
+
+    /// Full-band output gain. Stored as a linear gain multiplier but displayed in dB.
+    #[id = "gain"]
+    pub gain: FloatParam,
+}
+
+impl Default for Codename206 {
+    fn default() -> Self {
+        Self {
+            params: Arc::new(Codename206Params::default()),
+        }
+    }
+}
+
+impl Default for Codename206Params {
+    fn default() -> Self {
+        Self {
+            editor_state: EguiState::from_size(300, 140),
+
+            // Stored as linear gain, displayed/edited in dB. Skewed so the slider feels
+            // linear in decibels across the -30..+30 dB range.
+            gain: FloatParam::new(
+                "Gain",
+                util::db_to_gain(0.0),
+                FloatRange::Skewed {
+                    min: util::db_to_gain(-30.0),
+                    max: util::db_to_gain(30.0),
+                    factor: FloatRange::gain_skew_factor(-30.0, 30.0),
+                },
+            )
+            // Linear-gain storage needs logarithmic smoothing to avoid zipper noise.
+            .with_smoother(SmoothingStyle::Logarithmic(50.0))
+            .with_unit(" dB")
+            .with_value_to_string(formatters::v2s_f32_gain_to_db(2))
+            .with_string_to_value(formatters::s2v_f32_gain_to_db()),
+        }
+    }
+}
+
+impl Plugin for Codename206 {
+    const NAME: &'static str = "Codename 206";
+    const VENDOR: &'static str = "Mikkeli Matlock";
+    const URL: &'static str = env!("CARGO_PKG_HOMEPAGE");
+    const EMAIL: &'static str = "matlockib@gmail.com";
+
+    const VERSION: &'static str = env!("CARGO_PKG_VERSION");
+
+    const AUDIO_IO_LAYOUTS: &'static [AudioIOLayout] = &[
+        AudioIOLayout {
+            main_input_channels: NonZeroU32::new(2),
+            main_output_channels: NonZeroU32::new(2),
+            ..AudioIOLayout::const_default()
+        },
+        AudioIOLayout {
+            main_input_channels: NonZeroU32::new(1),
+            main_output_channels: NonZeroU32::new(1),
+            ..AudioIOLayout::const_default()
+        },
+    ];
+
+    const MIDI_INPUT: MidiConfig = MidiConfig::None;
+    const MIDI_OUTPUT: MidiConfig = MidiConfig::None;
+
+    const SAMPLE_ACCURATE_AUTOMATION: bool = true;
+
+    type SysExMessage = ();
+    type BackgroundTask = ();
+
+    fn params(&self) -> Arc<dyn Params> {
+        self.params.clone()
+    }
+
+    fn editor(&mut self, _async_executor: AsyncExecutor<Self>) -> Option<Box<dyn Editor>> {
+        let params = self.params.clone();
+        create_egui_editor(
+            self.params.editor_state.clone(),
+            (),
+            |_, _| {},
+            move |egui_ctx, setter, _state| {
+                egui::CentralPanel::default().show(egui_ctx, |ui| {
+                    ui.heading("Codename 206");
+                    ui.separator();
+                    ui.label("Gain");
+                    ui.add(widgets::ParamSlider::for_param(&params.gain, setter));
+                });
+            },
+        )
+    }
+
+    fn process(
+        &mut self,
+        buffer: &mut Buffer,
+        _aux: &mut AuxiliaryBuffers,
+        _context: &mut impl ProcessContext<Self>,
+    ) -> ProcessStatus {
+        for channel_samples in buffer.iter_samples() {
+            let gain = self.params.gain.smoothed.next();
+            for sample in channel_samples {
+                *sample *= gain;
+            }
+        }
+
+        ProcessStatus::Normal
+    }
+}
+
+impl ClapPlugin for Codename206 {
+    const CLAP_ID: &'static str = "com.mikkeli.codename-206";
+    const CLAP_DESCRIPTION: Option<&'static str> =
+        Some("Multiband compressor/limiter (landmark: full-band gain)");
+    const CLAP_MANUAL_URL: Option<&'static str> = Some(Self::URL);
+    const CLAP_SUPPORT_URL: Option<&'static str> = None;
+    const CLAP_FEATURES: &'static [ClapFeature] = &[
+        ClapFeature::AudioEffect,
+        ClapFeature::Stereo,
+        ClapFeature::Mono,
+        ClapFeature::Compressor,
+        ClapFeature::Limiter,
+    ];
+}
+
+impl Vst3Plugin for Codename206 {
+    const VST3_CLASS_ID: [u8; 16] = *b"Codename206Maxi!";
+    const VST3_SUBCATEGORIES: &'static [Vst3SubCategory] =
+        &[Vst3SubCategory::Fx, Vst3SubCategory::Dynamics];
+}
+
+nih_export_clap!(Codename206);
+nih_export_vst3!(Codename206);