Initial release — InstaShadow mastering compressor v1.0

Dual-stage compressor (optical + VCA) with output transformer saturation.
- Port-Hamiltonian T4B opto-cell model with implicit trapezoidal integration
- Feed-forward VCA with 7 ratios, 6 attack/release presets, Dual release mode
- 3 transformer types (Nickel/Iron/Steel) with 4x oversampled waveshaping
- Analog-style needle VU meters, horizontal GR meters
- Sidechain HPF, stereo link, independent section bypass
- Full state save/restore, CI/CD for Windows/macOS/Linux

Source/CompressorEngine.h

@@ -0,0 +1,64 @@
+#pragma once
+#include <JuceHeader.h>
+#include "OpticalCell.h"
+#include "VCACompressor.h"
+#include "TransformerSaturation.h"
+
+class CompressorEngine
+{
+public:
+    CompressorEngine();
+
+    void prepare (double sampleRate, int samplesPerBlock);
+    void processBlock (juce::AudioBuffer<float>& buffer);
+
+    // --- Optical section (GUI → audio) ---
+    std::atomic<float> optoThresholdDb  { -20.0f };
+    std::atomic<float> optoGainDb       { 0.0f };
+    std::atomic<float> optoScHpfHz      { 90.0f };
+    std::atomic<bool>  optoBypass       { false };
+
+    // --- Discrete VCA section ---
+    std::atomic<float> vcaThresholdDb   { -20.0f };
+    std::atomic<float> vcaGainDb        { 0.0f };
+    std::atomic<int>   vcaRatioIndex    { 1 };
+    std::atomic<int>   vcaAttackIndex   { 2 };
+    std::atomic<int>   vcaReleaseIndex  { 2 };
+    std::atomic<bool>  vcaBypass        { false };
+
+    // --- Transformer ---
+    std::atomic<int>   transformerType  { 0 };   // 0=Off, 1=Nickel, 2=Iron, 3=Steel
+
+    // --- Output / Global ---
+    std::atomic<float> outputGainDb     { 0.0f };
+    std::atomic<bool>  stereoLink       { true };
+    std::atomic<bool>  globalBypass     { false };
+
+    // --- Metering (audio → GUI) ---
+    std::atomic<float> optoGrDb         { 0.0f };
+    std::atomic<float> vcaGrDb          { 0.0f };
+    std::atomic<float> outputLevelL     { 0.0f };
+    std::atomic<float> outputLevelR     { 0.0f };
+
+    // Lookup tables
+    static constexpr float ratios[]   = { 1.2f, 2.0f, 3.0f, 4.0f, 6.0f, 10.0f, 20.0f };
+    static constexpr float attacks[]  = { 0.0001f, 0.0005f, 0.001f, 0.005f, 0.01f, 0.03f };
+    static constexpr float releases[] = { 0.1f, 0.25f, 0.5f, 0.8f, 1.2f, -1.0f }; // -1 = Dual
+    static constexpr int numRatios   = 7;
+    static constexpr int numAttacks  = 6;
+    static constexpr int numReleases = 6;
+
+private:
+    double currentSampleRate = 44100.0;
+
+    // Per-channel DSP
+    std::array<OpticalCell, 2> optoCells;
+    std::array<VCACompressor, 2> vcaComps;
+    TransformerSaturation transformer;
+
+    // Sidechain HPF (2nd order, per channel)
+    std::array<juce::dsp::IIR::Filter<float>, 2> scHpfFilters;
+    float lastScHpfFreq = 0.0f;
+
+    void updateScHpf (float freqHz);
+};