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/OpticalCell.h

@@ -0,0 +1,71 @@
+#pragma once
+#include <cmath>
+#include <algorithm>
+
+// ============================================================
+// Port-Hamiltonian T4B Electro-Optical Compressor Model
+//
+// Models the EL panel (capacitive energy store) coupled to a
+// CdS photoresistor (nonlinear dissipation) using implicit
+// trapezoidal integration with Newton-Raphson iteration.
+//
+// All parameters are normalized for audio-level (0..1) operation.
+// ============================================================
+class OpticalCell
+{
+public:
+    OpticalCell();
+
+    void prepare (double sampleRate);
+    void reset();
+
+    // Process one sample: sidechain input (linear), returns gain (0..1)
+    float processSample (float sidechainLevel, float thresholdLinear);
+
+    // Current GR in dB (for metering, always <= 0)
+    float getGainReductionDb() const;
+
+private:
+    double sr = 44100.0;
+    double dt = 1.0 / 88200.0;  // 2x oversampled time step
+
+    // ---- Port-Hamiltonian State (normalized units) ----
+
+    // EL panel: capacitive energy store
+    double q_el = 0.0;          // charge state
+    double C_el = 0.01;         // capacitance (~10ms attack with R_el=1)
+    double R_el = 1.0;          // series resistance (normalized)
+    double eta_el = 50.0;       // electro-optical efficiency (scaled for audio levels)
+
+    // CdS photoresistor: nonlinear dissipation
+    double R_cds = 100.0;       // current resistance (normalized)
+    double R_cds_dark = 100.0;  // dark resistance (no light → no compression)
+    double R_cds_min = 0.01;    // minimum resistance (max compression)
+    double k_cds = 1.0;         // CdS scaling factor
+    double gamma = 0.7;         // CdS nonlinearity exponent
+
+    // Memory effect (CdS illumination history)
+    double lightHistory = 0.0;
+    double memoryTau = 2.0;     // memory time constant (seconds)
+    double memoryAlpha = 0.3;   // history influence factor
+
+    // Light state
+    double lightOutput = 0.0;
+
+    // Signal path impedance for gain (normalized)
+    double R_fixed = 1.0;
+
+    // Current gain (linear)
+    double currentGain = 1.0;
+
+    // Implicit solver
+    static constexpr int maxNewtonIter = 5;
+    static constexpr double newtonTol = 1.0e-8;
+
+    // 2x oversampling
+    float prevInput = 0.0f;
+
+    // Core methods
+    void solveImplicitStep (double inputLevel);
+    void updateGain();
+};