chore: land janitor round 1 and graft integration

Round 1 findings and fixes, all previously uncommitted:
- FXProcessor per-slot DSP history repair (HEAD does not compile without it)
- SynthVoice::getModulationValue, editor control-lock guard
- ExactCompare.h naming the deliberate exact float comparisons
- KnobLookAndFeel replacing the never-installed SerumLookAndFeel
- 55 first-party compiler warnings to 0
- AGENT.md renamed to AGENTS.md across Source/
- graft repository context graph and its hooks
- JANITOR_TASKS.md and UI_UX_AUDIT.md records

Source/Filter.cpp

@@ -1,4 +1,5 @@
 #include "Filter.h"
+#include "ExactCompare.h"
 
 namespace serum
 {
@@ -18,14 +19,13 @@ namespace
     }
 }
 
-void Filter::prepare (double sampleRate, int maxBlockSize)
+void Filter::prepare (double sampleRate)
 {
     sr = sampleRate;
     combLine.assign ((size_t) sampleRate, 0.0f);   // 1 second of delay
     combWrite = 0;
     combDamp  = 0.0;
     reset();
-    (void) maxBlockSize;
 }
 
 void Filter::reset()
@@ -38,14 +38,22 @@ void Filter::reset()
     a1 = a2 = a3 = 0.0;
     stage.fill (0.0);
     for (auto& s : formantState) s.fill (0.0);
-    std::fill (combLine.begin(), combLine.end(), 0.0f);
+    // combLine is one second of samples per filter, and a preset change now
+    // resets on the audio thread. It only needs clearing when the comb has
+    // actually written to it.
+    if (combDirty)
+    {
+        std::fill (combLine.begin(), combLine.end(), 0.0f);
+        combDirty = false;
+    }
     combWrite = 0;
     combDamp  = 0.0;
 }
 
 void Filter::updateCoefficients (float cutoffHz, float res, int type) noexcept
 {
-    if (cutoffHz == lastCutoffHz && res == lastRes && type == lastType)
+    // Cache key: rebuild coefficients only when a parameter actually changes.
+    if (! changed (cutoffHz, lastCutoffHz) && ! changed (res, lastRes) && type == lastType)
         return;
     lastCutoffHz = cutoffHz;
     lastRes = res;
@@ -89,6 +97,8 @@ void Filter::updateCoefficients (float cutoffHz, float res, int type) noexcept
             updateSvf (g, k);
             break;
         }
+        case FilterModel::Comb:
+        case FilterModel::Count:
         default:
             break;
     }
@@ -96,7 +106,8 @@ void Filter::updateCoefficients (float cutoffHz, float res, int type) noexcept
 
 void Filter::updateSvf (double g, double k) noexcept
 {
-    if (g == lastG && k == lastK)
+    // Cache key: the SVF coefficients only change with g and k.
+    if (! changed (g, lastG) && ! changed (k, lastK))
         return;
     lastG = g;
     lastK = k;
@@ -105,17 +116,6 @@ void Filter::updateSvf (double g, double k) noexcept
     a3 = g * a2;
 }
 
-double Filter::svfLow (double in, double g, double k) noexcept
-{
-    updateSvf (g, k);
-    const double v3 = in - ic2eq;
-    const double v1 = a1 * ic1eq + a2 * v3;
-    const double v2 = ic2eq + a2 * ic1eq + a3 * v3;
-    ic1eq = 2.0 * v1 - ic1eq;
-    ic2eq = 2.0 * v2 - ic2eq;
-    return v2;
-}
-
 double Filter::svfBand (double in, double g, double k) noexcept
 {
     updateSvf (g, k);
@@ -127,17 +127,6 @@ double Filter::svfBand (double in, double g, double k) noexcept
     return v1;
 }
 
-double Filter::svfHigh (double in, double g, double k) noexcept
-{
-    updateSvf (g, k);
-    const double v3 = in - ic2eq;
-    const double v1 = a1 * ic1eq + a2 * v3;
-    const double v2 = ic2eq + a2 * ic1eq + a3 * v3;
-    ic1eq = 2.0 * v1 - ic1eq;
-    ic2eq = 2.0 * v2 - ic2eq;
-    return in - k * v1 - v2;
-}
-
 double Filter::ladder (double in, double g, double res, double drive, int stages, bool diode) noexcept
 {
     stages = juce::jlimit (1, 4, stages);
@@ -193,6 +182,7 @@ double Filter::comb (double in, double freqHz, double res, double drive) noexcep
     const float feedback = clampF ((float) res * 0.9f, 0.0f, 0.98f);
     combLine[(size_t) combWrite] = (float) in + (float) combDamp * feedback;
     combWrite = (combWrite + 1) % len;
+    combDirty = true;
 
     return (double) y;
 }
@@ -204,12 +194,12 @@ double Filter::formant (double in) noexcept
     for (int i = 0; i < 3; ++i)
     {
         const auto& c = formantCoefficients[(size_t) i];
-        const double a1 = c[0];
-        const double a2 = c[1];
-        const double a3 = c[2];
+        const double c0 = c[0];
+        const double c1 = c[1];
+        const double c2 = c[2];
         const double v3 = in - formantState[(size_t) i][1];
-        const double v1 = a1 * formantState[(size_t) i][0] + a2 * v3;
-        const double v2 = formantState[(size_t) i][1] + a2 * formantState[(size_t) i][0] + a3 * v3;
+        const double v1 = c0 * formantState[(size_t) i][0] + c1 * v3;
+        const double v2 = formantState[(size_t) i][1] + c1 * formantState[(size_t) i][0] + c2 * v3;
         formantState[(size_t) i][0] = 2.0 * v1 - formantState[(size_t) i][0];
         formantState[(size_t) i][1] = 2.0 * v2 - formantState[(size_t) i][1];
         out += v1 * gains[i];
@@ -269,6 +259,7 @@ float Filter::processSample (float in, float cutoffHz, float res, float drive, i
         case FilterModel::Screamer:
             out = screamer (in, drive);
             break;
+        case FilterModel::Count:
         default:
             break;
     }