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/FXProcessor.cpp

@@ -33,17 +33,18 @@ FXProcessor::~FXProcessor() = default;
 void FXProcessor::prepare (double sampleRate, int maxBlockSize)
 {
     for (auto& slotUnits : units)
-        for (auto& u : slotUnits)
-            u->prepare (sampleRate, maxBlockSize);
+        for (auto& unit : slotUnits)
+            unit->prepare (sampleRate, maxBlockSize);
     wet.setSize (2, maxBlockSize, false, false, true);
     reset();
 }
 
 void FXProcessor::reset()
 {
-    for (auto& u : units)
-        u->reset();
-    dry.clear();
+    for (auto& slotUnits : units)
+        for (auto& unit : slotUnits)
+            unit->reset();
+    activeTypes.fill ((int) FxType::Off);
     wet.clear();
 }
 
@@ -61,52 +62,50 @@ juce::String FXProcessor::fxTypeName (int type)
         case FxType::Compressor: return "Compressor";
         case FxType::Delay:      return "Delay";
         case FxType::Reverb:     return "Reverb";
+        case FxType::Count:      return {};
         default:                 return {};
     }
 }
 
 void FXProcessor::process (juce::AudioBuffer<float>& buffer, const FxSlotParams* slots, int numSlots)
 {
+    // The rack is stereo end to end; a mono buffer would read a channel that is not there.
+    jassert (buffer.getNumChannels() >= 2);
+    if (buffer.getNumChannels() < 2)
+        return;
+
     const int n = buffer.getNumSamples();
+    jassert (n <= wet.getNumSamples());
     if (n <= 0)
         return;
 
-    for (int s = 0; s < numSlots; ++s)
+    for (int s = 0; s < juce::jmin (numSlots, kNumFxSlots); ++s)
     {
         const FxSlotParams& slot = slots[s];
-        if (slot.type == (int) FxType::Off)
-            continue;
-
         const int unitIdx = slot.type - 1;
-        if (unitIdx < 0 || unitIdx >= (int) units.size())
+        if (unitIdx < 0 || unitIdx >= kNumEffectTypes)
+        {
+            activeTypes[(size_t) s] = (int) FxType::Off;
             continue;
+        }
 
-        dry.copyFrom (0, 0, buffer, 0, 0, n);
-        dry.copyFrom (1, 1, buffer, 1, 0, n);
+        auto& unit = *units[(size_t) s][(size_t) unitIdx];
+        if (activeTypes[(size_t) s] != slot.type)
+        {
+            unit.reset();
+            activeTypes[(size_t) s] = slot.type;
+        }
         wet.copyFrom (0, 0, buffer, 0, 0, n);
-        wet.copyFrom (1, 1, buffer, 1, 0, n);
-
-        units[(size_t) unitIdx]->process (wet.getWritePointer (0), wet.getWritePointer (1), n, slot.p);
+        wet.copyFrom (1, 0, buffer, 1, 0, n);
+        unit.process (wet.getWritePointer (0), wet.getWritePointer (1), n, slot.p);
 
         const float mix = juce::jlimit (0.0f, 1.0f, slot.mix);
-        if (mix >= 1.0f)
+        for (int ch = 0; ch < 2; ++ch)
         {
-            buffer.copyFrom (0, 0, wet, 0, 0, n);
-            buffer.copyFrom (1, 0, wet, 1, 0, n);
-        }
-        else if (mix > 0.0f)
-        {
-            const float* dL = dry.getReadPointer (0);
-            const float* dR = dry.getReadPointer (1);
-            const float* wL = wet.getReadPointer (0);
-            const float* wR = wet.getReadPointer (1);
-            float* oL = buffer.getWritePointer (0);
-            float* oR = buffer.getWritePointer (1);
+            float* out = buffer.getWritePointer (ch);
+            const float* effect = wet.getReadPointer (ch);
             for (int i = 0; i < n; ++i)
-            {
-                oL[i] = dL[i] * (1.0f - mix) + wL[i] * mix;
-                oR[i] = dR[i] * (1.0f - mix) + wR[i] * mix;
-            }
+                out[i] = out[i] * (1.0f - mix) + effect[i] * mix;
         }
     }
 }