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/GUI/Knob.cpp

@@ -3,6 +3,17 @@
 namespace serum
 {
 
+namespace
+{
+    // One shared look-and-feel for every knob. It outlives every Knob because
+    // it is a function-local static and the GUI owns the knobs.
+    KnobLookAndFeel& knobStyle()
+    {
+        static KnobLookAndFeel style;
+        return style;
+    }
+}
+
 Knob::Knob (const juce::String& name, std::function<juce::String (float)> fmt)
     : formatter (std::move (fmt))
 {
@@ -12,6 +23,10 @@ Knob::Knob (const juce::String& name, std::function<juce::String (float)> fmt)
     setDoubleClickReturnValue (true, 0.5);
     setName (name);
     setComponentID (name);
+
+    // Draw the dial and the name strip through the theme, not through the
+    // shared default look-and-feel.
+    setLookAndFeel (&knobStyle());
 }
 
 juce::String Knob::getTextFromValue (double value)
@@ -21,6 +36,32 @@ juce::String Knob::getTextFromValue (double value)
     return formatPercent ((float) value);
 }
 
+// The dial takes the top of the footprint and the name takes a strip at the
+// bottom, so the name is always visible without a tooltip hover.
+void Knob::resized()
+{
+    juce::Slider::resized();
+    textArea = getLocalBounds().removeFromBottom (
+        juce::jmin (KnobLookAndFeel::labelHeight, getHeight() / 2));
+}
+
+void Knob::paint (juce::Graphics& g)
+{
+    juce::Slider::paint (g);
+
+    if (textArea.isEmpty())
+        return;
+
+    // Dim while disabled, bright while hovered, otherwise the normal label
+    // colour, so the three states are distinguishable without colour alone.
+    const auto colour = isEnabled() ? (isMouseOverOrDragging() ? theme::text : theme::textDim)
+                                    : theme::outline;
+
+    g.setColour (colour);
+    g.setFont (juce::Font (11.0f));
+    g.drawText (getName(), textArea, juce::Justification::centred, false);
+}
+
 void Knob::mouseDown (const juce::MouseEvent& e)
 {
     juce::Slider::mouseDown (e);
@@ -56,6 +97,24 @@ void Knob::showValuePopup (const juce::MouseEvent& e)
     if (topLevel == nullptr)
         return;
 
+    constexpr int baseW = 84;
+    constexpr int baseH = 24;
+    constexpr int gap = 10;
+
+    // The interface scale is applied to a parent component, not to this slider.
+    // Measure it from the local-space distance between two neighbouring points,
+    // so a scaled interface does not leave the readout at a fixed size.
+    float scale = 1.0f;
+    if (auto* parent = getParentComponent())
+    {
+        const auto origin = getLocalPoint (parent, juce::Point<int> (0, 0)).toFloat();
+        const auto unitX  = getLocalPoint (parent, juce::Point<int> (1, 0)).toFloat();
+        scale = origin.getDistanceFrom (unitX);
+    }
+    scale = juce::jlimit (0.5f, 2.5f, scale);
+    const int w = juce::roundToInt (baseW * scale);
+    const int h = juce::roundToInt (baseH * scale);
+
     if (valuePopup == nullptr)
     {
         valuePopup = std::make_unique<juce::Label>();
@@ -63,19 +122,20 @@ void Knob::showValuePopup (const juce::MouseEvent& e)
         valuePopup->setInterceptsMouseClicks (false, false);
         valuePopup->setColour (juce::Label::backgroundColourId, juce::Colours::transparentBlack);
         valuePopup->setColour (juce::Label::textColourId, theme::text);
-        valuePopup->setFont (juce::Font (14.0f, juce::Font::bold));
         valuePopup->setJustificationType (juce::Justification::centred);
         topLevel->addAndMakeVisible (valuePopup.get());
     }
 
+    valuePopup->setFont (juce::Font (14.0f * scale, juce::Font::bold));
     valuePopup->setText (getTextFromValue (getValue()), juce::dontSendNotification);
 
-    constexpr int w = 84;
-    constexpr int h = 24;
-    constexpr int gap = 10;
-
-    const auto cursor = topLevel->getLocalPoint (nullptr, e.getScreenPosition());
-    valuePopup->setBounds (cursor.getX() - w / 2, cursor.getY() - h - gap, w, h);
+    // Keep the readout inside the window so a knob near an edge still shows it.
+    const auto popupPos = topLevel->getLocalPoint (nullptr, e.getScreenPosition());
+    valuePopup->setBounds (juce::jlimit (0, juce::jmax (0, topLevel->getWidth() - w),
+                                         popupPos.getX() - w / 2),
+                           juce::jlimit (0, juce::jmax (0, topLevel->getHeight() - h),
+                                         popupPos.getY() - h - gap),
+                           w, h);
 }
 
 void Knob::hideValuePopup()
@@ -83,4 +143,12 @@ void Knob::hideValuePopup()
     valuePopup.reset();
 }
 
+// A section switch can hide the view holding this knob mid-drag. The popup is a
+// sibling of that view, so it has to be taken down here or it stays on screen.
+void Knob::visibilityChanged()
+{
+    if (! isVisible())
+        hideValuePopup();
+}
+
 } // namespace serum