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/engine/AGENTS.md

@@ -3,16 +3,16 @@
 ## Related source files
 
 This directory contains guidance; the implementation remains in `../Engine.h`
-and `../Engine.cpp`. The preparation rules below are requirements for changes;
-current buffer resizing and lazy wavetable issues are recorded in the root AGENT.md.
+and `../Engine.cpp`.
 
 ## Rules
 
 - Own the voice pool, LFOs, wavetable library, FX rack, matrix and macros by value.
-- Read every APVTS value through the null-guarding `v()` helper.
-- Build the `RenderContext` once per block and pass it to voices as `const&`.
-- Size `mixBuffer` once in `prepare()` and only `clear()` it per block.
-- Prebuild wavetables in `prepare()` before the first render.
+- Bind APVTS pointers in `prepare()`; `v()` reads captured values without constructing parameter-name strings.
+- Build the `RenderContext` once per host block and refresh its modulation inputs for each render segment.
+- Render up to 64 samples at a time, splitting at MIDI event offsets and respecting prepared buffer capacity.
+- Size `mixBuffer` once in `prepare()`; use non-owning views for shorter segments.
+- Prebuild wavetables in the Engine constructor, before either GUI painting or audio rendering can read them.
 - Clamp the final output with the soft limiter.
 - Never call `setSize` on any buffer inside `processBlock`.
 
@@ -33,16 +33,18 @@ void processBlock (...)
 ```
 
 ```cpp
-// GOOD: size once, clear per block
+// GOOD: size once, then wrap a non-owning view per segment
 void prepare (double sr, int blockSize)
 {
     mixBuffer.setSize (2, blockSize, false, false, true);
 }
 void processBlock (...)
 {
-    mixBuffer.clear();
+    // No allocation; the view only borrows mixBuffer's channels.
+    juce::AudioBuffer<float> block (mixBuffer.getArrayOfWritePointers(), 2, segmentLength);
+    block.clear();
     ...
 }
 ```
 
-This file overrides /AGENT.md where they conflict.
+This file overrides /AGENTS.md where they conflict.