build: split the 1423-line root CMakeLists into per-directory files with shared target helpers

src/core/instrument/engine/CMakeLists.txt

@@ -0,0 +1,26 @@
+# The shifter is hand-rolled rather than WDL_SimplePitchShifter because that header drags
+# <windows.h> in via wdltypes.h, which cannot enter the pure engine.
+reasampler_pure_library(pitch_shift SOURCES pitch_shift.cpp LINK PUBLIC peaks)
+# Links only pitch_shift: linking more would break the plain-data-boundary proof — and
+# specifically the compile-time proof it does not drag in the WDL <windows.h> chain.
+reasampler_test(pitch_shift LINK pitch_shift)
+
+reasampler_pure_library(velocity_curve SOURCES velocity_curve.cpp)
+# Links only velocity_curve, deliberately not editor_geometry: the proof the engine can
+# depend on the curve without inheriting the editor's layout types.
+reasampler_test(velocity_curve LINK velocity_curve)
+
+reasampler_pure_library(master_gain SOURCES master_gain.cpp)
+reasampler_test(master_gain LINK master_gain)
+
+# Two TUs on the engine's own responsibility seam (per-note setup vs. note routing and
+# block render). The per-sample render half stays inline in voice.h precisely so this TU
+# boundary costs the hot path nothing.
+reasampler_pure_library(sampler_core
+    SOURCES voice.cpp voice_engine.cpp
+    LINK PUBLIC peaks pitch_shift velocity_curve)
+# Links only sampler_core: linking more would break the plain-data-boundary proof — a VST3
+# or REAPER type reaching the core would fail to compile or link here.
+reasampler_test(sampler_core LINK sampler_core)
+
+add_subdirectory(filter)

src/core/instrument/engine/filter/CMakeLists.txt

@@ -0,0 +1,15 @@
+# Control mapping, SVF coefficients, morph weights, and the filter type each get their own
+# TU; VoiceFilter::process stays header-inline so the kernel still inlines at the call site.
+reasampler_pure_library(filter SOURCES
+    filter_params.cpp
+    filter_coeffs.cpp
+    filter_morph.cpp
+    voice_filter.cpp)
+
+# Four test targets along the module's own seams so each asserts one domain. filter_tests
+# alone owns the analytic reference and the steady-state gain measurement — a forked copy of
+# a measurement reference is a worse defect than a long file.
+reasampler_test(filter_params LINK filter)
+reasampler_test(filter_morph LINK filter)
+reasampler_test(filter_state LINK filter)
+reasampler_test(filter LINK filter)