docs: document STRIP_GPU_COMPOSITE flag in BUILD.md

1 files changed, 13 insertions, 0 deletions

diff --git a/doc/BUILD.md b/doc/BUILD.md
index fd0c3d9..6537376 100644
--- a/doc/BUILD.md
+++ b/doc/BUILD.md
@@ -34,6 +34,19 @@ cmake --build build_final -j4
 
 **Note:** `DEMO_ALL_OPTIONS=ON` enables tests, tools, AND `STRIP_ALL`.
 
+### Manual Feature Stripping
+
+For additional size optimization, manually define these preprocessor flags:
+
+**`STRIP_GPU_COMPOSITE`** - Removes GPU texture compositing (~830 bytes):
+```bash
+cmake -S . -B build -DCMAKE_CXX_FLAGS="-DSTRIP_GPU_COMPOSITE"
+```
+- Strips `gen_blend_compute_wgsl` / `gen_mask_compute_wgsl` shaders
+- Removes TextureManager sampler cache & `dispatch_composite()` method
+- Disables multi-stage procedural texture composition
+- See `doc/GPU_PROCEDURAL_PHASE4.md` for details
+
 ## CMake Module Structure
 
 The build system uses a modular architecture with 10+ specialized modules. See `doc/CMAKE_MODULES.md` for: