docs: Add sub-task for type-safe shader composition

Low priority task to prevent recurrent error of forgetting to call
ShaderComposer::Compose() by using strong typing (ComposedShader class).

Would make it a compile-time error instead of runtime crash.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/TODO.md b/TODO.md
index a8cfdb4..c942fb5 100644
--- a/TODO.md
+++ b/TODO.md
@@ -93,6 +93,34 @@ This file tracks prioritized tasks with detailed attack plans.
 - **Impact**: Minimal (most shaders only use CommonUniforms anyway)
 - **Priority**: Low (nice-to-have for code organization)
 
+### Sub-task: Type-safe shader composition (Low Priority)
+- **Problem**: Recurrent error of forgetting `ShaderComposer::Get().Compose({}, code)` and using raw `code` directly
+  - Happened in: `create_post_process_pipeline`, `gpu_create_render_pass`, `gpu_create_compute_pass`, `CircleMaskEffect`
+  - Runtime error only (crashes demo, but tests may pass)
+- **Solution**: Use strong typing to make it a compile-time error
+  ```cpp
+  class ComposedShader {
+   private:
+    std::string code_;
+    friend class ShaderComposer;
+    explicit ComposedShader(std::string code) : code_(std::move(code)) {}
+   public:
+    const char* c_str() const { return code_.c_str(); }
+  };
+  ```
+- **Changes needed**:
+  - `ShaderComposer::Compose()` returns `ComposedShader` instead of `std::string`
+  - All shader creation functions take `const ComposedShader&` instead of `const char*`
+  - Cannot pass raw string to shader functions (compile error)
+- **Benefits**:
+  - Impossible to forget composition (type mismatch)
+  - Self-documenting API (signature shows shader must be composed)
+  - Catches errors at compile-time instead of runtime
+- **Trade-offs**:
+  - More verbose code (`auto shader = ShaderComposer::Get().Compose(...)`)
+  - Small overhead (extra std::string copy, but negligible)
+- **Priority**: Low (recurrent but rare, easy to catch in testing)
+
 ## Phase 2: Size Optimization (Final Goal)
 
 - [ ] **Task #34: Full STL Removal**: Replace all remaining `std::vector`, `std::map`, and `std::string` usage with custom minimal containers or C-style arrays to allow for CRT replacement. (Minimal Priority - deferred to end).