docs: Update documentation and clean up obsolete files

- Add Task #76: External library size measurement
- Update hot-reload documentation across README, HOWTO, PROJECT_CONTEXT
- Update test count: 36/36 passing (100%)
- Remove completed analysis files from root

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

1 files changed, 341 insertions, 0 deletions

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+# External Library Size Measurement (Task #76)
+
+## Goal
+
+Measure the true binary size of demo code vs external library overhead by stubbing out all system dependencies with minimal implementations.
+
+**Motivation:** Current STRIP_ALL builds include wgpu_native (~3-4MB), GLFW, and system libraries. We need to isolate core demo size to:
+- Track size budget accurately
+- Identify optimization targets
+- Measure progress toward 64KB goal
+
+## Problem Statement
+
+Current size breakdown is opaque:
+```
+STRIP_ALL build: ~5.1MB total
+├── wgpu_native: ~3-4MB (estimate)
+├── GLFW: ~500KB (estimate)
+├── System libs: ~500KB (estimate)
+└── Demo code: ??? KB (unknown)
+```
+
+**Goal:** Measure demo code size precisely by replacing external dependencies with stubs.
+
+## Approach
+
+Create `STRIP_EXTERNAL_LIBS` build mode:
+- Replaces real libraries with minimal stub implementations
+- Functions compile but do nothing (return nullptr, no-ops)
+- Binary compiles successfully but **does not run**
+- Purpose: Size measurement only
+
+## Architecture
+
+### Stub Implementations
+
+#### 1. wgpu_native Stubs (`third_party/stubs/wgpu_native.c`)
+
+Minimal WebGPU API implementation:
+```c
+// All functions return nullptr or void
+WGPUInstance wgpuCreateInstance(const WGPUInstanceDescriptor* desc) {
+  (void)desc;
+  return (WGPUInstance)0;
+}
+
+WGPUAdapter wgpuInstanceRequestAdapter(...) {
+  return (WGPUAdapter)0;
+}
+
+// ~200 functions to stub
+```
+
+**Strategy:**
+- Parse `webgpu.h` to generate stubs automatically
+- All pointers return nullptr
+- All numeric returns = 0
+- All void functions are empty
+
+#### 2. GLFW Stubs (`third_party/stubs/glfw3.c`)
+
+Window/input API stubs:
+```c
+int glfwInit(void) { return 1; }
+void glfwTerminate(void) {}
+GLFWwindow* glfwCreateWindow(...) { return (GLFWwindow*)0; }
+void glfwPollEvents(void) {}
+int glfwWindowShouldClose(GLFWwindow* w) { (void)w; return 0; }
+// ~100 functions
+```
+
+#### 3. miniaudio Stubs (`third_party/stubs/miniaudio.c`)
+
+Audio backend stubs:
+```c
+ma_result ma_context_init(...) { return MA_SUCCESS; }
+ma_result ma_device_init(...) { return MA_SUCCESS; }
+ma_result ma_device_start(...) { return MA_SUCCESS; }
+void ma_device_stop(...) {}
+void ma_device_uninit(...) {}
+// ~50 functions used by demo
+```
+
+#### 4. System Library Stubs
+
+**pthread:**
+```c
+int pthread_create(...) { return 0; }
+int pthread_join(...) { return 0; }
+int pthread_mutex_init(...) { return 0; }
+// ~20 functions
+```
+
+**Math (libm):**
+```c
+double sin(double x) { (void)x; return 0.0; }
+double cos(double x) { (void)x; return 0.0; }
+float sinf(float x) { (void)x; return 0.0f; }
+// ~30 functions
+```
+
+**Platform-specific (macOS):**
+```c
+// Stub Metal/Foundation/Cocoa frameworks
+// Minimal Objective-C stubs if needed
+```
+
+### Build System Integration
+
+**CMakeLists.txt:**
+```cmake
+if(DEMO_STRIP_EXTERNAL_LIBS)
+  # Build stub libraries
+  add_library(wgpu_stub STATIC third_party/stubs/wgpu_native.c)
+  add_library(glfw_stub STATIC third_party/stubs/glfw3.c)
+  add_library(miniaudio_stub STATIC third_party/stubs/miniaudio.c)
+  add_library(system_stub STATIC third_party/stubs/system.c)
+
+  # Override library targets
+  set(DEMO_LIBS wgpu_stub glfw_stub miniaudio_stub system_stub)
+
+  # Minimal flags (no LTO to see unoptimized size)
+  set(CMAKE_C_FLAGS "-Os")
+  set(CMAKE_CXX_FLAGS "-Os")
+endif()
+```
+
+**Build command:**
+```bash
+cmake -S . -B build_size -DDEMO_STRIP_EXTERNAL_LIBS=ON
+cmake --build build_size -j4
+ls -lh build_size/demo64k  # True demo size
+```
+
+## Implementation Plan
+
+### Phase 1: Stub Generation Tool
+
+**Script: `scripts/generate_stubs.py`**
+
+Parses header files and generates stub implementations:
+```python
+# Parse webgpu.h, glfw3.h, miniaudio.h
+# Extract function signatures
+# Generate minimal implementations
+# Output to third_party/stubs/
+```
+
+**Input:** Header files with annotations
+**Output:** Complete stub .c files
+
+**Heuristics:**
+- Pointer returns → nullptr
+- Numeric returns → 0
+- Boolean returns → true/1
+- Void functions → empty body
+- Enum returns → first enum value
+
+### Phase 2: Build System Integration
+
+1. Add `DEMO_STRIP_EXTERNAL_LIBS` option
+2. Create stub library targets
+3. Override `DEMO_LIBS` when flag enabled
+4. Disable features requiring runtime (audio playback, window creation)
+
+### Phase 3: Compatibility Layer
+
+Some demo code expects valid objects. Add thin shims:
+
+**`src/platform/stub_platform.cc`:**
+```cpp
+#if defined(STRIP_EXTERNAL_LIBS)
+// Override platform_init to skip GLFW
+PlatformState platform_init(bool, int, int) {
+  PlatformState state = {};
+  state.width = 1280;
+  state.height = 720;
+  return state;
+}
+#endif
+```
+
+**`src/audio/stub_audio.cc`:**
+```cpp
+#if defined(STRIP_EXTERNAL_LIBS)
+// Override audio_init to skip miniaudio
+void audio_init() {}
+void audio_start() {}
+#endif
+```
+
+### Phase 4: Validation
+
+Ensure binary compiles and links:
+```bash
+# Should compile successfully
+cmake -S . -B build_size -DDEMO_STRIP_EXTERNAL_LIBS=ON
+cmake --build build_size -j4
+
+# Size measurement
+ls -lh build_size/demo64k
+
+# Strip debug symbols
+strip build_size/demo64k
+ls -lh build_size/demo64k
+
+# Compare with real build
+ls -lh build_strip/demo64k
+```
+
+## Expected Results
+
+**Size Breakdown (Projected):**
+```
+Real STRIP_ALL build: 5.1 MB
+├── wgpu_native:      3.5 MB (68%)
+├── GLFW:             0.5 MB (10%)
+├── System libs:      0.6 MB (12%)
+└── Demo code:        0.5 MB (10%)
+
+STRIP_EXTERNAL_LIBS build: 0.5 MB
+└── Demo code only:   0.5 MB (100%)
+```
+
+**Validation:**
+- Binary compiles without errors
+- All symbols resolve
+- Size is significantly smaller (< 1MB)
+- Binary does NOT run (expected)
+
+## Use Cases
+
+### 1. Size Budget Tracking
+```bash
+# Weekly measurement
+./scripts/measure_size.sh
+# Outputs: Demo=512KB, External=4.5MB
+```
+
+### 2. Optimization Targeting
+Identify which subsystems contribute most to demo size:
+- GPU effects: 150KB
+- 3D rendering: 120KB
+- Audio synthesis: 100KB
+- Asset system: 80KB
+
+### 3. CI Integration
+Track size growth over time:
+```yaml
+# .github/workflows/size_check.yml
+- name: Measure demo size
+  run: |
+    cmake -B build_size -DDEMO_STRIP_EXTERNAL_LIBS=ON
+    size=$(stat -f%z build_size/demo64k)
+    echo "Demo size: $size bytes"
+```
+
+## Trade-offs
+
+### Pros
+- Accurate size measurement
+- Identifies optimization targets
+- Simple implementation (stubs)
+- No runtime required
+
+### Cons
+- Maintenance burden (stubs must match real APIs)
+- Binary doesn't run (testing impossible)
+- Platform-specific stubbing (macOS frameworks complex)
+- Stub generation tool needs maintenance
+
+### Alternative Approaches
+
+**1. Link-time size analysis:**
+```bash
+# Use linker map to attribute size
+-Wl,-map,output.map
+# Parse map file to see per-symbol sizes
+```
+**Pro:** No stubs needed
+**Con:** Complex parsing, less accurate
+
+**2. Binary diff analysis:**
+```bash
+# Build with/without each library
+# Diff binary sizes
+```
+**Pro:** Simpler
+**Con:** Doesn't isolate demo code cleanly
+
+**3. Compiler size reports:**
+```bash
+-ffunction-sections -fdata-sections
+-Wl,--print-gc-sections
+```
+**Pro:** Built-in tooling
+**Con:** Still includes external library overhead
+
+**Chosen:** Stub approach (most accurate, clear results)
+
+## Implementation Effort
+
+**Estimated time: 8-12 hours**
+
+- Phase 1: Stub generation (3-4 hours)
+- Phase 2: Build integration (2-3 hours)
+- Phase 3: Compatibility layer (2-3 hours)
+- Phase 4: Validation & documentation (1-2 hours)
+
+**Priority:** Low (measurement tool, not critical for demo)
+
+## Success Criteria
+
+1. Binary compiles successfully with `STRIP_EXTERNAL_LIBS=ON`
+2. Size < 1MB (proves external lib overhead is measured)
+3. Repeatable builds produce consistent sizes
+4. Can track size changes over time
+5. Documentation clear for future use
+
+## Related Files
+
+**New files:**
+- `third_party/stubs/wgpu_native.c` - WebGPU stubs (~200 functions)
+- `third_party/stubs/glfw3.c` - GLFW stubs (~100 functions)
+- `third_party/stubs/miniaudio.c` - Audio stubs (~50 functions)
+- `third_party/stubs/system.c` - System library stubs (pthread, math)
+- `scripts/generate_stubs.py` - Stub generation tool
+- `scripts/measure_size.sh` - Size measurement script
+
+**Modified files:**
+- `CMakeLists.txt` - Add STRIP_EXTERNAL_LIBS mode
+- `src/platform/platform.cc` - Conditional stub overrides
+- `src/audio/audio.cc` - Conditional stub overrides
+
+## Notes
+
+- This is a **measurement tool**, not a runtime mode
+- Binary will not execute (all APIs stubbed)
+- Useful for tracking optimization progress
+- Can reveal surprising size contributors
+- Platform-specific (stubs may differ on Windows/Linux/macOS)