Add comprehensive Windows build fix summary documentation

Co-authored-by: shauneccles <21007065+shauneccles@users.noreply.github.com>

Author: Copilot

WINDOWS_BUILD_FIX_SUMMARY.md

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+# Windows Build Fix Summary
+
+## Problem
+GitHub Actions Windows builds were failing with linker errors during Python extension compilation.
+
+## Investigation Process
+
+### Initial Error Analysis  
+Examined workflow run logs showing 7 unresolved SLEEF DFT symbols:
+- `__imp_Sleef_malloc`
+- `__imp_Sleef_free`
+- `__imp_SleefDFT_double_init1d`
+- `__imp_SleefDFT_double_execute`
+- `__imp_SleefDFT_float_init1d`
+- `__imp_SleefDFT_float_execute`
+- `__imp_SleefDFT_dispose`
+
+### Root Cause Identification
+The `__imp_` prefix indicated Windows linker was expecting DLL import symbols, not static library symbols. This revealed:
+
+1. **vcpkg's rubberband** on Windows is built expecting SLEEF as a DLL
+2. **Our static triplet** (`x64-windows-static-msvc-release.cmake`) tries to link everything statically
+3. **Fundamental incompatibility**: rubberband.lib references SLEEF with DLL import symbols even when SLEEF static libraries are present
+
+This is a **vcpkg packaging limitation**, not a build system configuration issue.
+
+## Solution Implemented
+
+### Commit 1: f234ec3 - Platform-specific library dependencies
+Added Windows system libraries required by FFmpeg when statically linking:
+- `ws2_32`: Winsock2 networking
+- `secur32`: Security Support Provider (SSPI/TLS)
+- `bcrypt`: Cryptography API
+- `mfuuid`, `strmiids`: Media Foundation GUIDs
+- `ole32`: Component Object Model
+
+Also added:
+- Linux: `pthread` and `libstdc++` for FFmpeg and rubberband C++ code
+- SLEEF DFT library detection (conditional on rubberband being found)
+
+### Commit 2: 78c2f7a - Remove rubberband from Windows
+After determining rubberband cannot be statically linked on Windows:
+- Changed vcpkg.json platform filters from `"!linux"` to `"osx"`
+- Affects: rubberband and sleef packages
+- Created documentation: WINDOWS_RUBBERBAND_REMOVAL.md
+
+## Impact
+
+### Functionality Changes
+- ✅ Windows builds will succeed
+- ❌ Windows loses rubberband time-stretch and pitch-shift effects
+- ✅ Core aubio functionality unchanged (onset, pitch detection, tempo, MFCC, etc.)
+- ✅ macOS retains full rubberband support
+- ✅ Linux unaffected (already didn't have rubberband)
+
+### Platform Matrix
+| Platform | Rubberband | Time-stretch | Pitch-shift |
+|----------|-----------|--------------|-------------|
+| Windows  | ❌        | Dummy impl   | Dummy impl  |
+| macOS    | ✅        | Full support | Full support|
+| Linux    | ❌        | Dummy impl   | Dummy impl  |
+
+## Technical Details
+
+### Why Not Fix vcpkg?
+Fixing this properly would require:
+1. Modifying vcpkg's rubberband port
+2. Ensuring SLEEF builds without DLL import expectations
+3. Testing across multiple Windows configurations
+4. Contributing changes upstream
+5. Waiting for vcpkg release cycle
+
+This is outside the scope of immediate CI fixes.
+
+### Why Not Use Dynamic Linking?
+- Defeats purpose of portable Python wheels
+- Requires bundling DLLs
+- Increases package size and complexity
+- Makes distribution error-prone
+
+### Why Not Use MinGW?
+- MSVC is the standard Windows toolchain
+- Better compatibility with vcpkg packages (especially FFmpeg)
+- Would require significant build system rework
+
+## Files Modified
+
+1. **vcpkg.json**: Platform filters for rubberband and sleef
+2. **python/meson.build**: Windows system library dependencies  
+3. **meson.build**: SLEEF DFT library detection
+4. **WINDOWS_RUBBERBAND_REMOVAL.md**: Detailed rationale documentation
+
+## Verification
+
+Expected build behavior:
+1. vcpkg skips rubberband/sleef installation on Windows
+2. Meson detects rubberband as "not found"
+3. `HAVE_RUBBERBAND` not defined in config.h
+4. Dummy timestretch/pitchshift implementations compile
+5. Python extension links successfully with FFmpeg system libraries
+6. Wheels build and package correctly
+
+## Future Work
+
+If rubberband on Windows becomes critical:
+- Investigate vcpkg rubberband port modifications
+- Consider contributing fix to vcpkg upstream
+- Or implement alternative pure-Python time-stretching solution