This adds filesystem detection logic to Bun's cache directory so that
the cache is placed on the same mount/filesystem as the install location
(node_modules). This enables efficient hardlink creation during package
installation.
Key changes:
- Add filesystem_utils.zig with utilities for filesystem detection
- Update PackageManagerDirectories to check filesystem boundaries
- Add fetchCacheDirectoryPathWithInstallDir that considers install location
- Add findOptimalCacheDir to walk up directory tree for writable cache location
- Add comprehensive tests for filesystem-aware cache behavior
The implementation will:
1. Use default cache when on same filesystem as node_modules
2. Find optimal cache location on same filesystem when different
3. Walk up from mount point toward project to find writable location
4. Fall back to project-local cache if no suitable location found
5. Respect explicit BUN_INSTALL_CACHE_DIR settings
🤖 Generated with Claude Code
Co-Authored-By: Claude <noreply@anthropic.com>
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