Bug: After brain.clear(), VFS operations failed with
"Source entity 00000000-0000-0000-0000-000000000000 not found"
Root causes fixed:
- VFS instance remained in memory pointing to deleted root entity
- FileSystemStorage.clear() set blobStorage=undefined but didn't reinit
- Write-through cache returned stale entity data after clear()
Changes:
- Re-initialize COW (BlobStorage) after storage.clear() in brainy.ts
- Reset and reinitialize VFS following checkout() pattern
- Add clearWriteCache() to BaseStorage, call in Memory/FileSystem adapters
- Add 7 integration tests for VFS clear functionality
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
