Root cause: SevenZip.initSevenZipFromPlatformJAR() was never called, so
native compression codecs (RAR5, LZMA2, etc.) were not loaded. Archives
could be opened (header parsing is pure Java) but all extractSlow() calls
returned UNSUPPORTEDMETHOD because no native decoder was available.
- Add ensureSevenZipInitialized() with lazy init before extraction
- Pass password to extractSlow(outStream, password) for RAR5 compatibility
- Add UNSUPPORTEDMETHOD -> legacy fallback in extractor.ts as safety net
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>