formatOf matched .tar.gz/.tgz as a combined format and then fell through to the bare .bz2 and .xz wrappers, so a .tar.bz2 was read as one compressed file: extracting it decompressed a single layer and left a .tar to extract again, while the same archive named .tar.gz unpacked in one step. The store listing advertised "extract ZIP, TAR, TAR.GZ, GZ, BZ2, XZ and 7z", which reads as though they all behave alike.
Found by extracting one archive of every supported format through the UI on the API 35 AVD rather than trusting the suite. A real z4.tar.bz2 left z4/z4.tar - raw ustar headers and all - beside z3.tar.gz fully unpacked to z3/a.txt and z3/sub/b.txt.
TAR_BZIP2 and TAR_XZ now sit alongside TAR_GZIP, detection consumes the whole tar suffix (.tar.bz2/.tbz2, .tar.xz/.txz) before the bare compressor, and the engine gains the two readArchive branches. The bare spellings still mean a single compressed file.
The suite had a gap that let this hide: only ZIP, GZIP, XZ and 7z had round-trip tests, so neither plain TAR nor TAR_GZIP did, and there was nothing for the asymmetry to contradict. All four tar spellings have one now, built in memory with the same library that reads them. 212 JVM tests, lint clean.
Also records the format sweep in EDGE_CASE_TESTING and re-measures the release artefacts (aab 4 838 235 / sha256 e1d23130..., apk 2 155 455 / sha256 37fb46cb...). The APK byte count happened to land on the same figure as the previous build, so the new literals were confirmed present in the shipped dex rather than trusted to the size.
The manifest had nothing but a LAUNCHER filter, so no other app could hand Plain Files anything. It now registers for ACTION_SEND and SEND_MULTIPLE (a bar over the browser: navigate to the folder, then Save here) and for GET_CONTENT and OPEN_DOCUMENT, where tapping a file hands it back through the existing FileProvider.
Both reuse the browser instead of a second screen, because both are navigate-to-a-folder with a different verb at the end. data/ gains one port, IncomingSource, to keep a ContentResolver out of the ViewModel the way DeleteRequestFactory keeps one out of the delete path. Shared files are named from the sender OpenableColumns, allocated by the same NameAllocator a paste uses, and deleted again if they cannot be read rather than left as zero-byte stubs. While providing, a tap on a file chooses it but a tap on a folder still navigates, or the user could never reach the file.
ACTION_VIEW is deliberately not registered: the app already hands files out through the system chooser, and registering as a viewer would offer Plain Files back to itself. No new permissions - the merged release manifest still declares no INTERNET.
Commons Compress declares its LZMA/LZMA2 support against org.tukaani:xz as an *optional* dependency, so nothing pulled it in transitively and nothing failed at build time. The app nevertheless advertised .xz as extractable, so the first user to open one would have got NoClassDefFoundError: org/tukaani/xz/FilterOptions. XZCompressorInputStream references org/tukaani/xz/XZInputStream directly. The library is now declared, and a round-trip test covers the path that was silently missing.
That same library is what 7z needs, and Commons Compress already ships a pure-Java 7z reader, so 7z extraction costs no native code and no further dependency. The docs had assumed the format was off limits and said so in three places, including the customer-facing store copy.
7z is the only format here that cannot arrive through a stream: its header sits at the end of the file, so the reader has to seek. That is now a capability the backend advertises, StorageSource.openSeekable: the all-files backend answers with a real FileChannel, the SAF fallback with null, so folder mode reports needs-a-seekable-file instead of failing obscurely. Entry names go through the same ArchivePath.safeRelativePath zip-slip guard. 7z creation stays deferred.
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