Covers, for both downloadFile and downloadThumbnail:
- a multi-chunk body whose TAG_FINAL chunk never arrived is rejected
with a truncation error;
- an empty body is rejected as truncation rather than written as a
zero-byte file;
- after a truncation or chunk-authentication failure the destination
path does not exist and no temporary scratch file is left behind;
- an existing file at the destination survives a failed download
byte for byte, and is replaced atomically by a successful one;
- the existing success cases still produce identical bytes and an
identical DownloadResult.
Adds an encryptMultiChunkBody helper that frames leading chunks at
exactly STREAM_CHUNK_SIZE so the downloader's fixed-size re-splitting
lines up, plus a multi-chunk success case as the positive control.
Also pins the new STREAM_TAG_FINAL crypto export against libsodium's
own constant, since it must be declared as a literal: libsodium
attaches its constants only after sodium.ready resolves, well after
this library's modules are evaluated.
These fail until the implementation lands, per the repo's TDD workflow.
sneak
1f894bad0e