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.
Tests for the entire crypto/ public surface, written against the API
shape declared in the README. The accompanying src/crypto/ modules are
stubs that throw 'not implemented' so the test files compile and tests
fail with clear errors rather than module-not-found.
Tests cover:
* init() resolves and is idempotent
* fromBase64 / toBase64 / toBase64URL round-trips, including URL-safe
input with stripped padding (the form Ente uses for auth tokens)
* deriveKEK matches sodium.crypto_pwhash with Argon2id parameters
* deriveLoginSubkey matches sodium.crypto_kdf_derive_from_key with
subkey id 1 and ctx 'loginctx', truncated to 16 bytes
* decryptBox round-trips, rejects tampering, wrong key, wrong nonce
* decryptSealed round-trips, rejects wrong keypair and tampering
* Secretstream pull decrypts multi-chunk streams in order, exposes
per-chunk tags, rejects tampering, wrong key, and out-of-order chunks
* Constants STREAM_CHUNK_SIZE (4 MiB) and STREAM_CHUNK_OVERHEAD (17)
Tests are commented to serve as the canonical API documentation per the
README development workflow policy. Verified: 29 tests fail (red), 3
trivial constant tests pass; lint and fmt-check are green.
eslint.config.mjs is updated to honour the leading-underscore convention
for intentionally unused parameters (the stubs).
