Refactor: HTTP handler becomes a thin shim over a pure WriteBackup(w,
userID, createdAt, iter) function. RowIterator abstracts the store, so
tests feed synthetic ChangeRow slices and production feeds
StreamAllUserChanges. Zero behavior change in production — same bytes
on the wire.
Tests (all pass):
- TestWriteBackup_Roundtrip: three rows across two apps, assert zip has
2 entries, events.jsonl has 3 JSON lines in order, insert omits
fieldTimestamps, update surfaces them, manifest apps are sorted,
eventsSha256 equals a recomputed sha of the decompressed body.
- TestWriteBackup_EmptyUser: empty userID refused up-front.
- TestWriteBackup_NoRows: zero-row export still produces a valid zip
with an empty events.jsonl and a manifest with eventCount=0 and a
non-empty sha (sha of empty input).
- TestWriteBackup_DefaultsSchemaVersionZeroRowsToOne: legacy rows with
schema_version=0 clamp to 1 so the manifest never claims a protocol
version that never existed.
Paired with the vitest zip parser suite on the TS side, this closes
the Go-writes / JS-reads round-trip without needing live mana-sync.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
