Phase 3 of the delta-sync plan — the inverse direction, so a future
client app holding an older local version can fetch only what changed:
- GET /api/files/{id}/manifest returns the file's chunk recipe
({file_hash, total_size, chunks}). Owner-scoped like the rest of the
delta surface (Read permission through the authz engine first, then
the chunk layer's possession standard; shared files use the regular
download endpoints). A manifest is immutable for a given file_hash,
so it is served with ETag = file_hash and If-None-Match answers 304 —
polling sync clients pay one header round-trip per unchanged file.
Legacy pre-CDC blobs are presented as a single-chunk manifest of
themselves, so clients need no special case.
- POST /api/files/delta/download streams the requested chunks as
[u32 BE length][bytes] frames in request order — the same wire format
the upload direction uses. Entitlement is the same possession rule as
negotiate/commit (chunks reachable through the caller's own files);
anything else returns 404 {not_available} — deliberately
indistinguishable from "never existed" — with a
delta_download.rejected audit event. Batches are bounded by the
chunk_max_bytes budget; Content-Length is exact (sizes come from the
dedup index) and peak RAM is one backend read frame.
Both endpoints share the delta rate limiter. New DedupService
primitives: manifest_chunk_list (with legacy fallback), chunk_sizes,
chunk_stream. OpenAPI regenerated; protocol doc gains the download
section; types.js maps the new wire shapes (plus the delta-upload
typedefs that a container reset had silently dropped from a previous
commit).
Verified end-to-end against PostgreSQL 16 with a simulated two-device
sync: device A uploaded 24 MB by bytes and delta-updated it (2 edits →
2 chunks); device B diffed the manifest against its WASM-chunked local
copy, needed 2/79 chunks, fetched 970 KB instead of 24 MB (96.1%
saved) and rebuilt the file byte-identical with the BLAKE3 verifying.
If-None-Match revalidation returned 304; a second user got 404 on both
the manifest and the chunk batch (with the not_available list and
audit lines); an unknown hash was indistinguishable from a denied one;
an empty hash list returned 400.
https://claude.ai/code/session_01WdNenpnujNR2sc32XVvwfS
Claude
ed9a204e49