Replaces the batched chunk-pack phase with per-chunk content-addressed
blob uploads to `blobs/<hash[:2]>/<hash[2:]>`. The metadata pack still
ships (small, fast to restore), but consumers no longer have to pull
multi-GB chunk packs to get queryable: `cold unpack --mode just-enough`
+ `ARBORIST_JIT_CHUNKS=1` fetches single chunks on cache miss.
Producer (`_stream_jit_blobs` in evict.py):
- ThreadPoolExecutor with bounded queue (workers*4) keeps memory flat
across millions of chunks
- HEAD-checks object_size for idempotent re-upload
- Mutually exclusive with chunk packs — manifest's `chunk_pack_hashes`
is empty in JIT mode (consumer reads that as "JIT-only")
Consumer (`hydrate_doc_jit` in cold_clone.py + `_maybe_jit_hydrate` in
qa/query.py):
- Detects both content shapes that need JIT: NULL (Tier B raw-clone) and
zeroblob placeholders (just-enough pack restore, per #53). Discriminator
is first-byte = NUL — zstd-framed bodies start with 0x28, plain UTF-8
prose never has leading NUL.
- Same placeholder filter applied to chunk-read sites in qa/query.py so
partial hydrate doesn't surface zero-bytes content into the LLM context.
Test (`TestJitBlobsPackMode` in tests/test_cold_unpack_routed.py):
- End-to-end push → just-enough hydrate → JIT-fetch → content matches
original byte-for-byte through `unpack_chunk`.
Docs (cold-object-store.md):
- Hard-invariant #1 updated: bucket holds packs by default; `blobs/`
and `clones/` are opt-in prefixes for the JIT and Tier-A flows.
- New "Three consumer modes" section: full-pack vs JIT-blobs vs raw-clone
comparison table + operator decision tree.
russell@unturf.com
d43714a503