grenadeandClaude Opus 5
14f8342cf8
Spec §7 says concurrent requests for the same uncached blob must produce exactly one upstream fetch, and that "subsequent callers subscribe to the same broadcast". Subscribing was the part that did not exist. A follower called `Flight::wait` and blocked -- no timeout, nothing on the wire -- until the leader's entire transfer finished. For a 3.3GB shard at 8MB/s that is 400+ seconds before the response headers are written, against a client that allows 10. Indistinguishable from a hung server, while the leader logs that it stored the blob. It could not be fixed by handing over the live stream: the bytes that already passed are gone from it, and the multipart upload is not readable until it completes. So add the missing buffer. The leader writes every chunk to `server.spool_dir` as it passes and publishes how much is safe to read; a follower opens that file and streams it from byte zero, following it as it grows, with the last chunk withheld until the flight reports the blob stored -- the same rule the tee follows, for the same reason. The spool is not state, and the bucket remains the whole of it. Losing the spool loses nothing: a blob is not recorded until it is durable, so a crash mid-transfer leaves an unreferenced blob and the next request refetches. It is the role the in-memory buffer already plays for small files, on disk so it can hold a large one. Every transfer is spooled rather than only large ones, because size-dependent behaviour is what this service has already been bitten by once. With `spool_dir` unset there is nothing to read and a follower is answered 503 rather than left hanging, which is the honest fallback. The new test asserts the thing that actually distinguishes streaming from waiting -- that the follower's first bytes arrive while the leader is still transferring -- because chunked delivery alone proves nothing: the old path returned chunks too, just all of them after the transfer had ended. It fails with spooling disabled. The eight-concurrent-clients test still sees exactly one upstream fetch, now through the spool. Closes #2 Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01PqNtYNhov3fukx46KS9R7L