MEM-041: sniff — error-path resource leaks in PATCH blob-write and POST commit

Two sniff error paths leak a resource because a bare call() sits between an acquisition and its release. write_blob (PATCH.c:229) FILECreate's an fd then call(FILEFeedAll, fd, data) — a write failure early-returns and leaks the open fd. POSTCommit (POST.c:2651, the core be post commit-emission) KEEPPackOpen's a keeper pack (fd + mmaps + heap) then a bare call(post_feed_empty_tree, ...) early-returns on KEEPPackFeed failure, leaking the whole pack. Both are reachable on a real I/O / pack error, missed by the happy-path suite. From the MEM sweep.

Issues

A bare call() between acquire and release leaks on its error return.

PATCH.c:229 write_blob: FILECreate fd, then call(FILEFeedAll) error-returns leaving the fd open.
POST.c:2651 POSTCommit: KEEPPackOpen (fd+mmaps+heap), then a bare call(post_feed_empty_tree) error-returns leaking the pack.

Blockers

None; sniff-internal. Use the close-before-return idiom already standard in this dir (capture result, release unconditionally, then check) — the same MEM-026 pattern.

Planned

Release the fd / pack on the error return before propagating.

Repro first (CLAUDE §17): force a write / pack-feed failure and assert the fd / pack is released (ASAN, fd-count stable).
write_blob: capture the FILEFeedAll result, FILEClose the fd unconditionally, then check.
POSTCommit: KEEPPackClose the pack on the post_feed_empty_tree error path.