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Sergey Galuza
00a4dceb94
Adoption moved the canonical settings.json aside with rename() and left
the path empty until publication, roughly 100 ms later. Claude Code or a
second `ccs` starting inside that window found no file and seeded an
empty placeholder; publication then failed with EEXIST because link() is
no-replace, and the rollback published a backup and unlinked the claim,
destroying the only remaining copy of the user's settings. Recovering
meant digging through sidecar files by hand.
Publish by replacement instead: write a temp file next to the canonical
inode and rename() it over the target, so the path always holds a regular
file and no placeholder can be seeded. A compare-and-swap guard on
(ino, mtime, size) runs immediately before the rename and refuses to
publish when the canonical inode changed since it was read, so a writer
that got there first is still never clobbered. The pre-image backup is
published before the replacement, keeping the old content recoverable if
publication is interrupted.
Drops the canonical claim entirely along with restoreCanonicalClaim, and
folds the two identical sidecar publishers into one helper.
recoverOrphanedCanonicalClaim stays, since claims written by older
versions may still be on disk.
New tests cover both writers seen in the incident: Claude Code seeding
`{}` with a trailing newline, and a second `ccs` seeding the 2-byte
variant from shared-dir-linker. Four tests that pinned the claim-based
design were rewritten, among them `preserves a canonical write that
lands during no-replace publication`, whose intent is now enforced by
the CAS guard instead of by an EEXIST from a no-replace link.
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