All three writeFileSync sites in the encrypted-credentials manager now delegate to src/utils/atomic-write.js atomicWriteJSON — rotateEncryptionKey save, _ensureFileExists bootstrap, and the _lockedUpdate commit under the proper-lockfile lock. A crash can no longer tear credentials.json mid-write: power loss through the old path could leave an empty/short file and silently drop every stored credential (DNS provider tokens etc). Lock-safety pre-study: proper-lockfile only stats its own sibling .lock dir, never the target file, so the rename swap cannot trip ECOMPROMISED. Test mock extended to the fd-level fs API (openSync/writeSync/ fsyncSync/closeSync/renameSync + fdMap/closedTmp state) so the canonical path is exercised end-to-end under the mock; write assertions moved from writeFileSync.mock.calls to destination-state reads. New DC-106 pins: wx+0600+fsync+rename discipline, plaintext-secret canary never on disk, fd-lifecycle order fsync->close->rename via invocationCallOrder, and atomic _ensureFileExists create at 0600. Eighth store migrated (DC-099..DC-105 preceded). Judge: GLM-5.3 cold read, round-1 B/ship (deleg_b3c038c2). URN urn:ump:vscequdet7wt5un7jhtl2nlg6cfkabsbazy5m2tjnyyguu5wstxa (readback verified: grade B, topic codex-judge-verdict). Sole finding is pre-existing and non-blocking: rotateEncryptionKey persists the new key before writing rotated creds (crash window) — queued as DC-107 follow-up. Full suite: 121 suites / 2783 tests green.