Drops user-store's private _atomicWriteJSON copy (pid+Date.now() tmp names, no fsync, no failure cleanup) in favor of src/utils/atomic-write.js (DC-099 canonical: fsync'd same-dir exclusive-create 0600 tmp -> rename -> parent-dir fsync, cleanup-on-failure). All 3 persisted files routed: users.json, authorized-users.json, .bootstrapped sentinel. Sole consumers are JSON.parse readers — dropped trailing newline unobservable (judge verified repo-wide). +2 store-level regression tests pin 0600 / complete JSON / no temp leftovers across all three files, incl. the bootstrap path writing three files back-to-back in one login. Judge: GLM-5.3 cold read, round-1 A, deleg_f632f05c. Verdict: urn:ump:5fivvveqhcbkl6os4dhidchkvjjzbvi7rgj6znaovp6bfnvmcmsq Full suite: 121 suites / 2772 tests green.