Limitcast 0.18.2: atomic state writes and mistyped-option errors

A mistyped option now fails with Unknown option --gaurd and exit 1 instead of running the plain command. Hooks are exempt and still fail open. Settings, the usage cache, last.json and the pruned samples.jsonl are written to a temp file and renamed, so a hook never reads a half-written file. results reads usage once (median 5.3 s to 4.2 s on a machine with 6,500 transcripts), and report --why says it is reading transcripts before a first read of more than 100.

Details are in the changelog. The audit behind this release, including what was not fixed: https://limitcast.dev/blog/limitcast-audit-2026-11-07/