loadSupporterBinaries reads the persisted tool→path override map; on first run (key absent) it probes the known tools once and persists the result — pinned thereafter, not re-detected each launch (D-104). Injected read/write so it stays Flutter-free and dart-test covered (3 new cases). Boot wiring next. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>