Reproducibility HIGH-findings closure (T548/T549, C-H2, C-H3)

## Что это ## Контекст PZD-56 T091 recon done. 3 HIGH remain: T548/T549 (defer), C-H2 (stopping flag race — PZD-105), C-H3 (per-entry load serialization — PZD-106), B-H1 (electron-builder collide — PZD-107), B-H2 (SHA-256 digest verification — PZD-108). ## Критерии приёмки - [ ] PZD-105 (C-H2 stopping race) merged - [ ] PZD-106 (C-H3 load serialization) merged - [ ] PZD-107 (B-H1 builder collide) merged - [ ] PZD-108 (B-H2 SHA-256 digest) merged - [ ] T548/T549 либо closed, либо явный defer-decision ## Статус Это задача из текущего backlog'а ROX.ONE (Linear). Текущий статус в Linear: `Triage`. Метки: `История` / `Story`, `Воспроизводимость` / `Reproducibility`. ## 🔗 Linear - [PZD-255](https://linear.app/kuhjie/issue/PZD-255/istoriya-reproducibility-high-findings-closure-t548t549-c-h2-c-h3) — backing ticket - Parent epic: [PZD-119](https://linear.app/kuhjie/issue/PZD-119)