Desktop truncates backend.log on every launch #278

Location: main.rs:1076
Severity: CRIT

fs::File::create(log_path) zeroes the previous session’s log. The natural user response to a crash is “restart and retry” — which erases exactly the evidence needed. This is why the Mac Mini reporter had nothing to paste.
Rotate on launch (backend.log → backend.log.1, keep 2–3 generations) or append with a size cap.

From the health report. Part of #272 (Phase 1 — Evidence).