- v1.3.89 cold proved two stacked stalls: ~5s in is_running() (sync httpx) and a
bigger ~13s BEFORE any background task runs, a silent event-loop freeze
- add faulthandler.dump_traceback_later(7s, repeat) to a temp file so a dump lands
inside the 13s window and names the exact synchronous call the loop is stuck in
- add an entry log to settings._boot_router_then_sync (first startup bg task)
- diagnostic only; reverted once the stall is pinned