- nightly_tune: write learned_params.json via tmp -> flush -> fsync ->
os.replace so a crash mid-dump can't leave the live loop parsing half a JSON
on its next boot (it reads this file on every restart).
- run_live_paper._load_learned: warns (boot log + one gated Telegram note) when
the file is older than LEARNED_PARAMS_MAX_AGE_DAYS (default 3) — the missing
signal that let the params sit 26 days stale. Loads anyway; never blocks boot.
Staleness math factored into _learned_params_age_days (naive ts = UTC).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>