The YAML-to-env-var bridge in load_gateway_config() mapped every Discord
and Telegram config key (require_mention, auto_thread, reactions, etc.)
except reply_to_mode. Users setting discord.reply_to_mode or
telegram.reply_to_mode in ~/.hermes/config.yaml got no effect — the
adapter only read the env var, which nothing populated from YAML.
Add the missing bridge for both platforms, following the existing pattern.
Top-level <platform>.reply_to_mode preferred, falls back to
<platform>.extra.reply_to_mode, env var never overwritten. Handles YAML
1.1 bare `off` → Python False coercion.
This is a re-submission of the work from #9837 and #13930, which both
implemented the same fix but neither landed (see co-authors below).
Co-authored-by: Matteo De Agazio <hypnosis.mda@gmail.com>
Co-authored-by: ishardo <239075732+ishardo@users.noreply.github.com>
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