When Telegram topic mode is enabled, cron messages delivered to the bot's
root DM (TELEGRAM_HOME_CHANNEL without a thread id) land in the system
lobby — replies there are rebuffed with the lobby reminder and
reply_to_message_id is dropped, so users cannot interact with the cron
output (#24409).
Add an optional TELEGRAM_CRON_THREAD_ID env var that overrides
TELEGRAM_HOME_CHANNEL_THREAD_ID for cron deliveries only. Operators can
create a "Cron" forum topic in the DM, point this var at its thread id,
and replies to cron messages will land in that topic's existing session
instead of the lobby. The home-channel thread id (used elsewhere, e.g.
restart notifications) is unchanged, and explicit
deliver="telegram:chat:thread" targets continue to win over the env var.
Per the reporter's clarification on 2026-05-13, option (a) (cron-side
route to a dedicated topic + config knob) was chosen.
Fixes#24409
a4fb0a3ac3