Salvaged from PRs #3767 (chalkers), #5236 (ygd58), #2641 (buntingszn).
Three improvements to Matrix cron delivery:
1. Live adapter path: when the gateway is running, cron delivery now uses
the connected MatrixAdapter via run_coroutine_threadsafe instead of
the standalone HTTP PUT. This enables delivery to E2EE rooms where
the raw HTTP path cannot encrypt. Falls back to standalone on failure.
Threads adapters + event loop from gateway -> cron ticker -> tick() ->
_deliver_result(). (from #3767)
2. HTML formatted_body: _send_matrix() now converts markdown to HTML
using the optional markdown library, with h1-h6 to bold conversion
for Element X compatibility. Falls back to plain text if markdown
is not installed. Also adds random bytes to txn_id to prevent
collisions. (from #5236)
3. Origin fallback: when deliver="origin" but origin is null (jobs
created via API/scripts), falls back to HOME_CHANNEL env vars
in order: matrix -> telegram -> discord -> slack. (from #2641)
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