Multi-participant parity with interactive send_message, which passes
HERMES_SESSION_USER_ID to gateway.mirror.mirror_to_session so the mirror
lands in the exact participant's session.
- cronjob_tools._origin_from_env now captures user_id from the session
context at job-create time (alongside platform/chat_id/thread_id).
- _maybe_mirror_cron_delivery forwards user_id to mirror_to_session.
- _deliver_result threads origin.user_id through for the origin target.
Effect: in a per-user-isolated group chat (group_sessions_per_user=True,
the default), the mirror resolves to the member who scheduled the job
instead of conservatively no-op'ing on ambiguous candidates. DMs and
shared group/thread sessions are unaffected (single candidate). Default
still OFF.
Tests: helper forwards user_id; E2E _deliver_result forwards origin
user_id. 17/17 in TestCronDeliveryMirror; 527 cron tests pass (4 failures
pre-existing: croniter-not-installed + TZ, identical on baseline).
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