Route heartbeat, cron, and message-tool deliveries through one gateway helper so user-visible proactive messages are available when the channel replies.
Made-with: Cursor
When heartbeat delivers output to a channel (e.g. Telegram), the message
is a raw OutboundMessage that bypasses the channel's session. If the user
replies, their reply enters a different session with no context about the
heartbeat message, so the agent cannot follow through.
This change injects the delivered heartbeat message as an assistant turn
into the target channel's session before publishing the outbound. When
the user replies, the channel session has conversational context.
Handles unified_session mode by resolving to UNIFIED_SESSION_KEY when
enabled, matching the agent loop's own session routing.
No changes to agent/loop.py, session/manager.py, channels, providers,
or config schema — uses existing add_message() and save() APIs.
