Description

When cron job announcements with HEARTBEAT_OK results are delivered to the main agent session while the agent is actively replying to the user, the HEARTBEAT_OK token leaks into user-visible messages instead of being silently suppressed.

Steps to Reproduce

1. Have multiple cron jobs running with announce delivery (e.g. meeting-reminder every 5 minutes)
2. When those jobs return HEARTBEAT_OK (nothing to report), the system queues them as announce messages to the main session
3. If the agent is mid-reply to the user, the HEARTBEAT_OK gets appended to the actual user-facing response
4. User sees HEARTBEAT_OK at the end of otherwise normal messages

Expected Behavior

Cron announce results that are HEARTBEAT_OK should be silently discarded before reaching the agent session. The agent should never need to handle or suppress these — they should be filtered at the delivery layer.

Actual Behavior

HEARTBEAT_OK tokens from cron announce deliveries leak into user-visible replies, appearing appended to normal assistant messages on Telegram (and likely other surfaces).

Environment

• OpenClaw version: 2026.3.1
• Channel: Telegram (direct chat)
• Cron jobs: meeting-reminder (every 5 min), tennis-live (every 30 min), etc.
• Multiple cron jobs returning HEARTBEAT_OK queued as announce messages

Additional Context

The NO_REPLY stripping fix in 2026.3.1 (Auto-reply/NO_REPLY: strip NO_REPLY token from mixed-content messages) addresses a similar class of issue for NO_REPLY, but HEARTBEAT_OK from cron announce paths is not similarly handled.

A potential fix would be to filter HEARTBEAT_OK results at the cron delivery layer before they reach the agent session, similar to how the system already handles delivery.mode: "none" jobs.