Description

Heartbeat prompts are being injected into active sub-agent sessions (agent:<id>:subagent:<uuid>), causing the sub-agent to respond HEARTBEAT_OK instead of completing its actual task. This effectively kills any sub-agent run that spans a heartbeat interval.

Steps to Reproduce

1. Configure heartbeat at 1hr interval (agents.defaults.heartbeat.every: "1h")
2. Spawn a sub-agent via sessions_spawn with a task that takes >10 minutes (e.g., building a price cache from yfinance, embedding 175K documents into LanceDB)
3. Wait for the next heartbeat to fire
4. Observe: the heartbeat prompt is injected into the sub-agent session
5. The sub-agent responds HEARTBEAT_OK
6. The announce system picks up HEARTBEAT_OK as the sub-agent result
7. The actual task work is lost

Evidence

Sub-agent session transcript shows the heartbeat injection as the final exchange:

seq 36 (user): "System: [2026-04-04 14:31:58 UTC] Exec completed (calm-ree, code 0) :: ...
Read HEARTBEAT.md if it exists (workspace context). Follow it strictly..."

seq 37 (assistant): "HEARTBEAT_OK"

This happened to 3 separate sub-agent sessions in the same hour:

• max-scorecard-v2 — was building a directional call scorecard (task completed but announce returned HEARTBEAT_OK)
• max-vectordb-v2 — was embedding 175K docs into LanceDB (task completed but announce returned HEARTBEAT_OK)
• sage-token-optimization — was researching token optimization strategies (stalled after heartbeat injection at ~28 min)

All three were running on anthropic/claude-sonnet-4-6 via sessions_spawn with mode: "run".

Expected Behavior

Heartbeat prompts should never be injected into sub-agent sessions (agent:*:subagent:*). Heartbeats are a main-session concern. Sub-agents have their own task context and should run to completion uninterrupted.

Environment

• OpenClaw version: 2026.4.1 (upgraded to 2026.4.2 after observing this)
• OS: Linux 6.8.0-101-generic (x64), Node v22.22.0
• Model: anthropic/claude-opus-4-6 (main), anthropic/claude-sonnet-4-6 (sub-agents)
• Channel: Signal
• Config: agents.defaults.heartbeat.every: "1h", direct Anthropic API key auth

Related Issues

• [Bug]: Heartbeat ignores lightContext: true, loads full agent context + unbounded session history #43767 — Heartbeat ignores lightContext: true
• [Bug] Heartbeat model override ignored in v2026.3.28 - falls back to main session model #56788 — Heartbeat model override ignored
• [Bug]: Heartbeat set to reply to Telegram group gets mixed up with direct chat #28639 — Heartbeat mixed up with direct chat (suggested fix: "Run heartbeats in an isolated sub-session")

Suggested Fix

The heartbeat runner should skip any session matching the sub-agent session key pattern (agent:*:subagent:*). Heartbeat should only target the main session (agent:*:main).

Workaround

Extending heartbeat interval to 2hr+ and setting agents.defaults.subagents.runTimeoutSeconds: 600 reduces the collision window but does not eliminate it.