PR #61976: fix: prevent heartbeat HEARTBEAT_OK replies from polluting session transcript

• Repository: openclaw/openclaw
• Author: jjjojoj
• State: closed | merged: False
• Link: https://github.com/openclaw/openclaw/pull/61976

Description (problem / solution / changelog)

Fixes #61952

Problem

When heartbeat triggers, the model replies with HEARTBEAT_OK. While stripHeartbeatToken correctly suppresses delivery to the user, the heartbeat prompt + response are still written to the session transcript. On subsequent heartbeats, the model sees accumulated HEARTBEAT_OK turns in history and keeps repeating them, causing an infinite loop that bloats the session context and consumes massive tokens.

This is especially prevalent with models like GLM-5.1 that tend to mimic patterns seen in conversation history.

Fix

When a heartbeat run produces no meaningful output (empty reply or pure HEARTBEAT_OK with shouldSkip=true), roll back the session transcript file to its pre-run state by truncating the bytes added during the heartbeat exchange.

Safety measures

• Only applies to non-isolated sessions (isolated sessions already use fresh session each run)
• Checks file size actually grew before truncating
• If the transcript file was created by the heartbeat run, removes it entirely
• Rollback failures are logged as warnings, never thrown

Not affected

• Meaningful heartbeat alerts (delivered to user, kept in transcript)
• Exec completion events and cron events
• Sessions with isolatedSession: true

Changed files

• src/infra/heartbeat-runner.ts (modified, +85/-1)