Bug type

Behavior bug (incorrect output/state without crash)

Beta release blocker

No

Summary

On 2026.4.11, a stripped-down embedded heartbeat using ollama/qwen2.5:3b-instruct-q4_K_M still fails in precheck with context overflow, even though:

Ollama is actually loading the model at CONTEXT 16384 config sets: agents.defaults.compaction.reserveTokens: 1000 agents.defaults.compaction.reserveTokensFloor: 0

At runtime, heartbeat precheck still logs reserveTokens=16384, leaving promptBudgetBeforeReserve=1 for an estimatedPromptTokens=35 heartbeat.

Steps to reproduce

1. Run OpenClaw 2026.4.11 on Windows with a local loopback gateway.
2. Configure heartbeat to use:
   • ollama/qwen2.5:3b-instruct-q4_K_M
   • prompt: "Reply exactly HEARTBEAT_OK."

• lightContext: true
  • isolatedSession: true
  • target: "none"
  • includeReasoning: false
• Configure compaction defaults to:
  • reserveTokens: 1000
  • reserveTokensFloor: 0
• Confirm ollama ps shows the model loaded at CONTEXT 16384.
• Trigger a heartbeat test:
  • openclaw system event --text "heartbeat test" --mode now --timeout 180000
• Inspect heartbeat logs / openclaw system heartbeat last.

Expected behavior

The heartbeat should fit comfortably inside a 16k context window and return HEARTBEAT_OK or otherwise complete without immediate precheck overflow.

At minimum, runtime should honor the configured compaction reserve and not use reserveTokens=16384.

Actual behavior

openclaw system event ... returns ok, but the embedded heartbeat immediately fails with:

• context-overflow-precheck
• promptBudgetBeforeReserve=1
• reserveTokens=16384
• auto-compaction skipped because there are no real conversation messages
• session restarted and retried

openclaw system heartbeat last then shows a skipped heartbeat with preview text indicating context limit/reset behavior.

OpenClaw version

2026.4.11 (769908e)

Operating system

Windows (local loopback gateway on 127.0.0.1:18789)

Install method

Global install under the user Node/npm global path (example runtime path: C:\Users\prapunsak\AppData\Roaming\npm\node_modules\openclaw\dist\index.js)

Model

ollama/qwen2.5:3b-instruct-q4_K_M

Provider / routing chain

Local Ollama provider for embedded heartbeat: ollama/qwen2.5:3b-instruct-q4_K_M

Additional provider/model setup details

Relevant heartbeat config: "heartbeat": { "every": "55m", "model": "ollama/qwen2.5:3b-instruct-q4_K_M", "includeReasoning": false, "target": "none", "directPolicy": "block", "prompt": "Reply exactly HEARTBEAT_OK.", "lightContext": true, "isolatedSession": true }

Relevant compaction config: "compaction": { "mode": "safeguard", "reserveTokensFloor": 0, "reserveTokens": 1000 }

Ollama runtime evidence: qwen2.5:3b-instruct-q4_K_M ... CONTEXT 16384

Logs, screenshots, and evidence

Successful trigger:
PS C:\WINDOWS\system32> openclaw system event --text "heartbeat test" --mode now --timeout 180000
ok

Overflow sequence:
06:41:41+00:00 warn agent/embedded ... low context window: ollama/qwen2.5:3b-instruct-q4_K_M ctx=16384 (warn<32000) source=modelsConfig
06:41:46+00:00 warn agent/embedded ... [context-overflow-precheck] ... estimatedPromptTokens=35 promptBudgetBeforeReserve=1 overflowTokens=34 ... reserveTokens=16384 ...
06:41:46+00:00 warn agent/embedded ... [context-overflow-diag] ... error=Context overflow: prompt too large for the model (precheck).
06:41:46+00:00 warn agent/embedded ... context overflow detected (attempt 1/3); attempting auto-compaction ...
06:41:51+00:00 info agent/embedded ... [compaction] skipping — no real conversation messages ...
06:41:51+00:00 warn agent/embedded ... auto-compaction failed ... no real conversation messages
06:41:51+00:00 error Auto-compaction failed (Context overflow: prompt too large for the model (precheck).). Restarting session ...

Heartbeat last output:
{
  "status": "skipped",
  "reason": "target-none",
  "preview": "⚠️ Context limit exceeded. I've reset our conversation to start fresh - please try again.",
  "durationMs": 116644
}

Impact and severity

Medium to high.

This blocks use of a tiny local model for embedded heartbeat even with an intentionally minimal heartbeat prompt/config, and suggests runtime is not honoring configured compaction reserve values.

Additional information

This appears to be a separate issue from earlier 2026.4.9 gateway/connect problems. On 2026.4.11, the system event connect path improved, but the embedded heartbeat overflow remains reproducible.

The core discrepancy is:

config shows reserveTokens: 1000 runtime logs reserveTokens=16384

That mismatch seems to be the heart of the bug.