Troubleshooting Guide: Nested Agent Sessions Blocking Each Other

Symptoms

If you are running multiple agent sessions simultaneously, you may encounter the following symptoms:

• Delayed or missing responses: One or more agent sessions appear to “freeze” or take significantly longer than expected to respond, even when the requested task is simple.
• Cross-session blocking: A long-running task on one session (such as an ACP Claude Code run) causes delays on completely unrelated sessions.
• Gateway timeouts: Error messages in logs indicating lane wait exceeded: lane=nested waitedMs=XXXXX queueAhead=1.
• Discord delivery failures: Assistant responses generated during the backlog are never delivered to Discord channels.
• Inconsistent behavior: Some sessions respond instantly while others sit idle for minutes, even when the underlying tasks are unrelated.

Root Cause

The root cause was a single global queue bottleneck in the nested agent execution system.

Previously, all nested agent operations across all sessions shared one lane named "nested" with maxConcurrent=1. This meant:

1. Every sessions_send, runAgentStep, and ACP dispatch competed for the same queue entry.
2. When session A ran a 10-minute task, sessions B, C, and D had to wait in line behind it.
3. The command queue treated every nested operation identically, regardless of which session it targeted.

This architectural limitation caused head-of-line blocking where a single long-running nested operation could stall all other agent sessions in the gateway.

Step-by-Step Fix

Option 1: Upgrade to the Fixed Version (Recommended)

Upgrade your OpenClaw installation to version v2026.4.19-beta.2 or later.

This version introduces per-session nested lanes that scope nested work to nested:<sessionKey>, allowing parallel execution across different sessions while maintaining concurrency invariants within each session.

Option 2: Verify Lane Configuration (For Manual Verification)

If you need to verify the fix is applied correctly, check your gateway logs for the lane names being used:

Before the fix, you would see logs like:

[agent:nested] Processing session A
[agent:nested] Processing session B

After the fix, you should see scoped lane names:

[agent:nested:session-A] Processing session A
[agent:nested:session-B] Processing session B

Option 3: Check the Lane State Map

In your gateway configuration, the lane state should now be keyed by the full session-scoped identifier rather than the bare "nested" string. Each entry should show:

• nested:<sessionKey> for standard sessions
• "nested" fallback for legacy cron paths only

Verification

To confirm the fix is working correctly:

1. Run multiple concurrent sessions: Set up two or more agent sessions that can receive nested operations.

2. Trigger a long-running task on one session: For example, invoke a task that takes several minutes to complete.

3. Send a quick task to another session: While the long task is running, send a simple request to a different session.

4. Verify parallel execution: The second session should respond immediately without waiting for the first session’s task to complete.

5. Check logs for scoped lanes: Look for [agent:nested:<sessionKey>] prefixes in your gateway logs confirming per-session lane isolation.

Expected test results after the fix:

pnpm test src/agents/lanes.test.ts         # 13 tests green
pnpm test src/gateway/server.sessions-send.test.ts  # 14 tests green
pnpm test 'src/agents/**/*.test.ts'        # 3841 tests green

Common Pitfalls

Session Key Handling

• Empty or whitespace-only session keys: These fall back to the unscoped "nested" lane. Ensure your session keys are properly populated before routing nested operations.

• Legacy cron paths: Cron integrations using resolveNestedAgentLane(lane) still use the unscoped fallback. This is intentional for backward compatibility.

Lane Name Collisions

• User-supplied lane names: If you have custom lanes with names like "nested:something", note that these are distinct from the system-generated nested:<sessionKey> lanes. The system lane uses a specific prefix convention matching the existing session:<key> pattern.

Memory Considerations

The lane-state Map now grows as new session keys appear. Each lane state entry is approximately 200 bytes. The realistic upper bound is the number of active sessions, which is already bounded by your gateway’s session management. A future enhancement for reaping idle nested lanes may be added if this becomes a concern.

Unrelated Issues

Two related issues mentioned in the original report remain out of scope for this fix:

• Session delivery context corruption
• Absence of delivery retry/DLQ mechanisms

These are architectural follow-ups tracked separately.

Related Errors

Affected Versions

• Fixed in: v2026.4.19-beta.2
• Affected versions: v2026.4.14 and earlier

Compatibility

This fix is fully backward compatible:

• The AGENT_LANE_NESTED constant is still exported
• Callers that continue to pass the constant directly retain their existing (unscoped) behavior
• No configuration changes are required
• No migration steps are needed

The fix strengthens session isolation without breaking existing integrations.