openclaw - 💡(How to fix) Fix [Bug]: VS Code ACP prompts hang with OpenClaw on Windows after `sendPrompt`** [1 participants]

Bug type

Crash (process/app exits or hangs)

Beta release blocker

No

Summary

OpenClaw connects and initializes normally as a VS Code ACP agent on Windows, but ACP prompts hang indefinitely after sendPrompt instead of returning a response.

Steps to reproduce

Run OpenClaw on Windows with the default available model openai-codex/gpt-5.4. Open VS Code and use the ACP Client extension. Select OpenClaw as the ACP agent. Send a simple prompt such as Reply with exactly: ACP OK. Observe that the prompt hangs indefinitely after being submitted. Repeat the test with openclaw acp client in a terminal and observe the same hanging behavior.

Expected behavior

The ACP prompt should return a normal assistant response instead of hanging.

Actual behavior

After OpenClaw is selected as the ACP agent and a prompt is sent, the prompt remains stuck with no response in the VS Code ACP Client panel. The VS Code ACP output shows session initialization succeeds and logs sendPrompt, but no completion arrives. The same hanging behavior occurs in openclaw acp client. OpenClaw logs show repeated WebSocket connect failed ... Unexpected server response: 500, plus Gateway disconnected: 1006 and connect ECONNREFUSED 127.0.0.1:18789.

OpenClaw version

2026.3.28

Operating system

Windows 11

Install method

pnpm

Model

openai-codex/gpt-5.4

Provider / routing chain

Provider / routing chain * Effective request path through gateways, proxies, providers, or model routers.

Additional provider/model setup details

OpenClaw is using the default main agent, and openclaw agents list reports its model as openai-codex/gpt-5.4. openclaw models list shows this is the only available model, so no alternate model/provider was selected in the ACP client. The VS Code ACP Client extension successfully spawns npx openclaw acp, initializes sessions, and sends prompts, so the failure appears after prompt submission rather than during agent startup or ACP session creation.

Logs, screenshots, and evidence

VS Code ACP output:

[time] SessionManager: connecting to agent "OpenClaw"
[time] Spawning agent "OpenClaw": npx openclaw acp
[time] ConnectionManager: initialized. Agent: openclaw-acp v2026.3.28
[time] Connected to agent OpenClaw, session <redacted-session-id>
[time] sendPrompt: session=<redacted-session-id>, text="hello..."

OpenClaw logs:

warn agent/embedded {"subsystem":"agent/embedded"} [ws-stream] WebSocket connect failed for session=<redacted-session-id>; falling back to HTTP. error=Error: Unexpected server response: 500

error Error handling request { method: 'session/prompt', params: { sessionId: '<redacted-session-id>' } } { code: -32603, message: 'Internal error', data: { details: 'Gateway disconnected: 1006: ' } }

error Error: connect ECONNREFUSED 127.0.0.1:18789

Additional evidence:
- The same hanging behavior also occurs in `openclaw acp client`.
- The VS Code ACP Client extension works with GitHub Copilot on the same machine, suggesting the ACP client itself is functioning and the issue is specific to OpenClaw as the ACP backend.
- Possible related issue: https://github.com/openclaw/openclaw/issues/55523

Impact and severity

Affects at least this Windows OpenClaw setup when used as an ACP agent from the VS Code ACP Client extension, and the same behavior is also reproduced with openclaw acp client. Severity is workflow-blocking for ACP use, because prompts can be submitted but do not return responses. Frequency appears intermittent-to-frequent based on observed testing: at least one prompt returned a reply once, but many subsequent prompts hung indefinitely. Practical consequence is that OpenClaw cannot be used reliably as a VS Code ACP chat agent in this environment, requiring cancellations, reconnects, and fallback to other agents such as GitHub Copilot.

Additional information

I did not verify a last known good OpenClaw version for this exact workflow, so regression bounds are unknown. openclaw status and openclaw gateway status indicated the gateway was healthy during troubleshooting, and the ACP Client extension successfully initialized OpenClaw sessions before prompts hung. The only available model in this setup is openai-codex/gpt-5.4, so I could not test whether the issue reproduces with a different model/provider path. A possibly related public issue is #55523, which reports openai-codex websocket failures with HTTP fallback, although that report says requests still succeed after fallback while this case hangs.

On a second Windows 11 PC with what appears to be the same OpenClaw setup, ACP fails differently: every message returns: "ACP error (ACP_SESSION_INIT_FAILED): ACP metadata is missing for agent:main:acp:<redacted-session-id>. Recreate this ACP session with /acp spawn and rebind the thread. next: If this session is stale, recreate it with /acp spawn and rebind the thread."

I have not confirmed whether that is the same root cause or a separate ACP session-state issue, but it may be related.