Lark/Feishu WebSocket connection fails with 404, then segfaults

[Aisht669]

Description

Summary
When configuring the Lark channel with receive_mode: "websocket" and use_feishu: true, nullclaw crashes immediately after "lark gateway
started" message. Investigation shows the WebSocket endpoint /ws/v2 returns 404 Not Found.

Steps to Reproduce

   1. Configure ~/.nullclaw/config.json:
   {
     "channels": {
       "lark": {
         "accounts": {
           "main": {
             "app_id": "cli_xxx",
             "app_secret": "xxx",
             "use_feishu": true,
             "receive_mode": "websocket",
             "allow_from": ["*"]
           }
         }
       }
     }
   }

2. Enable "Use long connection to receive events" (使用长连接接收事件) in Feishu Open Platform
3. Add event subscription: im.message.receive_v1
4. Run nullclaw gateway

Actual Behavior

nullclaw gateway runtime started
Gateway: http://127.0.0.1:3000
Components: 3 active
info(channel_manager): lark gateway started
timeout: the monitored command dumped core

Additional Investigation

Testing the WebSocket endpoint directly with Python:

ws_url = f"wss://open.feishu.cn/ws/v2?app_id={app_id}&access_token={app_access_token}"

Returns: Handshake status 404 Not Found

The API credentials are valid - tenant_access_token and app_access_token can be obtained successfully via HTTP API.

Expected Behavior

WebSocket should connect successfully to Feishu's long connection endpoint and receive events.

Environment

• nullclaw version: v2026.3.7
• OS: Linux x86_64 (Incus container)
• Feishu region: China (open.feishu.cn)
• Long connection: Enabled in Feishu Open Platform

Possible Cause

The WebSocket endpoint /ws/v2 used in src/channels/lark.zig may be outdated or incorrect. The official Feishu SDK (@larksuiteoapi/node-sdk)
uses internal WebSocket handling that works correctly, suggesting the endpoint or authentication method may have changed.

Reference: PR #300 mentions "known legacy segfault still appears" in the validation section.

Related

• [Bug] Lark channel always registers as webhook-only on Windows — receive_mode: websocket ignored #298 - Similar issue on Windows with receive_mode being ignored
• fix(lark): honor receive_mode for listener registration #300 - Fix for receive_mode listener registration