MCP prompts/list polling storm causes 100% CPU and renderer crash (TypeError: Failed to fetch) #27477

Issue: MCP prompts/list polling storm causes 100% CPU and renderer crash

Description

OpenCode aggressively polls the prompts/list method on ALL connected MCP servers at startup. Many MCP servers do not implement this method (returning -32601 Method not found), but OpenCode keeps retrying in an aggressive loop. This causes:

1. 100% CPU usage for 1-3 minutes on startup
2. Memory spike as MCP connection threads accumulate
3. HTTP server unresponsiveness - the main process is too busy polling MCPs to respond to renderer HTTP requests
4. Renderer crash - TypeError: Failed to fetch when oc:// protocol fetch to local API times out

Error Pattern

The log shows hundreds of these errors in milliseconds:

ERROR service=mcp clientName=oh-my-claudecode:t error=MCP error -32601: Method not found failed to get prompts
ERROR service=mcp clientName=mgrep error=MCP error -32601: Method not found failed to get prompts
ERROR service=mcp clientName=comet-bridge error=MCP error -32601: Method not found failed to get prompts
ERROR service=mcp clientName=open-computer-use error=MCP error -32601: Method not found failed to get prompts
ERROR service=mcp clientName=context7 error=MCP error -32601: Method not found failed to get prompts
ERROR service=mcp clientName=chrome-devtools error=MCP error -32601: Method not found failed to get prompts
ERROR service=mcp clientName=zai-mcp-server error=MCP error -32601: Method not found failed to get prompts
ERROR service=mcp clientName=hostinger-mcp error=MCP error -32601: Method not found failed to get prompts
ERROR service=mcp clientName=grep_app error=MCP error -32601: Method not found failed to get prompts

112 prompts/list errors were counted in the latest short-lived log before the crash.

Renderer Crash

The renderer eventually crashes with:

TypeError: Failed to fetch
    at fetch (oc://renderer/assets/main-DlaiLIQY.js:102686:45)
    at request (oc://renderer/assets/main-DlaiLIQY.js:58972:24)
    at async retry (oc://renderer/assets/main-DlaiLIQY.js:63575:14)
    at async fetchMessages (oc://renderer/assets/main-DlaiLIQY.js:65394:24)
    at async loadMessages (oc://renderer/assets/main-DlaiLIQY.js:65418:7)

The fetchMessages function tries to fetch from the local HTTP API via oc:// protocol, but the server is too busy processing MCP polling to respond.

System Info

• OpenCode v1.14.48
• Windows 11
• 8+ MCP servers configured
• 724MB SQLite database with 771 sessions

Steps to Reproduce

1. Configure 4+ MCP servers that don't implement prompts/list
2. Start OpenCode
3. Observe 100% CPU for 1-3 minutes
4. Renderer eventually shows Failed to fetch error

Suggested Fix

1. Add rate limiting or debouncing to prompts/list polling
2. Cache prompts/list results (MCP servers rarely change their prompts list)
3. Time out quickly if a MCP server returns -32601 Method not found and stop polling it
4. Process MCP polling asynchronously so HTTP server requests are not blocked
5. Consider making prompts/list optional in the MCP spec