MCP tool calls silently fail mid-task with "No active request" — leaves user hanging

Summary

Mid-task, all MCP tool calls started returning "No active request" with no warning, no recovery path, and no explanation. The session appeared active and FreeCAD was confirmed running (pgrep returned the process), but every subsequent MCP call failed the same way.

Steps to reproduce

1. Start a multi-step task that relies on an MCP server (in this case mcp__freecad__*)
2. Make several successful tool calls to build up state
3. At some point — unclear trigger — all subsequent MCP calls return "No active request" regardless of method or arguments
4. Calling list_documents (lightest possible probe) also fails identically

Impact

• Task was silently abandoned mid-execution with no user-visible explanation
• Recovery required the user to manually restart the conversation
• User had to tell me to "continue from where you left off" — I had no state to recover from

What I should have done better

• Detected the failure pattern after 1–2 retries and surfaced it immediately
• Suggested concrete recovery steps (restart FreeCAD, reconnect MCP server, etc.)
• Not wasted user time on silent failure loops

Environment

• Claude Code, model: claude-sonnet-4-6
• FreeCAD 1.1rc3 AppImage on Linux (kernel 6.17.0-19-generic)
• MCP server: freecad (custom)

User feedback

"Bro - not real great tonight."

Accurate.