claude-code - 💡(How to fix) Fix [BUG] preview_start spawns unlimited Node.js processes on Windows, consuming all available RAM

Bug Description

Triggering preview_start (via the "Start Preview" button in Claude Desktop or the mcp__Claude_Preview__preview_start MCP tool) spawns a brand new node.exe process every single time instead of reusing an existing one. On Windows, this results in 100+ Node.js processes accumulating in the background, consuming ALL available system RAM and causing repeated system crashes.

The tool description explicitly states "Reuses the server if already running" — this guarantee is completely broken on Windows.

Environment

• OS: Windows
• App: Claude Desktop
• Tool: mcp__Claude_Preview__preview_start
• Project type: Next.js 16 (next dev, port 3000)
• .claude/launch.json: present and correctly configured

Steps to Reproduce

1. Create .claude/launch.json with a Next.js dev server entry
2. Trigger preview_start (via Claude Desktop UI or MCP tool call)
3. Trigger it again — even just once more
4. Observe: a new node.exe process is spawned instead of reusing the existing one
5. Repeat a few times → Task Manager shows 100+ node.exe processes

Expected Behavior

preview_start detects an already-running server on the target port and reuses it. The reused field in the response should return true on subsequent calls.

Actual Behavior

• Every call spawns a fresh node.exe process (~31–33 MB each)
• 100+ node.exe processes accumulate, consuming all remaining system RAM
• System becomes completely unresponsive
• Machine crashed TWICE before the root cause was identified
• reused: false on every call, even repeated ones to the same named server

API Response Evidence

{
  "serverId": "d9907155-d833-4c27-8632-c0e9368a7d1f",
  "port": 3000,
  "name": "Next.js Dev",
  "reused": false
}

reused should be true on repeated calls — it never is.

Workaround

Kill all runaway processes via PowerShell:

Get-Process -Name "node" -ErrorAction SilentlyContinue | Stop-Process -Force

Then run npm run dev manually in a terminal instead of using preview_start.

Severity

Critical — causes repeated full system crashes on Windows by exhausting all available RAM. The bug is triggered by normal, expected usage of the feature.