[BUG] preview_start returns "No .claude/launch.json found" even when file exists

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Bug Description

preview_start consistently fails to detect .claude/launch.json even though
the file exists at exactly the path specified in the error message.

Actual Behavior

Returns "No .claude/launch.json found" despite the file existing, being valid
JSON, and having correct read permissions (-rw-r--r--).

Environment

• OS: macOS 25.3 (arm64)
• The file exists and is valid JSON (verified with python3 -c "import json; json.load(open('.claude/launch.json'))")
• Issue persists across multiple Claude Code sessions and after Claude Desktop updates

launch.json contents

{
"version": "0.0.1",
"configurations": [
{
"name": "Django Dev Server",
"runtimeExecutable": "/full/path/to/.new_env/bin/python3.9",
"runtimeArgs": ["manage.py", "runserver"],
"port": 8000
}
]
}

What Should Happen?

Expected Behavior

preview_start should read the existing file and start the server.

Error Messages/Logs

"No .claude/launch.json found"

Steps to Reproduce

Steps to Reproduce

1. Create .claude/launch.json in the project root with a valid configuration
2. Call preview_start with a server name from the config
3. Observe error: "No .claude/launch.json found. Create /path/to/.claude/launch.json"

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

Claude 1.1.5368 (d12d02) 2026-03-05T17:29:33.000Z - Claude Desktop

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_