preview_start (Claude_Preview MCP) fails with sandbox getcwd error on Rails dev server

Bug

preview_start (Claude_Preview MCP tool) fails with a sandbox error when launching a local Rails dev server, regardless of whether the target port is free or in use.

Error

shell-init: error retrieving current directory: getcwd: cannot access parent directories: Operation not permitted
shell-init: error retrieving current directory: getcwd: cannot access parent directories: Operation not permitted
job-working-directory: error retrieving current directory: getcwd: cannot access parent directories: Operation not permitted
/opt/homebrew/Cellar/rbenv/1.3.2/libexec/rbenv-version-file-read: line 11: <repo>/.ruby-version: Operation not permitted
ruby: Operation not permitted -- bin/rails (LoadError)

Repro

.claude/launch.json:

{
  "version": "0.0.1",
  "configurations": [
    {
      "name": "studio-link",
      "runtimeExecutable": "/Users/fernandocastaneda/.rbenv/shims/ruby",
      "runtimeArgs": ["/Users/fernandocastaneda/Documents/studio-link/bin/rails", "server", "-p", "3010"],
      "port": 3010,
      "cwd": "/Users/fernandocastaneda/Documents/studio-link",
      "env": {
        "SKIP_TAILWIND_PLUGIN": "1",
        "RAILS_ENV": "development"
      }
    }
  ]
}

1. Call preview_start with name: "studio-link".
2. Fails every time with the getcwd sandbox error above — even with the target port confirmed free beforehand.

Workaround

Running the exact same command via the Bash tool with dangerouslyDisableSandbox: true works without any issue:

SKIP_TAILWIND_PLUGIN=1 RAILS_ENV=development bin/rails server -p 3010

This strongly suggests the Claude_Preview MCP server spawns its child process under a stricter/different sandbox profile than the Bash tool, and that profile doesn't grant read access to the parent directories needed for getcwd() to resolve — even though the same cwd works fine for Bash.

Environment

• macOS (Darwin 24.1.0)
• Shell: zsh
• Ruby via rbenv (rbenv-version-file-read also fails with the same "Operation not permitted")