Nested session check blocks non-interactive subcommands like `claude plugin validate`

Summary

The nested session detection (CLAUDECODE env var check) blocks all claude subcommands when run from within a Claude Code session, including non-interactive utility commands like claude plugin validate. These commands don't create a competing session — they're stateless validation checks — but they're rejected with the same error as a full nested session.

Reproduction

1. Open a Claude Code session
2. From within the session (e.g., via a lint script), run:

``bash
claude plugin validate plugin.json
``

1. Result:

``
Error: Claude Code cannot be launched inside another Claude Code session.
Nested sessions share runtime resources and will crash all active sessions.
To bypass this check, unset the CLAUDECODE environment variable.
``

Expected behavior

Non-interactive subcommands (plugin validate, plugin list, --version, --help, etc.) should bypass the nested session check since they don't create a competing interactive session or share runtime resources.

Workaround

Clear the env var before invoking:

{
  "scripts": {
    "lint": "CLAUDECODE= claude plugin validate plugin.json"
  }
}

Context

This commonly hits when claude plugin validate is used as a lint step in package.json scripts, which then get invoked by pre-commit hooks or pnpm pre-commit during a Claude Code session. The error message suggests the check is designed to prevent interactive nested sessions from crashing, but the blast radius catches read-only utility commands too.