[FEATURE] Support nested claude -p calls from custom slash commands without nested session error

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

What problem does this solve:
When a custom slash command (e.g. /review) triggers a shell script that calls claude -p internally, Claude Code blocks it with: "Claude Code cannot be launched inside another Claude Code session." This makes it impossible to use headless Claude pipelines as slash commands.

What I expected:
/review would run my review_and_commit.sh pipeline which uses claude -p for automated code review and bug fixing.

What happened:
The nested session check blocked the inner claude -p calls, causing the pipeline to abort.

Proposed Solution

Suggested solution:
Either automatically unset the CLAUDECODE environment variable when running slash command shell scripts, add a --allow-nested flag for headless calls, or add clear documentation showing the recommended pattern for slash commands that use claude -p.

Environment:

Claude Code v2.1.70
macOS
Claude Pro subscription

Alternative Solutions

_No response_

Priority

Low - Nice to have

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_