[BUG] Hooks fail with posix_spawn '/bin/sh' ENOENT due to sandbox restrictions

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?

Plugin hooks (Stop, PostToolUse, etc.) fail with ENOENT: no such file or directory, posix_spawn '/bin/sh' when Claude Code's sandbox is active.

Error Message:

⏺ Ran 3 stop hooks
  ⎿  Stop hook error: Failed with non-blocking status code: Error occurred while executing hook command: ENOENT: no such file or directory, posix_spawn '/bin/sh'
  ⎿  Stop hook error: Failed with non-blocking status code: Error occurred while executing hook command: ENOENT: no such file or directory, posix_spawn '/bin/sh'
  ⎿  Stop hook error: Failed with non-blocking status code: Error occurred while executing hook command: ENOENT: no such file or directory, posix_spawn '/bin/sh'

Root Cause:

• /bin/sh exists on the system and works fine for normal Bash tool operations
• Hooks are wrapped internally by Claude Code using /bin/sh -c "..."
• The sandbox profile doesn't include /bin/sh in its visible filesystem for hook execution

Environment:

• macOS Darwin 25.2.0 (Apple Silicon)
• /bin/sh exists: -rwxr-xr-x 1 root wheel 101232 Nov 22 06:49 /bin/sh
• Plugins with Stop hooks: Axiom, Flow-next, Hookify

What Should Happen?

Hooks should execute successfully. The sandbox should either:

1. Include /bin/sh in the visible filesystem for hook execution
2. Use a different execution method that doesn't rely on /bin/sh
3. Fall back gracefully if /bin/sh is unavailable

Error Messages/Logs

ENOENT: no such file or directory, posix_spawn '/bin/sh'

Steps to Reproduce

1. Install plugins that register Stop hooks (e.g., Axiom, Flow-next, Hookify)
2. Start a Claude Code session
3. End the session (triggers Stop hooks)
4. Observe the 3 hook errors

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Latest (2026-01-22)

Platform

Anthropic Console (claude.ai)

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

Related to #15026 (pgrep ENOENT) - both are sandbox visibility issues where system binaries aren't accessible in the sandboxed hook execution context, despite being available for normal Bash tool operations.