statusLine: external binaries produce no captured stdout — requires bash -c wrapper

Description

When configuring statusLine.command in ~/.claude/settings.json, external binaries (py, python, python3, and likely any non-builtin command) produce no captured output. The statusline remains empty with no error message.

Bash builtins (echo, printf) work correctly. Wrapping the external command in bash -c '...' resolves the issue.

Reproduction

// Does NOT work — statusline empty, no error
{
  "statusLine": {
    "type": "command",
    "command": "python3 /path/to/statusline.py"
  }
}

// Works correctly
{
  "statusLine": {
    "type": "command",
    "command": "bash -c 'python3 /path/to/statusline.py'"
  }
}

Systematic test results

| Command | Type | Output captured? |
|---------|------|-----------------|
| echo TEST | bash builtin | Yes |
| printf 'text' | bash builtin | Yes |
| py statusline.py | external binary | No |
| python statusline.py | external binary | No |
| /full/path/to/python statusline.py | external, full path | No |
| python -c "print('X')" | external, inline | No |
| bash -c 'python -c "print(X)"' | external via bash -c | Yes |
| bash -c 'py statusline.py' | external via bash -c | Yes |

Diagnostic details

• The script produces correct output when run manually (echo JSON | py statusline.py)
• A debug wrapper confirmed Claude Code does send JSON to stdin and the script does produce stdout — but the output is not captured/displayed
• Full path to the binary does not help
• The pattern is consistent: bash builtins work, external binaries don't

Environment

• Claude Code v2.1.92
• Windows 11 Pro 10.0.26200
• Python 3.13.12 (py launcher)
• Terminal: Windows Terminal + bash

Expected behavior

External binaries in statusLine.command should have their stdout captured the same way bash builtins do.

Workaround

Wrap the command in bash -c '...':

"command": "bash -c 'python3 /path/to/script.py'"