Problem

The terminal tool's safety filter blocks legitimate commands when keywords like nohup, disown, or setsid appear inside quoted strings — e.g., in commit messages, Python -c code, gh pr create --body text, or grep patterns.

Examples that get incorrectly blocked:

python3 -c "x = 'preexec_fn=os.setsid'"
git commit -m "fix: replace preexec_fn=os.setsid with process_group=0"
gh pr create --body "We removed os.setsid..."
grep -r 'nohup' tests/

Root Cause

_foreground_background_guidance() in tools/terminal_tool.py uses:

_SHELL_LEVEL_BACKGROUND_RE = re.compile(r"\b(?:nohup|disown|setsid)\b", re.IGNORECASE)

This matches the keyword anywhere in the full command text, including inside quoted strings.

Fix

Two-layer approach:

1. _strip_quotes() helper — Removes single-quoted, double-quoted, and backtick-quoted content before pattern matching, so keywords inside strings are invisible to the regexes.

2. Position-aware regex — Tightened to only match keywords at shell command positions (after ^, ;, &&, ||, $() rather than at any word boundary.

Both layers are needed: quote stripping handles the common case (keywords in string literals), and the position-aware regex handles unquoted edge cases.

Testing

• All 14 test_terminal_tool.py tests pass
• All 45 test_terminal_compound_background.py + test_terminal_foreground_timeout_cap.py tests pass
• Verified 7 false-positive cases now pass (quoted keywords)
• Verified 5 true-positive cases still blocked (actual background wrapper usage)

Fixes #20064