fix(shell): replace polynomial-regex patterns flagged by CodeQL

[mabry1985]

Unblocks the dev → main promotion in PR #141.

CodeQL flagged two js/polynomial-redos alerts on the background-shell wrapper code landed in #140:

• shell.ts:292 — &+$ on a trimmed string
• shell.ts:305 — \s*&\s*$ on a trimmed string

Practical risk is low (inputs are bounded, model-emitted shell commands), but the alerts are gating PR #141. Swap each regex for a plain string-op equivalent — same intent, no quantifier-on-quantifier shape for the analyzer to flag.

55/55 shell tests still pass.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Refactor
  • Optimized internal shell command string processing logic for improved maintainability.

[coderabbitai]

Caution

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The pull request is closed.

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📥 Commits

Reviewing files that changed from the base of the PR and between e973040 and e8cd4e7.

📒 Files selected for processing (1)

• packages/core/src/tools/shell.ts

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Walkthrough

Modified trailing ampersand (&) normalization in shell command execution logic. Replaced regex-based removal with deterministic string operations for Windows background execution and non-Windows disk-captured background execution, without altering control flow or behavior.

Changes

Cohort / File(s)	Summary
Shell tool string cleanup packages/core/src/tools/shell.ts	Updated trailing & character removal from regex patterns (/&+$/) to explicit string operations using endsWith(), slice(), and trimEnd() for improved determinism in Windows and non-Windows background execution paths.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

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