fix(security): sanitize control characters in prompt file paths

[la14-1]

Why: Fixes terminal injection via unsanitized file paths in --prompt-file error messages. A crafted path containing ANSI escape sequences (e.g., $'\e[2J\e[H') could clear terminal output or display misleading messages in CI/CD environments parsing spawn output.

Fixes #3138

Changes

• Added stripControlChars() utility in security.ts for safe terminal display
• validatePromptFilePath() now rejects paths containing ASCII control characters (0x00-0x08, 0x0B-0x1F, 0x7F) early, before any file operations
• handlePromptFileError() in index.ts strips control characters as defense-in-depth
• Added 10 new tests covering control char rejection and stripping
• Version bump to 0.30.6

Test plan

• All 1987 existing tests pass
• Biome lint: zero errors
• New tests verify ANSI escape, null byte, bell, backspace, DEL rejection
• Normal paths still accepted

-- refactor/security-auditor

[louisgv]

Security Review

Verdict: APPROVED
Commit: eb96e3d

Summary

This PR addresses a HIGH severity terminal injection vulnerability by sanitizing control characters in prompt file paths. The fix is well-implemented with comprehensive test coverage.

Security Analysis

✅ Validation Layer (security.ts:649-655)

• Rejects paths containing control characters (0x00-0x08, 0x0B-0x1F, 0x7F) at validation time
• Prevents ANSI escape sequences, null bytes, and other dangerous characters
• Clear error message guides users

✅ Defense-in-Depth (index.ts:324)

• handlePromptFileError() sanitizes paths before displaying in error messages
• Protects error paths that run before validation (e.g., stat failures)
• Inlines the regex to avoid async import issues

✅ Helper Function (security.ts:564-566)

• stripControlChars() is properly exported for reuse
• Preserves tabs (0x09) and newlines (0x0A) for legitimate use cases
• Simple, correct regex implementation

✅ Test Coverage

• Comprehensive test suite with 21 passing tests
• Tests validation rejection for ANSI escapes, null bytes, bell, backspace, DEL
• Tests stripping function with edge cases (empty strings, preservation of tabs/newlines)
• Tests normal paths unchanged

Verification

• ✅ All tests pass (21/21)
• ✅ Biome lint clean (0 errors)
• ✅ Version bumped (0.30.5 → 0.30.6)

Threat Model

This fix mitigates:

• Terminal injection via crafted file paths (HIGH severity)
• Attackers could use ANSI escape sequences to manipulate terminal output
• Example: \x1b[2J\x1b[H (clear screen + move cursor) in file path

No findings.

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-- security/pr-reviewer