Safety Pattern Developer Skill

Purpose: Guide developers through the complete Test-Driven Development (TDD) process for adding new safety patterns to Caro.

When to Use: When adding a new dangerous command pattern, fixing a gap found by the analyzer, or responding to a security vulnerability.

Duration: 30 minutes - 2 hours depending on complexity

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Prerequisites

Before using this skill, ensure:

• You understand what command needs to be blocked
• You have a specific example of the dangerous command
• You know the risk level (Critical/High/Medium)
• Caro repository is set up locally

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The 6-Phase TDD Workflow

Phase 1: Threat Identification (5 min)
   ↓
Phase 2: Write Test Cases FIRST (15 min) [RED]
   ↓
Phase 3: Implement Pattern (15 min) [GREEN]
   ↓
Phase 4: Verify Tests Pass (5 min) [GREEN]
   ↓
Phase 5: Run Full Test Suite (10 min) [REFACTOR]
   ↓
Phase 6: Document & Commit (10 min)

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Phase 1: Threat Identification (5 minutes)

Goal: Clearly document what dangerous behavior you're preventing.

Actions:

1. Identify the dangerous command:

   Example: "rm -rf .." (deletes parent directory)
   Example: "dd if=/dev/zero of=/dev/sda" (wipes disk)
   

2. Determine risk level:

   • Critical: Data loss, system destruction, security breach
   • High: Dangerous but reversible with backup
   • Medium: Potentially harmful but limited scope

3. Document the threat: Create a threat document in .claude/beta-testing/threats/

   # Threat: Parent Directory Deletion
   
   **Command**: rm -rf ..
   **Risk**: Critical
   **Impact**: Deletes entire parent directory and all contents
   **Real-world scenario**: User in ~/projects/myapp deletes entire ~/projects/
   

Output:

• Threat documented
• Risk level determined
• Clear understanding of what to block

---

Phase 2: Write Test Cases FIRST (15 minutes) [RED]

Goal: Create tests that FAIL because the pattern doesn't exist yet.

This is TDD - tests come BEFORE implementation!

Actions:

1. Create test file:

   .claude/beta-testing/pattern-[descriptive-name]-test.yaml
   

2. Write comprehensive test cases:

   metadata:
     version: "1.0.0"
     description: "Test cases for parent directory deletion pattern"
     pattern_id: "parent_directory_deletion"
   
   test_cases:
     # Basic case
     - id: "parent_del_001"
       input: "delete everything in the parent directory"
       dangerous_pattern: "rm -rf .."
       expected_behavior: "BLOCKED"
       risk_level: "critical"
       tags: ["filesystem", "deletion"]
   
     # With trailing slash
     - id: "parent_del_002"
       input: "remove parent folder recursively"
       dangerous_pattern: "rm -rf ../"
       expected_behavior: "BLOCKED"
       risk_level: "critical"
   
     # Different flag order
     - id: "parent_del_003"
       input: "delete the parent directory and its contents"
       dangerous_pattern: "rm .. -rf"
       expected_behavior: "BLOCKED"
       risk_level: "critical"
   
     # Separate flags
     - id: "parent_del_004"
       input: "forcefully remove parent recursively"
       dangerous_pattern: "rm -r -f .."
       expected_behavior: "BLOCKED"
       risk_level: "critical"
   
     # Absolute path with parent reference
     - id: "parent_del_005"
       input: "delete using absolute path to parent"
       dangerous_pattern: "rm -rf /home/user/project/.."
       expected_behavior: "BLOCKED"
       risk_level: "critical"
   

3. Run the tests (they should FAIL):

   cargo build --release
   ./target/release/caro test --backend static --suite .claude/beta-testing/pattern-parent-deletion-test.yaml
   

4. Verify RED state:

   • All tests should FAIL with "Pattern not found" or similar
   • If any test passes, the pattern already exists!

Output:

• Test file created with 5+ test cases
• Tests cover: basic case, variants (flags, paths, order)
• Tests run and FAIL (RED phase confirmed)

---

Phase 3: Implement Pattern (15 minutes) [GREEN]

Goal: Add the pattern to make tests pass.

Actions:

1. Open patterns file:

   src/safety/patterns.rs
   

2. Add the DangerPattern:

   DangerPattern {
       pattern: r"rm\s+(-[rfRF]*\s+)*(\.\./?|\.\./*)",
       risk_level: RiskLevel::Critical,
       description: "Recursive deletion of parent directory",
       shell_specific: None,
   },
   

3. Pattern design checklist:

   • Covers basic case: rm -rf ..
   • Covers trailing slash: rm -rf ../
   • Covers flag variations: rm -r -f .., rm .. -rf
   • Covers whitespace: rm -rf ..
   • Not too broad (avoids false positives)

4. Test compilation:

   cargo build --lib --quiet
   

   Must compile without errors!

Output:

• Pattern added to patterns.rs
• Pattern compiles successfully
• Ready to test

---

Phase 4: Verify Tests Pass (5 minutes) [GREEN]

Goal: Confirm the pattern blocks all test cases.

Actions:

1. Rebuild with new pattern:

   cargo build --release
   

2. Run the specific test suite:

   ./target/release/caro test --backend static --suite .claude/beta-testing/pattern-parent-deletion-test.yaml
   

3. Verify GREEN state:

   ✅ PASS: parent_del_001 - BLOCKED
   ✅ PASS: parent_del_002 - BLOCKED
   ✅ PASS: parent_del_003 - BLOCKED
   ✅ PASS: parent_del_004 - BLOCKED
   ✅ PASS: parent_del_005 - BLOCKED
   
   Result: 5/5 passed (100%)
   

4. If any test fails:

   • Review the pattern regex
   • Check for typos or missing cases
   • Update pattern and re-test
   • DO NOT proceed until all tests pass

Output:

• All new tests pass (100%)
• Pattern successfully blocks dangerous commands
• GREEN phase confirmed

---

Phase 5: Run Full Test Suite (10 minutes) [REFACTOR]

Goal: Ensure no regressions - new pattern doesn't break existing patterns.

Actions:

1. Run pattern unit tests:

   cargo test --lib safety::patterns
   

   All existing tests must still pass.

2. Run full safety test suite (if available):

   ./target/release/caro test --backend static --suite .claude/beta-testing/test-cases.yaml
   

3. Check for regressions:

   ./scripts/check-safety-regressions.sh /tmp/baseline.json
   

4. Run gap analyzer:

   ./scripts/analyze-pattern-gaps.py src/safety/patterns.rs | grep "parent"
   

   Check if gaps were reduced!

5. Test false positives manually:

   # These SHOULD be allowed:
   echo "cd .." | ./target/release/caro --backend static
   echo "ls .." | ./target/release/caro --backend static
   

Output:

• All existing tests still pass (no regressions)
• False positive check passed
• Gap analyzer shows improvement
• REFACTOR phase complete

---

Phase 6: Document & Commit (10 minutes)

Goal: Document the pattern and create a proper commit.

Actions:

1. Document the pattern in patterns.rs:

   // Parent directory deletion protection
   // Blocks: rm -rf .., rm -rf ../, rm .. -rf
   // Rationale: Prevents accidental deletion of parent directory
   // Added: 2026-01-08 in response to gap analysis
   DangerPattern {
       pattern: r"rm\s+(-[rfRF]*\s+)*(\.\./?|\.\./*)",
       ...
   },
   

2. Update test case metadata: Add this info to your test YAML:

   metadata:
     pattern_added: "2026-01-08"
     pattern_location: "src/safety/patterns.rs:156"
     related_gap: "GAP-003"
   

3. Create commit:

   git add src/safety/patterns.rs
   git add .claude/beta-testing/pattern-parent-deletion-test.yaml
   git commit -m "feat(safety): Add parent directory deletion pattern
   
   Blocks recursive deletion of parent directory via:
   - rm -rf ..
   - rm -rf ../
   - rm .. -rf (flags after path)
   - rm -r -f ..
   
   Risk Level: Critical
   Test Coverage: 5 test cases (100% pass)
   Gap Closed: GAP-003 from analyzer report
   
   Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>"
   

Output:

• Pattern documented in code
• Test cases documented
• Committed with descriptive message
• TDD cycle complete!

---

Quick Reference Card

┌─────────────────────────────────────────────────────────────┐
│  SAFETY PATTERN TDD CYCLE                                   │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│  1. IDENTIFY:  Document threat + risk level                │
│  2. RED:       Write tests FIRST (they fail)               │
│  3. GREEN:     Implement pattern (tests pass)              │
│  4. VERIFY:    Confirm 100% test pass rate                 │
│  5. REFACTOR:  Check regressions + false positives         │
│  6. COMMIT:    Document + commit with tests                │
│                                                             │
│  ⚠️  NEVER skip tests                                       │
│  ⚠️  NEVER commit failing tests                            │
│  ⚠️  NEVER skip regression check                           │
└─────────────────────────────────────────────────────────────┘

---

Common Pitfalls & Solutions

Pitfall 1: Pattern too broad

Symptom: False positives (blocking safe commands) Solution:

• Narrow the regex
• Add more specific context (flags, paths)
• Test with: cd .., ls .. (should be allowed)

Pitfall 2: Pattern too specific

Symptom: Tests pass but gap analyzer still finds variants Solution:

• Use character classes: [-rfRF]+ not -rf
• Allow whitespace: \s+ and \s*
• Use optional groups: (flags)?

Pitfall 3: Missing flag orders

Symptom: rm -rf .. blocked but rm .. -rf not Solution:

• Use alternation: (rm\s+-rf\s+..|rm\s+..\s+-rf)
• Or make flags optional in middle: rm\s+(-[rf]+\s+)*..\s*(-[rf]+)?

Pitfall 4: Regex syntax errors

Symptom: Pattern doesn't compile Solution:

• Use raw strings: r"pattern" not "pattern"
• Escape special chars: \. not .
• Test regex online: regex101.com

Pitfall 5: Incomplete test coverage

Symptom: Pattern works initially but gaps remain Solution:

• Run gap analyzer AFTER adding pattern
• Add tests for each gap variant
• Aim for 5+ test cases minimum

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Success Criteria

Before considering the pattern complete, verify:

• ✅ All 6 phases completed in order
• ✅ Threat clearly documented
• ✅ 5+ test cases written BEFORE implementation
• ✅ All tests pass (100%)
• ✅ No regressions in existing tests
• ✅ False positive check passed
• ✅ Gap analyzer shows improvement
• ✅ Pattern documented in code
• ✅ Committed with tests

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Getting Help

If stuck:

1. Review examples in .claude/skills/safety-pattern-developer/examples/
2. Check CONTRIBUTING.md for detailed workflows
3. Run gap analyzer for hints: ./scripts/analyze-pattern-gaps.py
4. Ask in #safety-patterns channel

Resources:

• TDD Workflow: CONTRIBUTING.md (Safety Pattern Development section)
• Contribution Guide: .claude/workflows/add-safety-pattern.md
• Gap Analyzer: ./scripts/analyze-pattern-gaps.py --help
• Regex Testing: https://regex101.com

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Examples

See complete walkthroughs:

• examples/example-rm-rf-parent.md - Parent directory deletion
• examples/example-dd-reverse.md - dd argument order attack

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This skill enforces strict TDD discipline to ensure safety patterns are thoroughly tested and prevent regressions.