API Contract Auditor (L3 Worker) Skill

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API Contract Auditor (L3 Worker)

Type: L3 Worker

Specialized worker auditing API contracts, method signatures at service boundaries, and DTO usage patterns.

Purpose & Scope

Worker in ln-640 coordinator pipeline - invoked by ln-640-pattern-evolution-auditor
Audit API contracts at architecture level (service boundaries, layer separation)
Check layer leakage, DTO patterns, error contract consistency
Return structured analysis with 4 scores (compliance, completeness, quality, implementation)

Out of Scope (owned by ln-623-code-principles-auditor):

Code duplication (same DTO shape repeated, same mapping logic, same validation)
Report only ARCHITECTURE BOUNDARY findings (wrong layer, missing contract)

Input (from ln-640 coordinator)

- pattern: "API Contracts"     # Pattern name
- locations: string[]          # Service/API directories
- adr_reference: string        # Path to related ADR
- bestPractices: object        # Best practices from MCP Ref/Context7
- output_dir: string           # e.g., ".hex-skills/runtime-artifacts/runs/{run_id}/audit-report"

# Domain-aware (optional, from coordinator)
- domain_mode: "global" | "domain-aware"   # Default: "global"
- current_domain: string                   # e.g., "users", "billing" (only if domain-aware)
- scan_path: string                        # e.g., "src/users/" (only if domain-aware)

Workflow

Phase 0: Load References

MANDATORY READ: Load shared/references/two_layer_detection.md for detection methodology. Load references/detection_patterns.md -- language-specific Grep patterns for all 5 rules.

Phase 1: Discover Service Boundaries

scan_root = scan_path IF domain_mode == "domain-aware" ELSE codebase_root

1. Find API layer: Glob("**/api/**/*.py", "**/routes/**/*.ts", "**/controllers/**/*.ts", root=scan_root)
2. Find service layer: Glob("**/services/**/*.py", "**/services/**/*.ts", root=scan_root)
3. Find domain layer: Glob("**/domain/**/*.py", "**/models/**/*.py", root=scan_root)
4. Map: which services are called by which API endpoints

Phase 2: Analyze Contracts (5 Rules)

MANDATORY READ: Use detection_patterns.md for language-specific Grep patterns per rule.

| # | Rule | Severity | What to Check | |---|------|----------|---------------| | 1 | Layer Leakage | HIGH/MEDIUM | Service/domain accepts HTTP types (Request, parsed_body, headers) | | 2 | Missing DTO | MEDIUM/LOW | 4+ params repeated in 2+ methods without grouping DTO | | 3 | Entity Leakage | HIGH/MEDIUM | ORM entity returned from API without response DTO. Downgrade when: internal API with no external consumers -> LOW | | 4 | Error Contracts | MEDIUM/LOW | Mixed error patterns (raise + return None) in same service | | 5 | Redundant Overloads | LOW/MEDIUM | Method pairs with _with_/_and_ suffix differing by 1-2 params | | 6 | Architectural Honesty | HIGH/MEDIUM | Read-named function (get_/find_/check_/validate_/is_/has_) body contains write side-effects. Exclusions per shared/references/ai_ready_architecture.md |

Scope boundary: SKIP DUPLICATION findings (owned by ln-623), REPORT only ARCHITECTURE BOUNDARY findings.

Phase 3: Calculate 4 Scores

Compliance Score (0-100):

| Criterion | Points | |-----------|--------| | No layer leakage (HTTP types in service) | +35 | | Consistent error handling pattern | +25 | | Follows project naming conventions | +10 | | No hidden side-effects in read-named functions | +10 | | No entity leakage to API | +20 |

Completeness Score (0-100):

| Criterion | Points | |-----------|--------| | All service methods have typed params | +30 | | All service methods have typed returns | +30 | | DTOs defined for complex data | +20 | | Error types documented/typed | +20 |

Quality Score (0-100):

| Criterion | Points | |-----------|--------| | No boolean flag params in service methods | +15 | | No opaque return types hiding write actions | +10 | | No methods with >5 params without DTO | +25 | | Consistent naming across module | +25 | | No redundant overloads | +25 |

Implementation Score (0-100):

| Criterion | Points | |-----------|--------| | DTOs/schemas exist and are used | +30 | | Type annotations present | +25 | | Validation at boundaries (Pydantic, Zod) | +25 | | API response DTOs separate from domain | +20 |

Phase 3.5: Calculate Score

MANDATORY READ: Load shared/references/audit_worker_core_contract.md and shared/references/audit_scoring.md.

Primary score uses penalty formula (same as all workers):

penalty = (critical x 2.0) + (high x 1.0) + (medium x 0.5) + (low x 0.2)
score = max(0, 10 - penalty)

Diagnostic sub-scores (0-100 each) are calculated separately and reported in AUDIT-META for diagnostic purposes only.

Phase 4: Write Report

MANDATORY READ: Load shared/references/audit_worker_core_contract.md and shared/templates/audit_worker_report_template.md.

If summaryArtifactPath is present, write JSON summary per shared/references/audit_summary_contract.md. Compact text output is fallback only.

# Build markdown report in memory with:
# - AUDIT-META (extended: score [penalty-based] + diagnostic score_compliance/completeness/quality/implementation)
# - Checks table (layer_leakage, missing_dto, entity_leakage, error_contracts, redundant_overloads)
# - Findings table (issues sorted by severity)
# - DATA-EXTENDED: issues array with principle + domain fields (for cross-domain aggregation)

IF domain_mode == "domain-aware":
  Write to {output_dir}/643-api-contract-{current_domain}.md
ELSE:
  Write to {output_dir}/643-api-contract.md

Phase 5: Return Summary

Report written: .hex-skills/runtime-artifacts/runs/{run_id}/audit-report/643-api-contract-users.md
Score: 6.75/10 (C:65 K:70 Q:55 I:80) | Issues: 4 (H:2 M:1 L:1)

Critical Rules

MANDATORY READ: Load shared/references/audit_worker_core_contract.md.

Architecture-level only: Focus on service boundaries, not internal implementation
Read before score: Never score without reading actual service code
Scope boundary: SKIP duplication findings (owned by ln-623)
Detection patterns: Use language-specific Grep from detection_patterns.md
Domain-aware: When domain_mode="domain-aware", scan only scan_path, tag findings with domain

Definition of Done

MANDATORY READ: Load shared/references/audit_worker_core_contract.md.

[ ] Service boundaries discovered (API, service, domain layers)
[ ] Method signatures extracted and analyzed
[ ] All 5 rules checked using detection_patterns.md
[ ] Scope boundary applied (no duplication with ln-623)
[ ] 4 scores calculated with justification
[ ] Issues identified with severity, location, suggestion, effort
[ ] If domain-aware: findings tagged with domain field
[ ] Report written to {output_dir}/643-api-contract[-{domain}].md (atomic single Write call)
[ ] Summary written per contract

Reference Files

Detection patterns: references/detection_patterns.md
Scoring rules: ../ln-640-pattern-evolution-auditor/references/scoring_rules.md
Pattern library: ../ln-640-pattern-evolution-auditor/references/pattern_library.md

Version: 2.0.0 Last Updated: 2026-02-08

Agent Skills: API Contract Auditor (L3 Worker)

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