Agent Skills: Code Principles Auditor (L3 Worker)

Paths: File paths (shared/, references/, ../ln-*) are relative to skills repo root. If not found at CWD, locate this SKILL.md directory and go up one level for repo root.

Code Principles Auditor (L3 Worker)

Specialized worker auditing code principles (DRY, KISS, YAGNI) and design patterns.

Purpose & Scope

• Worker in ln-620 coordinator pipeline - invoked by ln-620-codebase-auditor
• Audit code principles (DRY/KISS/YAGNI, error handling, DI)
• Return structured findings with severity, location, effort, pattern_signature, recommendations
• Calculate compliance score (X/10) for Code Principles category

Inputs (from Coordinator)

MANDATORY READ: Load shared/references/task_delegation_pattern.md#audit-coordinator--worker-contract for contextStore structure.

Receives contextStore with: tech_stack, best_practices, principles, codebase_root, output_dir.

Domain-aware: Supports domain_mode + current_domain (see audit_output_schema.md#domain-aware-worker-output).

Workflow

1. Parse context — extract fields, determine scan_path (domain-aware if specified), extract output_dir
2. Load detection patterns
   • MANDATORY READ: Load references/detection_patterns.md for language-specific Grep/Glob patterns
   • Select patterns matching project's tech_stack
3. Scan codebase for violations
   • All Grep/Glob patterns use scan_path (not codebase_root)
   • Follow step-by-step detection from detection_patterns.md
   • Apply exclusions from detection_patterns.md#exclusions
4. Generate recommendations
   • MANDATORY READ: Load references/refactoring_decision_tree.md for pattern selection
   • Match each finding to appropriate refactoring pattern via decision tree
5. Collect findings with severity, location, effort, pattern_id, pattern_signature, recommendation
   • Tag each finding with domain: domain_name (if domain-aware)
   • Assign pattern_signature for cross-domain matching by ln-620
6. Calculate score using penalty algorithm
7. Write Report: Build full markdown report in memory per shared/templates/audit_worker_report_template.md, write to {output_dir}/623-principles-{domain}.md (or 623-principles.md in global mode) in single Write call. Include <!-- FINDINGS-EXTENDED --> JSON block with pattern_signature fields for cross-domain DRY analysis
8. Return Summary: Return minimal summary to coordinator (see Output Format)

Audit Rules

1. DRY Violations (Don't Repeat Yourself)

MANDATORY READ: Load references/detection_patterns.md for detection steps per type.

| Type | What | Severity | Default Recommendation | Effort | |------|------|----------|----------------------|--------| | 1.1 Identical Code | Same functions/constants/blocks (>10 lines) in multiple files | HIGH: business-critical (auth, payment). MEDIUM: utilities. LOW: simple constants <5x | Extract function → decide location by duplication scope | M | | 1.2 Duplicated Validation | Same validation patterns (email, password, phone, URL) across files | HIGH: auth/payment. MEDIUM: user input 3+x. LOW: format checks <3x | Extract to shared validators module | M | | 1.3 Repeated Error Messages | Hardcoded error strings instead of centralized catalog | MEDIUM: critical messages hardcoded or no error catalog. LOW: <3 places | Create constants/error-messages file | M | | 1.4 Similar Patterns | Functions with same call sequence/control flow but different names/entities | MEDIUM: business logic in critical paths. LOW: utilities <3x | Extract common logic (see decision tree for pattern) | M | | 1.5 Duplicated SQL/ORM | Same queries in different services | HIGH: payment/auth queries. MEDIUM: common 3+x. LOW: simple <3x | Extract to Repository layer | M | | 1.6 Copy-Pasted Tests | Identical setup/teardown/fixtures across test files | MEDIUM: setup in 5+ files. LOW: <5 files | Extract to test helpers | M | | 1.7 Repeated API Responses | Same response object shapes without DTOs | MEDIUM: in 5+ endpoints. LOW: <5 endpoints | Create DTO/Response classes | M | | 1.8 Duplicated Middleware Chains | Identical middleware/decorator stacks on multiple routes | MEDIUM: same chain on 5+ routes. LOW: <5 routes | Create named middleware group, apply at router level | M | | 1.9 Duplicated Type Definitions | Interfaces/structs/types with 80%+ same fields | MEDIUM: in 5+ files. LOW: 2-4 files | Create shared base type, extend where needed | M | | 1.10 Duplicated Mapping Logic | Same entity→DTO / DTO→entity transformations in multiple locations | MEDIUM: in 3+ locations. LOW: 2 locations | Create dedicated Mapper class/function | M |

Recommendation selection: Use references/refactoring_decision_tree.md to choose the right refactoring pattern based on duplication location (Level 1) and logic type (Level 2).

2. KISS Violations (Keep It Simple, Stupid)

| Violation | Detection | Severity | Recommendation | Effort | |-----------|-----------|----------|---------------|--------| | Abstract class with 1 implementation | Grep abstract class → count subclasses | HIGH: prevents understanding core logic | Remove abstraction, inline | L | | Factory for <3 types | Grep factory patterns → count branches | MEDIUM: unnecessary pattern | Replace with direct construction | M | | Deep inheritance >3 levels | Trace extends chain | HIGH: fragile hierarchy | Flatten with composition | L | | Excessive generic constraints | Grep <T extends ... & ...> | LOW: acceptable tradeoff | Simplify constraints | M | | Wrapper-only classes | Read: all methods delegate to inner | MEDIUM: unnecessary indirection | Remove wrapper, use inner directly | M |

3. YAGNI Violations (You Aren't Gonna Need It)

| Violation | Detection | Severity | Recommendation | Effort | |-----------|-----------|----------|---------------|--------| | Dead feature flags (always true/false) | Grep flags → verify never toggled | LOW: cleanup needed | Remove flag, keep active code path | M | | Abstract methods never overridden | Grep abstract → search implementations | MEDIUM: unused extensibility | Remove abstract, make concrete | M | | Unused config options | Grep config key → 0 references | LOW: dead config | Remove option | S | | Interface with 1 implementation | Grep interface → count implementors | MEDIUM: premature abstraction | Remove interface, use class directly | M | | Premature generics (used with 1 type) | Grep generic usage → count type params | LOW: over-engineering | Replace generic with concrete type | S |

4. Missing Error Handling

• Find async functions without try-catch
• Check API routes without error middleware
• Verify database calls have error handling

| Severity | Criteria | |----------|----------| | CRITICAL | Payment/auth without error handling | | HIGH | User-facing operations without error handling | | MEDIUM | Internal operations without error handling |

Effort: M

5. Centralized Error Handling

• Search for centralized error handler: ErrorHandler, errorHandler, error-handler.*
• Check if middleware delegates to handler
• Verify async routes use promises/async-await
• Anti-pattern: process.on("uncaughtException") usage

| Severity | Criteria | |----------|----------| | HIGH | No centralized error handler | | HIGH | Using uncaughtException listener (Express anti-pattern) | | MEDIUM | Middleware handles errors directly (no delegation) | | MEDIUM | Async routes without proper error handling | | LOW | Stack traces exposed in production |

Recommendation: Create single ErrorHandler class. Middleware catches and forwards. Use async/await. DO NOT use uncaughtException listeners.

Effort: M-L

6. Dependency Injection / Centralized Init

• Check for DI container: inversify, awilix, tsyringe (Node), dependency_injector (Python), Spring @Autowired (Java), ASP.NET IServiceCollection (C#)
• Grep for new SomeService() in business logic (direct instantiation)
• Check for bootstrap module: bootstrap.ts, init.py, Startup.cs, app.module.ts

| Severity | Criteria | |----------|----------| | MEDIUM | No DI container (tight coupling) | | MEDIUM | Direct instantiation in business logic | | LOW | Mixed DI and direct imports |

Recommendation: Use DI container. Centralize init in bootstrap module. Inject via constructor.

Effort: L

7. Missing Best Practices Guide

• Check for: docs/architecture.md, docs/best-practices.md, ARCHITECTURE.md, CONTRIBUTING.md

| Severity | Criteria | |----------|----------| | LOW | No architecture/best practices guide |

Recommendation: Create docs/architecture.md with layering rules, error handling patterns, DI usage, coding conventions.

Effort: S

Scoring Algorithm

MANDATORY READ: Load shared/references/audit_scoring.md for unified scoring formula.

Output Format

MANDATORY READ: Load shared/templates/audit_worker_report_template.md for file format.

Write report to {output_dir}/623-principles-{domain}.md (or 623-principles.md in global mode) with category: "Architecture & Design".

FINDINGS-EXTENDED block (required for this worker): After the Findings table, include a <!-- FINDINGS-EXTENDED --> JSON block containing all DRY findings with pattern_signature for cross-domain matching by ln-620 coordinator. See template for format.

pattern_id: DRY type identifier (dry_1.1 through dry_1.10). Omit for non-DRY findings.

pattern_signature: Normalized key for the detected pattern (e.g., validation_email, sql_users_findByEmail, middleware_auth_validate_ratelimit). Same signature in multiple domains triggers cross-domain DRY finding. See detection_patterns.md for format per DRY type.

Return summary to coordinator:

Report written: docs/project/.audit/623-principles-users.md
Score: X.X/10 | Issues: N (C:N H:N M:N L:N)

Critical Rules

• Do not auto-fix: Report only
• Domain-aware scanning: If domain_mode="domain-aware", scan ONLY scan_path
• Tag findings: Include domain field in each finding when domain-aware
• Pattern signatures: Include pattern_id + pattern_signature for every DRY finding
• Context-aware: Use project's principles.md to define what's acceptable
• Effort realism: S = <1h, M = 1-4h, L = >4h
• Exclusions: Skip generated code, vendor, migrations (see detection_patterns.md#exclusions)

Definition of Done

• contextStore parsed (including domain_mode, current_domain, output_dir)
• scan_path determined (domain path or codebase root)
• Detection patterns loaded from references/detection_patterns.md
• All 7 checks completed (scoped to scan_path):
  • DRY (10 subcategories: 1.1-1.10), KISS, YAGNI, Error Handling, Centralized Errors, DI/Init, Best Practices Guide
• Recommendations selected via references/refactoring_decision_tree.md
• Findings collected with severity, location, effort, pattern_id, pattern_signature, recommendation, domain
• Score calculated per shared/references/audit_scoring.md
• Report written to {output_dir}/623-principles-{domain}.md with FINDINGS-EXTENDED block (atomic single Write call)
• Summary returned to coordinator

Reference Files

• Worker report template: shared/templates/audit_worker_report_template.md
• Detection patterns: references/detection_patterns.md
• Refactoring decision tree: references/refactoring_decision_tree.md
• Audit scoring formula: shared/references/audit_scoring.md
• Audit output schema: shared/references/audit_output_schema.md

Version: 5.0.0 Last Updated: 2026-02-08