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/audit_worker_core_contract.md.

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

MANDATORY READ: Load shared/references/two_layer_detection.md for detection methodology.

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 (Layer 1)
   • 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. Analyze context per candidate (Layer 2)
   • DRY: read both code blocks to confirm true duplication (not just similar naming or shared interface)
   • KISS: check if abstraction serves DI pattern (valid single-impl interface) or is premature
   • YAGNI: check if feature flag was recently added (intentional) or dormant for months
5. Generate recommendations
   • MANDATORY READ: Load references/refactoring_decision_tree.md for pattern selection
   • Match each finding to appropriate refactoring pattern via decision tree
6. 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
7. Calculate score using penalty algorithm
8. 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
9. Return Summary: Return minimal summary to coordinator (see Output Format)

Two-Layer Detection (MANDATORY)

MANDATORY READ: shared/references/two_layer_detection.md

All findings require Layer 2 context analysis. Layer 1 finding without Layer 2 = NOT a valid finding. Before reporting, ask: "Is this violation intentional or justified by design?"

Finding Type	Layer 2 Downgrade Examples
DRY	Modules with different lifecycle/ownership → skip. Intentional duplication for decoupling → skip
KISS	Framework-required abstraction (e.g., DI in Spring) → downgrade. Single implementation today but interface for testing → skip
YAGNI	Feature flag used in A/B testing → skip. Config option used by ops team → skip
Error Handling	Centralized handler absent in 50-line script → downgrade to LOW
DI	Dependencies replaceable via params/closures → skip ARCH-DI

Audit Rules

1. DRY Violations (Don't Repeat Yourself)

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

Type	What	Severity	Exception (skip/downgrade)	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	Different lifecycle/ownership modules → skip. Intentional decoupling → skip	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	Different security contexts (auth vs public) → skip	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	User-facing strings requiring per-context wording → downgrade	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	Modules with divergent evolution expected → skip	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	Different bounded contexts; shared DB is worse than duplication → skip	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	Tests intentionally isolated for clarity/independence → downgrade	Extract to test helpers	M
1.7 Repeated API Responses	Same response object shapes without DTOs	MEDIUM: in 5+ endpoints. LOW: <5 endpoints	Responses with different versioning lifecycle → skip	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	Routes with different auth/rate-limit requirements → skip	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	Types with different ownership/evolution paths → skip	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	Mappings with different validation/enrichment rules → skip	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	Exception (skip/downgrade)	Recommendation	Effort
Abstract class with 1 implementation	Grep abstract class → count subclasses	HIGH: prevents understanding core logic	Interface for DI/testing → skip. Framework-required (Spring, ASP.NET) → skip	Remove abstraction, inline	L
Factory for <3 types	Grep factory patterns → count branches	MEDIUM: unnecessary pattern	Factory used for DI/testing swap → downgrade	Replace with direct construction	M
Deep inheritance >3 levels	Trace extends chain	HIGH: fragile hierarchy	Framework-mandated hierarchy (UI widgets, ORM models) → downgrade	Flatten with composition	L
Excessive generic constraints	Grep <T extends ... & ...>	LOW: acceptable tradeoff	Type safety for public API boundary → skip	Simplify constraints	M
Wrapper-only classes	Read: all methods delegate to inner	MEDIUM: unnecessary indirection	Adapter pattern for external API isolation → skip	Remove wrapper, use inner directly	M

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

Violation	Detection	Severity	Exception (skip/downgrade)	Recommendation	Effort
Dead feature flags (always true/false)	Grep flags → verify never toggled	LOW: cleanup needed	A/B testing flags → skip. Ops-controlled toggles → skip	Remove flag, keep active code path	M
Abstract methods never overridden	Grep abstract → search implementations	MEDIUM: unused extensibility	Plugin/extension point in public library → downgrade	Remove abstract, make concrete	M
Unused config options	Grep config key → 0 references	LOW: dead config	Env-specific configs (staging/prod) → verify before flagging	Remove option	S
Interface with 1 implementation	Grep interface → count implementors	MEDIUM: premature abstraction	Interface for DI/testing mock → skip	Remove interface, use class directly	M
Premature generics (used with 1 type)	Grep generic usage → count type params	LOW: over-engineering	Public library API designed for consumers → skip	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

Outcome Goal: All errors are logged with context and return clear user-facing messages. No error is silently swallowed. Stack traces never leak to production responses. Implementation choice (ErrorHandler class, middleware, decorator) depends on project stack and size.

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

Outcome Goal: Dependencies are replaceable for testing without modifying production code. No tight coupling between service instantiation and business logic. Implementation choice (DI container, factory functions, parameter injection, closures) depends on project size and stack.

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_worker_core_contract.md and shared/references/audit_scoring.md.

Output Format

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

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. Follow shared/templates/audit_worker_report_template.md.

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. Format is defined in references/detection_patterns.md.

Return summary to coordinator:

Report written: docs/project/.audit/ln-620/{YYYY-MM-DD}/623-principles-users.md
Score: X.X/10 | Issues: N (C:N H:N M:N L:N)

Critical Rules

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

• 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

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

• 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

• Detection patterns: references/detection_patterns.md
• Refactoring decision tree: references/refactoring_decision_tree.md

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Version: 5.0.0 Last Updated: 2026-02-08