ln-511-code-quality-checker

What this skill does

> **Paths:** File paths (`references/`, `../ln-*`) are relative to this skill directory.

# Code Quality Checker

**Type:** L3 Worker
**Category:** 5XX Quality

Analyzes Done implementation tasks with quantitative Code Quality Score based on metrics, MCP Ref validation, and issue penalties.

## Inputs

| Input | Required | Source | Description |
|-------|----------|--------|-------------|
| `storyId` | Yes | args, git branch, kanban, user | Story to process |

**Resolution:** Story Resolution Chain.
**Status filter:** In Progress, To Review

Tool policy: follow host AGENTS.md MCP preferences; load `references/mcp_tool_preferences.md` and `references/mcp_integration_patterns.md` only when host policy is absent or MCP behavior is unclear. - use `hex-graph` as the primary path for clone, architecture, and semantic quality evidence when the project is indexed. Fall back to Grep/Read only when graph is unavailable or unsupported.

## Purpose & Scope
- Load Story and Done implementation tasks (exclude test tasks)
- Calculate Code Quality Score using metrics and issue penalties
- **MCP Ref validation:** Verify optimality, best practices, and performance via external sources
- Check for DRY/KISS/YAGNI violations, architecture boundary breaks, security issues
- Produce quantitative verdict with structured issue list; never edits Linear or kanban

## Code Metrics

| Metric | Threshold | Penalty |
|--------|-----------|---------|
| **Cyclomatic Complexity** | ≤10 OK, 11-20 warning, >20 fail | -5 (warning), -10 (fail) per function |
| **Function size** | ≤50 lines OK, >50 warning | -3 per function |
| **File size** | ≤500 lines OK, >500 warning | -5 per file |
| **Nesting depth** | ≤3 OK, >3 warning | -3 per instance |
| **Parameter count** | ≤4 OK, >4 warning | -2 per function |

## Code Quality Score

Formula: `Code Quality Score = 100 - metric_penalties - issue_penalties`

**Issue penalties by severity:**

| Severity | Penalty | Examples |
|----------|---------|----------|
| **high** | -20 | Security vulnerability, O(n²)+ algorithm, N+1 query |
| **medium** | -10 | DRY violation, suboptimal approach, missing config |
| **low** | -3 | Naming convention, minor code smell |

**Score interpretation:**

| Score | Status | Verdict |
|-------|--------|---------|
| 90-100 | Excellent | PASS |
| 70-89 | Acceptable | CONCERNS |
| <70 | Below threshold | ISSUES_FOUND |

## Issue Prefixes

| Prefix | Category | Default Severity | MCP Ref |
|--------|----------|------------------|---------|
| SEC- | Security (auth, validation, secrets) | high | — |
| SEC-DESTR- | Destructive ops (guards: DB, FS, MIG, ENV, FORCE) | high/medium | — |
| PERF- | Performance (algorithms, configs, bottlenecks) | medium/high | ✓ Required |
| MNT- | Maintainability (DRY, SOLID, complexity, dead code) | medium | — |
| ARCH- | Architecture (layers, boundaries, patterns, contracts) | medium | — |
| BP- | Best Practices (implementation differs from recommended) | medium | ✓ Required |
| OPT- | Optimality (better approach exists for this goal) | medium | ✓ Required |

**OPT- subcategories:**

| Prefix | Category | Severity |
|--------|----------|----------|
| OPT-OSS- | Open-source replacement available | medium (high if >200 LOC) |

**ARCH- subcategories:**

| Prefix | Category | Severity |
|--------|----------|----------|
| ARCH-LB- | Layer Boundary: I/O outside infra, HTTP in domain | high |
| ARCH-TX- | Transaction Boundaries: commit() in 3+ layers, mixed UoW ownership | high (CRITICAL if auth/payment) |
| ARCH-DTO- | Missing DTO (4+ params without DTO), Entity Leakage (ORM entity in API response) | medium (high if auth/payment) |
| ARCH-DI- | Dependency Injection: dependencies not replaceable for testing (direct instantiation, no injection mechanism). Exception: small scripts/CLIs where params/closures suffice → skip | medium |
| ARCH-CEH- | Centralized Error Handling: errors silently swallowed, stack traces leak to prod, no consistent error logging. Exception: 50-line scripts → downgrade to LOW | medium (high if no handler at all) |
| ARCH-SES- | Session Ownership: DI session + local session in same module | medium |
| ARCH-AI-SEB | Side-Effect Breadth: 3+ side-effect categories in one **leaf** function. **Conflict Resolution:** orchestrator/coordinator functions (imports 3+ services AND delegates sequentially) are EXPECTED to have multiple categories — do NOT flag SEB | medium |
| ARCH-AI-AH | Architectural Honesty: read-named function with write side-effects | medium |
| ARCH-AI-FO | Flat Orchestration: **leaf** service imports 3+ other services. Orchestrator imports are expected — do NOT flag | medium |
| ARCH-EVENT- | Event Channel Consistency: publisher/subscriber name mismatch (MISMATCH), orphaned channel with no counterpart (ORPHAN) | high (mismatch), medium (orphan) |

**PERF- subcategories:**

| Prefix | Category | Severity |
|--------|----------|----------|
| PERF-ALG- | Algorithm complexity (Big O) | high if O(n²)+ |
| PERF-CFG- | Package/library configuration | medium |
| PERF-PTN- | Architectural pattern performance | high |
| PERF-DB- | Database queries, indexes | high |

**MNT- subcategories:**

| Prefix | Category | Severity |
|--------|----------|----------|
| MNT-DC- | Dead code: replaced implementations, unused exports/re-exports, backward-compat wrappers, unsupported aliases | medium (high if public API) |
| MNT-DRY- | DRY violations: duplicate logic across files | medium |
| MNT-GOD- | God Classes: class with >15 methods or >500 lines (not just file size) | medium (high if >1000 lines) |
| MNT-SIG- | Method Signature Quality: boolean flag params, unclear return types, inconsistent naming, >5 optional params | low |
| MNT-ERR- | Error Contract inconsistency: mixed raise + return None in same service | medium |

## When to Use
- All implementation tasks in Story status = Done
- Before tech debt cleanup and inline agent review

## Workflow (concise)

**MANDATORY READ:** Load `references/input_resolution_pattern.md`

1) **Resolve storyId:** Run Story Resolution Chain per guide (status filter: [In Progress, To Review]).
2) Load Story (full) and Done implementation tasks (full descriptions) via Linear; skip tasks with label "tests".
3) **Collect changed files** (`changed_files[]`):
   **MANDATORY READ:** Load `references/git_scope_detection.md`
   - IF invoked by ln-510: use `changed_files[]` from coordinator context → proceed to Enrich step in guide
   - IF invoked standalone: run full algorithm from guide
4) **Two-Layer Detection (MANDATORY):**
   **MANDATORY READ:** Load `references/two_layer_detection.md`
   All threshold-based findings require Layer 2 context analysis. Layer 1 finding without Layer 2 = NOT a valid finding. Before reporting any metric violation, ask: "Is this violation intentional or justified by design?" See Exception column in metrics below.

5) **Calculate code metrics:**
   - Cyclomatic Complexity per function (target ≤10; Exception: enum/switch dispatch, state machines, parser grammars → downgrade to LOW)
   - Function size (target ≤50 lines; Exception: orchestrator functions with sequential delegation)
   - File size (target ≤500 lines; Exception: config/schema/migration files, generated code)
   - Nesting depth (target ≤3)
   - Parameter count (target ≤4; Exception: builder/options patterns)

6) **MCP Ref Validation (MANDATORY for code changes — SKIP if `--skip-mcp-ref` flag passed):**
   **MANDATORY READ:** Load `references/research_tool_fallback.md`

   > **Fast-track mode:** When invoked with `--skip-mcp-ref`, skip this entire step (no OPT-, BP-, PERF- checks). Proceed directly to step 6 (static analysis). This reduces cost from ~5000 to ~800 tokens while preserving metrics + static analysis coverage.

   **Level 1 — OPTIMALITY (OPT-):**
   - Extract goal from task (e.g., "user authentication", "caching", "API rate limiting")
   - Research alternatives: `ref_search_documentation("{goal} approaches comparison {tech_stack} 2026")`
   - Compare chose