Code Review And Quality

# Code Review and Quality

## Overview

Multi-dimensional code review with quality gates. Every change gets reviewed before merge — no exceptions. Review covers five axes: correctness, readability, architecture, security, and performance.

**The approval standard:** Approve a change when it definitely improves overall code health, even if it isn't perfect. Perfect code doesn't exist — the goal is continuous improvement. Don't block a change because it isn't exactly how you would have written it. If it improves the codebase and follows the project's conventions, approve it.

## When to Use

- Before merging any PR or change
- After completing a feature implementation
- When another agent or model produced code you need to evaluate
- When refactoring existing code
- After any bug fix (review both the fix and the regression test)

## The Five-Axis Review

Every review evaluates code across these dimensions:

### 1. Correctness

Does the code do what it claims to do?

- Does it match the spec or task requirements?
- Are edge cases handled (null, empty, boundary values)?
- Are error paths handled (not just the happy path)?
- Does it pass all tests? Are the tests actually testing the right things?
- Are there off-by-one errors, race conditions, or state inconsistencies?

### 2. Readability & Simplicity

Can another engineer (or agent) understand this code without the author explaining it?

- Are names descriptive and consistent with project conventions? (No `temp`, `data`, `result` without context)
- Is the control flow straightforward (avoid nested ternaries, deep callbacks)?
- Is the code organized logically (related code grouped, clear module boundaries)?
- Are there any "clever" tricks that should be simplified?
- **Could this be done in fewer lines?** (1000 lines where 100 suffice is a failure)
- **Are abstractions earning their complexity?** (Don't generalize until the third use case)
- Would comments help clarify non-obvious intent? (But don't comment obvious code.)
- Are there dead code artifacts: no-op variables (`_unused`), backwards-compat shims, or `// removed` comments?

### 3. Architecture

Does the change fit the system's design?

- Does it follow existing patterns or introduce a new one? If new, is it justified?
- Does it maintain clean module boundaries?
- Is there code duplication that should be shared?
- Are dependencies flowing in the right direction (no circular dependencies)?
- Is the abstraction level appropriate (not over-engineered, not too coupled)?

### 4. Security

For detailed security guidance, see `security-and-hardening`. Does the change introduce vulnerabilities?

- Is user input validated and sanitized?
- Are secrets kept out of code, logs, and version control?
- Is authentication/authorization checked where needed?
- Are SQL queries parameterized (no string concatenation)?
- Are outputs encoded to prevent XSS?
- Are dependencies from trusted sources with no known vulnerabilities?
- Is data from external sources (APIs, logs, user content, config files) treated as untrusted?
- Are external data flows validated at system boundaries before use in logic or rendering?

### 5. Performance

For detailed profiling and optimization, see `performance-optimization`. Does the change introduce performance problems?

- Any N+1 query patterns?
- Any unbounded loops or unconstrained data fetching?
- Any synchronous operations that should be async?
- Any unnecessary re-renders in UI components?
- Any missing pagination on list endpoints?
- Any large objects created in hot paths?

## Change Sizing

Small, focused changes are easier to review, faster to merge, and safer to deploy. Target these sizes:

```
~100 lines changed   → Good.