code-review-and-quality

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# 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?
- **Is a new conditional bolted onto an unrelated flow?** That's a design smell, not a nit — push the logic into its own helper, state, or policy instead of tangling an existing path.
- **Do repeated conditionals on the same shape appear?** They signal a missing model or dispatcher. A "temporary" branch is usually permanent debt.

### 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)?
- **Does this refactor reduce complexity or just relocate it?** Count the concepts a reader must hold to follow the change. If a "cleaner" version leaves that count unchanged, it isn't cleaner — prefer the restructuring that makes whole branches, modes, or layers disappear over one that re-centralizes the same logic. Prefer deleting an abstraction to polishing it.
- **Is feature-specific logic leaking into a shared or general-purpose module?** Keep logic in its owning layer, reuse the existing canonical helper instead of a near-duplicate, and don't normalize architectural drift.
- **Are type boundaries explicit?** Question gratuitous `any`/`unknown`/optional/casts and silent fallbacks that paper over an unclear invariant — making the boundary explicit often makes the surrounding control flow simpler.

### 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?

## Structural Remedies

When you flag a structural problem, propose the move — not just the problem. A review that only says "this is complex" leaves the author guessing. Reach for a named restructuring:

- **Replace a chain of conditionals** with a typed model or an explicit dispatcher.
- **Collapse duplicate branches** into a single clearer flow.
- **Separate orchestration from business logic** so each reads on its own.
- **Move feature-specific logic** out of a shared module into the package that owns the concept.
- **Reuse the canonical helper** instead of a bespoke near-duplicate.
- **Make a type boundary explicit** so downstream branching disappears.
- **Delete a pass-through wrapper** that adds indirection without clarifying the API.
- **Extract a helper, or split a large file** into focused modules.

Prefer the remedy that removes moving pieces over one that spreads the same complexity around.

## Change Sizing

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

```
~100 lines changed   → Good. Reviewable in one sitting.
~300 lines changed   → Acceptable if it's a single logical change.
~1000 lines changed  → Too large. Split it.
```

**Watch file size, not just diff size.** A small diff can still push a file past a healthy boundary — around 1000 *total* lines in a single file (distinct from the ~1000 *changed*-lines threshold above) is a common inspection signal, not a hard cap. When a change materially grows an already-large file, ask whether to extract helpers, subcomponents, or modules *first*, before piling more on. Decompose, then add.

**What counts as "one change":** A single self-contained modification that addresses one thing, includes related tests, and keeps the system functional after submission. One part of a feature — not the whole feature.

**Splitting strategies when a change is too large:**

| Strategy | How | When |
|----------|-----|------|
| **Stack** | Submit a small change, start the next one based on it | Sequential dependencies |

From Qiuyi-Hong/pi-addyosmani-skills, MIT.

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