Code Verification Agent Skill

Code Verification Skill

A systematic post-implementation verification workflow that catches the bugs AI coding assistants most commonly introduce. This is NOT a code review for style or architecture — it is a mechanical correctness checklist that catches structural errors (TDZ, imports, dead code, mock leakage, CSS orphans, React anti-patterns) that humans and AI both miss during implementation.

When to Use

• After every code change (1-2 files changed -> run immediately)
• After a multi-file feature (run on all changed files in one pass)
• After writing/modifying tests (switch to Test Verification mode)
• Before marking any task complete (final gate)
• When a subagent completes work (verify their output)
• When user says: "verify", "check quality", "audit code", "run verification", "quality gate", "pre-commit check"

Quick Start

1. Identify changed files (git diff --name-only or manual list)
2. Run the 7-category checklist below on each file
3. Run automated checks (build, lint, tests)
4. Report findings as PASS / FAIL / WARNING
5. Fix all FAIL items before proceeding

The 7-Category Verification Checklist

Category 1: Variable Declaration Order (TDZ Prevention)

What to check: Variables, constants, and hooks used BEFORE their declaration in the same scope.

How it breaks: JavaScript const and let have a "temporal dead zone" — referencing them before their declaration line throws ReferenceError at runtime, but no build error.

React-specific: useMemo, useCallback, useEffect that reference state or derived values declared later in the component. This is the #1 AI-introduced bug.

Scan pattern:

• For every useMemo, useCallback, useEffect: check that ALL variables in the dependency array AND the callback body are declared ABOVE that hook.
• For every function that references a const/let: check the declaration is above the function definition.
• For every destructured import used in a module-level const: check for circular dependencies.

Real examples caught:

• activeQuestions useMemo referenced 150 lines before its declaration
• baseDeps used in JSX but handler functions declared 100 lines later
• DR_FIELDS referenced in NFR_CATALOG before export const DR_FIELDS line

Fix: Move the declaration above all usages. If it's a React hook, reorder hooks so dependencies come first.

Category 2: Import/Export Integrity

What to check: Every import resolves to a real export. Named vs default matches.

How it breaks: Build may succeed (tree-shaking ignores dead imports in dev mode) but runtime throws undefined is not a function.

Scan pattern:

• For each import { X } from './file': open ./file and confirm export { X } or export const X or export function X exists.
• For each import X from './file': confirm export default X exists.
• Flag: import { X } from './file' when file only has export default X (or vice versa).

Real examples caught:

• useResizeHandle imported as default when it's a named export
• ConfluencePagePicker imported as default when it's a named export
• Removed component still imported in 3 files

Automated check:

npx eslint --rule '{"import/named": "error", "import/default": "error"}' src/

Category 3: Reference Integrity

What to check: After any rename/remove/move, ALL usages of the old name are updated.

Scan pattern:

• Search for ALL usages of the old name across the project
• Verify zero references remain to removed identifiers
• Check that moved code doesn't reference variables from its old scope

Real examples caught:

• setPrdDocViewMode was removed but Cmd+E handler still called it
• Removed component still imported in 3 files

// BUG: setPrdDocViewMode was removed but Cmd+E handler still calls it
useEffect(() => {
  const handler = (e) => {
    if (e.metaKey && e.key === 'e') setPrdDocViewMode(prev => ...);  // ReferenceError
  };
}, []);

Category 4: Dead Code Detection

What to check: Unused imports, unreachable code, orphaned handlers.

Scan pattern:

• Unused imports: variable imported but never referenced in file body.
• Orphaned event handlers: onClick={handleFoo} removed from JSX but const handleFoo = ... still declared.
• Unreachable code: return before a code block, if (false) guard, feature-flagged code where flag is always false.
• State setters never called: const [x, setX] = useState() where setX appears nowhere.
• Functions defined but never called.

Automated check:

npx eslint --rule '{"no-unused-vars": "error", "no-unreachable": "error"}' src/file.jsx

Category 5: React State & Effects

What to check: State variables are used, effects clean up, no updates after unmount, correct dependencies.

5.1 Component Reuse Bugs

When the same component renders for multiple routes (e.g., OperationalDocEditor for DR/IRP/Recovery):

• Does it have a key={uniqueId} to force remount on route change?
• Does it reset internal state when props change?

5.2 Effect Dependencies

For every useEffect:

• Are all referenced variables in the dependency array?
• Are object/array deps stable (memoized) or will they trigger infinite re-renders?
• Does the cleanup function undo what the effect created?

5.3 Ref Safety

• Is ref.current used in the render return? (Should be state instead — ref changes don't trigger re-render)
• Are refs initialized before first access? (Common with resize handles)
• Does useRef get set in an effect that runs after the component mounts?

5.4 Async State Updates

• Does any async callback (fetch, setTimeout) update state after potential unmount?
• Is there a cleanup function that cancels pending operations?
• Every useEffect that calls an async function should have an abort/cancel mechanism.

Real examples caught:

• initialLoadRef set to true before async data arrived, blocking subsequent updates
• useResizeHandle ref null on mount because empty state rendered first (MutationObserver fix needed)
• DR/IRP/Recovery shared OperationalDocEditor reused state across route changes (fixed with key={docType})
• prdDocViewMode state removed but Cmd+E handler still called setPrdDocViewMode

Common React Anti-Patterns

| Anti-Pattern | Why It Breaks | Fix |

|---|---|---|

| Mutating state directly (state.push(x)) | React won't re-render | setState([...state, x]) |

| Object/array in useEffect deps | New reference every render -> infinite loop | useMemo the dep, or use primitive |

| ref.current in render return | Ref changes don't trigger re-render | Use state instead |

| history.pushState with #fragment in hash router | Double-hash URL breaks navigation | Use state-based tracking |

| Inline object as prop (style={{ color: 'red' }}) | New reference every render, breaks memo | Extract to useMemo or module-level const |

| useEffect missing cleanup for async | State update on unmounted component | AbortController or mounted flag |

Category 6: Mock Isolation (Test Files Only)

What to check: Mocks don't leak between tests. Fake timers are restored. Tests are meaningful.

6.1 Mock Leakage

• vi.mock() / jest.mock() at module level: OK
• mockImplementation() inside a describe without afterEach(() => mock.mockReset()): LEAK RISK
• vi.useFakeTimers() without corresponding vi.useRealTimers() in afterEach: LEAK
• mockResolvedValueOnce chains: fragile if test execution order changes. Prefer mockImplementation that inspects the call.
• Multiple describe blocks sharing the same fetch.mock without isolation: INTERFERENCE

6.2 Tautological Tests

Tests that can never fail:

• Asserting a mock's return value equals itself
• expect(x).toBeDefined() where x is hardcoded in setup
• expect(fn).toHaveBeenCalled() immediately after calling fn yourself
• expect(array.length).toBeGreaterThanOrEqual(0) (always true)

6.3 Query Specificity

• getByText / getByRole that matches multiple elements -> use getAllBy* or scope with within()
• Tests that pass because they find the wrong element (e.g., finding a button label that also appears in a tooltip)

6.4 Meaningful Assertions

• Every test should have at least one assertion
• Tests should assert behavior, not just "it renders"
• Snapshot tests should be small enough to review

Real examples caught:

• Jira test: mockResolvedValueOnce chain broke when test order changed; fixed with request-inspecting mockImplementation
• ConfluencePagePicker: fake timers from one test leaked into search filter test
• NFRTracker: missing SettingsContext mock caused cascading failures

Category 7: CSS Class Integrity

What to check: Every className in JSX has a corresponding CSS rule. No orphaned selectors.

7.1 Class Name Integrity

• Extract all className="..." and className={...} values from the JSX file.
• For each class, search the associated CSS file(s) for .classname.
• Flag: class used in JSX but not defined in CSS (will silently fail — no visual, no error).
• Flag: class defined in CSS but not used in any JSX (dead CSS — bloat).

Note: Dynamic classes like className={isActive ? 'active' : ''} need both branches checked.

7.2 CSS Variable Integrity

For every var(--token) in CSS:

• Is the variable defined in :root or a parent selector?
• Is it defined for both light and dark themes?

Automated Verification Script

Run these commands after any code change:

# 1. Build check
npm run build

# 2. Lint check (catches unused vars, unreachable code)
npx eslint src/path/to/changed/file.jsx

# 3. Test check (run tests for changed file)
npx vitest run src/path/to/changed/file.test.jsx

# 4. Full suite (after a feature is complete)
npx vitest run

# 5. Circular dependency check (if available)
npx madge --circular src/

Report Template

Use this format when reporting verification results:

## Verification Report — [Project Name]
**Date:** [YYYY-MM-DD]
**Files checked:** [list]
**Tool:** code-verification skill

### PASS
- `path/to/file.jsx` — All 7 categories checked, no issues

### FAIL (must fix before proceeding)
- `path/to/file.jsx:142` — [CAT 1: TDZ] `activeQuestions` referenced before declaration
  **Fix:** Move `const activeQuestions = useMemo(...)` to line 95 (before `showClarifyingQuestions`)

### WARNING (review, may be intentional)
- `path/to/file.jsx:88` — [CAT 4: DEAD CODE] `const [oldState, setOldState]` — setOldState never called
  **Likely:** Leftover from removed feature. Remove if confirmed unused.

### Summary
| Category | Pass | Fail | Warn |
|----------|------|------|------|
| 1. TDZ | 4 | 1 | 0 |
| 2. Imports | 5 | 0 | 0 |
| 3. References | 5 | 0 | 0 |
| 4. Dead Code | 4 | 0 | 1 |
| 5. React State | 3 | 0 | 2 |
| 6. Mocks | 3 | 0 | 1 |
| 7. CSS | 5 | 0 | 0 |

Integration with Agents

This skill is the workflow. The agents are the executors:

| Agent | Role | When |

|-------|------|------|

| verification-agent | Runs Categories 1-5, 7 on product code | After implementation |

| test-guardian | Runs Category 6 on test code | After writing tests |

| code-reviewer | Broader quality review (SOLID, perf, security) | Before merge/deploy |

Integration with Rules

| Rule | Role | When |

|------|------|------|

| quality-gate.mdc | Enforces 6 mandatory checks after every edit | Always (auto-applied) |

| pre-implementation-checklist.mdc | Prevents bugs before they're written | Always (auto-applied) |

Quick Commands

# Run all tests for a specific file
npx vitest run path/to/file.test.jsx

# Run full test suite
npx vitest run

# Build check
npm run build

# Lint check
npx eslint src/path/to/changed/file.jsx

When to Skip Verification

• Editing only markdown, docs, or comments (no executable code)
• Adding a TODO comment
• Changing only CSS values (not selectors or class names)
• Reverting a commit (restoring known-good state)

When Verification is MANDATORY (No Exceptions)

• Any .jsx, .js, .ts, .tsx file edit
• Any file rename or move
• Any import/export change
• Any React hook addition, removal, or reordering
• Any state variable addition or removal
• Any test file modification
• After running npm install or changing package.json
• After merging branches or resolving conflicts
• After a subagent completes work in another window