Skill: aposd-verifying-correctness

Before "Done" — scope check

Design quality ≠ correctness. Well-designed code can still have bugs, missing requirements, or safety issues.

Run every dimension check before claiming done — "I think I covered everything" without explicit mapping is exactly the gap this skill exists to close.

Dimension Detection & Checks

For each dimension: detect if it applies, then verify.

1. Requirements Coverage

Detect: Were requirements stated? (explicit list, user request, spec)

If YES, verify:

• ] List each requirement explicitly
• ] For each: point to code that implements it
• ] Any requirement without code? → Not done
• ] Any code without requirement? → Scope creep or missing requirement

Red flag: "I think I covered everything" without explicit mapping

2. Concurrency Safety

Detect: Any of these present?

• Multiple threads/processes accessing same data
• Async/await patterns
• Shared mutable state (class attributes, globals)
• "Thread-safe" in requirements or docstring
• Web handlers, queue workers, background tasks

If YES, verify:

• ] All shared mutable state identified
• ] Each access point protected (lock, atomic, queue, immutable)
• ] No time-of-check to time-of-use (TOCTOU) gaps
• ] Lock ordering consistent (if multiple locks)

Red flag: "It's probably fine" or "Python GIL handles it"

3. Error Handling

Detect: Can any operation fail?

• I/O (file, network, database)
• External calls (APIs, subprocesses)
• Resource acquisition (memory, connections)
• User input processing
• Parsing/deserialization

If YES, verify:

• ] Each failure point has explicit handling OR propagates
• ] No bare except: or except Exception: pass
• ] Error messages actionable (what failed, why, how to fix)
• ] Partial failures handled (rollback, cleanup, consistent state)
• ] No error path silently continues as if nothing happened (catch-log-continue, default returns on failure, swallowed callbacks all create silent failures — each error path either surfaces to the caller or is observable via logs/metrics/alerts)

Red flag: "Errors are rare" or "caller handles it" without checking caller

4. Resource Management

Detect: Does code acquire resources?

• File handles, sockets, connections
• Locks, semaphores
• Memory allocations (large buffers, caches)
• External service handles
• Background threads/processes

If YES, verify:

• ] Every acquire has corresponding release
• ] Release happens in finally/context manager/destructor
• ] Release happens on error paths too
• ] No resource leaks on repeated calls
• ] Bounded growth (caches have limits, queues have limits)

Red flag: "It cleans up eventually" or daemon threads without shutdown

5. Boundary Conditions

Detect: Does code handle variable-size input?

• Collections (lists, dicts, sets)
• Strings, byte arrays
• Numeric ranges
• Optional/nullable values

If YES, verify:

• ] Empty input: What happens with [], "", None, 0?
• ] Single item: Edge case often different from N items
• ] Maximum size: What if input is huge? Memory? Time?
• ] Invalid values: Negative numbers, NaN, special characters?
• ] Type boundaries: int overflow, float precision?

Red flag: "Nobody would pass that" or "that's an edge case"

6. Security (if applicable)

Detect: Does code handle untrusted input?

• User-provided data (forms, API requests)
• File contents from external sources
• URLs, paths, identifiers from users
• Data that becomes SQL, shell, HTML, or code

If YES, verify:

• ] Input validated before use
• ] No string concatenation for SQL/shell/HTML (use parameterized)
• ] Path traversal prevented (no ../ exploitation)
• ] Secrets not logged or exposed in errors
• ] Auth/authz checked before action, not after

Red flag: "It's internal only" (internals get exposed)

Detailed per-dimension checklists: Read(${CLAUDE_SKILL_DIR}/checklists.md)

Output Format

When verifying, output:

## Correctness Verification

### Requirements: [PASS/FAIL/N/A]
- Requirement 1 → implemented in X
- Requirement 2 → implemented in Y

### Concurrency: [PASS/FAIL/N/A]
- Shared state: [list]
- Protection: [how]

### Errors: [PASS/FAIL/N/A]
- Failure points: [list]
- Handling: [approach]

### Resources: [PASS/FAIL/N/A]
- Acquired: [list]
- Released: [how]

### Boundaries: [PASS/FAIL/N/A]
- Edge cases: [list]
- Handling: [approach]

### Security: [PASS/FAIL/N/A]
- Untrusted input: [list]
- Validation: [approach]

**Verdict:** [DONE / NOT DONE - list blockers]

Relationship to Other Skills

| Skill | Focus | When | |-------|-------|------| | aposd-designing-deep-modules | Design quality | FIRST—during design | | aposd-verifying-correctness | Actual correctness | BEFORE "done" | | cc-quality-practices | Testing/debugging | Throughout |

Order: Design → Implement → Verify (this skill) → Done

Chain

| After | Next | |-------|------| | All dimensions pass | Done (pre-commit gate) |