Canon Review — Unified Code & Design Review

The Canon Review skill provides a single entry point for evaluating code changes against canonical software engineering best practices drawn from seminal literature (Code Complete, Clean Code, A Philosophy of Software Design, Refactoring, Release It!, Designing Data-Intensive Applications, Domain-Driven Design, Team Topologies, etc.).

It unifies:

• Code Review (canon-pr-review): 20 Tier 2 practices covering implementation quality, module design, line-level reliability, and maintainability.
• Design Review (canon-design-review): 15 Tier 2 practices covering structural integrity, distributed resilience, and evolutionary architecture.

Phase 0: Auto-Routing & Mode Selection

Identify the review scope and select the review mode:

# 1. Fetch PR diff and file list if PR number/URL provided
gh pr view <NUMBER> --json title,body,changedFiles,baseRefName,headRefName
gh pr diff <NUMBER>

Routing Rules

Auto-Detection Logic (--mode auto)

1. Inspect changed file paths from the diff:
   • If any file touches architecture directories (services/, infrastructure/, platform/, domain/, core/), API contracts (**/api/*, **/schema*, *.proto), database migrations (**/migrations/*), or architecture docs (**/architecture*, **/design*, **/adr/*):
     • Select Full Review (runs both Code and Design evaluations).
   • Otherwise (standard feature PRs, bugfixes, utility changes):
     • Select Code Review.

Phase 1: Code Review Evaluation (20 Practices)

Evaluates the 4 dimensions from canon-pr-review. Each practice is scored 0–5.

Dimension 1: Code Quality

• CC-003 — Intention-Revealing Names: No cryptic abbreviations or single-letter variables (except loop indices). Names reflect purpose.
• CC-005 — Single Responsibility (Function): Functions do one thing without needing "and"/"or" descriptions.
• CC-006 — DRY (No Knowledge Duplication): Core business rules defined in a single authoritative place.
• CC-011 — Guard Clauses / Early Returns: Happy path at leftmost indentation; preconditions fail fast.
• CC-021 — Eliminate Code Smells: No long methods (>50 lines), large classes (>300 lines), feature envy, or data clumps.

Dimension 2: Module Design

• CC-027 — Deep Modules: Simple interfaces hiding significant internal complexity; no shallow wrappers.
• CC-015 — Composition Over Inheritance: Prefer composition over multi-level inheritance hierarchies.
• CC-028 — Interface Comments: Docstrings explain what and why, preconditions, errors, and non-obvious behavior.
• CC-017 — Encapsulate What Varies: Isolate variation points in data structures or strategy objects, not hardcoded switch chains.

Dimension 3: Reliability

• CC-014 — Explicit Error Handling: Never swallow exceptions (except: pass); transform to domain exceptions with context.
• CC-048 — Idempotency Across Network Boundaries: Mutating operations (POST/PUT, payments, retries) use idempotency keys or deduplication.
• CC-056 — Circuit Breakers: External dependency calls wrapped in circuit breakers to isolate failure.
• CC-058 — Explicit Timeouts: Every network call specifies explicit connect and read timeouts.
• CC-060 — Graceful Degradation: Non-critical dependency failures fall back gracefully rather than crashing the primary operation.

Dimension 4: Maintainability

• CC-019 — Small Refactoring Steps: Refactoring and feature changes isolated in behavior-preserving commits.
• CC-031 — Tests Before Legacy Changes: Modified code paths protected by characterization/unit tests.
• CC-093 — Fix Broken Windows: No untracked TODOs, unexplained # noqa suppressions, or skipped tests.
• CC-107 — Regression Tests: Bug fixes include a failing test that reproduces the issue before fixing.

Phase 2: Design Review Evaluation (15 Practices)

Evaluates the 3 assessment areas from canon-design-review. Each practice scored PASS / WARN / BLOCK / N/A.

Area 1: Structural Integrity

• Practice 1 — Bounded Context Alignment (CC-035): Explicit Anti-Corruption Layers (ACLs) or DTOs across context boundaries; no direct entity imports across services.
• Practice 2 — Layer Separation (CC-040): Handlers delegate to domain services; domain objects decoupled from raw DB/HTTP concerns.
• Practice 3 — Dependency Direction (CC-026): Dependencies point inward toward core domain; infrastructure implements domain interfaces.
• Practice 4 — Interface Segregation (CC-025): Narrow, caller-focused interfaces; no wide interfaces with stubbed implementations.
• Practice 5 — Cohesion (CC-119, CC-151): High cohesion within modules; single responsibility at module/service boundaries.

Area 2: Resilience & Operations

• Practice 6 — Circuit Breakers on External Dependencies: Fault-isolation wrapping for external services/databases.
• Practice 7 — Bulkheads (Isolated Failure Domains): Separate thread/connection pools per workload type; resource isolation.
• Practice 8 — Explicit Consistency Model: Documented consistency model (strong, eventual, saga/outbox pattern).
• Practice 9 — Backpressure Mechanisms: Bounded queues (maxsize), load-shedding, or rate-limiting for producers/consumers.
• Practice 10 — Health Checks & Graceful Shutdown: Liveness/readiness probes reflecting real health; SIGTERM handling with bounded connection draining.

Area 3: Evolutionary Design

• Practice 11 — Shearing Layers (CC-098): Fast-changing concerns (business rules, flags) separated from slow-changing concerns (schema, platform).
• Practice 12 — Start Simple / Gall's Law: Complex working systems evolved from simple working systems; no premature abstraction or distributed complexity.
• Practice 13 — Cognitive Load per Team: Service complexity fits single-team ownership without requiring deep knowledge of >3 external services.
• Practice 14 — API Versioning & Backward Compatibility: Non-breaking public API evolution; breaking changes versioned with deprecation windows.
• Practice 15 — ADR for Significant Decisions (CC-132): Architecture Decision Records recorded for significant technical choices (new DBs, service splits, consistency trade-offs).

Phase 3: Verdict Determination

Code Review Verdict Rules

• BLOCK: Any dimension score < 1, OR any individual Reliability practice scores 0.
• REQUEST_CHANGES: Any dimension score < 3 (with no BLOCKs).
• APPROVE: All four dimension scores ≥ 3.

Design Review Verdict Rules

• BLOCK: Any practice receives a BLOCK verdict.
• REQUEST_CHANGES: Any practice receives a WARN verdict (and 0 BLOCKs).
• APPROVE: All practices receive PASS or N/A.

Unified Verdict (Full Review Mode)

• BLOCK: If either Code Review OR Design Review yields BLOCK.
• REQUEST_CHANGES: If either Code Review OR Design Review yields REQUEST_CHANGES (and neither yields BLOCK).
• APPROVE: If both Code Review AND Design Review yield APPROVE.

Phase 4: Output Format

Post or render the review using the unified markdown structure:

## Canon Engineering Review — [PR Title or Component Name]

**Mode Executed**: [Code Review | Design Review | Full Review (Auto-Selected)]
**Scope**: [files reviewed]
**Overall Decision**: **[APPROVE / REQUEST_CHANGES / BLOCK]**

---

### Part 1: Code Review Scorecard (20 Practices)

| Dimension | Score | Gate | Key Findings |
|-----------|-------|------|--------------|
| **Code Quality** (naming, SRP, DRY, guard clauses, smells) | X/5 | ✅/⚠️/🚫 | [summary] |
| **Module Design** (deep modules, composition, docs, encapsulation) | X/5 | ✅/⚠️/🚫 | [summary] |
| **Reliability** (error handling, idempotency, circuit breakers, timeouts, degradation) | X/5 | ✅/⚠️/🚫 | [summary] |
| **Maintainability** (small steps, test coverage, broken windows, regression tests) | X/5 | ✅/⚠️/🚫 | [summary] |

---

### Part 2: Design Review Scorecard (15 Practices)

#### Structural Integrity
| # | Practice | Status | Notes / Evidence |
|---|----------|--------|------------------|
| 1 | Bounded Context Alignment | PASS / WARN / BLOCK / N/A | [finding] |
| 2 | Layer Separation | ... | ... |
| 3 | Dependency Direction | ... | ... |
| 4 | Interface Segregation | ... | ... |
| 5 | Cohesion | ... | ... |

#### Resilience & Operations
| # | Practice | Status | Notes / Evidence |
|---|----------|--------|------------------|
| 6 | Circuit Breakers | ... | ... |
| 7 | Bulkheads | ... | ... |
| 8 | Explicit Consistency Model | ... | ... |
| 9 | Backpressure | ... | ... |
| 10 | Health Checks + Shutdown | ... | ... |

#### Evolutionary Design
| # | Practice | Status | Notes / Evidence |
|---|----------|--------|------------------|
| 11 | Shearing Layers | ... | ... |
| 12 | Start Simple (Gall's Law) | ... | ... |
| 13 | Cognitive Load per Team | ... | ... |
| 14 | API Versioning | ... | ... |
| 15 | ADR for Significant Decisions | ... | ... |

**Design Score**: [PASS*100 + WARN*50] / [(15 - N/A) * 100] * 100 = [XX]%

---

### Specific Violations & Actionable Fixes

#### [Practice ID / Name] — Location: `path/to/file.py:line`
- **Issue**: [Description]
- **Offending Code**:
  ```language
  [verbatim code excerpt]

• Suggested Improvement:

  [remediation example]

To Unblock / Action Items

1. [Action item 1]
2. [Action item 2]

---

## Iron Laws & Anti-Rationalization

1. **Concrete Evidence Required**: Every violation (WARN or BLOCK) must quote verbatim code and cite `file:line`.
2. **No Skipping Dimensions**: In Full Review mode, evaluate both Code Quality and Design Architecture without ignoring either layer.
3. **Falsifiability**: Theoretical risks are not violations; violations must be demonstrably present in the diff or immediately affected context.