Domain Modeling

---
name: domain-modeling
description: "Use when designing schemas, querying, indexing, optimizing, and securing domain modeling databases and data models."
version: 6.0.0
last-updated: 2026-09-29
skills:
  - architecture
  - codebase-design
  - database-design
tools: Read, Grep, Glob, Bash, Edit, Write
scripts-binding:
  - .agent/scripts/lint_runner.js
  - .agent/scripts/verify_all.js
---

# Domain Modeling — Ubiquitous Language & Bounded Contexts

## Mandatory Pre-Flight Context Inspection
Before reading, generating, or refactoring code in the `domain-modeling` domain, inspect these 5 critical parameters:
1. **System Boundaries & Dependencies**: Verify that all required dependencies exist in target package manifests and environment paths.
2. **Runtime Context & Platform Invariants**: Confirm target platform constraints (Node.js, Browser, Mobile OS, Edge runtime) before applying APIs.
3. **Execution Guardrails**: Identify potential side-effects, state mutations, and unhandled asynchronous exceptions.
4. **Validation & Type Contracts**: Validate input data schemas and strict type constraints across all module interfaces.
5. **Observability & Proof of Execution**: Ensure execution produces tangible verification signals (terminal output, tests, metrics).


## Activation Boundaries
- **Activate when:** Use when designing schemas, querying, indexing, optimizing, and securing domain modeling databases and data models.
- **DO NOT activate when:** The task falls outside the `domain-modeling` domain or is managed by a different dedicated specialist agent.


## 🔁 Multi-Pass Execution Protocol

| Pass | Phase | Core Action | Adaptive Depth |
|:---|:---|:---|:---|
| **Pass 1** | **Understand** | Deconstruct the user's explicit objective, implicit requirements, and platform constraints. | Fast / Standard / Deep |
| **Pass 2** | **Plan** | Decompose task into smallest logical steps; map dependencies, affected files, and tool calls. | Standard / Deep |
| **Pass 3** | **Execute** | Implement solution with production-grade craft, zero placeholders, and strict typing. | All Modes |
| **Pass 4** | **Verify** | Run linters, unit tests, or compiler checks to validate structural correctness. | All Modes |
| **Pass 5** | **Attack & Falsify** | Perform adversarial search for edge-case failures, counterexamples, race conditions, and traps. | Standard / Deep |
| **Pass 6** | **Harden** | Eliminate discovered friction, optimize performance, and harden error boundaries. | Standard / Deep |
| **Pass 7** | **Quality Gate** | Enforce Verification-Before-Completion (VBC) with concrete terminal proof before finalizing. | All Modes |


---

## 🛠️ Technical Architecture & Reference Recipes

---

## 4 Domain Modeling Rules

### 1. Establish Ubiquitous Language

- Agree on strict, unambiguous terms used identically across domain experts, code variable names, database tables, and UI copy.
  - ❌ _User_, _Account_, _Member_, _Client_ used interchangeably for the same concept.
  - ✅ Define 1 clear term: **Customer** (for billing context) vs **User** (for authentication context).

### 2. Define Bounded Contexts

- Separate large systems into distinct bounded contexts. An entity named `Product` in the _Inventory Context_ (stock level, warehouse bin) has different attributes than `Product` in the _Catalog Context_ (hero image, pricing).

### 3. Aggregates & Invariants

- An **Aggregate Root** (e.g. `Order`) enforces internal business invariants across child entities (`OrderItem`).
- Never mutate a child entity (`OrderItem`) directly without passing through the aggregate root method (`order.addItem(product, qty)`).

### 4. Value Objects Over Primitives

- Wrap primitives into type-safe Value Objects to enforce validation logic:

```typescript
// Value Object enforcing domain rule
export class EmailAddress {
  private readonly value: string;

  constructor(email: string) {
    if (!email.includes('@')) throw new Error('Invalid email domain');
    this.value = email.toLowerCase().trim();
  }

  public toString(): string {
    return this.value;
  }
}
```

## 🚨 Edge-Case & Failure Mode Matrix

| Scenario | Risk | Production Mitigation |
|:---|:---|:---|
| **Empty or Null Inputs** | Unhandled exception or unexpected rendering collapse | Enforce fallback guards, optional chaining, and explicit empty state handlers |
| **Network Timeout / Latency** | Hanging operations or duplicate side-effects | Implement bounded abort controllers, exponential backoff, and idempotency keys |
| **Concurrency / Race Conditions** | Stale state overwrite or inconsistent data mutations | Use atomic transactions, mutex locking, or cancel-on-resubmit controls |
| **Invalid Schema / Malformed Payload** | Downstream runtime errors or security injection | Validate boundary payloads with Zod/Pydantic schemas prior to execution |
| **Resource / Memory Saturation** | OOM errors, frame drops, or memory leaks | Clean up listeners, cancel active timers, and enforce pagination/virtualization |


## 🤖 LLM-Specific Traps Table

| Anti-Pattern | What AI Commonly Does Wrong | What Is Actually Correct |
|:---|:---|:---|
| **Full Table Scan Blindspot** | Querying high-cardinality tables without index coverage | Verify query plans with EXPLAIN ANALYZE and add composite B-Tree indexes |
| **Non-Atomic Batch Mutation** | Executing multiple related DB writes sequentially without transaction wrapper | Wrap multi-table updates in an atomic transaction with automatic rollback |
| **Destructive Schema Migration** | Dropping or renaming columns in production without multi-phase migration | Use expand-and-contract: add new column, sync data, migrate callers, drop old |


## 🏛️ Tribunal Verification & Guardrails

**Active Reviewers:** `database-architect` · `sql-pro` · `security-auditor` · `schema-validator`
**Slash Command:** `/review` or `/tribunal-full`

### 🔬 Evidence Standard (Tri-State Verification)
Every finding, audit statement, or completion claim must classify its factual certainty:
- **`[OBSERVED]`**: Directly confirmed in the codebase or verified via executed terminal command.
- **`[INFERRED]`**: Logically deduced from code patterns, architectural data flow, or schema relations.
- **`[UNVERIFIED]`**: Speculative hypothesis or runtime possibility requiring active testing or measurement.

### ✅ Pre-Flight Self-Audit Checklist
```
✅ Are all queries parameterized against SQL injection vulnerabilities?
✅ Are composite indexes ordered by Equality, Sort, then Range (ESR)?
✅ Are multi-table writes wrapped in atomic transactions with rollback handlers?
✅ Are schema migrations backwards-compatible (expand-and-contract pattern)?
✅ Did I verify table and column names against active schema definitions?
```

### 🛑 Verification-Before-Completion (VBC) Protocol
**CRITICAL:** You must follow a strict "evidence-based closeout" state machine.
- ❌ **Forbidden:** Declaring a task complete because the output "looks correct."
- ✅ **Required:** You are explicitly forbidden from finalizing any task without providing **concrete evidence** (terminal output, passing test suites, compiler success, or equivalent operational proof) that your output works as intended.