domain-modeling

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• SKILL.md

SKILL.md (first lines)

> **Tool mapping (OpenCode):** This skill uses:
> - `question` tool for user prompts
> - `task` tool for subagents
> - `skill({ name: "..." })` to load other skills
> - `codegraph_explore`, `codegraph_search` for codebase exploration (preferred)
> - `grep`, `glob`, `read`, `bash` as fallback
>
> **Context rule:** This skill supersedes any prior skill instructions. Follow ONLY these instructions now.

# Domain Modeling

Actively build and sharpen the project's domain model as you design. This is the *active* discipline — challenging terms, inventing edge-case scenarios, and writing the glossary and decisions down the moment they crystallise. (Merely *reading* `CONTEXT.md` for vocabulary is not this skill — that's a one-line habit any skill can do. This skill is for when you're changing the model, not just consuming it.)

## File structure

Most repos have a single context:

```
/
├── CONTEXT.md
├── docs/
│   └── adr/
│       ├── 0001-event-sourced-orders.md
│       └── 0002-postgres-for-write-model.md
└── src/
```

If a `CONTEXT-MAP.md` exists at the root, the repo has multiple contexts. The map points to where each one lives:

```
/
├── CONTEXT-MAP.md
├── docs/
│   └── adr/                          ← system-wide decisions
├── src/
│   ├── ordering/
│   │   ├── CONTEXT.md
│   │   └── docs/adr/                 ← context-specific decisions
│   └── billing/
│       ├── CONTEXT.md
│       └── docs/adr/
```

Create files lazily — only when you have something to write. If no `CONTEXT.md` exists, create one when the first term is resolved. If no `docs/adr/` exists, create it when the first ADR is needed.

## During the session

### Challenge against the glossary

When the user uses a term that conflicts with the existing language in `CONTEXT.md`, call it out immediately. "Your glossary defines 'cancellation' as X, but you seem to mean Y — which is it?"

### Sharpen fuzzy language

When the user uses vague or overloaded terms, propose a precise canonical term. "You're saying 'account' — do you mean the Customer or the User? Those are different things."

### Discuss concrete scenarios

When domain relationships are being discussed, stress-test them with specific scenarios. Invent scenarios that probe edge cases and force the user to be precise about the boundaries between concepts.

### Cross-reference with code

When the user states how something works, check whether the code agrees. If you find a contradiction, surface it: "Your code cancels entire Orders, but you just said partial cancellation is possible — which is right?"

### Update CONTEXT.md inline

When a term is resolved, update `CONTEXT.md` right there. Don't batch these up — capture them as they happen.

`CONTEXT.md` should be totally devoid of implementation details. Do not treat `CONTEXT.md` as a spec, a scratch pad, or a repository for implementation decisions. It is a glossary and nothing else.

### Offer ADRs sparingly

Only offer to create an ADR when all three are true:

1. **Hard to reverse** — the cost of changing your mind later is meaningful
2. **Surprising without context** — a future reader will wonder "why did they do it this way?"
3. **The result of a real trade-off** — there were genuine alternatives and you picked one for specific reasons

If any of the three is missing, skip the ADR.

## Integration with other skills

This skill is invoked by:
- **grill-with-docs** — grill-me + domain-modeling combined
- **grill-me** — when a grill session surfaces domain terms that need recording
- **add-feature** Phase 3 (Design) — when domain terms need sharpening
- **improve-codebase-architecture** — when naming deepened modules
- **triage** — when grilling issues that need domain precision

## NEVER

- **NEVER put implementation details in CONTEXT.md**
  **Instead:** CONTEXT.md is a glossary only — terms, relationships, boundaries.
  **Why:** Implementation details rot; domain language is durable.

- **NEVER create an ADR for trivial decisions**
  **Instead:** Only when all three criteria (hard to reverse, surprising without context, real trade-off) are met.
  **Why:** ADR noise trains readers to skip them — save them for decisions that matter.

- **NEVER batch domain-term updates**
  **Instead:** Update CONTEXT.md inline as decisions crystallize.
  **Why:** Deferred updates lose nuance and forget the reasoning behind the term.

From Acauhi99/opencode-agent-system, MIT.

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