Domain Modeling

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 .github/context/shared-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 use .github/context/shared-context.md:

/
└── .github/
	├── context/
	│   ├── shared-context.md
	└── adr/
		├── 0001-event-sourced-orders.md
		└── 0002-postgres-for-write-model.md

If .github/context/context-map.md exists, the repo has multiple contexts. The map points to where each one lives:

/
└── .github/
	├── context/
	│   ├── context-map.md
	│   ├── shared-context.md
	│   ├── ordering-context.md
	│   └── billing-context.md
	└── adr/
		├── 0001-event-sourced-orders.md
		└── 0002-postgres-for-write-model.md

Create files lazily — only when you have something to write. If .github/context/shared-context.md does not exist, create it when the first term is resolved. If no ADR folder exists, create .github/adr/ 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 .github/context/shared-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 .github/context/shared-context.md inline

When a term is resolved, update .github/context/shared-context.md right there. Don't batch these up — capture them as they happen. Use the format in CONTEXT-FORMAT.md.

.github/context/shared-context.md should be totally devoid of implementation details. Do not treat it as a spec, a scratch pad, or a repository for implementation decisions. It is a glossary document.

Legacy fallback: if a repository still uses legacy context/ADR locations, read and update those until migrated.

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. Use the format in ADR-FORMAT.md.