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* `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.) ## Operating mode When Plan mode is active or the caller forbids writes, run analysis-only: do not create or update files. Return canonical terms, boundary and scenario conclusions, code contradictions, ADR-worthy decisions with their reasons, and unresolved choices to the caller. Let the caller handle any user questions. Otherwise, use documentation mode and maintain the files below lazily as conclusions crystallise. ## 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. Use the format in [CONTEXT-FORMAT.md](./CONTEXT-FORMAT.md). `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. Use the format in [ADR-FORMAT.md](./ADR-FORMAT.md).