Model Domain

Model Domain

Distinct from define-language and deepen-architecture: Use this skill to stress-test a plan through a grilling interview that resolves domain model decisions and captures invariants. Use define-language to produce a canonical glossary of terms. Use deepen-architecture to find module-level refactoring opportunities in code.

Interview me relentlessly about every aspect of this plan until we reach a shared understanding. Walk down each branch of the design tree, resolving dependencies between decisions one-by-one. For each question, provide your recommended answer.

HARD GATE — Capture invariants (what MUST always be true) and state machines (what transitions are legal) for core entities. If these are fuzzy, design will fail.

Ask the questions one at a time, waiting for feedback on each question before continuing.

If a question can be answered by exploring the codebase, explore the codebase instead.

Domain awareness

During codebase exploration, also look for existing documentation:

File structure

Most repos have a single context:

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

If a specs/tech-architecture/tech-stack.md exists, the repo has multiple contexts. The map points to where each one lives:

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

Create files lazily — only when you have something to write. If no specs/tech-architecture/tech-stack.md exists, create it when the first term is resolved. If no specs/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 specs/tech-architecture/tech-stack.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 specs/tech-architecture/tech-stack.md inline

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

Don't couple specs/tech-architecture/tech-stack.md to implementation details. Only include terms that are meaningful to domain experts.

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.

Concurrency safety audit

When the plan touches shared state, async, or multi-threaded code:

• List every shared mutable location (globals, singletons, module-level caches).
• For each: who reads, who writes, synchronization mechanism (lock, actor, immutable copy).
• Flag race risks (check-then-act, non-atomic read-modify-write) with severity.
• Record findings in specs/tech-architecture/tech-stack.md under ## Concurrency or in an ADR if architectural.