Cursor rule

1---
2description: "Grilling session that challenges your plan against the existing domain model, sharpens terminology, and updates specs/tech-architecture/tech-stack.md and specs/adr/ inline as decisions crystallise. Use when user wants to stress-test a plan against their project's domain language and documented decisions."
3alwaysApply: false
4---
5 
6# Model Domain
7 
8**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.
9 
10Interview 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.
11 
12> **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.
13 
14Ask the questions one at a time, waiting for feedback on each question before continuing.
15 
16If a question can be answered by exploring the codebase, explore the codebase instead.
17 
18## Domain awareness
19 
20During codebase exploration, also look for existing documentation:
21 
22### File structure
23 
24Most repos have a single context:
25 
26```
27/
28├── specs/
29│   ├── CONTEXT.md
30│   └── adr/
31│       ├── 0001-event-sourced-orders.md
32│       └── 0002-postgres-for-write-model.md
33└── src/
34```
35 
36If a `specs/tech-architecture/tech-stack.md` exists, the repo has multiple contexts. The map points to where each one lives:
37 
38```
39/
40├── specs/
41│   ├── CONTEXT-MAP.md
42│   └── adr/                          ← system-wide decisions
43└── src/
44    ├── ordering/
45    │   └── specs/
46    │       ├── CONTEXT.md
47    │       └── adr/                  ← context-specific decisions
48    └── billing/
49        └── specs/
50            ├── CONTEXT.md
51            └── adr/
52```
53 
54Create 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.
55 
56## During the session
57 
58### Challenge against the glossary
59 
60When 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?"
61 
62### Sharpen fuzzy language
63 
64When 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."
65 
66### Discuss concrete scenarios
67 
68When 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.
69 
70### Cross-reference with code
71 
72When 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?"
73 
74### Update specs/tech-architecture/tech-stack.md inline
75 
76When 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](./CONTEXT-FORMAT.md).
77 
78Don't couple `specs/tech-architecture/tech-stack.md` to implementation details. Only include terms that are meaningful to domain experts.
79 
80### Offer ADRs sparingly
81 
82Only offer to create an ADR when all three are true:
83 
841. **Hard to reverse** — the cost of changing your mind later is meaningful
852. **Surprising without context** — a future reader will wonder "why did they do it this way?"
863. **The result of a real trade-off** — there were genuine alternatives and you picked one for specific reasons
87 
88If any of the three is missing, skip the ADR. Use the format in [ADR-FORMAT.md](./ADR-FORMAT.md).
89 
90## Concurrency safety audit
91 
92When the plan touches shared state, async, or multi-threaded code:
93 
94- [ ] List every **shared mutable** location (globals, singletons, module-level caches).
95- [ ] For each: who reads, who writes, synchronization mechanism (lock, actor, immutable copy).
96- [ ] Flag **race risks** (check-then-act, non-atomic read-modify-write) with severity.
97- [ ] Record findings in `specs/tech-architecture/tech-stack.md` under `## Concurrency` or in an ADR if architectural.
98 
99 
100 
101<!-- story: e07s03 -->
102 
103---
104 
105# ADR Format
106 
107ADRs live in `docs/adr/` and use sequential numbering: `0001-slug.md`, `0002-slug.md`, etc.
108 
109Create the `docs/adr/` directory lazily — only when the first ADR is needed.
110 
111## Template
112 
113```md
114# {Short title of the decision}
115 
116{1-3 sentences: what's the context, what did we decide, and why.}
117```
118 
119That's it. An ADR can be a single paragraph. The value is in recording *that* a decision was made and *why* — not in filling out sections.
120 
121## Optional sections
122 
123Only include these when they add genuine value. Most ADRs won't need them.
124 
125- **Status** frontmatter (`proposed | accepted | deprecated | superseded by ADR-NNNN`) — useful when decisions are revisited
126- **Considered Options** — only when the rejected alternatives are worth remembering
127- **Consequences** — only when non-obvious downstream effects need to be called out
128 
129## Numbering
130 
131Scan `docs/adr/` for the highest existing number and increment by one.
132 
133## When to offer an ADR
134 
135All three of these must be true:
136 
1371. **Hard to reverse** — the cost of changing your mind later is meaningful
1382. **Surprising without context** — a future reader will look at the code and wonder "why on earth did they do it this way?"
1393. **The result of a real trade-off** — there were genuine alternatives and you picked one for specific reasons
140 
141If a decision is easy to reverse, skip it — you'll just reverse it. If it's not surprising, nobody will wonder why. If there was no real alternative, there's nothing to record beyond "we did the obvious thing."
142 
143### What qualifies
144 
145- **Architectural shape.** "We're using a monorepo." "The write model is event-sourced, the read model is projected into Postgres."
146- **Integration patterns between contexts.** "Ordering and Billing communicate via domain events, not synchronous HTTP."
147- **Technology choices that carry lock-in.** Database, message bus, auth provider, deployment target. Not every library — just the ones that would take a quarter to swap out.
148- **Boundary and scope decisions.** "Customer data is owned by the Customer context; other contexts reference it by ID only." The explicit no-s are as valuable as the yes-s.
149- **Deliberate deviations from the obvious path.** "We're using manual SQL instead of an ORM because X." Anything where a reasonable reader would assume the opposite. These stop the next engineer from "fixing" something that was deliberate.
150- **Constraints not visible in the code.** "We can't use AWS because of compliance requirements." "Response times must be under 200ms because of the partner API contract."
151- **Rejected alternatives when the rejection is non-obvious.** If you considered GraphQL and picked REST for subtle reasons, record it — otherwise someone will suggest GraphQL again in six months.
152 
153---
154 
155# CONTEXT.md Format
156 
157## Structure
158 
159```md
160# {Context Name}
161 
162{One or two sentence description of what this context is and why it exists.}
163 
164## Language
165 
166**Order**:
167A customer's request to purchase one or more items.
168_Avoid_: Purchase, transaction
169 
170**Invoice**:
171A request for payment sent to a customer after delivery.
172_Avoid_: Bill, payment request
173 
174**Customer**:
175A person or organization that places orders.
176_Avoid_: Client, buyer, account
177 
178## Relationships
179 
180- An **Order** produces one or more **Invoices**
181- An **Invoice** belongs to exactly one **Customer**
182 
183## Example dialogue
184 
185> **Dev:** "When a **Customer** places an **Order**, do we create the **Invoice** immediately?"
186> **Domain expert:** "No — an **Invoice** is only generated once a **Fulfillment** is confirmed."
187 
188## Flagged ambiguities
189 
190- "account" was used to mean both **Customer** and **User** — resolved: these are distinct concepts.
191```
192 
193## Rules
194 
195- **Be opinionated.** When multiple words exist for the same concept, pick the best one and list the others as aliases to avoid.
196- **Flag conflicts explicitly.** If a term is used ambiguously, call it out in "Flagged ambiguities" with a clear resolution.
197- **Keep definitions tight.** One sentence max. Define what it IS, not what it does.
198- **Show relationships.** Use bold term names and express cardinality where obvious.
199- **Only include terms specific to this project's context.** General programming concepts (timeouts, error types, utility patterns) don't belong even if the project uses them extensively. Before adding a term, ask: is this a concept unique to this context, or a general programming concept? Only the former belongs.
200- **Group terms under subheadings** when natural clusters emerge. If all terms belong to a single cohesive area, a flat list is fine.
201- **Write an example dialogue.** A conversation between a dev and a domain expert that demonstrates how the terms interact naturally and clarifies boundaries between related concepts.
202 
203## Single vs multi-context repos
204 
205**Single context (most repos):** One `CONTEXT.md` at the repo root.
206 
207**Multiple contexts:** A `CONTEXT-MAP.md` at the repo root lists the contexts, where they live, and how they relate to each other:
208 
209```md
210# Context Map
211 
212## Contexts
213 
214- Ordering — `src/ordering/CONTEXT.md` — receives and tracks customer orders
215- Billing — `src/billing/CONTEXT.md` — generates invoices and processes payments
216- Fulfillment — `src/fulfillment/CONTEXT.md` — manages warehouse picking and shipping
217 
218## Relationships
219 
220- **Ordering → Fulfillment**: Ordering emits `OrderPlaced` events; Fulfillment consumes them to start picking
221- **Fulfillment → Billing**: Fulfillment emits `ShipmentDispatched` events; Billing consumes them to generate invoices
222- **Ordering ↔ Billing**: Shared types for `CustomerId` and `Money`
223```
224 
225The skill infers which structure applies:
226 
227- If `CONTEXT-MAP.md` exists, read it to find contexts
228- If only a root `CONTEXT.md` exists, single context
229- If neither exists, create a root `CONTEXT.md` lazily when the first term is resolved
230 
231When multiple contexts exist, infer which one the current topic relates to. If unclear, ask.
232