domain-modeling

name	domain-modeling
description	Build and sharpen the project's domain model. Use when domain terminology needs defining or sharpening, an architectural decision crystallizes, or another skill needs to maintain the domain glossary during design work.
when_to_use	[feedforward] Triggered when domain terms need defining, sharpening, or when an architectural decision crystallizes. [feedback] Triggered when terminology conflicts are detected during other skills' work.

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

Single-context repos (default):

/
├── CONTEXT.md                    # Root-level domain glossary (glossary only)
├── docs/agent-harness/
│   └── adr/                      # Architecture Decision Records
│       ├── 0001-<topic>.md
│       └── index.md              # Auto-generated by index-knowledge-base.sh
└── src/

Multi-context repos (monorepo): a CONTEXT-MAP.md at root points to sub-contexts:

/
├── CONTEXT-MAP.md                # Points to each sub-context
├── src/
│   ├── ordering/
│   │   ├── CONTEXT.md
│   │   └── docs/adr/
│   └── billing/
│       ├── CONTEXT.md
│       └── docs/adr/

Create files lazily — only when you have something to write. If no CONTEXT.md exists when this skill is invoked, create it immediately with the scaffold header (# <Project> Domain Glossary). Do not ask the user "should I create it?" — just create it and start populating. The glossary is useful from the first term. If no docs/agent-harness/adr/ exists, create it when the first ADR is needed.

Lazy creation is the PRIMARY path, not a fallback. Most projects will get their CONTEXT.md this way — through brainstorming or other skills calling domain-modeling — rather than through harness-init. This ensures old projects (that never ran harness-init) still benefit from the feature.

During-session behaviors

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.

CONTEXT.md format

# <Project> Domain Glossary

## Order
A customer's request to purchase items, in a specific currency, with a shipping address.

_Avoid_: basket, cart (those are UI states pre-purchase)

## Cancellation
A request to void an Order before it ships. Partial cancellation is not supported.

_Avoid_: refund (that's a financial event, not a domain concept)

## Relationships
- An Order holds many Line Items
- A Cancellation targets exactly one Order

Rules:

• Glossary and nothing else. No implementation details, no specs, no scratch.
• Every term has a definition + _Avoid_ aliases (disambiguate).
• ## Relationships section is optional, for term-to-term relationships.

ADR format

---
spec_topic: adr
title: "0001-<topic>"
decision_summary: "<one sentence>"
date: <ISO-8601>
status: accepted
---

# ADR 0001: <title>

## Context
## Decision
## Consequences
## Alternatives considered

• spec_topic: adr lets index-knowledge-base.sh auto-index into adr/index.md.
• Numbering starts at 0001. Find the next available number — never overwrite.
• status: proposed / accepted / superseded / deprecated.

Integration points

• brainstorming — calls this skill during clarifying questions when terms crystallize.
• writing-plans — reads CONTEXT.md for vocabulary; plan tasks use domain terms.
• requesting-code-review — checks diff uses CONTEXT.md terms.
• harness-init — creates empty CONTEXT.md scaffold + docs/agent-harness/adr/.gitkeep for new projects.
• session-start hook — injects CONTEXT.md glossary summary into every new session (static segment, cache-friendly).
• validate-handoff — advisory check: spec's domain_terms field should anchor to CONTEXT.md headings.