Concept Design

Focus: what need must the application satisfy, and which independent concepts and synchronizations can fulfill it? Run only on explicit $concept-design invocation. Deliver the model, then continue into PRD or implementation only when already authorized.

Model

A concept is a coherent behavioral unit designed for one purpose; pages, entities, and code modules are only candidate clues.

• A concept purpose is an evaluable need explaining why one concept exists.
• The application purpose is the outcome a product should create through concept selection and composition; it is not the sum of concept purposes.
• An operational principle (OP) is a representative, discriminating scenario showing how behavior fulfills the concept purpose.
• State and actions define allowed behavior through invariants, preconditions, effects, and result cases.
• A synchronization connects completed concept actions to subsequent calls as an application rule.
• A misfit is a mismatch between designed behavior and the actual need.

The required argument is: contract supports OP; OP fulfills concept purpose; selected concepts and synchronizations support application scenarios; scenario outcomes fulfill application purpose. Composition must preserve each concept's allowed behavior. Facts require sources; label inferences and unresolved decisions.

Design Loop

1. Establish facts — Identify beneficiaries, application purpose, current state, desired outcome, and constraints. In an existing system, trace actual entry points, state ownership, failure paths, and tests. Separate current from desired behavior.
2. Define candidates — Read references/spec-format.md. Clarify terms and write the purpose, OP, minimum state, and complete actions. Test meaning with concrete scenarios; represent external identity through type parameters.
3. Review arguments and seams — Read references/criteria.md. Test the contract/OP argument and counterexamples, then specificity, completeness, independence, and familiarity. Record a reasoned seam decision for every candidate.
4. Test composition — Read references/sync-notation.md. Starting from application purpose and end-to-end scenarios, select and instantiate concepts; define entry, binding, response, concurrency, and failure behavior. Check under- and over-synchronization and derive both synchronization and product-dependency diagrams.
5. Revise and deliver — Correct evidenced misfits using the adjustment moves in the criteria. Preserve unresolved assumptions with evidence and impact; block only the dependent portion.

Output

## Application Purpose and Scenarios

<users, purpose, current state, outcome, constraints; sources/inferences/open decisions> <end-to-end
scenarios: condition → actions and syncs → observable result → purpose; misfits>

## Concepts

<purpose, state, actions, OP, optional queries/notes per references/spec-format.md> Argument: <why
contract supports OP and result fulfills purpose; counterexamples/open points> Seam:
<specificity/completeness/independence/familiarity conclusion and reasons>

## Synchronizations

<app/include/sync grouped by entry point or rule responsibility>

## Synchronization Diagram and Product Subsets

<when → rule → then; where reads marked separately> <A → B means including A requires B; MVP>

## Exclusions and Open Decisions

<candidate/action/assumption, conclusion, source, impact>

Concept sections remain independent of other concept definitions. Put application context in notes and coordination in synchronizations. Signatures, result cases, and state relations form the synchronization interface; an OP is representative rather than exhaustive.

Completion requires evidence for both concept and application purposes, parseable includes/actions/queries/parameters/outputs/bindings, explicit success and refusal behavior where responses are required, loop and exclusion policies, faithful multi-source/multi-target/query edges, and an MVP closed over entry points, remaining rules, dependencies, and resources. For a first full example read references/example-reserving.md; for source definitions read references/sources.md.