Share a contract without making everything depend on everything

First, build a mental model

An application assembles behavior for users. A package exports a cohesive contract for consumers. Dependency direction tells you what must be understood or changed together.

1. npm workspaces let one repository declare related local packages. Each package still needs a clear purpose, public entry points and explicit dependencies.
2. Prefer a domain package that accepts facts and returns results without importing application screens. Presentation and infrastructure can depend on shared rules without the rules depending on every consumer.
3. Imports through stable public exports keep consumers away from accidental internals. Dependency cycles make initialization, testing and change impact harder to reason about.
4. A shared change must be checked in the package and its affected consumers. Not every project needs a monorepo: a cohesive single application can retain simpler structure until real reuse justifies more boundaries.

{
  "name": "synthetic-workspace",
  "private": true,
  "workspaces": ["apps/*", "packages/*"]
}

1. Consumers

   A shop interface and a CLI can call the same reviewed order-rule contract.

2. Dependency direction

   Both applications depend on order-rules; order-rules does not import the shop's UI state.

3. Change impact

   Updating the shared contract requires checking both consumers, even if only one initially requested the change.