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Context

ADR 0001 gave every member a place. Nothing yet says which member may depend on which. Without a direction rule a library can import an app “just for a type”, and the library can then no longer be built or shipped without that app. The easy edge to add by accident is library to app, not library to service.

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Decision

Every workspace member carries exactly one tier tag in its own turbo.jsonc ("tags": ["tier:<x>"]), and the root turbo.jsonc boundaries block denies each tier everything above it.
  • A library never imports an app, a service or encore.dev. If a library needs a shape from above, the shape moves down into a contract package (0117).
  • An app reaches a service over the wire only, through a generated client, never through its source.
  • A service never imports another service’s internals (0010).
  • The tier is implied by the directory. A member whose tag disagrees with its directory fails.

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Consequences

  • A package stays usable by any number of deployables.
  • Moving a member between tiers is an ADR, not a rename.
  • Product literals and process.env in packages are a related rule; see /constitution/boundaries.

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Enforcement

  • turbo boundaries (pnpm boundaries, part of pnpm verify) reads the tags.
  • tools/scripts/validate-repository.mjs requires exactly one tier tag, equal to the one the directory implies.
  • packages/tooling/oxlint/src/boundaries.jsonc bans imports of apps/**, services/**, encore.dev and ~encore/* from packages/**.
  • Planned: a check that packages contain no product literal and read no process.env.

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Supersedes and sources

Supersedes: none. Sources: basalt adr/0021-tier-dependency-direction; figentra docs/constitution/boundaries.md.