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Accepted by the owner on 2026-10-28 (design-system session c6, STA-1072). It writes down one rule for every session; it changes no version.

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Context

TypeScript 7 (the native compiler) checks and builds every member from catalog:build (7.0.2). It does not ship the JavaScript compiler API yet, so a tool that loads typescript as a library fails on it (ts.TypeFlags is undefined). Four places need that API today: the Expo CLI, tools/scripts/doc-standard.mjs, @stackra/gen discovery (0294 decision 26, 0263) and the @stackra/showcase generator. Each session has solved this on its own, so the rule needs to be stated once.

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Decision

  1. TypeScript 7 for every typecheck and build. Every member takes typescript from catalog:build. tsc, the presets (0300), tsdown declarations and CI run TypeScript 7. No member downgrades its compiler.
  2. TypeScript 6 only as a library, under the alias typescript6. Code that calls the compiler API imports typescript6 (catalog:tooling, npm:typescript@6.0.3), never typescript, so the TypeScript 7 binary stays the one on PATH. Today: @stackra/gen (its fallback host) and @stackra/showcase (scripts/props.reader.ts, scripts/omitted-names.function.ts).
  3. typescript at 6.0.3 only where a third-party tool requires that name. The root tooling (doc-standard.mjs) and the mobile app (the Expo CLI) take typescript from catalog:tooling; a code comment beside each entry says why. A new entry of this kind names its tool in the catalog comment.
  4. No ts-morph and no third version. Nothing pins TypeScript 5 or a nightly.
  5. Exit. When TypeScript 7 ships its JS API, typescript6 and the 6.0.3 catalog:tooling entries are removed in one change, and gen’s TypeScript 7 host becomes the only one.

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Consequences

  • A tool that crashes on typescript with an undefined ts.* member is moved to typescript6, not the member’s compiler.
  • Two TypeScript versions stay in the lockfile until the exit in decision 5.

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Enforcement

Planned: a validate-repository.mjs row that refuses import … from "typescript" in a file that also reads ts.TypeFlags, ts.createProgram or ts.createSourceFile, outside the catalog:tooling members named in decision 3. Until then, review.