Require tests for new build and pipeline scripts

[pomfrida]

Context

The review rounds on #5209 highlighted a gap: repo scripts (e.g. packages/eds-tokens/scripts/*.mjs) often run unattended — the Tokens Studio release workflow has no CI on its PRs — so an embedded runtime guard is frequently the only automated check. Runtime guards protect the output against bad input, but nothing protects the scripts against regressions when they are edited later. The NaN-threshold bug found in review (a non-numeric argument silently disabled the guard's checks) is exactly the class of bug a unit test catches immediately.

Task

Establish the convention that new scripts containing logic must ship with tests, and document it in AGENTS.md (the canonical conventions file) so it applies to human and AI contributions alike.

Suggested shape of the convention:

• Applies to new scripts with branching/transformation logic under packages/*/scripts/ and workflow-invoked tooling; trivial one-liner wrappers are exempt
• CLI-style scripts (top-level await, no exports) are tested by spawning them as child processes against fixtures in a temp directory — this also covers the CLI contract (arguments, exit codes, error messages) that workflows actually consume
• Use the package's existing test runner (vitest in eds-tokens, jest in eds-core-react)
• Precedent: build-dark-scope in eds-tokens-build already has tests

Done when

• The convention is written into AGENTS.md
• Tool-specific configs need no change (they reference AGENTS.md)

Backfilling tests for existing untested scripts (e.g. generate-css-bundle.mjs, assert-no-light-dark.mjs, generate-ts-tokens.mjs) is deliberately not part of this task — split into separate issues as needed.

[claude]

These issues may be related, as they concern the same Tokens Studio pipeline and the specific scripts this testing convention would cover:

• Establish a new Token build & publishing pipeline #5108 — Establish a new Token build & publishing pipeline (closed): established the build/pipeline scripts whose release workflow runs without CI, which is the gap this convention addresses.
• Generate TypeScript tokens in the Tokens Studio pipeline #5164 — Generate TypeScript tokens in the Tokens Studio pipeline (closed): created generate-ts-tokens.mjs, one of the untested scripts explicitly named here as a backfill candidate.
• Add a bundled variables.css to the Tokens Studio release workflow #5201 — Add a bundled variables.css to the Tokens Studio release workflow (open): concerns generate-css-bundle.mjs in the same CI-less release workflow, another script named as a backfill candidate.

This comment was generated by an LLM and may be inaccurate. Please verify that the linked issues are actually relevant.