[coretl]

What

The tutorial's copy-paste blocks pinned this project at a literal <tag> placeholder readers had to fix by hand. This replaces them with a __LATEST_TAG__ sentinel and adds a build-only MyST transform that swaps it for the repo's latest tag at build time, so the rendered snippets carry a real, current ref (v0.16.0 today).

How

• docs/_ext/inject-latest-tag.mjs — a document-stage MyST transform that replaces __LATEST_TAG__ in text/code nodes. Build-only (never runs in the browser, unlike version-switcher.mjs), so it's free to touch git. Lives under docs/_ext/, not plugins/, since it's docs tooling, not the shipped widget.
• package.json — a latest-tag script (git describe --tags --abbrev=0, falling back to git fetch --tags && describe for the shallow CI checkout, which has no tags) feeds LATEST_TAG into docs/docs-dev via a LATEST_TAG=… sh -c '…' wrapper so the env actually reaches myst.
• docs/myst.yml — registers the plugin.
• docs/tutorials/adding-to-a-fresh-repo.md — the 4 copy-paste code blocks + the inline pin use __LATEST_TAG__; reworded the two prose lines that referenced the old placeholder.

If no tag resolves, the transform leaves the sentinel and emits a build warning rather than silently shipping __LATEST_TAG__.

Scope & known limitation

• Tutorial only — reference/ and explanations/ keep the literal <tag>.
• MyST's auto per-page Markdown download (book-theme "Downloads" menu) still shows the sentinel: it's a source snapshot serialized before transforms run, so it's outside the transform's reach. Left as-is by design — it's "the source," consistent with the GitHub "Edit this page" link. The rendered pages (the actual copy-paste surface) are all correct.

Verification

• Clean build → every rendered tutorial page shows v0.16.0; no sentinel in the rendered HTML.
• npm test → 22/22; biome clean; prek passes.

🤖 Generated with Claude Code