Import EmailBuilder.js templates into the SendLit editor

Background

EmailBuilder.js (@usewaypoint/email-builder, MIT, React) is the default free editor that platforms find when they want to embed one. Numbers:

For comparison, @sendlit/email-editor had 383 downloads last month (npm).

Upstream is effectively dormant and won't fill the gaps its users ask for:

#164 "Is this project still maintained?" is open. The one reply says "Looks abandoned."
React 19 support PRs were closed unmerged: #190, #186 and #183.
#101 asked for merge tags / variables. The co-founder replied that they "keep EmailBuilder.js pretty stripped down as we have a pro version on Waypoint".
Forkers are rebuilding the gaps themselves (e.g. SparkDynamic's fork, and several forks on npm).

A lossless importer gives those users a one-step move to a maintained React 19 editor that has merge tags and sending built in.

Source: Waypoint competitor profile (Oct 2026), takeaway #1.

Add importEmailBuilderJs(doc) to @sendlit/email-editor, exported from the package entry point. It converts an EmailBuilder.js document (the root → EmailLayout → childrenIds tree of block_* entries) into a SendLit editor document.
- Map blocks: Text, Heading, Button, Image, Divider, Spacer, Html, Avatar, Columns/ColumnsContainer and Container to their SendLit equivalents.
- Map styles: padding, colors, font family and size, alignment, and the layout's backdrop and canvas colors.
- Unmapped blocks or props: keep them as an HTML block, or drop them with a warning. Never throw. Return { document, warnings[] }.
- Validation: validate the input with a schema and return a clear error for invalid JSON.
Add fixtures. Use EmailBuilder.js's own sample templates (MIT) as test input.
Add docs: a "Migrating from EmailBuilder.js" guide in docs/ and the package README. Cover the API differences (props and events), the importer, merge tags, and React 19.
Optionally, add a small CLI or script, npx @sendlit/email-editor import-emailbuilder in.json > out.json.
The playground sub-issue (phase 3) and the app's template editor use this importer through an "Import EmailBuilder.js JSON" action.

importEmailBuilderJs is exported, typed, and documented in the package README.
All official EmailBuilder.js sample templates import without throwing. Rendered HTML matches the original visually (block order, text, links, images, colors), checked with snapshot tests.
Unknown block types produce a warning and a fallback, not a crash. Invalid input returns a clear error.
A round trip works: an imported document → edit → save → reload in the editor.
The "Migrating from EmailBuilder.js" guide is published in docs and linked from the README.
A changeset is added, and the package version is bumped and released.