All ongoing development is done on the next branch. When preparing for a release, we'll create a release branch which will eventually be merged into master. This way, what's on master is always what's published on npm.
Release management is currently a manual process, to be performed by core team members only. Here's the process:
Create a release branch, usually based on next.
Open a pull request for release -> master
Write the release notes in the PR description.
Decide on the version number, taking care to follow semver. Do a pre-release before doing the actual release.
Run yarn bump to increment the version number in all package.json files as well as lerna.json.
Commit the version change as "Release vX.X.X" (using the correct version number).
Tag the release commit with git tag vX.X.X (using the correct version number).
Push the release commit AND tag: git push --follow-tags
Publish each package (in ./packages) to npm using the script below.
Create a new release on GitHub and copy the release notes there.