Apparently the check that topics entries meet the allowed syntax is a server-side check; we had a PR pass our CI, including the dry-run publish check, but then fail to actually publish in post-submit and thus break the tree with:

Invalid topics value (platform views): must consist of lowercase alphanumerical characters or dash (but no double dash), starting with a-z and ending with a-z or 0-9.

We should put that validation logic into our existing pubspec validation.