Versioned comment anchors

One hard technical problem in TiVA is keeping comments and change proposals attached to the right text.

The document is collaboratively edited and fully versioned. A comment anchor cannot only live in the database, because the editor needs to render it. It also cannot only live in the document, because versions, review state, and permissions live outside the editor.

The working approach stores the anchor twice: as a database entry and as a marker in the document. When a version snapshot is created, the IDs are rewritten on both levels together so an old version remains stable.

That sounds small, but it ruled out several existing collaboration and comment frameworks. They assumed a different storage model and did not combine cleanly with field-based versioning.