Link two aggregates

This page links one aggregate to another, with tags and notes as the worked example. A note names its tags by id (tagIds), and a tag knows nothing of notes. Here the tag is the parent and the note the child.

You need:

• Both aggregates built (the aggregate reference).

• The link is its own table (note_tags). The group's change log records every change to it. Deleting a tag removes its links and never touches a note's row or version.
• The child's write carries the ids, and the server ignores unknown ones. It answers with the links the note really has, so a client never needs to know whether a tag still exists.
• Moving the child maps the parent by name. A moved note keeps its tags by name. The target group gets any tag it lacks, each with its own audit event.
• The parent is capped per group (TAG_MAX_PER_GROUP), because its list has no pages. The repository counts after its insert, in the transaction that holds the group's row, so two creates at once cannot both pass.
• A move whose tags do not fit is refused whole (TAG_LIMIT_REACHED). Moving the notes without their tags would lose them silently.
• Offline, the parent's collection comes first in offline/index.ts, and the child names it in its dependencies (parents, on, without). The four rules are in offline-writes.md.
• The child's screens read the parent's store (state/tags.ts) for their picker, labels and filter. The filter lives in the address (useUrlFilters) and runs over the local list.

The steps of the aggregate reference, as tags fill them:

The public website has no session, so tags exist in the SPA only.

• Delete, move and export an aggregate
• Make an aggregate work offline