Entry Anchors

Anchor Link field: a block's title and its anchor. The anchor follows the title while the block is new and is kept after that, so links keep working when the title changes. The front end renders it as the heading's id with anchor_id(). Two subtle buttons copy the link to the block and its anchor.

Anchor dropdown for linked entries: when an editor picks an entry in a Link field, a dropdown next to it lists the anchors on that entry (the Anchor Link fields on the entry and its nested entries, in page order). The chosen anchor is stored in the Link field's URL suffix as #slug, so link.url ends with it. No template changes needed.

Anchor dropdown for the same page: Link fields whose URL type allows anchors get a dropdown with the anchors of the page the field is on; choosing one sets the URL to #slug.