Replace a content item's shares

Replace the entire share set for one content item. Each entry targets exactly one of a node, a user, or a role. Requires the item's own share permission at its home node.

Notes.

• Replaces every share of the item in one step. Besides the screen.view gate, the caller needs the kind's share permission at the item's location (media: at the workspace root).
• A row targets one location (and everything under it), one person or one role; a row with no target shares with every location.
• The response echoes the request's rows rather than the stored ones.