Add named project snapshots

AGENTS.md

@@ -230,6 +230,11 @@ command and one undo step. Explicit renumbering uses the collision-safe
 Immutable revision metadata is available through the paginated
 `GET /api/projects/:projectId/history/revisions` endpoint; it does not expose
 stored command payloads.
+Named logical snapshots can be created and listed through project-scoped API
+endpoints. Their schema-versioned payload contains the complete supported
+project runtime state and a SHA-256, excludes global/upgrade-only data and does
+not change the project revision or undo/redo stacks. Restore is not implemented
+yet.
 Insertions and generated move targets use client-generated stable UUIDs, and
 undo restores the same ids from complete server snapshots. The tree response
 supplies the optimistic `currentRevision`; obsolete direct field PATCH,
@@ -301,7 +306,7 @@ Users must be able to override sizing suggestions.
 
 ## Current Deferred Work
 
-- named logical snapshots and restore
+- snapshot restore, snapshot UI and periodic snapshot policy
 - Revit/CSV/IFCGUID round-trip
 - full electrical sizing
 - multi-user/PostgreSQL operation