Persist Revit CSV configuration

AGENTS.md

@@ -250,13 +250,20 @@ not change the project revision or undo/redo stacks. Restoring a server-stored
 snapshot verifies its checksum and the current-state hash, replaces supported
 project data atomically and records a new `restore` revision with a complete
 inverse command. Restore can therefore be undone and redone after a restart.
-Current snapshot schema version 2 additionally stores whether the project is a
-public building. Supported baseline version 1 snapshots are upgraded with
-`isPublicBuilding = false`; pre-baseline snapshots remain unsupported. Both
-versions contain circuit-group identity, distribution-board components and the
+Current snapshot schema version 3 additionally stores the optional project-wide
+Revit CSV configuration. Version 2 snapshots are upgraded with an empty external
+configuration. Supported baseline version 1 snapshots are additionally upgraded
+with `isPublicBuilding = false`; pre-baseline snapshots remain unsupported. All
+supported versions contain circuit-group identity, distribution-board components and the
 separate circuit/component protection records. Portable duplicate imports
 remap component ids and protection-owner references together with the existing
 project graph.
+Project-wide Revit CSV configuration uses
+`external-csv-configuration.update`. Its complete expected/target snapshot is
+persisted through the shared project-command transaction, so create, update,
+delete, Undo and Redo are revision-safe. Snapshot schema 3, restore and portable
+project duplication preserve the configuration; duplication remaps its internal
+id and project link.
 The central revision boundary creates an automatic logical snapshot after each
 25 new revisions and retains only the newest 12 automatic snapshots per
 project. Named snapshots are never removed by this retention policy.