ReadHistory
ReadDocument. Returns HistoryState containing DocumentHandle document, Revision revision, bool can_undo, and bool can_redo.
Availability can change after the query. Reading it does not grant history navigation permission or bypass document protection.
Undo and Redo
ReadDocument and History. HistoryRequest contains DocumentHandle document and a mandatory nonzero Revision expected_revision.
These commands navigate the application’s history. They can undo or redo a user’s edit or another integration’s edit. Your session does not have a private undo stack, and 0.2 does not expose a command to undo only its own operation.
Avatar height and measurement commands also use this history, with captured body parameters for undo and redo. Tool activation creates no history entry; a change to active tools or viewport context can still invalidate a copied snapshot.
Supply a revision from a fresh snapshot. The host checks document state and history availability. If there is no entry to navigate, an otherwise valid request returns success with changed = false.
After a successful operation, refresh metadata and reacquire any part identities that may have been retired or restored. Follow readback handling if the result contains refresh_error.
PollChanges
ReadDocument. Refreshes host state and compares after with the current session revision.
Pass your last snapshot revision. If
requires_refresh is true, call ReadDocument() and replace your cached snapshot. Passing zero requests a refresh indication; passing a revision in the future returns InvalidArgument.
Polling is coarse invalidation, not an event journal. Multiple edits can be observed together. It does not provide a list of changed vertices, callbacks, event ordering, or delivery of every intermediate edit.
Use polling on the host’s owning thread while the application can expose consistent state. Do not spin continuously when it returns Busy. On DocumentClosed, discard old document handles and decide whether to start again with the new document.