NavigationRejection enum

A departure guard returned false.

The caller's token was cancelled before the commit.

The navigator or the region is closed.

The request came from a hook of an in-flight transition of the same region, or of a region that holds it or is held by it (an ancestor or a descendant region). The rejection is conservative: such a request could wait on the transition that is running the hook.

A back request found no retained entry.

The expected current entry is not current.

The back-to target is not in the region.