History entries name the section by file identity and the page by its own
identity, so a section renamed, moved into a group or reordered, and a page
moved to another section, still resolve. Entries that no longer resolve (page
or section deleted, notebook closed) are dropped and skipped silently; Back and
Forward are disabled when nothing valid remains. Forward after renaming the
target section used to alert "Couldn't open / entity not found".

File and network failures in alerts now read in plain words ("This page was
moved or deleted.") through crate::plain.

Assisted-by: claude-opus-5.5