The workbook to track, or null.
true when the file is encrypted or a password has been set for it.
Reads Origin.isEncrypted(), which covers both: a read or a completed write records what is on
disk, and Origin.setPassword records the intent immediately — the same latitude
Origin.setName has. One source, one onChange to follow, so a lock appears the moment a
password is set rather than only after the save that applies it.
Tracks whether a workbook is — or, once saved, will be — encrypted, as React state.