entryId property
Which entry this read is of — the settling key, exactly as
InspectTree.entryId: a tree naming another entry is a read from before
the switch, not an empty one.
Null until the guest has a tree to report. Enabling semantics takes a frame, so the extension withholds the entry id rather than settling a poll on "nothing yet" — an absence with a name would read as the answer.
Implementation
final String? entryId;