Reads one row of a brain as a snapshot, with the form its scope id was read in (TraceSnapshot.scopeIdForm);
undefined when there is no such row. The record is read before the row and, while it names the plain form, after
it: a re-file writes the record in the transaction that moves the rows, once, so when both reads find the plain form
the row was read in it. A re-file that commits between them leaves the row read in either form, and the row is read
again.
Reads one row of a brain as a snapshot, with the form its scope id was read in (TraceSnapshot.scopeIdForm);
undefinedwhen there is no such row. The record is read before the row and, while it names the plain form, after it: a re-file writes the record in the transaction that moves the rows, once, so when both reads find the plain form the row was read in it. A re-file that commits between them leaves the row read in either form, and the row is read again.