The one-step reader was named _link_rows, which shadowed
MaintenanceOperations._link_rows on PromptDatabase and broke the Missing
links preview and apply; it is now _one_step_link_rows, and a test pins
that the maintenance reader is not shadowed.
An interrupted read (Move library retiring the connection) is raised as
before instead of falling back and spending the one warning; a JSON text
over SQLite's length limit (DataError) streams like the other value
failures. The equivalence test compares value types per path rather than
by row order, and a test checks that the read leaves no WAL snapshot
pinned.