UndoDBProvider.undo()method

Restore the wrapped provider to the state the log first observed, undoing this provider's writes.

• Applies the state-establishing operations in reverse order, so the earliest observed state of each item wins: reads restore the item that was observed (or delete it when the read confirmed it absent), and adds delete (the item did not exist before).
• Restores touched items unconditionally, so concurrent writes made to those items since the recording are overwritten.
• Writes directly to source without recording, so the log still describes the original operations afterwards.