Unique Rectangle Type 2
This deduction assumes the puzzle has exactly one solution and that all earlier candidate removals were sound. A Type 2 Unique Rectangle starts from a candidate state in which swapping two digits across the construction would preserve every touched row, column and box. The rescue cells share an extra digit that must occur in at least one of them, so the digit is removed from every candidate that sees all of them.
What is Unique Rectangle Type 2?
This deduction assumes the puzzle has exactly one solution and that all earlier candidate removals were sound. First verify the complete two-value structure: four unsolved cells at the corners of two rows and two columns across exactly two boxes, each holding the same two base digits among its candidates. Exchanging those digits between the corners must move no given and must leave each affected house with one occurrence of each base digit. Type 2 then applies its additional rescue condition; an arbitrary rectangle is not enough.
In Type 2 the rescue cells share one extra digit. At least one rescue cell must take it, so the digit is removed from every outside candidate that sees all of the rescue cells.
How to spot it
Verify four unsolved corners in two rows, two columns, and exactly two boxes. The rescue cells share an extra digit, and they share a house or otherwise give the proposed target visibility to every rescue occurrence. The extra digit is true in at least one rescue cell, so remove it only from candidates seeing all of them.
The logic
If no rescue cell used the shared extra digit, the complete deadly swap would remain. Therefore at least one rescue cell uses the extra digit, and a candidate seeing every possible rescue occurrence cannot use it.