- Only update the selected-file state on a successful SELECT (SW1 in
61/62/63/90/91/92/9E/9F); a failed SELECT (e.g. 6A82) leaves the
current file unchanged.
- Track the file structure from the FCP (GET RESPONSE after SELECT).
- Skip file decoding for record ops (READ/UPDATE/SEARCH RECORD) when the
selected file is transparent/DF, marking the result 'stale' instead of
decoding garbage — this catches silently-dropped SELECTs.