The Government agent is here to stay (9)
I believe the answer is:
residency
'the government agent' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'here to stay' is the wordplay.
'here' becomes 'ncy' (I can't justify this - if you can you should believe this answer much more).
'to' means one lot of letters go next to another (I've seen this in other clues).
'stay' becomes 'reside' (I've seen this in another clue).
'ncy' put after 'reside' is 'RESIDENCY'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for residency that I've seen before include "Fact of living in a place" , "temporary post as artist" , "Position in house" , "circumstance of living in a particular place" , "live-in post" .)