Firm agreement in Moscow for concluding passage (4)
I believe the answer is:
coda
'concluding passage' is the definition.
(I've seen this before)
'firm agreement in moscow' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'agreement in moscow' becomes 'da' (Russian for yes).
'co'+'da'='CODA'
'for' is the link.
(Other definitions for coda that I've seen before include "Concluding passage of a musical composition" , "Tailpiece" , "Concluding passage of piece of music" , "bit at the end" , "Musical finale" .)