Manual mud cave construction involved yours truly (4,5)
I believe the answer is:
vade mecum
'manual' is the definition.
(thesaurus)
'mud cave construction involved yours truly' is the wordplay.
I cannot quite understand how this works, but
'yours truly' could be 'me' (the person that set this crossword) and 'me' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for vade mecum that I've seen before include "guidebook" , "Handbook, guide" .)