> OK, i've tried to follow the code in this area but 
is 
> isn't easy  :)  
> ...can you tell me: 
> Is it guarenteed that the 'transfer-status' callback 
> (wrapper) is ALWAYS called BEFORE the original file 
is 
> overwritten with the 404 message file? If i can rely 

NO - this is the countrary: the back_finalize() 
function ("transfer-status" log) is called when the 
engine has finished a transfer and wants to finalize 
(store in cache, close pending connection) it.

Oh, one tip: activate the 
'Options'/'Build'/'No error pages'
AND
'Option'/'Option'/'Build'/'Do Not Purge Old Files'
this may do the trick, and keep files. (the 'No error 
pages' should force the engine to NEVER erase local 
files with error pages, and the 'Do not purge' option 
should prevent it from erasing)

If not, try to hack the filecreate() function in 
htscore.c, but this might NOT be sufficient..