Process question: port commits -> FTP package generation

[grarpamp]

How do commits to a port ultimately make it out to
the FTP mirrors in package form?
For instance, the following update dates indicate there is no
automated dependency engine doing this (surely to avoid
some chaos and engine difficulty).
With the exception of the 4 month spread in the file dates for 9i,
it seems plausible the other three branches were all built in
one run during the up to 4 day spread in their ls dates.
Is there a doc I can read about this overall process?
Is there a tinderbox with interim builds and logs and things?

8a Oct 11 20:08 CHECKSUM.MD5
8i Sep 17 14:26 CHECKSUM.MD5
9a Oct 16 23:13 CHECKSUM.MD5
9i Oct 26 10:21 CHECKSUM.MD5