upekkha100: Good questions. I revised the post to address three of them. Also, I will soon publish a post on how tanha actually grows with one’s upadana via vaci sankhara.
” Is saṃkhittena a form of sankhara dukkha? Is the “sam” in saṃkhittena same as san?”
Yes. It could be connected to “san”. It is “san” + “khittena”, where is “san” is what we accumulate for sansaric journey; see, “What is “San”? Meaning of Sansāra (or Samsāra)“. “Khitta” is actions; see, “Does the First Noble Truth Describe only Suffering?“.
So, we create our own dukkha by doing things to accumulate “san” (with icca and tanha).
This is what is also meant by “panca upadanakkhandha” willingly embracing the pancakkhandha. We do this by generating vaci and kaya sankhara.
In most translations, though, “samkhittena” is taken to mean “in brief” or “in summary”.
So, both could be valid.