sukkah on shmini atzeret - an analysis of rashi

Last week I wrote about asking “mah kashe l’Rashi” in gemara and said I liked the close reading of Rashi so much I may make it a regular feature. Well, here goes round #1 and I’ll see if I continue. Just as an editorial aside, I think I chose a far too long Rashi to start the ball rolling, but it has something to do with an earlier post, so I got hooked. (BTW, my daughter came home with a chumash Rashi worksheet last night, and sure enough, first question was to identify Rashi’s question).

Gemara Eiruvin 96a debates whether there is an issur of bal tosif in performing a mitzvah without kavanah in a time period where no obligation exists (shelo b’zmano) – e.g. is there an issur of bal tosif in putting on tefilin without mitzvah-kavanah at night?

Asks the gemara, if there is an issur of bal tosif shelo b’zmano even without kavanah, “hayashein b’sukkah b’shmini yilkeh” – one should get malkos for sleeping in the sukkah on the eighth day of sukkos.

Rashi d”h hayashein: “d’mosif shmini al shevi’i, v’anan meisav yasvinan b’shmini b’safeik shevi’i l’chatchila – elah, she’lo b’zmano b’lo kavanah lav tosefes hu ul’hachi sharinan, d’i shmini hu lo mechavein l’miztvas sukkah”

Just in case my transliteration (sorry, no Hebrew keyboard) is unclear, the gist of Rashi is that we sit in sukkah l’chatchila on the eighth day [i.e. the day after sukkos] because of a safeik whether it might really still be the seventh day, proving that a mitzvah done shelo b’zmano without kavanah is not bal tosif, for we have in mind that if it really is the eighth day [i.e. not sukkos] we have no kavanah.

A long and unusually verbose Rashi, which is a usually a tip-off that lots of explanation of something is called for:
1) What in the text demands explanation?
2) “HaYashein”=one who sleeps. Is there a difference with respect to this din between sleeping and eating in sukkah according to Rashi? Why might you think otherwise?
3) Why does Rashi stress that we sit in sukkah “l’chatchila”?
4a) Rashi presents a scenario of someone in chutz l’aretz who eats in sukkah on the eighth day because of sfeika d’yoma. What other simpler scenario fits the words “hayashein b’sukkah b’shmini”?
4b) Why didn’t Rashi give that simpler case as a scenario?
5) See Rashi Rosh haShana 28b d”h hayahein: “shelo l’shum mitzvah”. No explanation of the scenario! It certainly seems striking in comparison to the long explanation of Rashi in Eiruvin. Significant omission/difference or not?

Something to think about over Shabbos : )