[Avodah] תשובה: bracha hallel

[Shlomo Pick]

I followed rabbi wolpoe's remarks here (sourcing tosefta pasch 10), and it
the previous posting (cryptic as usual), and started with the sources.  I
went to pasch 10 and checked tosefta kepshuta who immediately reffered me to
Sukka 3:2 in Lieberman edition (also found in responsa project). There the
tosefta states (and is the source of the yerushalmi) that 18 days a year and
one night we read the hallel.  There is no need for Sephardic logic, it's
mandated by tosefta (and I presume there is no makhlokes between the
toseftot), yerushalmi and massechet soferim which even obligates both nites
of the diaspora.
And that's objectively from the sources. Usually tosophot have this
objective reading in his questions, especially about minhag. their answers
become subjective in order to preserve the minhag.
As far as a bracha bezibbur, that's dependent on the story of rav in bavel
and when he walked into the shul where they were saying the hallel already
(kesef mishna) or he was there from the beginning and they made a bracha as
tosophost says in taanit 28b s.v. amar.  For a summary of the rishonim,
including rashi who did not say a bracha on hallel of rosh chodesh because
it's a minhag and one doesn't make a bracha on minhag, also for alternative
readings in the gemorah ta'anit, such as Rach, see tosophost r. Yehuda
meParis, brachot 14a, mahadurat  harav nissim zachs, vol.1, pp. 171 ff. 
And no slam dunk, already the behag says in the sugya that even a zibbur is
a yachid since there was no takanna. 
No matter what, from the tosophot, you see they were bothered by both the
concept of yachid and also the problem of bracha on minhag.  whether their
pshat is the best, there are alternative readings of the texts and certainly
differing explications of those texts, like how to understand yachid as well
as how to understand the totality of the texts (like no bracha on minhag as
per sukka 44b, and hallel on rosh chodesh is minhag -> no bracha on hallel
of rosh chodesh at all, per rambam and per rashi)
Chodesh tov
shlomo