Reb.
“I think also there is a kinyan of “ani ha’mehapech b’charara” (a poor person circling around a food item) and kinyan daled amos b’r’shus ha’rabbim ”
May Hashem bless you! you are gevaldig, and an outstanding Lamdan (or lamdanit)!!
However, both of these are not applicable in the case of siddurim and seats.
עני המהפך בחררה — asides its limited parameters and conditions, as is a major maclokes Rishonim, Rab Tam’s shitah is known, that it does not apply wherein there is no other of the item in concern, (e.g hefker: the aggressor can not obtain the item via a diff matter — its free) it only applies to מכר where the Ani can say: go find yourself a diff ילך וישתכר במקום אחר” why mines!
So in this case, where there are no siddurim left etc, he can not utilize the taynah of עני מהפך בחררה. Lfi R Tam. Now even Rashi in this case, where there are no kinyanim involved and, not יורד לתוך אומנות חבירו Ani meHapech is לכאורה not applicable, siddurim and seats are only an zchus השתמשות and I don’t think that was included in the takaneh of עני מהפך בחררה..