Tos' d"h Ad-
Tosfos says that rabeinu tam was ragil when he davened beyachid to bend when the tzibur got up to modim.He specifies that it was with out any amira, and specifically in the middle of the brocho. However then he says lechatchila "lo laasos ken cedemashma hacha" .then he bring rashi" shita in succa that about shomeia ceoneh, and how it is not a safek if you are quiet when the sh"tz says kedusha bec.it's shomeiah k oneh.
1. what does tos mean when he says not to do this lechatchila? not to do what? Also are we to think that the rabeinu tam was not doing something lechatchila?
2. Why does tos' say cedemashama hachi, where is it mashma from the machlokes r"h, and r"ybl that you should not not do what rabbeinu tam did? Does the gemarah here not seem to be discussing the issue of someone who comes late?
3.What does the whole gemarah in succah have to do with what tos' is discussing.
4.tos' on 13b d"h shoel says that rabbeinu tam would wait in between oseh pheleh and sh"e in order that he would be ale to answer and kedushah How can this shita be connected with this tos'
5. The rosh in the dapei harosh 12b seems to make some connection between the these 2 shitas of the rabbeinu tam but i do not understand what it is saying?
Thank you very much you would be a great help
1. Le'Chatchilah, one should not begin Shemoneh Esreh with intention to bend (in the middle of a blessing) at the moment that the Tzibur says Modim, unless he is able to get to Modim in his own Shemoneh Esreh at the time that the Tzibur gets to Modim.
Rabeinu Tam would bend in the middle of a blessing only if he had begun his Shemoneh Esreh in a permissible fashion le'Chatchilah (that is, he began when the Tzibur began), but said his Shemoneh Esreh slower than the Tzibur so that by the time the Shaliach Tzibur came to Modim in the Chazaras ha'Shatz, Rabeinu Tam came to Modim in his own Shemoneh Esreh.
2. It seems from the Sugya that one should not begin Shemoneh Esreh when he is unable to finish by the time the Shaliach Tzibur gets to Modim, with intention to bend in the middle of another blessing.
3. The Sugya here implies that one should not begin the Shemoneh Esreh when he cannot finish it by the time the Shaliach Tzibur gets to Kedushah, and to rely on listening quietly to Kedushah as "Shomei'a k'Oneh." Tosfos is bothered why this is not permitted. Tosfos answers (a) according to Rashi, one should not do this le'Chatchilah, and (b) according to Rabeinu Tam, it is forbidden to do this because it is a Hefsek.
4. Tosfos' intention is to say that this is what one should do le'Chatchilah (as in #1 above).
5. I did not find the statement of the Rosh which you describe.
All the best!