No.
If so, would that also not mean that Paul is here boasting about disobeying the Torah?
It is not so, so the question is moot.
What "truth of the gospel" is he preserving by refusing to allow a Gentile Christian to be circumcised?
There is no requirement for circumcision of adult males in Torah. There were many 'righteous gentiles' living among the Israelis from the very beginning.
So when God said that uncircumcised males would be cut off from their people, He didn't really mean it?
No.
Then please describe the nature of the controversy over Titus in Jerusalem in Galatians 2.
There is no requirement for circumcision of adult males in Torah. There were many 'righteous gentiles' living among the Israelis from the very beginning.
Any uncircumcised male who is not circumcised in the flesh of his foreskin shall be cut off from his people; he has broken my covenant. (Gen. 17:14)
Circumcision was a covenant sign both for the Abrahamic covenant, but the Mosaic one. To whom is the above verse referring? Uncircumcised adult males, or uncircumcised infants?
If a stranger shall sojourn with you and would keep the Passover to the Lord, let all his males be circumcised. Then he may come near and keep it; he shall be as a native of the land. But no uncircumcised person shall eat of it. (Exod. 12:48)
If there was no requirement for adult males to be circumcised, then why are they forbidden from participating in the passover? In fact, the very next verse tells us,
There shall be one law for the native and for the stranger who sojourns among you. (12:49)
Why did Joshua circumcise the entire nation of Israel (Josh. 5), the generation that was not born in Egypt, if there was no requirement that males be circumcised?