The gemara on the top of the page asks when one violates the prohibition of shehiya by leaving a pot on the stove in a way where it is prohibited (acc. to chananya/rama when it is not yet ma'achal ben drusai, and acc. to rabbonon/shulchan aruch when it is still נצטמק ויפה לו), we make no distinction between shogeg and meizid. R. Nachman bar Yitzchok explains that although when one violates a d'oraysa such as actual bishul on shabbos, if done by accident it is mutar for him to eat it on shabbos (acc. to r. meir), here we are more machmir and forbid it on shabbos because people are מערים to do it intentionally and claim it is an accident. However, in the braisa, Rav Meir makes it clear that if the food was fully cooked, even though it was נצטמק ויפה לו, we will not be machmir to forbid it bidieved. Even the opinion (rabba and rav yosef) who is more lenient for shehiya done accidentally because no ma'aseh was done, would presumably be machmir by chazara because an action of violation is done. Therefore, if one violated chazara by accident, the food would be assur until shabbos is over. The Rama (253) writes that since chazara is violated by a ma'aseh, even if done by accident, the food would be forbidden until after shabbos even if it were fully cooked, and one would even have to wait כדי שיעשו. But if chazara was violated on something that is fully cooked and נצטמק ורע לו, the Rama permits it to be eaten since there is no benefit from the violation.
When a goy does chazara, the Rama says that we give it the status of an accidental violation of shehiya and permit the food if it were fully cooked, even if it were נצטמק ויפה לו, but if it weren't fully cooked it is assur until after shabbos. The Biur Halacha points out that even according to the minhag to follow chananya and permit shehiya when it is כמאכל בן דרוסאי, chazara would still be forbidden, therefore unless it is fully cooked, the food would be assur, even if done by a goy. It is clear from the Rama that we don't allow chazara to be done by a goy. However, the biur halacha (end of siman) cites the pri megadim (38) who says that since we permit shevus d'shevus for the sake of shabbos, it is permitted to have a goy to chazara on a solid cooked item (on which there is no bishul issue). The Chazon Ish takes issue with this and explains that the concept of shevus d'shevus only permits an issur where the violation is the ma'aseh, but chazara is like shehiya were the violation is the situation, not the act of putting it on. Therefore, even if a goy would put it on the Jew is obligated to pull it off and not maintain a situation that is מחזי כמבשל. This argument between the pri megadim and chazon ish is the basis for discrepancy in shabbos kashrus policies between the star-k and ou.