In my opinion, in a Torah-level matter it is forbidden to put oneself into a situation of duress. See here:

Unfortunately I don’t have time to listen to the lecture, but these are old and well-known points. The medieval authorities already discussed the issue regarding setting sail on a ship before the Sabbath, and regarding an infant whose hot water spilled out. But one has to distinguish between different situations. In our case, in my opinion there is no reason to forbid it, since eating is a reasonable act that a person does routinely every day, and there is no reason to prevent him from doing this act because afterward he will not recite the blessing. This is not comparable to someone directly putting himself into a situation of duress in order to commit a transgression. All the more so since here it is only the neglect of a positive commandment.
Moreover, one may note the Talmud in Sanhedrin regarding Zimri, who could have killed Pinchas under the law of a pursuer. The later authorities asked: after all, he could have stopped sinning and then would have been saved, so this is a case where he could be saved by injuring one of his limbs, and how then was he permitted to kill Pinchas? According to my approach, this is very well understood, because he is doing his act not in order to enter a state of duress but for his own reason, namely that he wants pleasure—even though it is a transgression. Therefore he is not obligated to stop so that he will not have to kill Pinchas. And this is so even though he is obligated to stop simply because the act itself is a transgression. See on this in Kli Chemdah at the end of Parashat Balak.
I would further note from the Ritva in Chullin (and quite a number of later halakhic decisors) who discussed someone who recited a blessing and then changed his mind and no longer wants to eat. Is he obligated to eat in order to rescue the blessing? Many concluded that he is not obligated, and if he now does not want to eat, he need not eat. True, various explanations were given for this, but if we understand that when he does not want to eat he is not required to do so merely to avoid a blessing in vain, then likewise he is not required not to eat in order to avoid eating without a blessing. I discussed this at length in the fourth book of the Talmudic Logic series.

I agree with you that the distinction between setting sail on a ship and circumcising the baby on the Sabbath and then heating water is whether this is normal behavior or an intentional entry into duress—and not like the distinction made by the Kehillot Yaakov and Rabbi Zalman Nechemia and others, who distinguished between a person already being in the midst of the Sabbath and a case before the Sabbath—but I distinguish between entering duress with respect to a transgression and entering duress with respect to refraining from a positive commandment.

Well, here it is refraining from an action.
Even according to the distinction of the later authorities, here he is not yet obligated in the blessing, since he still has not eaten.

I wrote the opposite. In a case of duress involving being saved from a transgression, I agree with you; in refraining from a positive commandment—I do not.
At some point I’ll write this up properly and upload it here, with God’s help.

Does a religious court compel someone not to put himself into a situation of duress that would cancel a positive commandment, just as they compel fulfillment of a positive commandment?
And if someone puts himself into a situation of duress in order to violate a prohibition, do we warn him at the time he enters that situation or at the time of the act itself? And how can he receive lashes if he is under duress? (Maimonides, Foundations of the Torah 5:4—even regarding idolatry, if he transgressed under duress, although he was forbidden to do so, he does not receive lashes.) Obviously in the laws of bailees this would not be considered “it began with negligence and ended with duress,” but rather all negligence; but there there is a contractual obligation, so we do not judge the moment of the damage separately.
If someone puts himself into a situation of duress by mistake—he thought it was permitted to put himself into duress—but the transgression itself he committed intentionally, does he receive lashes?

You are making a connection that is not necessary. It may be that there is a prohibition against putting oneself into a situation of duress, but that does not mean that he violates the prohibition itself, nor that he is punished. Just as Maimonides says that one who violated one of the three cardinal sins under duress is not punished.

Where does such a prohibition come from if it is not the prohibition itself and not a special exegetical derivation? I mentioned Maimonides, but one could discuss a case where someone puts himself into duress regarding a prohibition—for example, he puts himself into a life-threatening situation in which, if he does not eat pork, he will die—so perhaps at the time of the act it is permitted for him to eat, and nevertheless he receives lashes because the whole thing is really willful. As with bailees, where this would be considered negligence. And it is not comparable to duress regarding the three cardinal sins, where it is only forbidden to him, but in the end there is no element of will here at all.

The prohibition is that very prohibition itself, but on a lower level, and therefore there is no punishment. We find this with several prohibitions, and the three cardinal sins are one example of that. A partial measure, according to Rabbi Yochanan, which is forbidden by Torah law, may be another example. So too idolatry out of love or fear, and more.

For a partial measure, if it is Torah-level, then there is a derivation from “any fat.”
It is hard to compare duress regarding the three cardinal sins to someone who willingly puts himself into duress.
Why did you bring proof from idolatry? Do you mean that if he worshipped out of love or fear and did not accept it as a god, then according to Maimonides he is exempt but it is still forbidden? Are examples of “exempt but forbidden” lacking? On the face of it, “exempt but forbidden” is only a rabbinic prohibition.

Regarding a partial measure, there is a source from reasoning: it is fit to combine. The later authorities discussed its relation to the source from “any fat.”
In my opinion, exempt from punishment but still forbidden by Torah law. And I think I have seen commentators explain it that way.

Exempt from punishment but forbidden by Torah law, but not because it is a general prohibition, or because it involves no action, or because it is linked to a positive commandment—right?

Indeed. It is actually a phenomenon I have wondered about more than once. There are examples where the level of transgression is lighter and you are not punished even though it is forbidden by Torah law.
Now I recall that the Pnei Yehoshua writes that a labor not needed for its own purpose is a Torah prohibition without punishment. There are other examples I have encountered in the past.

Cases of doubt, according to the one who says that in a Torah-level doubt one must be stringent by Torah law.