On legumes and sourdough

Ready for joy,
Thank you for the compliments (I’m not sure I deserve them).
As for your point, I did indeed assume the current accepted reason here. You can also see it in the explanations given today (all those who report that even today they find leaven grains mixed with legumes. These discussions also came up on Talkbacks).
It is possible that what you describe was originally the basis for the custom (I have not yet read the sources you sent), but even if it is the basis, I do not see a compelling reason for it. And the fact is that there are many reasons for this custom, all of which come retrospectively, which suggests that none of them really hold water (I mention Rabbi Midan in his well-known adage that he knows 22 explanations for reading the Book of Ruth on Shavuot but only one for reading the Book of Esther on Purim. Maybe I brought that up there? I can’t remember anymore). After all, according to this method, legumes should be divided according to what creates hard leaven and what does not, and not according to the question of what was in their time and was included in the custom and what was not, or green legumes and what is not, and all the other divisions that are made in this context.
Regarding my halakhic position, you are indeed right. On the surface, this is not the accepted position, at least not on the declared level. But if you examine more deeply, you will see that it is indeed the accepted position. Ultimately, everything that follows the Talmud can be argued about, but things have inertia and different weights. It is not easy to change something that has become entrenched, but there is no mandatory authority here like the Talmud. However, in the kabbalah discourse, people enthusiastically declare that there are additions to the halakhic canon that are binding throughout the generations, and do not notice that these are only additions of weight (in the accepted legal terminology). I also accept this in principle. It is not just about semantics. Things are important, because in the event that there is a significant need to change, there is no reason not to do so. After all, there are clear sources for arguments of authority (do not deviate, accept the aliyya, perhaps accept the nation, etc.).
But on a principled level, I’m not so impressed, even if that were the accepted position. The more important question is what is right and not what is done in practice. What is desirable and proper and not what is currently happening. Although what was accepted has weight, of course. Like the law of “sugain da’lama” on the issue of error in judgment and the like (I will note that I also discussed this, and I argued that, contrary to the accepted approach, “sugain da’lama” is only a sign and not a cause. If there is something that is true and has not spread, it will have the same status, and the one who is wrong about it will be wrong in judgment. And if there is something that has spread and is not true, the one who is wrong about it will not be considered wrong. Like a foolish custom and the like). Beyond that, accepted positions are also created in some way. If I succeed in convincing the public, then my position will be the accepted one. Rabbi Blumentweig once said that in our relationship to custom there is an inherent contradiction, because custom is created by deviating from the accepted (the principle of law), and from the moment it is created there is an obligation not to deviate from it. This is the fixation of exceptions. And so on.

Happy Holidays and thanks again for the comments and compliments,