I am trying to understand the definition of tzuras hapas in halacha. I have seen rishonim say that noodles are never bread or considered pas haba bkisnin even if baked because they have no tzuras hapas. Where do we draw the line? Little hard pretzels are basically noodles that are shaped into a little pretzel and baked but they are considered pas haba bkisnin. Also do wraps (the thin kind) have a tzuras hapas?
As you write, it is sometimes hard to draw the line.
The basic definition of tzuras hapas is an item that looks baked. It doesn’t need to resemble bread in shape and form (the lechem hapanim didn’t), but it needs to look baked. Noodles do not look baked, and do not have tzuras hapas even if baked. Likewise, most poskim write that Bran Flakes do not have tzuras hapas; the same would apply to Cheerios.
There are differences of opinion as to whether very small hard-pretzels (which the question mentions), blintzes, mandel-type soup croutons, very thin wafers, and wraps, have tzuras hapas. For Triscuits, for instance, Rav Belsky is quoted as maintaining that the don’t have tzuras hapas, and Rav Schachter was stating they do.
My leaning is that wraps do have tzuras hapas, because they are associated with burekas and other baked items used to contain fillings, but it is difficult to reach a concrete decision.
Sources: see Rashi, Menachos 75b; see Vezos Haberacha, and other modern-day Berachos books, which quote different opinons concerning a variety of foods.