Once you get to a certain complexity of notebooks, I find it only serves to complicate my mental model to “experiment” out of order. It makes me far more likely to forget to “commit” an ordering change.

Jupyter notebooks do store the execution order of the cells. Just enforce a pre-commit or pre-merge hook that doesn't allow adding notebooks that have out-of-order cells.

marimo still allows you to run cells one at a time (and has many built-in UI elements for very rapid experimentation). But the distinction is that in marimo, running a cell runs the subtree rooted at it (or if you have enabled lazy execution, marks its descendants as stale), keeping code and outputs consistent while also facilitating very rapid experimentation. The subtree is determined by statically parsing code into a dependency graph on cells.