The shell section already states the three size bands and the promise that no action is unreachable at any of them; how the header chooses what to give up belongs beside them, because the promise is what decides it. Two measured facts go to NOTES.md rather than here. `scrollWidth` counts a box's left padding and not its right, so the obvious fit predicate under-reports by a gutter and passed on a bar with a control jammed against the window edge. And the overflow is 11px idle and 262px while working, which is why the issue was filed twice with different numbers — a seeded app that has finished scanning is idle by the time you resize it. Closes #143