A full pass on the break-loop display, off a dogfooding session that
met a BoundsError and read design notes instead of values.
The headline now carries the condition's own fields — BoundsError
reads as 'low 648, high 648, length 100' with nothing special-casing
it — over one short status line, and under it the trap's own site with
the source line and a caret at the column, Elm-style. Fields render
with values through the new condition op, falling back to the layout
with one sentence per missing value.
Every choice goes out by restart-at now, so a shadowed restart is
takeable rather than refused, and its line says only whose name it
repeats. The abort line says what abort does. The bracketed
implementation notes are gone from every string that could print, and
a fixture pins that as a property of the rendering.