A parameter change can break a feature without failing the command that
made it; parameters.change reports it only in its `errors`. `run` then
exited 0 and exported the bodies as they were before the failing feature:
a shrunk sheet-metal tray whose unfold failed came out folded, without
the holes and cut-outs made after the unfold.
`run` now checks the evaluated timeline before writing anything. Any
feature with an error fails the run with status 1, lists the failing
features on stderr and writes none of the --out and --save files, as a
failing command already does. --allow-errors writes them anyway. `eval`
is unchanged and still reports the errors in its timeline.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
