e3818fa6c9
PF1e (CRB Movement): "You can't run or charge across difficult terrain". _execute_run checked the explicit destination against the full cost field (which routes through difficult terrain at 2x) but descended with avoid_difficult=True, so a destination beyond rubble was accepted (ok=True) yet silently truncated at the obstacle. _destination_reachable now takes the same avoid_difficult constraint (difficult cells removed from the field; a destination whose footprint touches difficult terrain is not a legal run endpoint either), so verdict and path agree. The test that pinned the old silent-stop-short convention now expects unreachable_destination; README updated. Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent) Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>