load_errors_check.py loads deliberately broken .tum fixtures in batch on the
build under test (like lsp_check.py) and asserts each fails with its specific
located message and without a raw traceback. Wired into run.sh just before the
main suite, so it runs for every channel.
The run validation items now point their sub-instance log at the gitignored
report dir, so a GUI run no longer litters the tree with sub_*.log files.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>