test(validation): negative load-error checks; keep run logs out of the repo

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>

test/validation/run.sh

@@ -158,6 +158,12 @@ echo "-- launch: ${CMD[*]}"
 echo "-- LSP check ($MODE)"
 "$VENV_PYTHON" "$SCRIPT_DIR/lsp_check.py" "${CMD[@]}"
 
+# ---------- load-error check (this exact channel) -----------------------------
+# Deliberately broken .tum files must fail to load with a specific, located
+# message (not a raw traceback): guards the load-time error handling.
+echo "-- load-error check ($MODE)"
+"$VENV_PYTHON" "$SCRIPT_DIR/load_errors_check.py" "${CMD[@]}"
+
 if [ "$GUI" -eq 1 ]; then
     echo "-- GUI mode: the suite is loaded; press Start to run. Window stays open."
 fi