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/items/run/test.tum

@@ -2,24 +2,31 @@
 # In batch mode the sub-instance runs with -b; in GUI mode with -r.
 # The run item result is SUCCESS if the sub-instance launched successfully,
 # regardless of its own test result.
+#
+# log_file points the sub-instance log at the throwaway report dir (gitignored)
+# so a GUI run does not litter the repo with sub_*.log files.
 
 - run:
     name: run PASS (valid file, passing sub-test)
     key: $(test)_PASS
     tum: $(test_path)$(psep)sub_pass.tum
+    log_file: $(validation_report_path)$(psep)run_sub.log
 
 - run:
     name: run PASS (valid file, failing sub-test)
     key: $(test)_PASS
     tum: $(test_path)$(psep)sub_fail.tum
+    log_file: $(validation_report_path)$(psep)run_sub.log
 
 - run:
     name: run FAIL (file not found)
     key: $(test)_FAIL
     tum: $(test_path)$(psep)non_existent.tum
+    log_file: $(validation_report_path)$(psep)run_sub.log
 
 - run:
     name: run FAIL (wait_for_exec without time window)
     key: $(test)_FAIL
     tum: $(test_path)$(psep)sub_pass.tum
     wait_for_exec: true
+    log_file: $(validation_report_path)$(psep)run_sub.log