diff --git a/test/validation/items/run/test.tum b/test/validation/items/run/test.tum
index e54c1c1..80d3d7a 100644
--- a/test/validation/items/run/test.tum
+++ b/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
diff --git a/test/validation/load_errors/bad_include.tum b/test/validation/load_errors/bad_include.tum
new file mode 100644
index 0000000..f517f5c
--- /dev/null
+++ b/test/validation/load_errors/bad_include.tum
@@ -0,0 +1,9 @@
+main:
+  name: root
+  steps:
+    - sleep:
+        name: ok
+        timeout: 0
+    # The structural error lives in the included file; the message must point
+    # the user at that file, not at this one.
+    - !include bad_include_inc.tum
diff --git a/test/validation/load_errors/bad_include_inc.tum b/test/validation/load_errors/bad_include_inc.tum
new file mode 100644
index 0000000..d8cb455
--- /dev/null
+++ b/test/validation/load_errors/bad_include_inc.tum
@@ -0,0 +1,4 @@
+# Included as a bare list of steps. The unknown item below must be reported
+# with THIS file as the location.
+- frobnicate_in_include:
+    name: nope
diff --git a/test/validation/load_errors/group_no_steps.tum b/test/validation/load_errors/group_no_steps.tum
new file mode 100644
index 0000000..745b799
--- /dev/null
+++ b/test/validation/load_errors/group_no_steps.tum
@@ -0,0 +1,6 @@
+main:
+  name: root
+  steps:
+    # A container item (group) without its mandatory 'steps:' list.
+    - group:
+        name: g
diff --git a/test/validation/load_errors/scalar_body.tum b/test/validation/load_errors/scalar_body.tum
new file mode 100644
index 0000000..d37247c
--- /dev/null
+++ b/test/validation/load_errors/scalar_body.tum
@@ -0,0 +1,5 @@
+main:
+  name: root
+  steps:
+    # The body of an item must be a mapping of parameters, not a scalar.
+    - sleep: 5
diff --git a/test/validation/load_errors/step_not_mapping.tum b/test/validation/load_errors/step_not_mapping.tum
new file mode 100644
index 0000000..4c03826
--- /dev/null
+++ b/test/validation/load_errors/step_not_mapping.tum
@@ -0,0 +1,5 @@
+main:
+  name: root
+  steps:
+    # A step that is a bare scalar instead of a '<item>: ...' mapping.
+    - just some text
diff --git a/test/validation/load_errors/two_steps.tum b/test/validation/load_errors/two_steps.tum
new file mode 100644
index 0000000..91b9f64
--- /dev/null
+++ b/test/validation/load_errors/two_steps.tum
@@ -0,0 +1,11 @@
+main:
+  name: root
+  steps:
+    # Two items wrongly packed under a single '-' marker (a frequent indent
+    # mistake): the second key belongs one '-' lower.
+    - sleep:
+        name: s
+        timeout: 0
+      group:
+        name: g
+        steps: []
diff --git a/test/validation/load_errors/unknown_action.tum b/test/validation/load_errors/unknown_action.tum
new file mode 100644
index 0000000..fb2ea75
--- /dev/null
+++ b/test/validation/load_errors/unknown_action.tum
@@ -0,0 +1,8 @@
+main:
+  name: root
+  steps:
+    - console:
+        console_name: c1
+        steps:
+          - opens:
+              device: /dev/ttyUSB0
diff --git a/test/validation/load_errors/unknown_item.tum b/test/validation/load_errors/unknown_item.tum
new file mode 100644
index 0000000..089a1ce
--- /dev/null
+++ b/test/validation/load_errors/unknown_item.tum
@@ -0,0 +1,5 @@
+main:
+  name: root
+  steps:
+    - frobnicate:
+        name: nope
diff --git a/test/validation/load_errors_check.py b/test/validation/load_errors_check.py
new file mode 100644
index 0000000..cc77905
--- /dev/null
+++ b/test/validation/load_errors_check.py
@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+"""Per-channel check of test-load error reporting.
+
+Given the channel's testium invocation as argv (e.g. ``flatpak run
+--command=testium org.testium.Testium``, a PyInstaller binary path, or
+``python -m testium``), load each deliberately broken ``.tum`` under
+``load_errors/`` in batch mode and verify that:
+
+  1. the load FAILS (non-zero exit), and
+  2. the output carries the *specific, located* message we expect — not a bare
+     Python traceback and not the generic 'crashed for any reason'.
+
+This guards the load-time error handling in ``test_set.load_test_recursively``
+and ``item_actions.load`` (a structural mistake in a ``.tum`` must always reach
+the user as a readable ``TUM file syntax error`` naming the offending file,
+item path and value). The historical failure mode was an unknown console
+action crashing the error formatter itself with ``'dict_keys' object is not
+subscriptable``.
+
+Exits non-zero (with a diagnostic) on the first failure so the validation run
+fails loudly. Used by ``run.sh`` before launching the main suite.
+"""
+import os
+import re
+import subprocess
+import sys
+
+HERE = os.path.dirname(os.path.abspath(__file__))
+FIXTURES = os.path.join(HERE, "load_errors")
+
+# testium colourises its log; strip the ANSI escapes before matching messages.
+_ANSI = re.compile(r"\x1b\[[0-9;]*m")
+
+# fixture file -> substrings that must all appear in the load output.
+CASES = [
+    ("unknown_item.tum",     ["TUM file syntax error", "is not a known test item",
+                              "frobnicate", "Known items:"]),
+    ("unknown_action.tum",   ["unknown action", "opens", "Known actions:"]),
+    ("two_steps.tum",        ["must define exactly one test item"]),
+    ("scalar_body.tum",      ["body of test item 'sleep'", "must be a mapping"]),
+    ("group_no_steps.tum",   ["No 'steps' list found", "'group' item 'g'"]),
+    ("step_not_mapping.tum",  ["is not a valid test item"]),
+    # The error is inside the included file: the message must name that file.
+    ("bad_include.tum",      ["bad_include_inc.tum", "frobnicate_in_include",
+                              "is not a known test item"]),
+]
+
+
+def fail(msg):
+    print(f"LOAD-ERROR CHECK: FAIL — {msg}", file=sys.stderr)
+    sys.exit(1)
+
+
+def check_case(cmd, fixture, needles):
+    path = os.path.join(FIXTURES, fixture)
+    try:
+        out = subprocess.run(cmd + ["-b", path], capture_output=True, timeout=120)
+    except Exception as e:  # noqa: BLE001
+        fail(f"`{' '.join(cmd)} -b {fixture}` could not run: {e}")
+    blob = _ANSI.sub("", (out.stdout + out.stderr).decode(errors="replace"))
+
+    if out.returncode == 0 or "Test run success." in blob:
+        fail(f"{fixture}: load was expected to fail but succeeded "
+             f"(exit {out.returncode}).")
+    # A raw Python traceback reaching the user is exactly what we are guarding
+    # against: every load error must be funnelled through a TUM*Error.
+    if "Traceback (most recent call last)" in blob:
+        fail(f"{fixture}: a raw Python traceback leaked to the user:\n"
+             f"{blob[-600:]}")
+    missing = [n for n in needles if n not in blob]
+    if missing:
+        fail(f"{fixture}: load message is missing {missing}.\n"
+             f"--- got ---\n{blob[-800:]}")
+    print(f"LOAD-ERROR CHECK: {fixture} OK")
+
+
+def main():
+    cmd = sys.argv[1:]
+    if not cmd:
+        fail("usage: load_errors_check.py <testium-invocation...>")
+    for fixture, needles in CASES:
+        check_case(cmd, fixture, needles)
+    print("LOAD-ERROR CHECK: PASS")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/test/validation/run.sh b/test/validation/run.sh
index 086dfde..ff7ee73 100755
--- a/test/validation/run.sh
+++ b/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