diff --git a/wizard-work/beam/CHECK b/wizard-work/beam/CHECK
index 397b2d3..5b354e7 100755
--- a/wizard-work/beam/CHECK
+++ b/wizard-work/beam/CHECK
@@ -1,6 +1,46 @@
 #!/bin/bash
 # CHECK: verify all beam reliability primitives
+#
+# Runner note (Q105, 2026-10-28). This lane writes its tests in two styles:
+# unittest.TestCase subclasses and bare module-level `def test_*` / `assert`.
+# `python3 -m unittest discover` collects only the first -- 276 of the 407
+# tests in this directory -- so a green CHECK said nothing about the other
+# 131, and test_fenwick.py's 8 cells could be broken without moving the gate.
+# pytest collects both styles, so pytest is the runner here.
+#
+# `--import-mode=importlib` is deliberate: two files share the basename
+# `test_toposort.py` (this directory and toposort/), and pytest's default
+# `prepend` mode aborts collection on that duplicate module name. importlib
+# mode keys modules by path instead. `toposort/test_toposort.py` is a plain
+# script (8 PASS lines + ALL), not a pytest module, so it keeps its own line.
+#
+# Exit codes follow the repo's tools/ contract: 0 clean, 1 graded a fault,
+# 2 could not grade. pytest's own codes are mapped onto that contract:
+#   0 -> 0            all collected tests passed
+#   1 -> 1            a test failed
+#   2 -> 1            collection error: a test module does not import (a fault)
+#   5 -> 1            no tests collected: the gate is measuring nothing
+# A missing pytest is 2, never a silent 0 -- a gate that cannot run the 131
+# tests must not report success.
 set -e
+set -o pipefail
 cd "$(dirname "$(readlink -f "$0")")"
-python3 -m unittest discover -p 'test_*.py' -v
+
+if ! python3 -m pytest --version >/dev/null 2>&1; then
+    echo "CHECK: pytest not importable -- cannot grade." >&2
+    echo "CHECK: unittest discover would run 276 of 407 tests and skip 131 (Q105)." >&2
+    exit 2
+fi
+
+set +e
+python3 -m pytest -q -p no:cacheprovider --import-mode=importlib test_*.py
+rc=$?
+set -e
+case $rc in
+    0) ;;
+    1) echo "CHECK: pytest reported failing test(s)." >&2; exit 1 ;;
+    5) echo "CHECK: pytest collected no tests -- the gate is measuring nothing." >&2; exit 1 ;;
+    *) echo "CHECK: pytest exited $rc -- collection or internal error (a module that will not import is a fault)." >&2; exit 1 ;;
+esac
+
 python3 toposort/test_toposort.py