test(b-gate): the mutant that survived -- a docstring that NAMES the door is not touching it

Mutant M12 against the delivered tree: let _meaningful return the whole body, so a
string standing alone counts. 85 of 85 GREEN. That is a finding, not a pass: the
repair's own rule -- "the gate never reads a string that stands alone" -- had no arm
watching it, and without one the fix would have drifted back to "mentioning the door
is touching it", which is the same defect one floor in.

The arm carries its rc-0 control first (a real probe WITH a docstring still counts),
then breaks each half on its own: a probe whose docstring names the real door while
its call drives another module, and one whose docstring names the step while its call
passes another word. Both must be refused, each with its own reason.

12 of 12 mutants now felled, control 86 of 86.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_b_gate.py

@@ -158,18 +158,22 @@ def _write_probe(
     door: str = "fakesrc.driver",
     needle: str = "gjoer_noe",
     asserts: bool = True,
+    docstring: str = "",
     nodeid: str = _FAKE_PROBE,
 ) -> str:
     """En probe som DRIVER døren: kaller kommandoen og asserter på det den gjorde.
 
-    Hvert av de tre trekkene gaten måler kan skrus av her, ett om gangen: hvilken dør den rører
-    (``door``), hvilket steg den navngir (``needle``), og om den asserter i det hele tatt."""
+    Hvert av de fire trekkene gaten måler kan skrus av her, ett om gangen: hvilken dør den rører
+    (``door``), hvilket steg den navngir (``needle``), om den asserter i det hele tatt, og hva
+    den bare OMTALER uten å røre (``docstring``)."""
     file_part, _, name = nodeid.partition("::")
+    said = f'    """{docstring}"""\n' if docstring else ""
     body = (
         "import subprocess\n"
         "import sys\n\n\n"
         f"def {name}(tmp_path):\n"
-        f'    proc = subprocess.run([sys.executable, "-m", "{door}", "--steg", "{needle}"])\n'
+        + said
+        + f'    proc = subprocess.run([sys.executable, "-m", "{door}", "--steg", "{needle}"])\n'
         + ("    assert proc.returncode == 0\n" if asserts else "    return proc\n")
     )
     _write(root / file_part, body)
@@ -1143,6 +1147,30 @@ def test_a_probe_that_drives_the_door_without_naming_the_step_proves_the_door_on
     assert any("navngir ikke steget" in x for x in row.exceptions), row.exceptions
 
 
+def test_a_probe_that_only_mentions_the_door_or_the_step_proves_neither(tmp_path: Path) -> None:
+    """FUNN 19.09, mutant M12 overlevde: leses HELE probens kropp, holder det å NEVNE døren og
+    steget i docstringen. Da er «rører døren» en omtale igjen, ikke en atferd — nøyaktig feilen
+    ett hakk lenger inne. Gaten leser derfor aldri en streng som står alene."""
+    src = _fake_src(tmp_path, chat_client=False)
+    _write_probe(tmp_path, docstring="en ekte probe, den kaller fakesrc.driver med gjoer_noe")
+    row = gate.score_toolbox(_one_step(), src, _fake_run_path(), _FAKE_PASSED, tmp_path)
+    assert (row.k, row.n) == (1, 1), row.exceptions
+
+    _write_probe(
+        tmp_path,
+        door="fakesrc.enhelt_annen_modul",
+        docstring="denne proben kjører fakesrc.driver",
+    )
+    row = gate.score_toolbox(_one_step(), src, _fake_run_path(), _FAKE_PASSED, tmp_path)
+    assert (row.k, row.n) == (0, 1), row.exceptions
+    assert any("rører ikke døren" in x for x in row.exceptions), row.exceptions
+
+    _write_probe(tmp_path, needle="et_annet_navn", docstring="beviser steget gjoer_noe")
+    row = gate.score_toolbox(_one_step(), src, _fake_run_path(), _FAKE_PASSED, tmp_path)
+    assert (row.k, row.n) == (0, 1), row.exceptions
+    assert any("navngir ikke steget" in x for x in row.exceptions), row.exceptions
+
+
 def test_a_probe_that_asserts_nothing_is_not_a_behaviour_probe(tmp_path: Path) -> None:
     src = _fake_src(tmp_path, chat_client=False)
     _write_probe(tmp_path)