test(round-builder): the sum's own guard, measured apart from the one upstream of it

A green mutation is a finding. Of the twelve planted against this file, eleven fell and
one survived: dropping `row["validated"]` from validated_ore's filter changed nothing.

It is equivalent — but only for as long as the OTHER guard holds. derive_outcome already
refuses to put a refused row's figure into (d), so on every outcome this builder writes,
validated_nok is None wherever validated is False and the two guards are
indistinguishable from the outside. Deleting either one alone is free today; deleting
both is the leak, and nothing witnessed that.

validated_ore is public and takes any outcome mapping, so the arm that separates them
hands it the outcome a future coverage writer could produce: a refused row whose amount
already sits in validated_nok. 137 000 002 øre, counted from the table, against the
227 000 002 a leak would give.

12 of 12 mutants now fall; control in the clone is 40 of 40.

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

tests/test_round_builder_loadbearing.py

@@ -453,6 +453,30 @@ def test_a_refused_rows_amount_never_becomes_a_validated_saving(tmp_path: Path)
     assert "2 270 000,02" not in text, "a refused claim was counted as a validated saving"
 
 
+def test_only_a_validated_row_counts_even_when_a_refused_one_carries_a_figure() -> None:
+    """The SECOND of the two guards, measured on its own.
+
+    ``derive_outcome`` already refuses to put a refused row's figure into (d), so on every outcome
+    this builder writes the two guards are indistinguishable — measured 19.09, the mutant that
+    drops the sum's own guard survives the whole file for exactly that reason, and it is
+    equivalent only for as long as the first guard holds. ``validated_ore`` is public and takes
+    any outcome mapping, so the arm that separates them hands it the outcome a future coverage
+    writer could produce: a refused row with an amount already sitting in ``validated_nok``."""
+    leaky: dict[str, Any] = {
+        "approaches": [
+            {"id": aid, "validated": status == "validated", "validated_nok": nok}
+            for aid, _label, status, nok, *_rest in _SPEC
+        ]
+    }
+    leaked_rows = [
+        row["id"]
+        for row in leaky["approaches"]
+        if not row["validated"] and row["validated_nok"] is not None
+    ]
+    assert leaked_rows == ["a2-faerre-kummer"], "the table lost the row this arm needs"
+    assert rb.validated_ore(leaky) == _VALIDATED_ORE == 137_000_002
+
+
 def test_the_outcome_is_derived_row_for_row_from_the_runs_own_coverage(tmp_path: Path) -> None:
     """(a)-(d) per approach, counted from the table. ``feedback_ids`` is empty on every row: no
     run records which feedback item produced which row, and the builder invents no tracking."""