Measure household_weight from typed frame weights in the parity universe

packages/populace-build/src/populace/build/us_runtime/nonzero_shares.py

@@ -82,4 +82,20 @@ def us_nonzero_shares(
             if requested is not None and column not in requested:
                 continue
             shares[column] = nonzero_share(table[column])
+
+    # Frame weights are typed pipeline state, not ordinary table data. The US
+    # adapter materializes the authoritative vector as ``household_weight``
+    # when writing PolicyEngine H5, and the coverage gate mirrors that export
+    # behavior; mirror it here too so the parity universe measures what is
+    # persisted instead of reading the deliberately absent table column as an
+    # all-zero layer (the Build M sparse failure: the reference's finished
+    # export carries the column, the candidate keeps it as typed state).
+    if (
+        (requested is None or "household_weight" in requested)
+        and "household_weight" not in shares
+        and "household" in frame.weighted_entities
+    ):
+        shares["household_weight"] = nonzero_share(
+            pd.Series(frame.weights_for("household").values)
+        )
     return shares

packages/populace-build/tests/test_us_nonzero_shares.py

@@ -100,3 +100,31 @@ def test_column_restriction_filters_raw_source_columns(self) -> None:
         )
 
         assert set(shares) == {"student_loan_interest"}
+
+
+class TestTypedWeightMirror:
+    def test_household_weight_measures_typed_frame_weights(self) -> None:
+        """The parity universe measures weights as the export persists them.
+
+        Frame weights are typed pipeline state, not a table column; the H5
+        adapter materializes them as ``household_weight`` and the coverage
+        gate mirrors that. Build M's sparse run failed eCPS parity because
+        this module read the deliberately absent table column as an all-zero
+        layer while the reference's finished export carries it — the mirror
+        keeps the two gates and the export telling one story.
+        """
+
+        shares = us_nonzero_shares(_frame(), columns=["household_weight"])
+        assert shares["household_weight"] == 1.0
+
+    def test_table_column_still_wins_when_present(self) -> None:
+        frame = _frame()
+        tables = {entity: frame.table(entity).copy() for entity in frame.entities}
+        tables["household"]["household_weight"] = [0.0, 5.0]
+        rebuilt = Frame(
+            tables,
+            frame.schema,
+            {entity: frame.weights_for(entity) for entity in frame.weighted_entities},
+        )
+        shares = us_nonzero_shares(rebuilt, columns=["household_weight"])
+        assert shares["household_weight"] == 0.5