test(opps): enforce CF correctness in CI via a real Addendum B fixture

The self-consistency check previously skipped in headless CI (no aco
DuckDB), so CI only guarded that the CFs were *unchanged*, not that they
were *correct*. Add a committed slice of 30 real Addendum B rows
(fixtures/addendum_b_sample.csv — real published payment_rate, weights
~0.05 to ~700, CY2021-CY2026) and reconcile OppsPricer against it in an
in-memory DuckDB. This runs in CI with no external data, and because the
rows are real, a wrong conversion factor makes weight × CF diverge from
the published rate and fails the build.

Verified fail-closed: reverting the CY2026 CF to the old wrong value
fails the golden test, this fixture test, and the full-DB check together.

tests/opps/fixtures/addendum_b_sample.csv

@@ -0,0 +1,31 @@
+hcpcs,status_indicator,relative_weight,payment_rate,year
+C2645,U,0.0566,4.69,2021
+37195,T,3.7532,310.75,2021
+51040,J1,21.6552,1792.99,2021
+58561,J1,53.2572,4409.54,2021
+69930,J1,415.8068,34427.56,2021
+C2645,U,0.0557,4.69,2022
+11982,Q1,3.2928,277.18,2022
+15946,T,20.7807,1749.26,2022
+0430T,J1,39.7464,3345.73,2022
+38240,J1,487.3894,41026.98,2022
+C2645,U,0.0548,4.69,2023
+95707,S,3.2723,280.06,2023
+43242,J1,20.3492,1741.59,2023
+19330,Q2,40.1682,3437.8,2023
+38240,J1,493.4673,42233.4,2023
+C2645,U,0.0537,4.69,2024
+57156,T,3.5016,305.98,2024
+15220,T,19.9049,1739.33,2024
+15958,T,39.1593,3421.82,2024
+38240,J1,596.4656,52120.36,2024
+C2645,U,0.0526,4.69,2025
+91132,S,3.4922,311.4,2025
+15100,T,20.5142,1829.23,2025
+0717T,T,41.0565,3660.97,2025
+38240,J1,663.2611,59142.33,2025
+C2645,U,0.0513,4.69,2026
+28630,T,2.7568,252.01,2026
+31238,J1,19.8922,1818.45,2026
+19371,J1,43.7591,4000.24,2026
+38240,J1,702.9866,64263.52,2026

tests/opps/test_rules.py

@@ -2,8 +2,8 @@
 
 The OPPS conversion factor per year is correctness-critical reference
 data: OppsPricer computes national APC rates as ``weight × CF`` and
-reconciles them against CMS's published Addendum B. Two guards keep it
+reconciles them against CMS's published Addendum B. Three guards keep
-bulletproof:
+it bulletproof:
 
 1. ``TestGoldenConversionFactors`` pins every year's CF to the value
    taken from that year's Federal Register OPPS Final Rule (CY2014-
@@ -12,19 +12,28 @@ bulletproof:
    CY2026). Runs everywhere (no data needed), so any accidental edit
    fails CI. Changing a value requires updating the citation below too.
 
-2. ``TestAddendumBSelfConsistency`` (skipped when the aco DuckDB is
+2. ``TestAddendumBFixtureConsistency`` reconciles OppsPricer against a
-   absent, e.g. headless CI) proves the CFs actually reproduce CMS's
+   committed slice of *real* Addendum B rows (fixtures/addendum_b_
-   published Addendum B rate to the cent — the independent check that
+   sample.csv — real published payment_rate, not computed). It runs in
-   the golden values above are *correct*, not merely *unchanged*.
+   CI with no external data, and because the rows are real a wrong CF
+   fails here — the independent correctness proof, enforced in CI.
+
+3. ``TestAddendumBSelfConsistency`` (skipped when the aco DuckDB is
+   absent, e.g. headless CI) does the same against the full loaded
+   Addendum B — broader coverage where the data is present.
 """
 
 from __future__ import annotations
 
+from pathlib import Path
+
 import pytest
 
 from conf import path
 from opps.rules import RULES
 
+_FIXTURE = Path(__file__).parent / "fixtures" / "addendum_b_sample.csv"
+
 # Full OPPS conversion factor — the rate for hospitals that MEET quality
 # reporting (not the reduced/OQR-penalty CF).
 #
@@ -84,6 +93,44 @@ class TestGoldenConversionFactors:
                 assert cur_cf > prev_cf
 
 
+class TestAddendumBFixtureConsistency:
+    """CI-runnable correctness proof against a committed slice of real
+    Addendum B rows.
+
+    The fixture holds real published ``payment_rate`` values (never
+    computed), spanning APC weights from ~0.05 to ~700 across CY2021-
+    CY2026. If any of those years' conversion factors is wrong, the
+    calculated ``weight × CF`` diverges from the published rate and this
+    fails — no external dataset required, so the correctness check runs
+    in headless CI.
+    """
+
+    def test_fixture_reconciles_to_the_cent(self) -> None:
+        import duckdb
+
+        from rec.engine import reconcile
+        from rec.pricers.opps import OppsPricer
+
+        con = duckdb.connect(":memory:")
+        con.execute("CREATE SCHEMA opps")
+        con.execute(
+            "CREATE TABLE opps.addendum_b AS SELECT * FROM read_csv_auto(?)",
+            [str(_FIXTURE)],
+        )
+        pricer = OppsPricer()
+        years = pricer.years_available(con)
+        assert years == [2021, 2022, 2023, 2024, 2025, 2026]
+        for year in years:
+            r = reconcile(pricer, con, year)
+            assert r.matched_rows > 0, f"CY{year}: no fixture rows"
+            assert r.exact_matches == r.matched_rows, (
+                f"CY{year}: {r.matched_rows - r.exact_matches} of "
+                f"{r.matched_rows} real Addendum B rows do not match "
+                f"weight × CF to the cent — the CY{year} conversion "
+                f"factor is wrong."
+            )
+
+
 @pytest.mark.skipif(not _HAS_ACO_DB, reason="data/aco.duckdb not present")
 class TestAddendumBSelfConsistency:
     """Prove weight × CF reproduces CMS's published Addendum B rate.