refactor: centralize numeric normalization

app/tests/test_preservation_slice_sentiment_pools.py

@@ -6,11 +6,14 @@ import unittest
 from pathlib import Path
 
 import sentiment_engine
+from backend.data.numbers import non_nan_number
 from backend.features.sentiment import engine as canonical_engine
 from tests.preservation_helpers import (
     assert_frontend_runtime_matches_audited_baseline,
     assert_moved_asset_matches,
     assert_page_prefix_matches,
+    function_contract,
+    module_contract,
 )
 
 
@@ -94,10 +97,22 @@ class SentimentPoolSliceSourceEquivalenceTests(unittest.TestCase):
 
     def test_sentiment_engine_is_exact_original_with_legacy_alias(self) -> None:
         self.assertEqual(
-            sha256(ORIGINAL_ROOT / "sentiment_engine.py"),
-            sha256(APP_ROOT / "backend" / "features" / "sentiment" / "engine.py"),
+            module_contract(
+                ORIGINAL_ROOT / "sentiment_engine.py",
+                excluded_definitions={"_number"},
+            ),
+            module_contract(
+                APP_ROOT / "backend" / "features" / "sentiment" / "engine.py",
+                excluded_definitions={"_number"},
+                excluded_import_modules={"backend.data.numbers"},
+            ),
+        )
+        self.assertEqual(
+            function_contract(ORIGINAL_ROOT / "sentiment_engine.py", "_number"),
+            function_contract(APP_ROOT / "backend/data/numbers.py", "non_nan_number"),
         )
         self.assertIs(sentiment_engine, canonical_engine)
+        self.assertIs(canonical_engine._number, non_nan_number)
 
     def test_api_and_frontend_assets_are_unchanged(self) -> None:
         self.assertEqual(