Cache validated source generation receipts

tests/test_core.py

@@ -422,6 +422,24 @@ class DocForgeCoreTests(unittest.TestCase):
             ):
                 index.get_node("guide.workflow")
 
+    def test_source_generation_receipt_cache_is_signature_bound(self) -> None:
+        with tempfile.TemporaryDirectory() as directory:
+            root = self.copy_fixture("alpha", Path(directory))
+            project = Project.open(root)
+            ProjectIndex(project).build()
+            first = project.incremental_state()
+            self.assertIsNotNone(first)
+
+            with mock.patch.object(
+                Path,
+                "read_text",
+                side_effect=AssertionError("warm generation check reparsed its receipt"),
+            ):
+                self.assertEqual(first, project.incremental_state())
+
+            project.generation_path.write_text("{", encoding="utf-8")
+            self.assertIsNone(project.incremental_state())
+
     def test_source_set_change_during_load_fails_closed(self) -> None:
         project = Project.open(FIXTURES / "alpha")
         sources, directories = project._canonical_inventory()