diff --git a/tests/unit/test_documentation_consistency.py b/tests/unit/test_documentation_consistency.py
index 163ab56..53acfa1 100644
--- a/tests/unit/test_documentation_consistency.py
+++ b/tests/unit/test_documentation_consistency.py
@@ -133,6 +133,7 @@ TRAINING_M41_RELEASE_INDEX_GUARD_TEST_INVENTORY = (
     "test_training_m70_release_index_source_shape_fixture_guard_methods_constant_inventory_source_exactness_bridge_duplicate_guard_positive_diagnostic_self_lock",
     "test_training_m71_release_index_source_shape_fixture_guard_methods_constant_exactness_bridge_triplet_source_shape_self_lock",
     "test_training_m72_release_index_source_shape_fixture_guard_methods_constant_exactness_bridge_triplet_rejects_dynamic_sources",
+    "test_training_m73_release_index_source_shape_fixture_guard_methods_constant_exactness_bridge_triplet_diagnostics_are_locked",
     "test_training_m53_release_index_doc_category_coverage_is_exact",
     "test_training_case_product_doc_reflects_current_m40_maturity",
 )
@@ -639,6 +640,9 @@ class DocumentationConsistencyTests(unittest.TestCase):
             "required_snippet_inventory_source_shape_fixture_constant_exactness_bridge_triplet_negative_sources": (
                 "test_training_m72_release_index_source_shape_fixture_guard_methods_constant_exactness_bridge_triplet_rejects_dynamic_sources"
             ),
+            "required_snippet_inventory_source_shape_fixture_constant_exactness_bridge_triplet_diagnostics": (
+                "test_training_m73_release_index_source_shape_fixture_guard_methods_constant_exactness_bridge_triplet_diagnostics_are_locked"
+            ),
             "per_doc_helper_exact_category_coverage": (
                 "test_training_m53_release_index_doc_category_coverage_is_exact"
             ),
@@ -806,6 +810,7 @@ class DocumentationConsistencyTests(unittest.TestCase):
             "test_training_m70_release_index_source_shape_fixture_guard_methods_constant_inventory_source_exactness_bridge_duplicate_guard_positive_diagnostic_self_lock",
             "test_training_m71_release_index_source_shape_fixture_guard_methods_constant_exactness_bridge_triplet_source_shape_self_lock",
             "test_training_m72_release_index_source_shape_fixture_guard_methods_constant_exactness_bridge_triplet_rejects_dynamic_sources",
+            "test_training_m73_release_index_source_shape_fixture_guard_methods_constant_exactness_bridge_triplet_diagnostics_are_locked",
             "test_training_m53_release_index_doc_category_coverage_is_exact",
             "test_training_case_product_doc_reflects_current_m40_maturity",
         )
@@ -1486,6 +1491,68 @@ class DocumentationConsistencyTests(unittest.TestCase):
                         source
                     )
 
+    def test_training_m73_release_index_source_shape_fixture_guard_methods_constant_exactness_bridge_triplet_diagnostics_are_locked(
+        self,
+    ) -> None:
+        constant_name = "TRAINING_M41_RELEASE_INDEX_EXACTNESS_BRIDGE_GUARD_METHODS"
+        guard_name = (
+            "test_training_m73_release_index_source_shape_fixture_guard_methods_constant_exactness_bridge_triplet_diagnostics_are_locked"
+        )
+        literal_methods = (
+            "literal_bridge_alpha",
+            "literal_bridge_beta",
+            "literal_bridge_gamma",
+        )
+        valid_triplet_source = (
+            f"({literal_methods[0]!r}, {literal_methods[1]!r}, "
+            f"{literal_methods[2]!r})"
+        )
+        invalid_sources = {
+            "missing_assignment": (
+                "UNRELATED_BRIDGE_GUARD_METHODS = ('literal_bridge_alpha',)",
+                "must have one assignment",
+            ),
+            "duplicate_top_level_assignment": (
+                f"{constant_name} = {valid_triplet_source}\n"
+                f"{constant_name} = {valid_triplet_source}",
+                "must have one assignment",
+            ),
+            "multiple_assignment_targets": (
+                f"{constant_name} = bridge_methods = {valid_triplet_source}",
+                "must use one simple assignment",
+            ),
+            "empty_tuple": (
+                f"{constant_name} = ()",
+                "must be a literal triplet tuple assignment",
+            ),
+            "two_item_tuple": (
+                f"{constant_name} = ({literal_methods[0]!r}, {literal_methods[1]!r})",
+                "must be a literal triplet tuple assignment",
+            ),
+            "four_item_tuple": (
+                f"{constant_name} = ("
+                f"{literal_methods[0]!r}, {literal_methods[1]!r}, "
+                f"{literal_methods[2]!r}, 'literal_bridge_delta')",
+                "must be a literal triplet tuple assignment",
+            ),
+            "integer_literal_method_name": (
+                f"{constant_name} = ({literal_methods[0]!r}, 123, {literal_methods[2]!r})",
+                "must use literal method names",
+            ),
+            "none_literal_method_name": (
+                f"{constant_name} = ({literal_methods[0]!r}, None, {literal_methods[2]!r})",
+                "must use literal method names",
+            ),
+        }
+
+        self.assertIn(guard_name, TRAINING_M41_RELEASE_INDEX_GUARD_TEST_INVENTORY)
+        for fixture_name, (source, error_snippet) in invalid_sources.items():
+            with self.subTest(fixture_name=fixture_name):
+                with self.assertRaisesRegex(AssertionError, re.escape(error_snippet)):
+                    self._release_index_exactness_bridge_guard_method_names_from_source(
+                        source
+                    )
+
     def test_training_m47_release_index_per_doc_helper_inventory_self_lock_is_current(self) -> None:
         helper_name = "_release_index_missing_required_snippets_by_doc"
         docs_guard_name = "test_training_readmes_expose_m1_m40_release_index_without_raw_test_modules"