test: close runtime decision mutation gaps

obliteratus/runtime_contracts.py

@@ -111,7 +111,7 @@ def attention_projection_names(
     all_names = outputs + tuple(input_names)
     if num_kv_shared_layers <= 0:
         return all_names
-    if num_layers <= 0 or not 0 <= layer_index < num_layers:
+    if not 0 <= layer_index < num_layers:
         raise ValueError("shared-KV projection requires a valid layer index and layer count")
     if num_kv_shared_layers > num_layers:
         raise ValueError("num_kv_shared_layers cannot exceed the model layer count")

tests/test_runtime_contracts.py

@@ -109,7 +109,7 @@ def test_model_load_policy_precedence_is_explicit(overrides, expected):
 
 
 def test_model_load_policy_rejects_unsupported_quantization_before_branching():
-    with pytest.raises(ValueError, match="Unknown quantization '3bit'"):
+    with pytest.raises(ValueError) as error:
         resolve_model_load_policy(
             device="auto",
             resolved_device="cuda",
@@ -119,6 +119,7 @@ def test_model_load_policy_rejects_unsupported_quantization_before_branching():
             device_map_auto_supported=True,
             bitsandbytes_supported=True,
         )
+    assert str(error.value) == "Unknown quantization '3bit'. Choose None, '4bit', or '8bit'"
 
 
 @pytest.mark.parametrize("quantization", ["4bit", "8bit"])
@@ -166,6 +167,17 @@ def test_output_only_projection_is_independent_of_shared_kv_layout():
     ) == _OUTPUT_NAMES
 
 
+def test_nonshared_projection_does_not_require_shared_storage_ownership_metadata():
+    assert attention_projection_names(
+        projection_target="all",
+        layer_index=-1,
+        num_layers=0,
+        num_kv_shared_layers=0,
+        output_names=_OUTPUT_NAMES,
+        input_names=_INPUT_NAMES,
+    ) == _OUTPUT_NAMES + _INPUT_NAMES
+
+
 @pytest.mark.parametrize(
     ("layer_index", "expected"),
     [
@@ -186,6 +198,17 @@ def test_shared_kv_owner_projects_storage_once_and_borrowers_skip_it(layer_index
     ) == expected
 
 
+def test_single_layer_can_own_kv_storage_shared_by_the_whole_model():
+    assert attention_projection_names(
+        projection_target="all",
+        layer_index=0,
+        num_layers=1,
+        num_kv_shared_layers=1,
+        output_names=_OUTPUT_NAMES,
+        input_names=_INPUT_NAMES,
+    ) == _OUTPUT_NAMES + _INPUT_NAMES
+
+
 @pytest.mark.parametrize(
     ("layer_index", "num_layers", "shared_layers", "message"),
     [
@@ -201,7 +224,7 @@ def test_shared_kv_layout_rejects_impossible_ownership(
     shared_layers,
     message,
 ):
-    with pytest.raises(ValueError, match=message):
+    with pytest.raises(ValueError) as error:
         attention_projection_names(
             projection_target="all",
             layer_index=layer_index,
@@ -210,6 +233,12 @@ def test_shared_kv_layout_rejects_impossible_ownership(
             output_names=_OUTPUT_NAMES,
             input_names=_INPUT_NAMES,
         )
+    expected = (
+        "num_kv_shared_layers cannot exceed the model layer count"
+        if message == "cannot exceed"
+        else "shared-KV projection requires a valid layer index and layer count"
+    )
+    assert str(error.value) == expected
 
 
 @pytest.mark.parametrize(