Cover the decorator's refusal paths and the runtime-only lazy-init branches

The two TypeError guards in deferred_model and plain warm() were
untested, and coverage.py counts the never-taken false arc of the
`if not TYPE_CHECKING:` guards around the lazy module attributes; that
arc belongs to the type checker, so declare it partial by design next
to the existing exclusion rules.

Author: maxisbey

pyproject.toml

@@ -306,6 +306,9 @@ exclude_also = [
     "@overload",
     "raise NotImplementedError",
 ]
+# `if not TYPE_CHECKING:` installs runtime-only lazy module attributes; its
+# false arc belongs to the type checker and never runs (like `if TYPE_CHECKING:`).
+partial_also = ["if not TYPE_CHECKING:"]
 
 # https://coverage.readthedocs.io/en/latest/config.html#paths
 [tool.coverage.paths]

tests/types/test_deferred.py

@@ -71,6 +71,28 @@ class Child(Root):
         assert str(inspect.signature(cls)) == expected
 
 
+def test_the_decorator_refuses_a_root_that_would_not_defer_or_that_owns_a_subclass_hook() -> None:
+    """`@deferred_model` marks a *deferred* hierarchy root and installs its own subclass hook:
+    a class without `defer_build`, or one defining `__pydantic_init_subclass__` itself (which
+    the installed hook would replace), is refused at decoration time."""
+
+    class Eager(BaseModel):
+        value: int
+
+    class OwnsHook(BaseModel):
+        model_config = ConfigDict(defer_build=True)
+        value: int
+
+        @classmethod
+        def __pydantic_init_subclass__(cls, **kwargs: object) -> None:
+            raise NotImplementedError  # never runs: the decorator refuses the class first
+
+    with pytest.raises(TypeError):
+        deferred_model(Eager)
+    with pytest.raises(TypeError):
+        deferred_model(OwnsHook)
+
+
 def test_unresolvable_model_falls_back_to_the_generic_signature() -> None:
     """A model whose build cannot complete (a forward reference that does not resolve at
     that point) reports the generic initializer signature, as pydantic does for any

tests/types/test_methods.py

@@ -1113,6 +1113,8 @@ def test_warming_a_version_leaves_nothing_for_its_first_messages_to_build():
 
 def test_warm_is_idempotent_and_gates_unknown_versions():
     """SDK-defined: repeating a `warm()` builds nothing more; an unknown version is a ValueError."""
+    baseline = methods.warm()  # the version-independent set (this process may already have built it)
+    assert baseline.elapsed_ms >= 0
     methods.warm(everything=True)
     again = methods.warm(everything=True)
     assert (again.models, again.adapters) == (0, 0)