diff --git a/libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_composition.py b/libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_composition.py
index ada493e1cb5..24b933c7997 100644
--- a/libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_composition.py
+++ b/libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_composition.py
@@ -1,19 +1,19 @@
 """Unit tests for _chain_model_call_handlers handler composition."""
 
-from typing import TYPE_CHECKING, cast
+from collections.abc import Callable
+from typing import Any, TypedDict, cast
 
 from langchain_core.messages import AIMessage
+from langgraph.runtime import Runtime
 
+from langchain.agents import AgentState
 from langchain.agents.factory import _chain_model_call_handlers
 from langchain.agents.middleware.types import ModelRequest, ModelResponse
 
-if TYPE_CHECKING:
-    from langgraph.runtime import Runtime
 
-
-def create_test_request(**kwargs):
+def create_test_request(**kwargs: Any) -> ModelRequest:
     """Helper to create a `ModelRequest` with sensible defaults."""
-    defaults = {
+    defaults: dict[str, Any] = {
         "messages": [],
         "model": None,
         "system_prompt": None,
@@ -27,10 +27,10 @@ def create_test_request(**kwargs):
     return ModelRequest(**defaults)
 
 
-def create_mock_base_handler(content="test"):
+def create_mock_base_handler(content: str = "test") -> Callable[[ModelRequest], ModelResponse]:
     """Helper to create a base handler that returns `ModelResponse`."""
 
-    def mock_base_handler(req):
+    def mock_base_handler(req: ModelRequest) -> ModelResponse:
         return ModelResponse(result=[AIMessage(content=content)], structured_response=None)
 
     return mock_base_handler
@@ -47,7 +47,9 @@ class TestChainModelCallHandlers:
     def test_single_handler_returns_unchanged(self) -> None:
         """Test that single handler is wrapped to normalize output."""
 
-        def handler(request, base_handler):
+        def handler(
+            request: ModelRequest, base_handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             return base_handler(request)
 
         result = _chain_model_call_handlers([handler])
@@ -59,13 +61,17 @@ class TestChainModelCallHandlers:
         """Test basic composition of two handlers."""
         execution_order = []
 
-        def outer(request, handler):
+        def outer(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             execution_order.append("outer-before")
             result = handler(request)
             execution_order.append("outer-after")
             return result
 
-        def inner(request, handler):
+        def inner(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             execution_order.append("inner-before")
             result = handler(request)
             execution_order.append("inner-after")
@@ -90,19 +96,25 @@ class TestChainModelCallHandlers:
         """Test composition of three handlers."""
         execution_order = []
 
-        def first(request, handler):
+        def first(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             execution_order.append("first-before")
             result = handler(request)
             execution_order.append("first-after")
             return result
 
-        def second(request, handler):
+        def second(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             execution_order.append("second-before")
             result = handler(request)
             execution_order.append("second-after")
             return result
 
-        def third(request, handler):
+        def third(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             execution_order.append("third-before")
             result = handler(request)
             execution_order.append("third-after")
@@ -129,10 +141,14 @@ class TestChainModelCallHandlers:
         """Test inner handler retrying before outer sees response."""
         inner_attempts = []
 
-        def outer_passthrough(request, handler):
+        def outer_passthrough(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             return handler(request)
 
-        def inner_with_retry(request, handler):
+        def inner_with_retry(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse | AIMessage:
             for attempt in range(3):
                 inner_attempts.append(attempt)
                 try:
@@ -147,7 +163,7 @@ class TestChainModelCallHandlers:
 
         call_count = {"value": 0}
 
-        def mock_base_handler(req):
+        def mock_base_handler(req: ModelRequest) -> ModelResponse:
             call_count["value"] += 1
             if call_count["value"] < 3:
                 msg = "fail"
@@ -163,20 +179,24 @@ class TestChainModelCallHandlers:
     def test_error_to_success_conversion(self) -> None:
         """Test handler converting error to success response."""
 
-        def outer_error_handler(request, handler):
+        def outer_error_handler(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse | AIMessage:
             try:
                 return handler(request)
             except Exception:
                 # Middleware can return AIMessage - it will be normalized to ModelResponse
                 return AIMessage(content="Fallback response")
 
-        def inner_passthrough(request, handler):
+        def inner_passthrough(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             return handler(request)
 
         composed = _chain_model_call_handlers([outer_error_handler, inner_passthrough])
         assert composed is not None
 
-        def mock_base_handler(req):
+        def mock_base_handler(req: ModelRequest) -> ModelResponse:
             msg = "Model failed"
             raise ValueError(msg)
 
@@ -191,13 +211,17 @@ class TestChainModelCallHandlers:
         """Test handlers modifying the request."""
         requests_seen = []
 
-        def outer_add_context(request, handler):
+        def outer_add_context(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             modified_request = create_test_request(
                 messages=[*request.messages], system_prompt="Added by outer"
             )
             return handler(modified_request)
 
-        def inner_track_request(request, handler):
+        def inner_track_request(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             requests_seen.append(request.system_prompt)
             return handler(request)
 
@@ -212,15 +236,26 @@ class TestChainModelCallHandlers:
 
     def test_composition_preserves_state_and_runtime(self) -> None:
         """Test that state and runtime are passed through composition."""
+
+        class CustomState(AgentState[Any]):
+            test: str
+
+        class CustomContext(TypedDict):
+            test: str
+
         state_values = []
         runtime_values = []
 
-        def outer(request, handler):
+        def outer(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             state_values.append(("outer", request.state))
             runtime_values.append(("outer", request.runtime))
             return handler(request)
 
-        def inner(request, handler):
+        def inner(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             state_values.append(("inner", request.state))
             runtime_values.append(("inner", request.runtime))
             return handler(request)
@@ -228,8 +263,8 @@ class TestChainModelCallHandlers:
         composed = _chain_model_call_handlers([outer, inner])
         assert composed is not None
 
-        test_state = {"test": "state"}
-        test_runtime = {"test": "runtime"}
+        test_state = CustomState(messages=[], test="state")
+        test_runtime = Runtime(context=CustomContext(test="runtime"))
 
         # Create request with state and runtime
         test_request = create_test_request(state=test_state, runtime=test_runtime)
@@ -245,11 +280,15 @@ class TestChainModelCallHandlers:
         """Test handler that retries multiple times."""
         call_count = {"value": 0}
 
-        def outer_counts_calls(request, handler):
+        def outer_counts_calls(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             call_count["value"] += 1
             return handler(request)
 
-        def inner_retries(request, handler):
+        def inner_retries(
+            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
+        ) -> ModelResponse:
             try:
                 return handler(request)
             except ValueError:
@@ -261,7 +300,7 @@ class TestChainModelCallHandlers:
 
         attempt = {"value": 0}
 
-        def mock_base_handler(req):
+        def mock_base_handler(req: ModelRequest) -> ModelResponse:
             attempt["value"] += 1
             if attempt["value"] == 1:
                 msg = "fail"