diff --git a/samples/python/src/roles/shopping_agent/subagents/payment_method_collector/tools.py b/samples/python/src/roles/shopping_agent/subagents/payment_method_collector/tools.py
index f24fe572..a876fa53 100644
--- a/samples/python/src/roles/shopping_agent/subagents/payment_method_collector/tools.py
+++ b/samples/python/src/roles/shopping_agent/subagents/payment_method_collector/tools.py
@@ -20,6 +20,7 @@
 
 from google.adk.tools.tool_context import ToolContext
 
+from ap2.types.mandate import CartMandate
 from ap2.types.payment_request import PAYMENT_METHOD_DATA_DATA_KEY
 from common.a2a_message_builder import A2aMessageBuilder
 from common import artifact_utils
@@ -41,7 +42,7 @@ async def get_payment_methods(
   Returns:
     A dictionary of the user's applicable payment methods.
   """
-  cart_mandate = tool_context.state["cart_mandate"]
+  cart_mandate = CartMandate.model_validate(tool_context.state["cart_mandate"])
   message_builder = (
       A2aMessageBuilder()
       .set_context_id(tool_context.state["shopping_context_id"])
diff --git a/samples/python/src/roles/shopping_agent/subagents/shopper/tools.py b/samples/python/src/roles/shopping_agent/subagents/shopper/tools.py
index cee16eff..5c23ba72 100644
--- a/samples/python/src/roles/shopping_agent/subagents/shopper/tools.py
+++ b/samples/python/src/roles/shopping_agent/subagents/shopper/tools.py
@@ -65,7 +65,7 @@ def create_intent_mandate(
           datetime.now(timezone.utc) + timedelta(days=1)
       ).isoformat(),
   )
-  tool_context.state["intent_mandate"] = intent_mandate
+  tool_context.state["intent_mandate"] = intent_mandate.model_dump()
   return intent_mandate
 
 
@@ -84,9 +84,10 @@ async def find_products(
   Raises:
     RuntimeError: If the merchant agent fails to provide products.
   """
-  intent_mandate = tool_context.state["intent_mandate"]
-  if not intent_mandate:
+  intent_mandate_data = tool_context.state["intent_mandate"]
+  if not intent_mandate_data:
     raise RuntimeError("No IntentMandate found in tool context state.")
+  intent_mandate = IntentMandate.model_validate(intent_mandate_data)
   risk_data = _collect_risk_data(tool_context)
   if not risk_data:
     raise RuntimeError("No risk data found in tool context state.")
@@ -106,7 +107,7 @@ async def find_products(
 
   tool_context.state["shopping_context_id"] = task.context_id
   cart_mandates = _parse_cart_mandates(task.artifacts)
-  tool_context.state["cart_mandates"] = cart_mandates
+  tool_context.state["cart_mandates"] = [cm.model_dump() for cm in cart_mandates]
   return cart_mandates
 
 
@@ -117,7 +118,10 @@ def update_chosen_cart_mandate(cart_id: str, tool_context: ToolContext) -> str:
     cart_id: The ID of the chosen cart.
     tool_context: The ADK supplied tool context.
   """
-  cart_mandates: list[CartMandate] = tool_context.state.get("cart_mandates", [])
+  cart_mandates = [
+      CartMandate.model_validate(cm)
+      for cm in tool_context.state.get("cart_mandates", [])
+  ]
   for cart in cart_mandates:
     print(
         f"Checking cart with ID: {cart.contents.id} with chosen ID: {cart_id}"
diff --git a/samples/python/src/roles/shopping_agent/tools.py b/samples/python/src/roles/shopping_agent/tools.py
index 1d8b7bf1..280bf1e2 100644
--- a/samples/python/src/roles/shopping_agent/tools.py
+++ b/samples/python/src/roles/shopping_agent/tools.py
@@ -76,8 +76,8 @@ async def update_cart(
       _parse_cart_mandates(task.artifacts)
   )
 
-  tool_context.state["cart_mandate"] = updated_cart_mandate
-  tool_context.state["shipping_address"] = shipping_address
+  tool_context.state["cart_mandate"] = updated_cart_mandate.model_dump()
+  tool_context.state["shipping_address"] = shipping_address.model_dump()
 
   return updated_cart_mandate
 
@@ -163,7 +163,7 @@ def store_receipt_if_present(task, tool_context: ToolContext) -> None:
   )
   if payment_receipts:
     payment_receipt = artifact_utils.only(payment_receipts)
-    tool_context.state["payment_receipt"] = payment_receipt
+    tool_context.state["payment_receipt"] = payment_receipt.model_dump()
 
 
 def create_payment_mandate(
@@ -181,10 +181,12 @@ def create_payment_mandate(
   Returns:
     The payment mandate.
   """
-  cart_mandate = tool_context.state["cart_mandate"]
+  cart_mandate = CartMandate.model_validate(tool_context.state["cart_mandate"])
 
   payment_request = cart_mandate.contents.payment_request
-  shipping_address = tool_context.state["shipping_address"]
+  shipping_address = ContactAddress.model_validate(
+      tool_context.state["shipping_address"]
+  )
 
   payment_method = os.environ.get("PAYMENT_METHOD", "CARD")
   if payment_method == "x402":
@@ -215,7 +217,7 @@ def create_payment_mandate(
       ),
   )
 
-  tool_context.state["payment_mandate"] = payment_mandate
+  tool_context.state["payment_mandate"] = payment_mandate.model_dump()
   return payment_mandate
 
 
@@ -238,8 +240,12 @@ def sign_mandates_on_user_device(tool_context: ToolContext) -> str:
   Returns:
       A string representing the simulated user authorization signature (JWT).
   """
-  payment_mandate: PaymentMandate = tool_context.state["payment_mandate"]
-  cart_mandate: CartMandate = tool_context.state["cart_mandate"]
+  payment_mandate = PaymentMandate.model_validate(
+      tool_context.state["payment_mandate"]
+  )
+  cart_mandate = CartMandate.model_validate(
+      tool_context.state["cart_mandate"]
+  )
   cart_mandate_hash = _generate_cart_mandate_hash(cart_mandate)
   payment_mandate_hash = _generate_payment_mandate_hash(
       payment_mandate.payment_mandate_contents
@@ -250,7 +256,7 @@ def sign_mandates_on_user_device(tool_context: ToolContext) -> str:
   payment_mandate.user_authorization = (
       cart_mandate_hash + "_" + payment_mandate_hash
   )
-  tool_context.state["signed_payment_mandate"] = payment_mandate
+  tool_context.state["signed_payment_mandate"] = payment_mandate.model_dump()
   return payment_mandate.user_authorization