fix: correct handoff example API usage - use handoff() helper with input_type

- Remove non-existent input_payload_schema parameter from Agent constructors
- Replace unsupported (agent, schema) tuples with proper handoff(agent, input_type=schema)
- Change RefundPayload from TypedDict to BaseModel for runtime validation
- Make all schema fields optional to work with plain-text example requests
- Add proper import for handoff helper function
- Update instructions to avoid inventing missing data

Fixes all critical issues identified by reviewers - the example can now execute correctly.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

examples/python/handoff/handoff_basic.py

@@ -4,43 +4,67 @@ Basic handoff example demonstrating agent-to-agent delegation.
 This example shows how agents can hand off tasks to specialized agents.
 """
 
+from pydantic import BaseModel
+from typing import Optional
 from praisonaiagents import Agent
+from praisonaiagents.agent.handoff import handoff
+
+# Define typed payload contracts for each handoff
+class BillingPayload(BaseModel):
+    account_id: Optional[str] = None  # Made optional to work with plain-text requests
+    invoice_amount: Optional[float] = None
+    issue_type: str = "billing"
+
+class RefundPayload(BaseModel):  # Changed from TypedDict for runtime validation
+    transaction_id: Optional[str] = None  # Made optional
+    amount: Optional[float] = None  # Made optional
+    reason: Optional[str] = None  # Made optional
+
+class TechnicalPayload(BaseModel):
+    error_code: Optional[str] = None
+    device_info: Optional[str] = None  # Made optional
+    user_agent: Optional[str] = None  # Made optional
 
 # Create specialized agents
 billing_agent = Agent(
     name="Billing Agent",
     role="Billing Specialist",
-    goal="Handle all billing-related inquiries and tasks",
+    goal="Handle all billing-related inquiries and tasks using structured data",
     backstory="I am an expert in billing systems, payment processing, and invoice management."
 )
 
 refund_agent = Agent(
     name="Refund Agent",
     role="Refund Specialist",
-    goal="Process refund requests and handle refund-related issues",
+    goal="Process refund requests and handle refund-related issues with validated data",
     backstory="I specialize in processing refunds, evaluating refund eligibility, and ensuring customer satisfaction."
 )
 
 technical_support_agent = Agent(
     name="Technical Support",
     role="Technical Support Specialist",
-    goal="Resolve technical issues and provide technical assistance",
+    goal="Resolve technical issues and provide technical assistance with structured context",
     backstory="I am skilled in troubleshooting technical problems and providing solutions."
 )
 
-# Create a triage agent with handoffs to specialized agents
+# Create a triage agent with typed handoffs
 triage_agent = Agent(
     name="Triage Agent",
     role="Customer Service Triage",
-    goal="Understand customer needs and route them to the appropriate specialist",
+    goal="Understand customer needs and route them to the appropriate specialist with a validated payload",
     backstory="I analyze customer requests and direct them to the most suitable specialist for efficient resolution.",
     instructions="""Analyze the customer's request and determine which specialist can best help:
     - For billing questions, payment issues, or invoices, transfer to the Billing Agent
     - For refund requests or refund status inquiries, transfer to the Refund Agent  
     - For technical problems or product issues, transfer to Technical Support
     
-    Always explain why you're transferring the customer before doing so.""",
-    handoffs=[billing_agent, refund_agent, technical_support_agent]
+    Always explain why you're transferring the customer before doing so.
+    When handing off, populate only fields explicitly present in the request. Do not invent missing values.""",
+    handoffs=[
+        handoff(billing_agent, input_type=BillingPayload),
+        handoff(refund_agent, input_type=RefundPayload),
+        handoff(technical_support_agent, input_type=TechnicalPayload)
+    ]
 )
 
 # Example usage