Enable signature registration in other signatures for cross-task execution

[yedidyakfir]

Summary

• Enhanced chain task functionality to support passing kwargs to all subtasks in a chain
• Modified chain assertions to properly propagate kwargs alongside return values between chain tasks
• This enables signatures to register and execute code within other task contexts

Changes

• Updated assert_chain_done to copy kwargs for each chain task and merge with return values
• Modified chain integration test to properly set kwargs on chain signature before execution
• Changed message type from ContextMessage to EmptyModel and moved context data to kwargs

Test plan

• Run existing chain integration tests
• Verify kwargs are properly propagated through chain execution
• Ensure backward compatibility with existing chain behavior

🤖 Generated with Claude Code