fix(handoffs): filter duplicate items from model input when nest_handoff_history is enabled

[AnkanMisra]

Fixes #2171

Problem

When nest_handoff_history is enabled, the next agent receives duplicate conversation items:

Before this fix:

1. Summary message with <CONVERSATION HISTORY> containing tool calls as text
2. Raw function_call items (duplicated)
3. Raw function_call_output items (duplicated)

This causes the model to see the same information twice, wasting tokens and potentially causing confusion.

Solution

Introduced separation between items sent to the model vs items preserved for session history:

• Model input: Filtered - excludes function_call and function_call_output items already in the summary
• Session history: Unfiltered - preserves all items for observability and session saving

Key changes:

• Added input_items field to HandoffInputData for filtered model input
• Added session_step_items field to SingleStepResult for full session history
• Updated generated_items property to use session items when available
• Streaming events now use unfiltered items for full observability

Behavior

Scenario	Before	After
Model receives	Summary + raw tool items (duplicated)	Summary only (no duplicates)
Session saves	All items	All items (unchanged)
Streaming events	All items	All items (unchanged)

Testing

• Added 6 dedicated tests covering the fix
• Updated existing test assertions to reflect new expected counts
• All 1111 tests pass

[AnkanMisra]

@seratch Please review for any fixes

[chatgpt-codex-connector]

💡 Codex Review

openai-agents-python/src/agents/run.py

Lines 747 to 751 in effc877

	guardrail_result.output.tripwire_triggered
	for guardrail_result in input_guardrail_results
	):
	await self._save_result_to_session(
	session, [], turn_result.new_step_items

Session save drops unfiltered handoff items

For handoffs, new_step_items now holds the filtered model input while session_step_items keeps the full turn, but _save_result_to_session is still called with turn_result.new_step_items. With nest_handoff_history enabled this means tool call/output items removed from input_items are never persisted to the session even though they’re retained in session_step_items, contradicting the stated goal that session history remains unfiltered.

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[seratch]

Thanks for sharing this. We're going to move the nested handoff feature to an opt-in starting in 0.7.0: #2211 We'll continue improving the quality, but for now, I'll focus on completing other priorities.

[AnkanMisra]

Makes sense! Thanks for the context
Happy to help improve the feature further once it's in opt-in mode