Summary

Fixes #12708

ChatHistoryTruncationReducer.reduce() can orphan TOOL role messages by truncating the preceding assistant message that contains the tool_calls, causing OpenAI to reject the history with:

messages with role 'tool' must be a response to a preceding message with 'tool_calls'

Root Cause

locate_safe_reduction_index() uses contains_function_call_or_result() to detect tool-related messages during its backward scan. This function only checks msg.items for FunctionCallContent/FunctionResultContent instances.

However, TOOL role messages can contain only text content (no FunctionResultContent in items), which causes the backward scan to treat them as regular messages. The truncation point then lands between the tool_calls assistant message and its TOOL responses, orphaning the tool results.

Fix

Added AuthorRole.TOOL check to contains_function_call_or_result():

if msg.role == AuthorRole.TOOL:
    return True

This ensures any TOOL role message is recognized as part of a tool call/result pair, regardless of whether it has FunctionResultContent in its items.

Test

Added test_locate_safe_reduction_index_tool_role_without_function_result_content that verifies TOOL role messages with only text content are not separated from their tool call.