Fix: Preserve OpenAI item ID on FunctionCall in Realtime sessions

[StianHanssen]

Problem

In _handle_response_output_item_done, the FunctionCall emitted through function_ch does not preserve the OpenAI-assigned item ID. It creates a new local UUID instead:

self._current_generation.function_ch.send_nowait(
    llm.FunctionCall(
        call_id=item.call_id,
        name=item.name,
        arguments=item.arguments,
    )
)

This means agent._chat_ctx and _remote_chat_ctx end up with different IDs for the same function_call item. Every other item type (assistant messages, user messages) correctly preserves the OpenAI ID, this is the only one that doesn't.

This causes update_chat_ctx(agent.chat_ctx) to produce delete+recreate diffs for function_call items, since compute_chat_ctx_diff matches by ID. In our case, this leads to previous_item_id not found errors when update_chat_ctx is called during active tool execution even if you are supposed to only change items furthest back in the context (we call it as part of a context summarization strategy).

Fix

Pass id=item_id to the FunctionCall constructor.

[CLAassistant]

All committers have signed the CLA.

[devin-ai-integration]

Devin Review found 1 potential issue.

🐛 1 issue in files not directly in the diff

🐛 Same missing id=item_id bug exists in realtime_model_beta.py but was not fixed (livekit-plugins/livekit-plugins-openai/livekit/plugins/openai/realtime/realtime_model_beta.py:1412-1416)

The PR fixes the missing id=item_id in realtime_model.py but the identical bug exists in realtime_model_beta.py. The FunctionCall constructor at this location does not pass id=item_id, so it generates a new local UUID instead of preserving the OpenAI-assigned item ID.

Root Cause

realtime_model_beta.py:1412 creates a FunctionCall without passing the id parameter, just like the original bug in realtime_model.py that this PR fixes. The item_id is already extracted at realtime_model_beta.py:1402 via assert (item_id := event.item.id) is not None but is never passed to the FunctionCall constructor.

This causes the same ID mismatch between agent._chat_ctx and _remote_chat_ctx described in the PR description, leading to previous_item_id not found errors when update_chat_ctx is called during active tool execution.

Impact: The same delete+recreate diffs and previous_item_id not found errors will occur for users of the beta realtime model.

View 2 additional findings in Devin Review.