Bug Report

Environment

• livekit-agents: 1.5.2 - livekit-plugins-aws: 1.5.2
• Python: 3.12
• Model: Nova Sonic 2.0 (amazon.nova-sonic-v1:0)
• Region: us-east-1

Description

When running multiple concurrent rooms with Nova Sonic 2 and registered @function_tools, some rooms fail to execute tools and the following error appears
in the logs:

agent_turn: TypeError: string indices must be integers, not 'str'

The error is intermittent — it only affects some rooms under concurrent load, not all.

Steps to Reproduce

1. Set up an AgentSession with Nova Sonic 2 and at least one @function_tool that takes a string argument.
2. Simulate 10+ concurrent rooms where participants speak and trigger the tool.
3. Observe that some rooms fail with the TypeError above instead of executing the tool.