Constant DEFAULT_MAX_PARALLEL_TOOLS 

pub const DEFAULT_MAX_PARALLEL_TOOLS: usize = 5;

Default value for AgentConfig::max_parallel_tools.

Mirrors MAX_PARALLEL_TOOLS = 5 from the TypeScript frontend. Used both in AgentConfig::default and in super::events::AGENT_EVENT_CHANNEL_CAPACITY so the channel size accounts for the correct number of concurrent tool events.