Function project_search 

pub fn project_search(
    activator: &mut dyn ModeActivator,
    query: String,
    options: ProjectSearchOptions,
    registry: CommandRegistryHandle,
    lang_registry: Option<Arc<LangRegistry>>,
) -> Option<BufferId>

Open a project-search multibuffer view for query under options.root. Returns the view’s BufferId immediately; scan runs on a spawned tokio task and streams results via typed events.

Returns None when ProjectSearchService or EventBus isn’t registered (boot path didn’t wire the provider) — caller logs + recovers.