Function start_on_localhost 

pub async fn start_on_localhost(
    pool: S3ClientPoolHandle,
    registry: TokenRegistryHandle,
    session_id: String,
) -> Result<MediaServerHandle, AppError>

Start the loopback media server and return a MediaServerHandle.

Binds to 127.0.0.1:0 (OS-assigned port), spawns the server on the current Tokio runtime, and returns immediately.

The caller is responsible for calling handle.shutdown.send(()) on app exit to stop the server, and calling registry.revoke_session(session_id) to sweep all live tokens.

Arguments

• pool — S3 client pool passed through to each request handler.
• registry — shared token registry.
• session_id — UUID v4 string minted at app start; tags all tokens.