Function emit_pi_interactive_with_host 

pub fn emit_pi_interactive_with_host(
    ir: &WarbleIr,
    out_dir: &Path,
    purpose: Option<NativePurpose>,
    native_scope: Option<NativeSessionScope>,
    native_mcp: Option<NativeMcpDescriptor>,
    native_host: Option<NativeHost>,
    model: &PiModel,
) -> Result<(), DispatchError>

Explicit host-owned composition, requiring a v5-aware consumer.