/**
 * Kernel Runtime — contracts.
 *
 * RuntimeBackend is the narrow interface between the kernel execution service
 * and any concrete runtime system (Phantom/SubAgentRuntime today; a lighter
 * git-native executor in a future PR).
 *
 * Rule: KernelExecutionService.execute() depends on RuntimeBackend, not on
 * SubAgentRuntime or any Phantom class directly. Phantom becomes an internal
 * implementation detail of PhantomRuntimeBackend.
 */
export {};
