SpawnArgs overview

Mode-agnostic abstract spawn descriptor returned by `Adapter.buildSpawnArgs()` — `{ command, args, env, cwd, stdin?, shell? }`. The pure `buildInvocationCommand()` transform rewrites SpawnArgs into the concrete host command for the chosen InvocationMode. Source: docs/adapters/reference/13-invocation-modes.md + packages/core/src/spawn-invocation.ts.