fusion/.changeset/FN-4643-sandbox-streaming.md

@runfusion/fusion

@runfusion/fusion
patch

Extend internal SandboxBackend abstraction to cover the spawn-based verification runner (runVerificationCommand / execWithProcessGroup) via a new runStreaming method on the backend. Native passthrough only — no behavior change. Foundation for FN-4637/FN-4638 to wrap the verification path the same way they wrap runConfiguredCommand.