feat(FN-4636): complete Step 1 — define sandbox backend interface

Fusion-Task-Id: FN-4636
Fusion-Task-Lineage: 38ff2f48-4cb1-42c2-8f64-eb3b8d3d7f2c

packages/engine/src/sandbox/__tests__/types.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+
+import type { SandboxBackend, SandboxCapabilities, SandboxPolicy, SandboxRunOptions, SandboxRunResult } from "../types.js";
+
+describe("SandboxBackend types", () => {
+  it("accepts a minimal mock backend", async () => {
+    const backend: SandboxBackend = {
+      capabilities(): SandboxCapabilities {
+        return {
+          id: "native",
+          supportsNetworkPolicy: false,
+          supportsFilesystemPolicy: false,
+          platform: "any",
+        };
+      },
+      async prepare(_policy: SandboxPolicy): Promise<void> {},
+      async run(_command: string, _options: SandboxRunOptions): Promise<SandboxRunResult> {
+        return {
+          stdout: "",
+          stderr: "",
+          exitCode: 0,
+          signal: null,
+          timedOut: false,
+          bufferExceeded: false,
+        };
+      },
+      async dispose(): Promise<void> {},
+    };
+
+    await expect(backend.prepare({ allowNetwork: true })).resolves.toBeUndefined();
+    await expect(backend.dispose()).resolves.toBeUndefined();
+  });
+});