feat(FN-4642): complete Step 2 — add container backend prototype

Fusion-Task-Id: FN-4642
Fusion-Task-Lineage: a42a36f8-2d2a-43fe-b7c1-d7cf1ad321c3

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

@@ -0,0 +1,112 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+import * as containerArgv from "../container-argv.js";
+import { ContainerSandboxBackend } from "../container.js";
+
+const { mockExec, mockExecFile } = vi.hoisted(() => ({
+  mockExec: vi.fn(),
+  mockExecFile: vi.fn(),
+}));
+
+vi.mock("node:child_process", () => ({
+  exec: mockExec,
+  execFile: mockExecFile,
+  spawn: vi.fn(),
+}));
+
+describe("ContainerSandboxBackend", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockExec.mockImplementation((_command: string, _options: unknown, callback: (error: Error | null, stdout: string, stderr: string) => void) => {
+      callback(null, "podman version", "");
+      return {} as never;
+    });
+  });
+
+  it("returns success result when command succeeds", async () => {
+    mockExecFile.mockImplementation(
+      (_file: string, _args: string[], _options: unknown, callback: (error: Error | null, stdout: string, stderr: string) => void) => {
+        callback(null, { stdout: "ok", stderr: "" } as unknown as string, "");
+        return {} as never;
+      },
+    );
+    const backend = new ContainerSandboxBackend({ runtime: "podman" });
+    await backend.prepare({ allowNetwork: true });
+
+    const result = await backend.run("echo ok", { cwd: "/tmp/work", timeoutMs: 1000, maxBuffer: 1024 });
+
+    expect(result).toMatchObject({
+      stdout: "ok",
+      stderr: "",
+      exitCode: 0,
+      timedOut: false,
+      bufferExceeded: false,
+    });
+  });
+
+  it("maps non-zero exit without throwing", async () => {
+    mockExecFile.mockImplementation(
+      (_file: string, _args: string[], _options: unknown, callback: (error: Error) => void) => {
+        callback({ code: 2, stdout: "", stderr: "bad" } as unknown as Error);
+        return {} as never;
+      },
+    );
+    const backend = new ContainerSandboxBackend({ runtime: "podman" });
+
+    const result = await backend.run("false", { cwd: "/tmp/work", timeoutMs: 1000, maxBuffer: 1024 });
+
+    expect(result.exitCode).toBe(2);
+    expect(result.stderr).toBe("bad");
+  });
+
+  it("maps timeout errors", async () => {
+    mockExecFile.mockImplementation(
+      (_file: string, _args: string[], _options: unknown, callback: (error: Error) => void) => {
+        callback({ killed: true, signal: "SIGTERM", message: "Command timed out" } as unknown as Error);
+        return {} as never;
+      },
+    );
+    const backend = new ContainerSandboxBackend({ runtime: "podman" });
+
+    const result = await backend.run("sleep 10", { cwd: "/tmp/work", timeoutMs: 1000, maxBuffer: 1024 });
+
+    expect(result.timedOut).toBe(true);
+    expect(result.signal).toBe("SIGTERM");
+  });
+
+  it("maps maxBuffer errors", async () => {
+    mockExecFile.mockImplementation(
+      (_file: string, _args: string[], _options: unknown, callback: (error: Error) => void) => {
+        callback({ code: "ERR_CHILD_PROCESS_STDIO_MAXBUFFER", message: "maxBuffer" } as unknown as Error);
+        return {} as never;
+      },
+    );
+    const backend = new ContainerSandboxBackend({ runtime: "podman" });
+
+    const result = await backend.run("cat big", { cwd: "/tmp/work", timeoutMs: 1000, maxBuffer: 10 });
+
+    expect(result.bufferExceeded).toBe(true);
+  });
+
+  it("returns structured spawnError when runtime probe fails", async () => {
+    const runtimeError = Object.assign(new Error("not found"), { code: "ENOENT" });
+    mockExec.mockImplementation((_command: string, _options: unknown, callback: (error: Error) => void) => {
+      callback(runtimeError);
+      return {} as never;
+    });
+    const argvSpy = vi.spyOn(containerArgv, "buildContainerArgv");
+
+    const backend = new ContainerSandboxBackend({ runtime: "podman" });
+    const result = await backend.run("echo ok", { cwd: "/tmp/work", timeoutMs: 1000, maxBuffer: 1024 });
+
+    expect(result.exitCode).toBeNull();
+    expect(result.spawnError).toBe(runtimeError);
+    expect(mockExecFile).not.toHaveBeenCalled();
+    expect(argvSpy).not.toHaveBeenCalled();
+  });
+
+  it("reports configured runtime through capabilities", () => {
+    const backend = new ContainerSandboxBackend({ runtime: "docker" });
+    expect(backend.capabilities().id).toBe("docker");
+  });
+});