feat(FN-4642): complete Step 1 — add container argv builder

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

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

@@ -0,0 +1,93 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+import { buildContainerArgv } from "../container-argv.js";
+import type { SandboxPolicy, SandboxRunOptions } from "../types.js";
+
+describe("buildContainerArgv", () => {
+  const options: SandboxRunOptions = {
+    cwd: "/tmp/worktree",
+    timeoutMs: 1_000,
+    maxBuffer: 1024,
+  };
+
+  const policy: SandboxPolicy = {
+    allowNetwork: true,
+  };
+
+  afterEach(() => {
+    vi.unstubAllEnvs();
+  });
+
+  it("uses podman keep-id userns and docker uid:gid", () => {
+    const podmanArgv = buildContainerArgv("podman", "echo hi", options, policy);
+    expect(podmanArgv).toContain("--userns=keep-id");
+
+    const dockerArgv = buildContainerArgv("docker", "echo hi", options, policy);
+    const uid = process.getuid?.();
+    const gid = process.getgid?.();
+    if (typeof uid === "number" && typeof gid === "number") {
+      expect(dockerArgv).toContain("--user");
+      expect(dockerArgv).toContain(`${uid}:${gid}`);
+      return;
+    }
+    expect(dockerArgv).not.toContain("--user");
+  });
+
+  it("adds network none only when network is disallowed", () => {
+    const noNetwork = buildContainerArgv("podman", "echo hi", options, { ...policy, allowNetwork: false });
+    expect(noNetwork).toContain("--network=none");
+
+    const networkAllowed = buildContainerArgv("podman", "echo hi", options, policy);
+    expect(networkAllowed).not.toContain("--network=none");
+  });
+
+  it("merges policy and options env with options overriding duplicates", () => {
+    const argv = buildContainerArgv(
+      "podman",
+      "echo hi",
+      {
+        ...options,
+        env: {
+          SHARED: "from-options",
+          OPTIONS_ONLY: "present",
+        },
+      },
+      {
+        ...policy,
+        env: {
+          SHARED: "from-policy",
+          POLICY_ONLY: "present",
+        },
+      },
+    );
+
+    expect(argv).toEqual(
+      expect.arrayContaining([
+        "--env",
+        "SHARED=from-options",
+        "--env",
+        "POLICY_ONLY=present",
+        "--env",
+        "OPTIONS_ONLY=present",
+      ]),
+    );
+    expect(argv).not.toContain("SHARED=from-policy");
+  });
+
+  it("bind mounts cwd and sets /work workdir", () => {
+    const argv = buildContainerArgv("podman", "echo hi", options, policy);
+    expect(argv).toEqual(expect.arrayContaining(["--workdir", "/work", "--volume", "/tmp/worktree:/work"]));
+  });
+
+  it("honors image override from env", () => {
+    vi.stubEnv("FUSION_SANDBOX_CONTAINER_IMAGE", "ghcr.io/example/sandbox:latest");
+    const argv = buildContainerArgv("podman", "echo hi", options, policy);
+    expect(argv).toContain("ghcr.io/example/sandbox:latest");
+  });
+
+  it("passes command through sh -c with command as single element", () => {
+    const command = "echo hello && echo world";
+    const argv = buildContainerArgv("podman", command, options, policy);
+    expect(argv.slice(-3)).toEqual(["sh", "-c", command]);
+  });
+});

packages/engine/src/sandbox/container-argv.ts

@@ -0,0 +1,44 @@
+import type { SandboxPolicy, SandboxRunOptions } from "./types.js";
+
+const DEFAULT_CONTAINER_IMAGE = "docker.io/library/alpine:3.20";
+
+/**
+ * Builds runtime argv for containerized sandbox command execution.
+ */
+export function buildContainerArgv(
+  runtime: "podman" | "docker",
+  command: string,
+  options: SandboxRunOptions,
+  policy: SandboxPolicy,
+): string[] {
+  const argv = [runtime, "run", "--rm", "-i", "--workdir", "/work", "--volume", `${options.cwd}:/work`];
+
+  if (runtime === "podman") {
+    argv.push("--userns=keep-id");
+  } else {
+    const uid = process.getuid?.();
+    const gid = process.getgid?.();
+    if (typeof uid === "number" && typeof gid === "number") {
+      argv.push("--user", `${uid}:${gid}`);
+    }
+  }
+
+  if (!policy.allowNetwork) {
+    argv.push("--network=none");
+  }
+
+  const mergedEnv: NodeJS.ProcessEnv = {
+    ...(policy.env ?? {}),
+    ...(options.env ?? {}),
+  };
+
+  for (const [key, value] of Object.entries(mergedEnv)) {
+    if (value === undefined) {
+      continue;
+    }
+    argv.push("--env", `${key}=${value}`);
+  }
+
+  argv.push(process.env.FUSION_SANDBOX_CONTAINER_IMAGE ?? DEFAULT_CONTAINER_IMAGE, "sh", "-c", command);
+  return argv;
+}