fix: harden exec spawn fallback

src/process/spawn-utils.test.ts

@@ -0,0 +1,64 @@
+import { EventEmitter } from "node:events";
+import { PassThrough } from "node:stream";
+import type { ChildProcess } from "node:child_process";
+import { describe, expect, it, vi } from "vitest";
+
+import { spawnWithFallback } from "./spawn-utils.js";
+
+function createStubChild() {
+  const child = new EventEmitter() as ChildProcess;
+  child.stdin = new PassThrough() as ChildProcess["stdin"];
+  child.stdout = new PassThrough() as ChildProcess["stdout"];
+  child.stderr = new PassThrough() as ChildProcess["stderr"];
+  child.pid = 1234;
+  child.killed = false;
+  child.kill = vi.fn(() => true) as ChildProcess["kill"];
+  queueMicrotask(() => {
+    child.emit("spawn");
+  });
+  return child;
+}
+
+describe("spawnWithFallback", () => {
+  it("retries on EBADF using fallback options", async () => {
+    const spawnMock = vi
+      .fn()
+      .mockImplementationOnce(() => {
+        const err = new Error("spawn EBADF");
+        (err as NodeJS.ErrnoException).code = "EBADF";
+        throw err;
+      })
+      .mockImplementationOnce(() => createStubChild());
+
+    const result = await spawnWithFallback({
+      argv: ["echo", "ok"],
+      options: { stdio: ["pipe", "pipe", "pipe"] },
+      fallbacks: [{ label: "safe-stdin", options: { stdio: ["ignore", "pipe", "pipe"] } }],
+      spawnImpl: spawnMock,
+    });
+
+    expect(result.usedFallback).toBe(true);
+    expect(result.fallbackLabel).toBe("safe-stdin");
+    expect(spawnMock).toHaveBeenCalledTimes(2);
+    expect(spawnMock.mock.calls[0]?.[2]?.stdio).toEqual(["pipe", "pipe", "pipe"]);
+    expect(spawnMock.mock.calls[1]?.[2]?.stdio).toEqual(["ignore", "pipe", "pipe"]);
+  });
+
+  it("does not retry on non-EBADF errors", async () => {
+    const spawnMock = vi.fn().mockImplementationOnce(() => {
+      const err = new Error("spawn ENOENT");
+      (err as NodeJS.ErrnoException).code = "ENOENT";
+      throw err;
+    });
+
+    await expect(
+      spawnWithFallback({
+        argv: ["missing"],
+        options: { stdio: ["pipe", "pipe", "pipe"] },
+        fallbacks: [{ label: "safe-stdin", options: { stdio: ["ignore", "pipe", "pipe"] } }],
+        spawnImpl: spawnMock,
+      }),
+    ).rejects.toThrow(/ENOENT/);
+    expect(spawnMock).toHaveBeenCalledTimes(1);
+  });
+});