fix(cli): render starts in a sandbox that forbids lowering CPU priority (#5814)

packages/cli/src/renderSetupWorker.priority.test.ts

@@ -1,5 +1,5 @@
 import { constants } from "node:os";
-import { afterEach, expect, it, vi } from "vitest";
+import { afterEach, beforeEach, expect, it, vi } from "vitest";
 
 const os = vi.hoisted(() => ({ setPriority: vi.fn() }));
 vi.mock("node:os", async (importOriginal) => ({
@@ -8,11 +8,15 @@ vi.mock("node:os", async (importOriginal) => ({
 }));
 vi.mock("./utils/lintProject.js", () => ({ lintProject: vi.fn(async () => ({ ok: true })) }));
 
+beforeEach(() => {
+  vi.resetModules();
+  os.setPriority.mockReset();
+  process.argv[2] = "lint";
+  process.env.HYPERFRAMES_RENDER_SETUP_INPUT = JSON.stringify({ projectDir: "/project" });
+});
 afterEach(() => vi.restoreAllMocks());
 
 it("lints at the lowest CPU priority so it never competes with a Studio boot", async () => {
-  process.argv[2] = "lint";
-  process.env.HYPERFRAMES_RENDER_SETUP_INPUT = JSON.stringify({ projectDir: "/project" });
   const write = vi.spyOn(process.stdout, "write").mockImplementation(() => true);
 
   await import("./renderSetupWorker.js");
@@ -20,3 +24,17 @@ it("lints at the lowest CPU priority so it never competes with a Studio boot", a
   expect(os.setPriority).toHaveBeenCalledWith(constants.priority.PRIORITY_LOW);
   expect(write).toHaveBeenCalledWith(expect.stringContaining('{"ok":true}'));
 });
+
+it("still lints when a sandbox forbids lowering the priority", async () => {
+  os.setPriority.mockImplementation(() => {
+    throw new Error("uv_os_setpriority returned EPERM (operation not permitted)");
+  });
+  const write = vi.spyOn(process.stdout, "write").mockImplementation(() => true);
+  const warn = vi.spyOn(process.stderr, "write").mockImplementation(() => true);
+
+  await import("./renderSetupWorker.js");
+
+  expect(write).toHaveBeenCalledWith(expect.stringContaining('{"ok":true}'));
+  expect(warn).toHaveBeenCalledTimes(1);
+  expect(warn).toHaveBeenCalledWith(expect.stringContaining("EPERM"));
+});

packages/cli/src/renderSetupWorker.ts

@@ -18,11 +18,19 @@ const disposeSignalHandlers = installRenderSetupSignalHandlers(
   process.env.HYPERFRAMES_RENDER_DETACHED !== "1",
 );
 
+function lowerPriority(): void {
+  try {
+    setPriority(constants.priority.PRIORITY_LOW);
+  } catch (error) {
+    process.stderr.write(`Lint runs at normal priority: ${(error as Error).message}\n`);
+  }
+}
+
 async function runMode(): Promise<unknown> {
   if (mode === "browser") return ensureBrowser(input);
   if (mode === "lint") {
     // Nobody waits on a background lint the way they wait on a Studio boot, so it takes idle CPU only.
-    setPriority(constants.priority.PRIORITY_LOW);
+    lowerPriority();
     return lintProject(
       input.projectDir,
       input.entryFile,