diff --git a/scripts/runner.node.mjs b/scripts/runner.node.mjs
index d54ae66faade..b45bf04e27da 100755
--- a/scripts/runner.node.mjs
+++ b/scripts/runner.node.mjs
@@ -28,7 +28,7 @@ import {
   writeFileSync,
 } from "node:fs";
 import { readFile } from "node:fs/promises";
-import { availableParallelism, userInfo } from "node:os";
+import { availableParallelism } from "node:os";
 import { basename, dirname, extname, join, relative, sep } from "node:path";
 import { createInterface } from "node:readline";
 import { setTimeout as setTimeoutPromise } from "node:timers/promises";
@@ -54,6 +54,7 @@ import {
   getOs,
   getSecret,
   getShell,
+  getUserInfo,
   getWindowsExitReason,
   isAndroid,
   isBuildkite,
@@ -844,7 +845,14 @@ async function runTests() {
       const absoluteTestPath = join(testsPath, testPath);
       const title = relative(cwd, absoluteTestPath).replaceAll(sep, "/");
       if (isNodeTest(testPath)) {
-        const testContent = readFileSync(absoluteTestPath, "utf-8");
+        let testContent = "";
+        try {
+          testContent = readFileSync(absoluteTestPath, "utf-8");
+        } catch (error) {
+          // Gone since discovery (a wiped checkout). The step below fails on
+          // it with bun's own error instead of this throw ending the whole run.
+          if (error?.code !== "ENOENT") throw error;
+        }
         const flagsMatch = /^\/\/ Flags:[^\S\r\n]+(--[^\r\n]*)$/m.exec(testContent);
         const testFlags = flagsMatch
           ? flagsMatch[1].split(/\s+/).filter(flag => resolutionGatingFlags.has(flag.split("=")[0]))
@@ -1762,7 +1770,7 @@ function getCombinedPath(execPath) {
 async function spawnBun(execPath, { args, cwd, timeout, gracefulTimeout, idleTimeout, env, stdout, stderr }) {
   const path = getCombinedPath(execPath);
   const tmpdirPath = mkdtempSync(join(tmpdir(), "buntmp-"));
-  const { username, homedir } = userInfo();
+  const { username, homedir } = getUserInfo();
   const shellPath = getShell();
   const bunEnv = {
     ...process.env,
diff --git a/scripts/utils.mjs b/scripts/utils.mjs
index 75da2ff08d2e..b4ce6416a74b 100755
--- a/scripts/utils.mjs
+++ b/scripts/utils.mjs
@@ -1609,11 +1609,42 @@ export function getHostname() {
 }
 
 /**
- * @returns {string}
+ * @typedef {object} UserInfo
+ * @property {string | undefined} username
+ * @property {string | undefined} homedir
+ */
+
+/** @type {UserInfo | undefined} */
+let cachedUserInfo;
+
+/**
+ * The user that runs this process, looked up once. `os.userInfo()` is a
+ * getpwuid_r() lookup that can fail at runtime: a macOS host that is shutting
+ * down answers ENOENT for its own uid once opendirectoryd is gone. The login
+ * session exported the same values, so a failed lookup falls back to them.
+ * @returns {UserInfo}
+ */
+export function getUserInfo() {
+  if (!cachedUserInfo) {
+    try {
+      const { username, homedir } = userInfo();
+      cachedUserInfo = { username, homedir };
+    } catch (error) {
+      cachedUserInfo = {
+        username: getEnv("USER", false) || getEnv("LOGNAME", false) || getEnv("USERNAME", false),
+        homedir: getEnv("HOME", false) || getEnv("USERPROFILE", false),
+      };
+      console.warn("os.userInfo() failed, using USER and HOME from the environment instead:", error);
+    }
+  }
+  return cachedUserInfo;
+}
+
+/**
+ * @returns {string | undefined}
  */
 export function getUsername() {
-  const { username } = userInfo();
-  return username;
+  return getUserInfo().username;
 }
 
 /**
diff --git a/test/internal/runner-user-info.test.ts b/test/internal/runner-user-info.test.ts
new file mode 100644
index 000000000000..1ac96d967caa
--- /dev/null
+++ b/test/internal/runner-user-info.test.ts
@@ -0,0 +1,35 @@
+/**
+ * scripts/runner.node.mjs sets USER and HOME for every `bun test` it spawns
+ * from getUserInfo() in scripts/utils.mjs. spawnBun used to call os.userInfo()
+ * per test file instead, and that call throws (`uv_os_get_passwd returned
+ * ENOENT`) on a macOS agent whose host has begun to shut down, which ended the
+ * whole shard with exit 1. getUserInfo() looks the user up once and falls back
+ * to the environment when the lookup fails.
+ */
+import { expect, mock, test } from "bun:test";
+import * as os from "node:os";
+import { getUserInfo, getUsername } from "../../scripts/utils.mjs";
+
+test("getUserInfo() falls back to USER and HOME when os.userInfo() throws, and looks the user up once", () => {
+  const real = { ...os };
+  let calls = 0;
+  mock.module("node:os", () => ({
+    ...real,
+    userInfo: () => {
+      calls++;
+      throw new Error("A system error occurred: uv_os_get_passwd returned ENOENT (no such file or directory)");
+    },
+  }));
+  try {
+    const { env } = process;
+    const expected = { username: env.USER || env.LOGNAME || env.USERNAME, homedir: env.HOME || env.USERPROFILE };
+
+    const first = getUserInfo();
+    expect(first).toEqual(expected);
+    expect(getUserInfo()).toBe(first);
+    expect(getUsername()).toBe(expected.username);
+    expect(calls).toBe(1);
+  } finally {
+    mock.module("node:os", () => real);
+  }
+});