diff --git a/scripts/__tests__/lint-no-hardcoded-runners.test.mjs b/scripts/__tests__/lint-no-hardcoded-runners.test.mjs
index 709ac63ed..d13c2ad9f 100644
--- a/scripts/__tests__/lint-no-hardcoded-runners.test.mjs
+++ b/scripts/__tests__/lint-no-hardcoded-runners.test.mjs
@@ -1,4 +1,4 @@
-import { execFileSync } from 'node:child_process'
+import { spawnSync } from 'node:child_process'
 import { mkdtempSync, readFileSync, rmSync, writeFileSync } from 'node:fs'
 import { tmpdir } from 'node:os'
 import { join, resolve } from 'node:path'
@@ -11,14 +11,12 @@ const SCRIPT = resolve(
 )
 
 function runScript(script, ...targets) {
-  try {
-    execFileSync(process.execPath, [script, ...targets], { encoding: 'utf8' })
-    return { exitCode: 0, output: '' }
-  } catch (err) {
-    return {
-      exitCode: err.status,
-      output: String(err.stdout) + String(err.stderr),
-    }
+  const result = spawnSync(process.execPath, [script, ...targets], {
+    encoding: 'utf8',
+  })
+  return {
+    exitCode: result.status,
+    output: String(result.stdout) + String(result.stderr),
   }
 }
 
@@ -26,6 +24,69 @@ function run(target) {
   return runScript(SCRIPT, target)
 }
 
+function runWithReaddirError(code, { afterParent = false } = {}) {
+  const probe = resolve(
+    fileURLToPath(import.meta.url),
+    '../../walk-error-probe.mjs',
+  )
+  const dir = mkdtempSync(join(tmpdir(), 'lint-hardcoded-runners-walk-'))
+  const replacement = afterParent
+    ? `let readdirCalls = 0
+async function readdir() {
+  readdirCalls += 1
+  if (readdirCalls === 1) {
+    return [{ name: 'vanished', isDirectory: () => true }]
+  }
+  const err = new Error('readdir failed')
+  err.code = '${code}'
+  throw err
+}`
+    : `async function readdir() { const err = new Error('readdir failed'); err.code = '${code}'; throw err }`
+  const src = readFileSync(SCRIPT, 'utf8').replace(
+    "import { readdir } from 'node:fs/promises'",
+    replacement,
+  )
+  try {
+    writeFileSync(probe, src)
+    return runScript(probe, dir)
+  } finally {
+    rmSync(probe, { force: true })
+    rmSync(dir, { recursive: true, force: true })
+  }
+}
+
+function runWithReadFileError(code) {
+  const probe = resolve(
+    fileURLToPath(import.meta.url),
+    '../../read-error-probe.mjs',
+  )
+  const dir = mkdtempSync(join(tmpdir(), 'lint-hardcoded-runners-read-'))
+  const src = readFileSync(SCRIPT, 'utf8')
+    .replace(
+      "import { readFileSync, statSync } from 'node:fs'",
+      `import { readFileSync as realReadFileSync, statSync } from 'node:fs'
+function readFileSync(path, ...args) {
+  if (String(path).endsWith('vanished.ts')) {
+    const err = new Error('read failed')
+    err.code = '${code}'
+    throw err
+  }
+  return realReadFileSync(path, ...args)
+}`,
+    )
+    .replace(
+      "import { readdir } from 'node:fs/promises'",
+      "async function readdir() { return [{ name: 'vanished.ts', isDirectory: () => false }] }",
+    )
+  try {
+    writeFileSync(probe, src)
+    return runScript(probe, dir)
+  } finally {
+    rmSync(probe, { force: true })
+    rmSync(dir, { recursive: true, force: true })
+  }
+}
+
 describe('lint-no-hardcoded-runners', () => {
   const fx = (name) =>
     resolve(fileURLToPath(import.meta.url), `../fixtures/${name}`)
@@ -34,6 +95,19 @@ describe('lint-no-hardcoded-runners', () => {
     expect(run(fx('clean.ts')).exitCode).toBe(0)
   })
 
+  it('captures stderr from a successful script', () => {
+    const dir = mkdtempSync(join(tmpdir(), 'lint-hardcoded-runners-stderr-'))
+    const probe = join(dir, 'stderr-probe.mjs')
+    try {
+      writeFileSync(probe, "process.stderr.write('successful warning\\n')\n")
+      const r = runScript(probe)
+      expect(r.exitCode).toBe(0)
+      expect(r.output).toContain('successful warning')
+    } finally {
+      rmSync(dir, { recursive: true, force: true })
+    }
+  })
+
   it('fails on a hardcoded `npx ...` string literal', () => {
     const r = run(fx('offender.ts'))
     expect(r.exitCode).toBe(1)
@@ -51,6 +125,30 @@ describe('lint-no-hardcoded-runners', () => {
     expect(r.output).not.toMatch(/at ModuleJob/)
   })
 
+  it('skips a directory that vanished after its parent was enumerated', () => {
+    const r = runWithReaddirError('ENOENT', { afterParent: true })
+    expect(r.exitCode).toBe(0)
+    expect(r.output).toContain('OK')
+  })
+
+  it('rethrows unexpected errors encountered while walking', () => {
+    const r = runWithReaddirError('EACCES')
+    expect(r.exitCode).not.toBe(0)
+    expect(r.output).toContain('EACCES')
+  })
+
+  it('skips a file that vanished after its directory was enumerated', () => {
+    const r = runWithReadFileError('ENOENT')
+    expect(r.exitCode).toBe(0)
+    expect(r.output).toContain('OK')
+  })
+
+  it('rethrows unexpected errors reading an enumerated file', () => {
+    const r = runWithReadFileError('EACCES')
+    expect(r.exitCode).not.toBe(0)
+    expect(r.output).toContain('EACCES')
+  })
+
   // Matches the sibling linter: a target outside the repo rendered as a
   // `../../../../..` chain out of the root instead of naming the file.
   it('renders an absolute path for an offender outside the repo root', () => {
diff --git a/scripts/__tests__/vitest-config.test.mjs b/scripts/__tests__/vitest-config.test.mjs
new file mode 100644
index 000000000..1ad8a56da
--- /dev/null
+++ b/scripts/__tests__/vitest-config.test.mjs
@@ -0,0 +1,8 @@
+import { describe, expect, it } from 'vitest'
+import scriptsVitestConfig from '../vitest.config.mjs'
+
+describe('scripts vitest config', () => {
+  it('keeps script test files serialized', () => {
+    expect(scriptsVitestConfig.test.fileParallelism).toBe(false)
+  })
+})
diff --git a/scripts/lint-no-hardcoded-runners.mjs b/scripts/lint-no-hardcoded-runners.mjs
index 26c6a2548..bdf058650 100644
--- a/scripts/lint-no-hardcoded-runners.mjs
+++ b/scripts/lint-no-hardcoded-runners.mjs
@@ -159,7 +159,17 @@ for (const target of TARGETS) {
     const shown = rel.startsWith('..') ? file : rel
     if (ALLOWLISTED_PATHS.has(rel)) continue
     if (/\.(test|spec)\.(ts|tsx|mts|cts)$/.test(file)) continue
-    const lines = readFileSync(file, 'utf8').split('\n')
+    let source
+    try {
+      source = readFileSync(file, 'utf8')
+    } catch (err) {
+      // A file can vanish after its directory was enumerated, just as a
+      // directory can vanish before the recursive readdir above. There is
+      // nothing left to lint; unexpected read failures must still surface.
+      if (err?.code === 'ENOENT') continue
+      throw err
+    }
+    const lines = source.split('\n')
     lines.forEach((line, idx) => {
       const matches = NPX_TOKEN.test(line)
       if (!matches) return