diff --git a/scripts/sandbox/publish.ts b/scripts/sandbox/publish.ts
index 3797c06c8bda..10a92c982a1f 100755
--- a/scripts/sandbox/publish.ts
+++ b/scripts/sandbox/publish.ts
@@ -11,6 +11,7 @@ import { dirname, join, relative } from 'path';
 import { temporaryDirectory } from '../../code/core/src/common/utils/cli.ts';
 import { REPROS_DIRECTORY } from '../utils/constants.ts';
 import { commitAllToGit } from './utils/git.ts';
+import { sanitizePublishedSandboxes } from './utils/sanitize-published-sandbox.ts';
 import { getTemplatesData, renderTemplate } from './utils/template.ts';
 
 export const logger = console;
@@ -70,6 +71,13 @@ const publish = async (options: PublishOptions & { tmpFolder: string }) => {
   logger.log(`🚛 Moving all the repros into the repository`);
   await cp(REPROS_DIRECTORY, tmpFolder, { recursive: true });
 
+  logger.log(`🧼 Sanitizing published sandboxes (after-storybook .yarnrc.yml + install artifacts)`);
+  const sanitizeResult = await sanitizePublishedSandboxes(tmpFolder);
+  logger.log(
+    `🧼 Sanitize summary: stripped ${sanitizeResult.strippedKeyCount} key(s) from ` +
+      `${sanitizeResult.filteredYarnrcCount} .yarnrc.yml file(s); removed ${sanitizeResult.removedPaths} excluded path(s)`
+  );
+
   await commitAllToGit({ cwd: tmpFolder, branch });
 
   logger.info(`
diff --git a/scripts/sandbox/utils/sanitize-published-sandbox.test.ts b/scripts/sandbox/utils/sanitize-published-sandbox.test.ts
new file mode 100644
index 000000000000..2ac61336e0aa
--- /dev/null
+++ b/scripts/sandbox/utils/sanitize-published-sandbox.test.ts
@@ -0,0 +1,168 @@
+import { mkdir, mkdtemp, readFile, stat, writeFile } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+
+import {
+  EXCLUDE_GLOBS,
+  STRIP_KEYS,
+  sanitizePublishedSandboxes,
+} from './sanitize-published-sandbox.ts';
+
+const exists = async (path: string) => {
+  try {
+    await stat(path);
+    return true;
+  } catch {
+    return false;
+  }
+};
+
+describe('STRIP_KEYS', () => {
+  it('contains exactly the documented host-local / verdaccio keys', () => {
+    // Mutating this list requires deliberate code review — if you are touching it,
+    // make sure the published sandboxes repository contract is intentional.
+    expect([...STRIP_KEYS]).toEqual([
+      'npmRegistryServer',
+      'unsafeHttpWhitelist',
+      'enableImmutableInstalls',
+      'enableMirror',
+      'logFilters',
+      'npmMinimalAgeGate',
+      'pnpFallbackMode',
+      'enableGlobalCache',
+      'checksumBehavior',
+    ]);
+  });
+});
+
+describe('EXCLUDE_GLOBS', () => {
+  it('targets only known install / build artifacts', () => {
+    expect([...EXCLUDE_GLOBS]).toEqual([
+      '**/.yarn/cache/**',
+      '**/.yarn/install-state.gz',
+      '**/.yarn/build-state.yml',
+      '**/.yarn/unplugged/**',
+      '**/.pnp.cjs',
+      '**/.pnp.loader.mjs',
+      '**/node_modules/**',
+      '**/.cache/**',
+      '**/storybook-static/**',
+    ]);
+  });
+});
+
+describe('sanitizePublishedSandboxes', () => {
+  let root: string;
+
+  beforeEach(async () => {
+    root = await mkdtemp(join(tmpdir(), 'sanitize-sandbox-'));
+  });
+
+  afterEach(async () => {
+    // tmpdir cleanup is best-effort; not strictly required for correctness
+  });
+
+  it('strips every STRIP_KEYS entry from after-storybook/.yarnrc.yml', async () => {
+    const afterDir = join(root, 'react-vite', 'default-ts', 'after-storybook');
+    await mkdir(afterDir, { recursive: true });
+    const yarnrc = [
+      'nodeLinker: node-modules',
+      'npmRegistryServer: "http://localhost:6001/"',
+      'unsafeHttpWhitelist: "localhost"',
+      'enableImmutableInstalls: false',
+      'enableMirror: false',
+      'logFilters: []',
+      'npmMinimalAgeGate: 0',
+      'pnpFallbackMode: none',
+      'enableGlobalCache: true',
+      'checksumBehavior: ignore',
+      '',
+    ].join('\n');
+    await writeFile(join(afterDir, '.yarnrc.yml'), yarnrc);
+
+    const result = await sanitizePublishedSandboxes(root);
+
+    expect(result.filteredYarnrcCount).toBe(1);
+    expect(result.strippedKeyCount).toBe(STRIP_KEYS.length);
+
+    const sanitized = await readFile(join(afterDir, '.yarnrc.yml'), 'utf-8');
+    for (const key of STRIP_KEYS) {
+      expect(sanitized).not.toContain(key);
+    }
+    // Non-stripped keys are preserved
+    expect(sanitized).toContain('nodeLinker');
+  });
+
+  it('leaves before-storybook/.yarnrc.yml untouched', async () => {
+    const beforeDir = join(root, 'react-vite', 'default-ts', 'before-storybook');
+    await mkdir(beforeDir, { recursive: true });
+    const yarnrc = [
+      'nodeLinker: node-modules',
+      'enableGlobalCache: true',
+      '',
+    ].join('\n');
+    await writeFile(join(beforeDir, '.yarnrc.yml'), yarnrc);
+
+    const result = await sanitizePublishedSandboxes(root);
+
+    expect(result.filteredYarnrcCount).toBe(0);
+    const preserved = await readFile(join(beforeDir, '.yarnrc.yml'), 'utf-8');
+    expect(preserved).toContain('enableGlobalCache');
+    expect(preserved).toContain('nodeLinker');
+  });
+
+  it('removes EXCLUDE_GLOBS matches from the tree', async () => {
+    const afterDir = join(root, 'react-vite', 'default-ts', 'after-storybook');
+    const beforeDir = join(root, 'react-vite', 'default-ts', 'before-storybook');
+    const afterCache = join(afterDir, '.yarn', 'cache');
+    const beforeNodeModules = join(beforeDir, 'node_modules', 'some-pkg');
+
+    await mkdir(afterCache, { recursive: true });
+    await writeFile(join(afterCache, 'pkg.zip'), 'binary blob');
+    await mkdir(beforeNodeModules, { recursive: true });
+    await writeFile(join(beforeNodeModules, 'index.js'), 'export {}');
+    await writeFile(join(afterDir, '.pnp.cjs'), '/* zero install */');
+    await writeFile(join(afterDir, 'README.md'), '# kept');
+
+    const result = await sanitizePublishedSandboxes(root);
+
+    expect(result.removedPaths).toBeGreaterThan(0);
+    expect(await exists(afterCache)).toBe(false);
+    expect(await exists(beforeNodeModules)).toBe(false);
+    expect(await exists(join(afterDir, '.pnp.cjs'))).toBe(false);
+    // Non-excluded files survive
+    expect(await exists(join(afterDir, 'README.md'))).toBe(true);
+  });
+
+  it('writes an empty file when stripping leaves no keys', async () => {
+    const afterDir = join(root, 'svelte-vite', 'default-ts', 'after-storybook');
+    await mkdir(afterDir, { recursive: true });
+    await writeFile(
+      join(afterDir, '.yarnrc.yml'),
+      'npmRegistryServer: "http://localhost:6001/"\n'
+    );
+
+    await sanitizePublishedSandboxes(root);
+
+    const sanitized = await readFile(join(afterDir, '.yarnrc.yml'), 'utf-8');
+    expect(sanitized).toBe('');
+  });
+
+  it('is idempotent — a second run is a no-op', async () => {
+    const afterDir = join(root, 'react-vite', 'default-ts', 'after-storybook');
+    await mkdir(afterDir, { recursive: true });
+    await writeFile(
+      join(afterDir, '.yarnrc.yml'),
+      'nodeLinker: node-modules\nnpmRegistryServer: "http://localhost:6001/"\n'
+    );
+
+    await sanitizePublishedSandboxes(root);
+    const second = await sanitizePublishedSandboxes(root);
+
+    expect(second.filteredYarnrcCount).toBe(0);
+    expect(second.strippedKeyCount).toBe(0);
+    expect(second.removedPaths).toBe(0);
+  });
+});
diff --git a/scripts/sandbox/utils/sanitize-published-sandbox.ts b/scripts/sandbox/utils/sanitize-published-sandbox.ts
new file mode 100644
index 000000000000..d10c283018ed
--- /dev/null
+++ b/scripts/sandbox/utils/sanitize-published-sandbox.ts
@@ -0,0 +1,108 @@
+import { readFile, rm, writeFile } from 'node:fs/promises';
+
+// eslint-disable-next-line depend/ban-dependencies
+import { glob } from 'glob';
+import yml from 'yaml';
+
+/**
+ * Keys stripped from `after-storybook/.yarnrc.yml` before publishing to the public sandboxes
+ * repository. These are host-local or Verdaccio-bootstrap settings that would either break a
+ * consumer's install (e.g. `npmRegistryServer: http://localhost:6001/`) or weaken their default
+ * supply-chain protections (e.g. `npmMinimalAgeGate: 0`).
+ *
+ * Mutating this list requires a deliberate code review (the integrity test asserts the exact set).
+ */
+export const STRIP_KEYS = [
+  'npmRegistryServer',
+  'unsafeHttpWhitelist',
+  'enableImmutableInstalls',
+  'enableMirror',
+  'logFilters',
+  'npmMinimalAgeGate',
+  'pnpFallbackMode',
+  'enableGlobalCache',
+  'checksumBehavior',
+] as const;
+
+/**
+ * Paths excluded from the published sandbox copy. These are install artifacts or build outputs
+ * that bloat the repo without providing value to consumers (who will re-run `yarn install` against
+ * the committed lockfile).
+ */
+export const EXCLUDE_GLOBS = [
+  '**/.yarn/cache/**',
+  '**/.yarn/install-state.gz',
+  '**/.yarn/build-state.yml',
+  '**/.yarn/unplugged/**',
+  '**/.pnp.cjs',
+  '**/.pnp.loader.mjs',
+  '**/node_modules/**',
+  '**/.cache/**',
+  '**/storybook-static/**',
+] as const;
+
+export type SanitizeResult = {
+  filteredYarnrcCount: number;
+  strippedKeyCount: number;
+  removedPaths: number;
+};
+
+/**
+ * Sanitize a directory tree that is about to be published to `storybookjs/sandboxes`.
+ *
+ * - Removes `STRIP_KEYS` from every `**\/after-storybook/.yarnrc.yml` (verdaccio/host config).
+ * - Removes paths matching `EXCLUDE_GLOBS` from the tree (install artifacts, build output).
+ *
+ * `before-storybook/.yarnrc.yml` is intentionally left untouched: it contains only the
+ * user-facing Yarn setup we want consumers to reproduce.
+ */
+export const sanitizePublishedSandboxes = async (rootDir: string): Promise<SanitizeResult> => {
+  const yarnrcFiles = await glob('**/after-storybook/.yarnrc.yml', {
+    cwd: rootDir,
+    absolute: true,
+    dot: true,
+  });
+
+  let filteredYarnrcCount = 0;
+  let strippedKeyCount = 0;
+
+  for (const file of yarnrcFiles) {
+    const original = await readFile(file, 'utf-8');
+    if (!original.trim()) {
+      continue;
+    }
+
+    const doc = (yml.parse(original) ?? {}) as Record<string, unknown>;
+    let modified = false;
+
+    for (const key of STRIP_KEYS) {
+      if (key in doc) {
+        delete doc[key];
+        modified = true;
+        strippedKeyCount++;
+      }
+    }
+
+    if (modified) {
+      const updated = Object.keys(doc).length === 0 ? '' : yml.stringify(doc);
+      await writeFile(file, updated);
+      filteredYarnrcCount++;
+    }
+  }
+
+  const excluded = await glob([...EXCLUDE_GLOBS], {
+    cwd: rootDir,
+    absolute: true,
+    dot: true,
+  });
+
+  for (const target of excluded) {
+    await rm(target, { recursive: true, force: true });
+  }
+
+  return {
+    filteredYarnrcCount,
+    strippedKeyCount,
+    removedPaths: excluded.length,
+  };
+};