feat: let plugin frames run work they can stop in a worker

lib/__tests__/proxy-security-headers.test.ts

@@ -181,6 +181,17 @@ describe('frame-ancestors of the mail UI', () => {
     else process.env.ALLOWED_FRAME_ANCESTORS = original;
   });
 
+  // Send checks run the admin's patterns in a worker they can stop; only
+  // plugin frames get it, the app keeps its script-src fallback.
+  it('lets plugin frames, and only them, start workers from blobs', async () => {
+    vi.mocked(configManager.getPolicy).mockReturnValueOnce({ features: { pluginsEnabled: true } } as never);
+    const frame = await proxy(new NextRequest('http://localhost:3000/plugin-sandbox', {
+      headers: { 'sec-fetch-dest': 'iframe', 'sec-fetch-mode': 'navigate', 'sec-fetch-site': 'same-origin' },
+    }));
+    expect(frame.headers.get('content-security-policy')).toContain("worker-src 'self' blob:");
+    expect((await load('/en/mail/folder/inbox')).headers.get('content-security-policy')).not.toContain('worker-src');
+  });
+
   it('allows only the app itself by default', async () => {
     delete process.env.ALLOWED_FRAME_ANCESTORS;
     const res = await load('/en/mail/folder/inbox');

proxy.ts

@@ -420,6 +420,10 @@ export async function proxy(request: NextRequest) {
     isSandboxPath ? `form-action 'none'` : `form-action ${["'self'", ...wopiOrigins].join(" ")}`,
     `frame-ancestors ${frameAncestors}`,
     `media-src ${mediaSrc}`,
+    // A plugin frame may run work it has to stop at a deadline (send checks'
+    // admin patterns) in a worker made from a blob; it gets the frame's own
+    // connect-src, so it reaches nothing the frame can't.
+    ...(isSandboxPath ? [`worker-src 'self' blob:`] : []),
   ].join("; ");
 
   // Skip intl middleware for routes outside the localized app tree.