fix(posting): clarify direct file links

src/lib/utils/__tests__/url-utils.test.ts

@@ -11,6 +11,7 @@ vi.mock('../clipboard-utils', () => ({
 import {
   copyShareLinkToClipboard,
   getHostname,
+  getPublishURLFilename,
   is5chanLink,
   isPrivateNetworkHostname,
   isValidCrossboardPattern,
@@ -57,6 +58,8 @@ describe('url-utils', () => {
     expect(isValidPublishURL('https://i.imgur.com/YpB7qfa.jpg')).toBe(true);
     expect(isValidPublishURL('ftp://example.com/file.jpg')).toBe(false);
     expect(isValidPublishURL('not-a-url')).toBe(false);
+    expect(getPublishURLFilename('https://example.com/images/file%20name.jpg?size=large')).toBe('file name.jpg');
+    expect(getPublishURLFilename('not-a-url')).toBeNull();
   });
 
   it('copies share links for threads and catalog pages using the production fallback base url', async () => {

src/lib/utils/url-utils.ts

@@ -75,6 +75,24 @@ export const isValidPublishURL = (url: string) => {
   }
 };
 
+export const getPublishURLFilename = (url: string): string | null => {
+  if (!isValidPublishURL(url)) {
+    return null;
+  }
+
+  const parsedUrl = new URL(normalizePublishURL(url));
+  const filename = parsedUrl.pathname.split('/').filter(Boolean).pop();
+  if (!filename) {
+    return null;
+  }
+
+  try {
+    return decodeURIComponent(filename);
+  } catch {
+    return filename;
+  }
+};
+
 const CHAN_5_HOSTNAMES = ['5chan.app', '5chan.eth.limo', '5chan.eth.link', '5chan.eth.sucks', '5chan.netlify.app'];
 
 function getShareBaseUrl(): string {