fix(downloads): align credential recovery after properties edits

- Fixes #37.
- Mark username-only and username-without-password edits for credential recovery immediately.
- Keep in-memory and persisted retry behavior aligned without reusing stale request credentials.

src/store/useDownloadStore.test.ts

@@ -211,6 +211,54 @@ describe('useDownloadStore', () => {
     expect(useDownloadStore.getState().downloads[0].credentialsRequired).toBe(false);
   });
 
+  it('marks a username-only properties change for credential recovery', async () => {
+    useDownloadStore.setState({
+      downloads: [{
+        id: 'username-only-properties',
+        url: 'https://secure.example.com/file.bin',
+        fileName: 'file.bin',
+        status: 'failed',
+        category: 'Other',
+        dateAdded: '',
+      }] as any[],
+    });
+
+    await useDownloadStore.getState().applyProperties('username-only-properties', {
+      username: 'alice',
+    });
+
+    expect(useDownloadStore.getState().downloads[0]).toMatchObject({
+      username: 'alice',
+      credentialsRequired: true,
+    });
+  });
+
+  it('keeps the recovery marker when clearing a password leaves a username', async () => {
+    useDownloadStore.setState({
+      downloads: [{
+        id: 'username-without-password',
+        url: 'https://secure.example.com/file.bin',
+        fileName: 'file.bin',
+        status: 'failed',
+        category: 'Other',
+        dateAdded: '',
+        username: 'alice',
+        password: 'secret',
+        credentialsRequired: false,
+      }] as any[],
+    });
+
+    await useDownloadStore.getState().applyProperties('username-without-password', {
+      password: undefined,
+    });
+
+    expect(useDownloadStore.getState().downloads[0]).toMatchObject({
+      username: 'alice',
+      password: undefined,
+      credentialsRequired: true,
+    });
+  });
+
   it('clears a persisted Torrent removal reservation when a paused item disables cleanup', async () => {
     useDownloadStore.setState({
       downloads: [{

src/store/useDownloadStore.ts

@@ -1255,8 +1255,11 @@ export const useDownloadStore = create<DownloadState>((set, get) => {
         throw error;
       }
     };
-    const credentialsUpdated = (['password', 'cookies', 'headers'] as const)
+    const credentialsUpdated = (['username', 'password', 'cookies', 'headers'] as const)
       .some(field => Object.prototype.hasOwnProperty.call(updates, field));
+    const nextUsernameMaterial = hasCredentialMaterial(
+      Object.prototype.hasOwnProperty.call(updates, 'username') ? updates.username : item.username,
+    );
     const nextCredentialMaterial = (['password', 'cookies', 'headers'] as const)
       .some(field => field === 'headers'
         ? hasCredentialBearingHeaders(
@@ -1272,7 +1275,7 @@ export const useDownloadStore = create<DownloadState>((set, get) => {
         : { ...updates, fileName: canonicalizeDownloadFileName(updates.fileName) }),
       ...(credentialsUpdated && nextCredentialMaterial
         ? { credentialsRequired: false }
-        : credentialsUpdated && item.credentialsRequired === true
+        : credentialsUpdated && (nextUsernameMaterial || item.credentialsRequired === true)
           ? { credentialsRequired: true }
           : {}),
       ...(item.isTorrent === true