refactor(runtime): gate settings backup file save by capability

apps/web/src/app/settings/settings.component.spec.ts

@@ -911,6 +911,65 @@ describe('SettingsComponent', () => {
         expect(component.isExportingData()).toBe(false);
     });
 
+    it('falls back to browser backup download when desktop file-save preload is incomplete', async () => {
+        fixture.destroy();
+        const saveFileDialog = jest.fn().mockResolvedValue('/tmp/backup.json');
+        window.electron = {
+            platform: 'linux',
+            saveFileDialog,
+        } as unknown as typeof window.electron;
+
+        const createObjectURL = jest.fn().mockReturnValue('blob:backup');
+        const revokeObjectURL = jest.fn();
+        const originalCreateObjectURL = window.URL.createObjectURL;
+        const originalRevokeObjectURL = window.URL.revokeObjectURL;
+        Object.defineProperty(window.URL, 'createObjectURL', {
+            configurable: true,
+            value: createObjectURL,
+        });
+        Object.defineProperty(window.URL, 'revokeObjectURL', {
+            configurable: true,
+            value: revokeObjectURL,
+        });
+        const clickSpy = jest
+            .spyOn(HTMLAnchorElement.prototype, 'click')
+            .mockImplementation();
+
+        try {
+            const partialFileSaveFixture =
+                TestBed.createComponent(SettingsComponent);
+            const partialFileSaveComponent =
+                partialFileSaveFixture.componentInstance;
+            partialFileSaveComponent.checkAppVersion = jest.fn();
+            partialFileSaveComponent.fetchLocalIpAddresses = jest
+                .fn()
+                .mockResolvedValue(undefined);
+            partialFileSaveFixture.detectChanges();
+
+            expect(partialFileSaveComponent.isDesktop).toBe(true);
+            expect(partialFileSaveComponent.supportsDesktopFileSave).toBe(
+                false
+            );
+
+            await partialFileSaveComponent.exportData();
+
+            expect(saveFileDialog).not.toHaveBeenCalled();
+            expect(createObjectURL).toHaveBeenCalledWith(expect.any(Blob));
+            expect(clickSpy).toHaveBeenCalled();
+            expect(revokeObjectURL).toHaveBeenCalledWith('blob:backup');
+        } finally {
+            clickSpy.mockRestore();
+            Object.defineProperty(window.URL, 'createObjectURL', {
+                configurable: true,
+                value: originalCreateObjectURL,
+            });
+            Object.defineProperty(window.URL, 'revokeObjectURL', {
+                configurable: true,
+                value: originalRevokeObjectURL,
+            });
+        }
+    });
+
     it('shows a failure snackbar and skips refresh when clearing EPG data rejects', async () => {
         (window.electron.clearEpgData as jest.Mock).mockRejectedValueOnce(
             new Error('boom')

apps/web/src/app/settings/settings.component.ts

@@ -137,6 +137,7 @@ export class SettingsComponent implements OnInit, OnDestroy {
 
     /** Flag that indicates whether the app runs in electron environment */
     readonly isDesktop = this.runtime.isElectron;
+    readonly supportsDesktopFileSave = this.runtime.supportsDesktopFileSave;
     readonly supportsEpg = this.runtime.supportsEpg;
     readonly supportsExternalPlayerPathSettings =
         this.runtime.supportsExternalPlayerPathSettings;
@@ -699,7 +700,7 @@ export class SettingsComponent implements OnInit, OnDestroy {
         try {
             const backup = await this.playlistBackupService.exportBackup();
 
-            if (this.isDesktop && window.electron?.saveFileDialog) {
+            if (this.supportsDesktopFileSave && window.electron) {
                 const savePath = await window.electron.saveFileDialog(
                     backup.defaultFileName,
                     [

docs/architecture/pwa-self-hosted.md

@@ -79,7 +79,8 @@ panels (`fetchEpg`, `getChannelPrograms`, `checkEpgFreshness`,
 `searchEpgPrograms`), `supportsPlaylistRefresh` requires the native playlist
 refresh/cancel/progress bridge, `supportsXtreamSectionNavigation` is available
 in PWA and in Electron when either the SQLite Xtream data source or the Xtream
-API transport is available, and
+API transport is available, `supportsDesktopFileSave` requires both
+`saveFileDialog` and `writeFile`, and
 `supportsManagedExternalPlayers` requires the MPV and VLC preload launch and
 path-setting methods (`openInMpv`, `openInVlc`, `setMpvPlayerPath`, and
 `setVlcPlayerPath`); a partial Electron bridge must not expose desktop-only

libs/services/src/lib/runtime-capabilities.service.spec.ts

@@ -258,6 +258,24 @@ describe('RuntimeCapabilitiesService', () => {
         expect(service.supportsDownloads).toBe(true);
     });
 
+    it('requires both desktop file-save preload methods', () => {
+        testWindow.electron = {
+            saveFileDialog: jest.fn(),
+        };
+
+        const service = new RuntimeCapabilitiesService();
+
+        expect(service.isElectron).toBe(true);
+        expect(service.supportsDesktopFileSave).toBe(false);
+
+        testWindow.electron = {
+            saveFileDialog: jest.fn(),
+            writeFile: jest.fn(),
+        };
+
+        expect(service.supportsDesktopFileSave).toBe(true);
+    });
+
     it('requires the complete playlist refresh preload surface', () => {
         testWindow.electron = {
             refreshPlaylist: jest.fn(),