fix(browser): explicitly close guest web contents on unregister

webview.remove() in the renderer does not synchronously destroy the
underlying Chromium web contents — the media session stays alive until
GC, letting media keys (F8 play/pause) still control a closed tab.
Call webContents.close() from the main process during unregisterGuest
to tear down the guest immediately.

src/main/browser/browser-manager-grab.test.ts

@@ -59,7 +59,8 @@ function makeGuest(id: number) {
     executeJavaScriptInIsolatedWorld: guestExecuteJavaScriptInIsolatedWorldMock,
     getZoomFactor: guestGetZoomFactorMock,
     capturePage: guestCapturePageMock,
-    getURL: vi.fn(() => 'https://example.com/')
+    getURL: vi.fn(() => 'https://example.com/'),
+    close: vi.fn()
   } as unknown as Electron.WebContents
 }
 

src/main/browser/browser-manager.test.ts

@@ -1181,7 +1181,8 @@ describe('browserManager', () => {
       setWindowOpenHandler: guestSetWindowOpenHandlerMock,
       on: guestOnMock,
       off: guestOffMock,
-      openDevTools: guestOpenDevToolsMock
+      openDevTools: guestOpenDevToolsMock,
+      close: vi.fn()
     }
     webContentsFromIdMock.mockReturnValue(guest)
 
@@ -1314,7 +1315,8 @@ describe('browserManager', () => {
       setWindowOpenHandler: guestSetWindowOpenHandlerMock,
       on: guestOnMock,
       off: guestOffMock,
-      openDevTools: guestOpenDevToolsMock
+      openDevTools: guestOpenDevToolsMock,
+      close: vi.fn()
     }
     webContentsFromIdMock.mockImplementation((id: number) => {
       if (id === guest.id) {
@@ -2009,7 +2011,8 @@ describe('browserManager', () => {
       setWindowOpenHandler: guestSetWindowOpenHandlerMock,
       on: guestOnMock,
       off: guestOffMock,
-      openDevTools: guestOpenDevToolsMock
+      openDevTools: guestOpenDevToolsMock,
+      close: vi.fn()
     }
     const item = createDownloadItem()
     webContentsFromIdMock.mockImplementation((id: number) => {
@@ -2032,6 +2035,7 @@ describe('browserManager', () => {
 
     browserManager.unregisterGuest('browser-1')
 
+    expect(guest.close).toHaveBeenCalledTimes(1)
     expect(item.cancel).toHaveBeenCalledTimes(1)
     expect(rendererSendMock).toHaveBeenCalledWith(
       'browser:download-finished',
@@ -2739,6 +2743,7 @@ describe('browserManager', () => {
       on: guestOnMock,
       off: guestOffMock,
       openDevTools: guestOpenDevToolsMock,
+      close: vi.fn(),
       getURL: vi.fn(() => 'https://example.com/'),
       debugger: {
         isAttached: vi.fn(() => false),

src/main/browser/browser-manager.ts

@@ -1073,6 +1073,14 @@ export class BrowserManager {
     const wcId = this.webContentsIdByTabId.get(browserTabId)
     if (wcId !== undefined) {
       this.tabIdByWebContentsId.delete(wcId)
+      // Why: webview.remove() in the renderer does not synchronously destroy
+      // the guest web contents — Chromium keeps its media session alive until
+      // GC, so media keys (F8 play/pause) still control a "dead" tab.
+      // Explicitly closing the web contents here tears it down immediately.
+      const wc = webContents.fromId(wcId)
+      if (wc && !wc.isDestroyed()) {
+        wc.close()
+      }
     }
     this.webContentsIdByTabId.delete(browserTabId)
     this.rendererWebContentsIdByTabId.delete(browserTabId)