feat(x): browser screen-share picker, web notifications, Chrome extensions

Three capability upgrades to the embedded browser pane:

- Screen share: getDisplayMedia() in the browser partition now shows a
  Chrome-style source picker (screens/windows with thumbnails, optional
  system audio for screens) instead of silently capturing the primary
  screen. Requests are denied when the pane is hidden. The app's own
  session keeps its auto-loopback handler for meeting transcription.

- Notifications: the browser partition grants the notifications
  permission so sites (WhatsApp Web, Gmail, ...) can post native OS
  notifications while loaded. Background Web Push remains unavailable.

- Extensions: electron-chrome-extensions wired to the browser session.
  Unpacked extensions load from ~/.rowboat/extensions/<name>/; tab
  lifecycle is mirrored into chrome.tabs, and a <browser-action-list>
  toolbar hosts action icons/popups next to the address bar. NOTE: the
  library is GPL-3.0/Patron dual-licensed — licensing decision required
  before shipping in a release build.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/x/packages/shared/src/browser-control.ts

@@ -23,6 +23,22 @@ export const HttpAuthRequestSchema = z.object({
   realm: z.string().optional(),
 });
 
+// A screen or window offered to the user when a page in the embedded browser
+// calls getDisplayMedia() (e.g. "Present now" in Google Meet). Main gathers
+// these via desktopCapturer and the renderer shows a picker dialog.
+export const DisplayMediaSourceSchema = z.object({
+  id: z.string(),
+  name: z.string(),
+  kind: z.enum(['screen', 'window']),
+  thumbnailDataUrl: z.string(),
+  appIconDataUrl: z.string().nullable(),
+});
+
+export const DisplayMediaRequestSchema = z.object({
+  requestId: z.string(),
+  sources: z.array(DisplayMediaSourceSchema),
+});
+
 export const BrowserPageElementSchema = z.object({
   index: z.number().int().positive(),
   tagName: z.string(),
@@ -144,6 +160,8 @@ export const BrowserControlResultSchema = z.object({
 export type BrowserTabState = z.infer<typeof BrowserTabStateSchema>;
 export type BrowserState = z.infer<typeof BrowserStateSchema>;
 export type HttpAuthRequest = z.infer<typeof HttpAuthRequestSchema>;
+export type DisplayMediaSource = z.infer<typeof DisplayMediaSourceSchema>;
+export type DisplayMediaRequest = z.infer<typeof DisplayMediaRequestSchema>;
 export type BrowserPageElement = z.infer<typeof BrowserPageElementSchema>;
 export type BrowserPageSnapshot = z.infer<typeof BrowserPageSnapshotSchema>;
 export type BrowserControlAction = z.infer<typeof BrowserControlActionSchema>;

apps/x/packages/shared/src/ipc.ts

@@ -19,7 +19,7 @@ import type { SessionBusEvent, SessionIndexEntry, SessionState } from './session
 import { RowboatApiConfig } from './rowboat-account.js';
 import { ZListToolkitsResponse } from './composio.js';
 import { AppSummarySchema, RegistryRecordSchema, RowboatAppManifestSchema } from './rowboat-app.js';
-import { BrowserStateSchema, HttpAuthRequestSchema } from './browser-control.js';
+import { BrowserStateSchema, DisplayMediaRequestSchema, HttpAuthRequestSchema } from './browser-control.js';
 import { BillingInfoSchema } from './billing.js';
 import { EmailBlockSchema, GmailThreadSchema } from './blocks.js';
 import { PermissionDecision, ApprovalPolicy, CodingAgent, type CodeRunFeedEvent } from './code-mode.js';
@@ -2303,6 +2303,30 @@ const ipcSchemas = {
     }),
     res: z.object({ ok: z.boolean() }),
   },
+  // Screen-share picker for pages calling getDisplayMedia() in the embedded
+  // browser (main → renderer push). The renderer shows a source picker and
+  // answers via browser:displayMediaResponse.
+  'browser:displayMediaRequest': {
+    req: DisplayMediaRequestSchema,
+    res: z.null(),
+  },
+  // Main → renderer: a pending display-media request was resolved without the
+  // renderer answering (timed out, or the window went away), so the renderer
+  // must drop the corresponding picker dialog.
+  'browser:displayMediaResolved': {
+    req: z.object({ requestId: z.string() }),
+    res: z.null(),
+  },
+  // Renderer → main. Omit sourceId to cancel the request; `audio` asks for
+  // system-audio loopback alongside the shared screen.
+  'browser:displayMediaResponse': {
+    req: z.object({
+      requestId: z.string(),
+      sourceId: z.string().optional(),
+      audio: z.boolean().optional(),
+    }),
+    res: z.object({ ok: z.boolean() }),
+  },
   // Billing channels
   'billing:getInfo': {
     req: z.null(),