fix(mobile): serve the host index route on the hosted page

Shared session code exits to `/h/<hostId>` when there is no history to pop
(leaveSession after a fresh page load into a session, the missing-worktree
bounce). The hosted page only listed workspaces at `/`, so those exits
rendered expo-router's Unmatched Route screen. Alias the host index to the
hosted list.

Claude-Session: https://claude.ai/code/session_01JNnE9qzUZMMnqpZWCqM3nb

mobile/host-web-app/h/[hostId]/index.tsx

@@ -0,0 +1,4 @@
+// Why: shared session code leaves to `/h/<hostId>` (leaveSession with no history, the
+// missing-worktree bounce). The hosted page lists workspaces at `/`, so without this alias
+// those exits landed on expo-router's Unmatched Route screen.
+export { default } from '../../index'

mobile/src/mobile-web/hosted-host-index-route.test.ts

@@ -0,0 +1,20 @@
+import { existsSync, readFileSync } from 'node:fs'
+import { describe, expect, it } from 'vitest'
+
+const hostedRoot = new URL('../../host-web-app/', import.meta.url)
+const hostIndexRoute = new URL('h/[hostId]/index.tsx', hostedRoot)
+const leaveSessionSource = readFileSync(
+  new URL('../session/use-mobile-session-markdown-actions.ts', import.meta.url),
+  'utf8'
+)
+const bounceSource = readFileSync(new URL('../host-route-notice.ts', import.meta.url), 'utf8')
+
+describe('hosted host index route', () => {
+  it('serves the host index that shared session exits navigate to', () => {
+    // Both exits target /h/<hostId>; a hosted page without that route renders Unmatched Route.
+    expect(leaveSessionSource).toContain('router.replace(`/h/${hostId}`)')
+    expect(bounceSource).toContain('`/h/${encodeURIComponent(hostId)}?notice=${notice}`')
+    expect(existsSync(hostIndexRoute)).toBe(true)
+    expect(readFileSync(hostIndexRoute, 'utf8')).toContain("export { default } from '../../index'")
+  })
+})