[client] Hand covered windows over when a popup closes under another

Closing the browser-login popup while the install-progress popup was
still up restored the main window the login had hidden, even though the
install popup was meant to own the screen until it finished. The owner
tag on each hidden entry only stops a popup from restoring another's
windows; it says nothing about what to do with its own when a second
popup still covers them.

Track which popups currently own the screen and, on restore, re-tag the
entries another live popup covers to that popup instead of showing them.
A popup is never handed its own window, so closing the popup on top still
brings the one below back.

client/ui/services/windowmanager_test.go

@@ -18,6 +18,7 @@ func newTestWindowManager() *WindowManager {
 		pendingOps:   map[string][]windowOp{},
 		pendingClose: map[string]windowCloser{},
 		restoreGen:   map[string]uint64{},
+		hiding:       map[string]bool{},
 		generation:   map[string]uint64{},
 	}
 }
@@ -448,6 +449,78 @@ func TestInstallDuringLoginKeepsMainHiddenUntilLoginCloses(t *testing.T) {
 	require.Empty(t, s.hiddenWindows)
 }
 
+func TestLoginClosingUnderInstallHandsMainToInstall(t *testing.T) {
+	main := newFakeWindow(windowMain)
+	login := newFakeWindow(windowBrowserLogin)
+	install := newFakeWindow(windowInstallProgress)
+	install.visible = false
+	s := newTestWindowManager()
+	d := newFakeDesktop(s, main, login, install)
+
+	s.hideOtherWindows(windowBrowserLogin)
+	install.visible = true
+	s.hideOtherWindows(windowInstallProgress)
+	require.False(t, main.visible)
+	require.False(t, login.visible, "the install popup hides the login popup")
+
+	// The login popup closes while the install popup is still up: the main window it
+	// hid must not resurface under the install popup, it is handed over instead.
+	s.restoreHiddenWindows(windowBrowserLogin)
+	require.False(t, main.visible, "the install popup still covers the main window")
+	require.Equal(t, 0, d.raised)
+	require.Equal(t, []string{windowInstallProgress, windowInstallProgress}, ownersOf(s.hiddenWindows))
+
+	s.restoreHiddenWindows(windowInstallProgress)
+	require.True(t, main.visible, "the install popup restores the handed-over main window")
+	require.Equal(t, 1, d.raised)
+	require.Empty(t, s.hiddenWindows)
+}
+
+func TestInstallClosingUnderLoginHandsMainToLogin(t *testing.T) {
+	main := newFakeWindow(windowMain)
+	install := newFakeWindow(windowInstallProgress)
+	login := newFakeWindow(windowBrowserLogin)
+	login.visible = false
+	s := newTestWindowManager()
+	d := newFakeDesktop(s, main, install, login)
+
+	s.hideOtherWindows(windowInstallProgress)
+	login.visible = true
+	s.hideOtherWindows(windowBrowserLogin)
+	require.False(t, install.visible, "the login popup hides the install popup")
+
+	s.restoreHiddenWindows(windowInstallProgress)
+	require.False(t, main.visible, "the login popup still covers the main window")
+	require.Equal(t, 0, d.raised)
+	require.Equal(t, []string{windowBrowserLogin, windowBrowserLogin}, ownersOf(s.hiddenWindows))
+
+	s.restoreHiddenWindows(windowBrowserLogin)
+	require.True(t, main.visible)
+	require.Equal(t, 1, d.raised)
+	require.Empty(t, s.hiddenWindows)
+}
+
+func TestPopupClosingReshowsTheCoveringPopupItself(t *testing.T) {
+	main := newFakeWindow(windowMain)
+	install := newFakeWindow(windowInstallProgress)
+	login := newFakeWindow(windowBrowserLogin)
+	login.visible = false
+	s := newTestWindowManager()
+	d := newFakeDesktop(s, main, install, login)
+
+	s.hideOtherWindows(windowInstallProgress)
+	login.visible = true
+	s.hideOtherWindows(windowBrowserLogin)
+
+	// The login popup hid the install popup itself; closing the login popup must bring
+	// the install popup back rather than hand it over to its own owner.
+	s.restoreHiddenWindows(windowBrowserLogin)
+	require.True(t, install.visible, "a popup is never handed over to itself")
+	require.False(t, main.visible, "the main window stays with the install popup")
+	require.Equal(t, 0, d.raised)
+	require.Equal(t, []string{windowInstallProgress}, ownersOf(s.hiddenWindows))
+}
+
 func TestRestoreHiddenWindowsUnknownOwnerKeepsEverything(t *testing.T) {
 	main := newFakeWindow(windowMain)
 	s := newTestWindowManager()