[client] Drop the pending session extend on a profile switch

The profile-switch cleanup dropped the pending login flow and the
account-prompt flag, but left extendAuthSessionFlow untouched. Its device
code was issued by the previous profile's IdP client, so a
WaitExtendAuthSession still parked on the browser leg would submit the
resulting token against the new profile's engine.

client/server/login_account_test.go

@@ -103,12 +103,20 @@ func TestSwitchProfile_DropsAccountPromptAndPendingFlow(t *testing.T) {
 		waitCancel: func() { cancelled = true },
 	}
 
+	extendCancelled := false
+	s.extendAuthSessionFlow.Set(&stubOAuthFlow{}, auth.AuthFlowInfo{DeviceCode: "device"})
+	s.extendAuthSessionFlow.SetWaitCancel(func() { extendCancelled = true })
+
 	_, err := s.SwitchProfile(ctx, nil)
 	require.NoError(t, err)
 	require.False(t, s.forceAccountPrompt, "the prompt flag leaked across a profile switch")
 	require.Nil(t, s.oauthAuthFlow.flow, "the previous profile's flow leaked across a profile switch")
 	require.Empty(t, s.oauthAuthFlow.hint)
 	require.True(t, cancelled, "the pending wait was not cancelled")
+
+	require.True(t, extendCancelled, "the pending extend wait was not cancelled")
+	_, _, pending := s.extendAuthSessionFlow.Get()
+	require.False(t, pending, "the previous profile's extend flow leaked across a profile switch")
 }
 
 func newSSOTestServer(t *testing.T, hint string, accountPrompted bool, tokenEmail string) *Server {

client/server/server.go

@@ -1286,6 +1286,12 @@ func (s *Server) SwitchProfile(callerCtx context.Context, msg *proto.SwitchProfi
 	s.oauthAuthFlow = oauthAuthFlow{}
 	s.forceAccountPrompt = false
 
+	// A pending session extend belongs to the previous profile too: its device
+	// code was issued by that profile's IdP client, and WaitExtendAuthSession
+	// would submit the resulting token against the new profile's engine.
+	s.extendAuthSessionFlow.CancelWait()
+	s.extendAuthSessionFlow.Clear()
+
 	if msg != nil && msg.ProfileName != nil {
 		s.publishProfileListChanged(*msg.ProfileName)
 	}