fix: resolve collaborators presence panel flicker (#523)

frontend/taskdeck-web/src/tests/views/BoardView.spec.ts

@@ -3,6 +3,15 @@ import { mount } from '@vue/test-utils'
 import { reactive } from 'vue'
 import BoardView from '../../views/BoardView.vue'
 
+const mockSessionStore = reactive<{ userId: string | null; username: string | null }>({
+  userId: 'user-abc',
+  username: 'alice',
+})
+
+vi.mock('../../store/sessionStore', () => ({
+  useSessionStore: () => mockSessionStore,
+}))
+
 const routerMock = vi.hoisted(() => ({
   push: vi.fn(),
 }))
@@ -122,6 +131,8 @@ describe('BoardView', () => {
     vi.clearAllMocks()
     localStorage.clear()
     routeMock.params.id = 'board-1'
+    mockSessionStore.userId = 'user-abc'
+    mockSessionStore.username = 'alice'
     mockBoardStore.currentBoard = {
       id: 'board-1',
       name: 'Ops Board',
@@ -228,4 +239,29 @@ describe('BoardView', () => {
 
     expect(addCardToggleMock).toHaveBeenCalledTimes(1)
   })
+
+  it('seeds presence with the current user immediately on mount so the panel never flickers to empty', async () => {
+    // Verify setBoardPresenceMembers is called with the current user before
+    // fetchBoard and realtime.start resolve — no empty-state window (#523).
+    mountView()
+    await waitForUi()
+
+    const firstCall = mockBoardStore.setBoardPresenceMembers.mock.calls[0]
+    expect(firstCall).toBeDefined()
+    expect(firstCall[0]).toEqual([
+      { userId: 'user-abc', displayName: 'alice', editingCardId: null },
+    ])
+  })
+
+  it('seeds presence with empty array when no user session is active', async () => {
+    mockSessionStore.userId = null
+    mockSessionStore.username = null
+
+    mountView()
+    await waitForUi()
+
+    const firstCall = mockBoardStore.setBoardPresenceMembers.mock.calls[0]
+    expect(firstCall).toBeDefined()
+    expect(firstCall[0]).toEqual([])
+  })
 })

frontend/taskdeck-web/src/views/BoardView.vue

@@ -2,6 +2,7 @@
 import { onBeforeUnmount, onMounted, ref, computed, watch } from 'vue'
 import { useRoute, useRouter } from 'vue-router'
 import { useBoardStore } from '../store/boardStore'
+import { useSessionStore } from '../store/sessionStore'
 import { useKeyboardShortcuts } from '../composables/useKeyboardShortcuts'
 import { createBoardRealtimeController } from '../composables/useBoardRealtime'
 import { useBoardDragDrop } from '../composables/useBoardDragDrop'
@@ -20,6 +21,7 @@ import { isClientOnboardingDemoBoardName } from '../utils/boardDemo'
 const route = useRoute()
 const router = useRouter()
 const boardStore = useBoardStore()
+const sessionStore = useSessionStore()
 
 const newColumnName = ref('')
 const showColumnForm = ref(false)
@@ -33,6 +35,17 @@ const presenceMembers = ref<BoardPresenceMember[]>([])
 
 const boardLoadPerf = usePerformanceMark('board-load')
 
+/**
+ * Build a presence entry for the current authenticated user so the panel
+ * shows immediately on mount, without waiting for the async SignalR
+ * BoardJoined push event. This eliminates the empty-state flicker.
+ */
+function currentUserPresenceSeed(): BoardPresenceMember[] {
+  const uid = sessionStore.userId
+  if (!uid) return []
+  return [{ userId: uid, displayName: sessionStore.username ?? null, editingCardId: null }]
+}
+
 
 const boardId = ref(route.params.id as string)
 const realtime = createBoardRealtimeController({
@@ -81,11 +94,19 @@ const {
   resetSelection,
 } = useBoardKeyboardNav(sortedColumns)
 
+function applyPresenceSeed() {
+  const seed = currentUserPresenceSeed()
+  presenceMembers.value = seed
+  boardStore.setBoardPresenceMembers(seed)
+}
+
 onMounted(async () => {
   boardLoadPerf.start()
   try {
-    presenceMembers.value = []
-    boardStore.setBoardPresenceMembers([])
+    // Seed presence with the current user immediately so the panel never
+    // shows "No active collaborators" while waiting for the SignalR
+    // BoardJoined push event (fixes #523 flicker).
+    applyPresenceSeed()
     boardStore.setEditingCard(null)
     await boardStore.fetchBoard(boardId.value)
     await realtime.start(boardId.value)
@@ -106,8 +127,8 @@ watch(
 
     boardId.value = nextBoardId
     resetSelection()
-    presenceMembers.value = []
-    boardStore.setBoardPresenceMembers([])
+    // Seed with current user on board switch for the same reason as onMounted.
+    applyPresenceSeed()
     boardStore.setEditingCard(null)
 
     try {