diff --git a/packages/web/src/components/modals/InviteModal.tsx b/packages/web/src/components/modals/InviteModal.tsx
index c21c745c..32ef6d99 100644
--- a/packages/web/src/components/modals/InviteModal.tsx
+++ b/packages/web/src/components/modals/InviteModal.tsx
@@ -12,9 +12,12 @@ export function InviteModal() {
   const closeModal = useUIStore((s) => s.closeModal);
   const generateInvite = useServerStore((s) => s.generateInvite);
   const currentServerId = useServerStore((s) => s.currentServerId);
+  const servers = useServerStore((s) => s.servers);
+  const currentServer = servers.find(s => s.id === currentServerId);
+  const instanceOrigin = currentServer?._instanceOrigin ?? '';
 
   const isOpen = activeModal === 'invite';
-  const inviteUrl = inviteCode ? `${window.location.origin}/join/${inviteCode}` : '';
+  const inviteUrl = inviteCode ? `${instanceOrigin || window.location.origin}/join/${inviteCode}` : '';
 
   useEffect(() => {
     if (isOpen && currentServerId) {
diff --git a/packages/web/src/hooks/useWebSocket.ts b/packages/web/src/hooks/useWebSocket.ts
index 6583142a..0164cf77 100644
--- a/packages/web/src/hooks/useWebSocket.ts
+++ b/packages/web/src/hooks/useWebSocket.ts
@@ -172,7 +172,7 @@ function handleEvent(origin: string, event: ServerEvent): void {
         if (currentVoiceChannelId && isLiveKitConnected) {
           const voiceOrigin = getChannelOrigin(currentVoiceChannelId);
           if (voiceOrigin === origin) {
-            const myId = isHome ? event.user.id : useAuthStore.getState().user?.id;
+            const myId = event.user.id;
             if (myId) addVoiceUser(currentVoiceChannelId, myId);
             wsSend({ type: 'voice_join', channelId: currentVoiceChannelId }, origin);
             wsSend({ type: 'voice_status', isMuted, isDeafened, isCameraOn, isScreenSharing }, origin);
diff --git a/packages/web/src/stores/chatStore.ts b/packages/web/src/stores/chatStore.ts
index 77bf33bc..1b28e2f7 100644
--- a/packages/web/src/stores/chatStore.ts
+++ b/packages/web/src/stores/chatStore.ts
@@ -132,9 +132,12 @@ export const useChatStore = create<ChatState>((set, get) => ({
 
   loadMessages: async (channelId: string, force?: boolean) => {
     if (!force && get().hasMore.has(channelId)) return;
+    const isDm = isDmChannel(channelId);
+    // For server channels, bail if we don't know which instance owns this channel yet.
+    // The remote WS ready handler will call loadMessages once the map is populated.
+    if (!isDm && !useServerStore.getState().channelOriginMap.has(channelId)) return;
     set({ isLoading: true, loadError: null });
     try {
-      const isDm = isDmChannel(channelId);
       const origin = getChannelOrigin(channelId);
       const client = getApiForOrigin(origin);
       const messages = isDm
diff --git a/packages/web/src/stores/instanceStore.ts b/packages/web/src/stores/instanceStore.ts
index 3926e605..5ba57afb 100644
--- a/packages/web/src/stores/instanceStore.ts
+++ b/packages/web/src/stores/instanceStore.ts
@@ -2,7 +2,7 @@ import { create } from 'zustand';
 import type { User, InstanceInfoResponse, ReplicatedInstance, AuthResponse } from '@backspace/shared';
 import { BackspaceApiClient, createApiClient, api } from '../api/client';
 import { useAuthStore } from './authStore';
-import { setApiForOriginResolver, useServerStore } from './serverStore';
+import { setApiForOriginResolver, setUserIdForOriginResolver, useServerStore } from './serverStore';
 import { connectInstance, disconnectInstance, disconnectAllRemote } from '../hooks/useWebSocket';
 
 // ─── Types ───────────────────────────────────────────────────────────────────
@@ -505,3 +505,12 @@ setApiForOriginResolver((origin: string): BackspaceApiClient => {
   if (!instance) return api;
   return instance.api;
 });
+
+// ─── User ID resolution (federation) ──────────────────────────────────────────
+// Maps an origin to the local user's ID on that remote instance.
+// Used by voice join/leave to optimistically add/remove the correct user ID.
+
+setUserIdForOriginResolver((origin: string): string | undefined => {
+  const instance = useInstanceStore.getState().instances.find(i => i.origin === origin);
+  return instance?.user.id;
+});
diff --git a/packages/web/src/stores/serverStore.ts b/packages/web/src/stores/serverStore.ts
index 8a38f15b..cbd76746 100644
--- a/packages/web/src/stores/serverStore.ts
+++ b/packages/web/src/stores/serverStore.ts
@@ -144,7 +144,8 @@ export const useServerStore = create<ServerState>((set, get) => ({
     try {
       // Resolve the correct API client based on the server's instance origin
       const server = get().servers.find(s => s.id === serverId);
-      const origin = server?._instanceOrigin ?? '';
+      if (!server) return; // Not populated yet — remote WS ready will trigger reload
+      const origin = server._instanceOrigin ?? '';
       const client = getApiForOrigin(origin);
 
       const detail = await client.servers.get(serverId);
@@ -233,7 +234,10 @@ export const useServerStore = create<ServerState>((set, get) => ({
   },
 
   generateInvite: async (serverId: string) => {
-    const result = await api.servers.invite(serverId);
+    const server = get().servers.find(s => s.id === serverId);
+    const origin = server?._instanceOrigin ?? '';
+    const client = getApiForOrigin(origin);
+    const result = await client.servers.invite(serverId);
     return result.inviteCode;
   },
 
@@ -550,3 +554,23 @@ export function getApiForOrigin(origin: string): BackspaceApiClient {
   if (!origin || !_getApiForOrigin) return api;
   return _getApiForOrigin(origin);
 }
+
+// ─── User ID resolution (federation) ──────────────────────────────────────────
+// Same resolver pattern as getApiForOrigin — registered by instanceStore on
+// import to break the circular dependency chain.
+
+let _getUserIdForOrigin: ((origin: string) => string | undefined) | null = null;
+
+export function setUserIdForOriginResolver(resolver: (origin: string) => string | undefined): void {
+  _getUserIdForOrigin = resolver;
+}
+
+/**
+ * Returns the local user's ID on a given instance origin.
+ * '' or falsy = home instance (returns authStore user ID).
+ * 'https://...' = remote instance (returns the federated user ID on that instance).
+ */
+export function getMyUserIdForOrigin(origin: string): string | undefined {
+  if (!origin) return useAuthStore.getState().user?.id;
+  return _getUserIdForOrigin?.(origin);
+}
diff --git a/packages/web/src/stores/voiceStore.ts b/packages/web/src/stores/voiceStore.ts
index 7b54728f..0f76ce39 100644
--- a/packages/web/src/stores/voiceStore.ts
+++ b/packages/web/src/stores/voiceStore.ts
@@ -2,8 +2,7 @@ import { create } from 'zustand';
 import { persist, createJSONStorage } from 'zustand/middleware';
 import type { ParticipantInfo } from '../hooks/useLiveKit';
 import { AudioManager } from '../audio/AudioManager';
-import { useServerStore } from './serverStore';
-import { useAuthStore } from './authStore';
+import { useServerStore, getChannelOrigin, getMyUserIdForOrigin } from './serverStore';
 
 export interface ScreenShareConfig {
   height: 1080 | 720 | 540;
@@ -294,7 +293,7 @@ export const useVoiceStore = create<VoiceState>()(
       // Leave voice without wiping the voiceUsers map (so sidebar still shows others)
       leaveVoice: () => {
         const channelId = get().currentVoiceChannelId;
-        const myId = useAuthStore.getState().user?.id;
+        const myId = channelId ? getMyUserIdForOrigin(getChannelOrigin(channelId)) : undefined;
 
         set((state) => {
           // Optimistic: immediately remove self from the channel's voice users
diff --git a/packages/web/src/utils/voice.ts b/packages/web/src/utils/voice.ts
index 51c1b6b9..8bf56412 100644
--- a/packages/web/src/utils/voice.ts
+++ b/packages/web/src/utils/voice.ts
@@ -1,6 +1,5 @@
 import { useVoiceStore } from '../stores/voiceStore';
-import { useAuthStore } from '../stores/authStore';
-import { getChannelOrigin } from '../stores/serverStore';
+import { getChannelOrigin, getMyUserIdForOrigin } from '../stores/serverStore';
 import { wsSend } from '../hooks/useWebSocket';
 
 /**
@@ -13,8 +12,6 @@ export function joinVoiceChannel(channelId: string): void {
   const { currentVoiceChannelId, setCurrentVoiceChannel, addVoiceUser, removeVoiceUser } = useVoiceStore.getState();
   if (currentVoiceChannelId === channelId) return;
 
-  const myId = useAuthStore.getState().user?.id;
-
   // Leave old instance if switching cross-origin
   if (currentVoiceChannelId) {
     const oldOrigin = getChannelOrigin(currentVoiceChannelId);
@@ -22,12 +19,14 @@ export function joinVoiceChannel(channelId: string): void {
     if (oldOrigin !== newOrigin) {
       wsSend({ type: 'voice_leave' }, oldOrigin);
     }
-    // Optimistic: immediately remove self from old channel
-    if (myId) removeVoiceUser(currentVoiceChannelId, myId);
+    // Optimistic: immediately remove self from old channel (using origin-aware ID)
+    const myOldId = getMyUserIdForOrigin(oldOrigin);
+    if (myOldId) removeVoiceUser(currentVoiceChannelId, myOldId);
   }
 
   setCurrentVoiceChannel(channelId);
   // voice_join is now sent by useLiveKit after successful LiveKit connection
-  // Optimistic: immediately show self in new channel
-  if (myId) addVoiceUser(channelId, myId);
+  // Optimistic: immediately show self in new channel (using origin-aware ID)
+  const myNewId = getMyUserIdForOrigin(getChannelOrigin(channelId));
+  if (myNewId) addVoiceUser(channelId, myNewId);
 }