perf(P6A.T5): pre-warm Supabase + avatar loading hints

Fire a no-await profiles query in AuthContext on session establish to absorb
cold-connection latency before the first user-triggered request. Add
loading='lazy' default to the central Avatar component so all off-screen
avatars (chat list, friends list, popovers, message senders) skip eager
Supabase Storage fetches; set loading='eager' on ConversationHeader (active
conv header) and CallParticipantTile inline imgs (both AudioContent and
VideoStub) which are always above-the-fold when visible.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/desktop/src/components/Avatar.tsx

@@ -11,6 +11,11 @@ interface Props {
   // brand-tinted fallback; callers can override (e.g. to colour-by-id).
   fallbackClass?: string;
   alt?: string;
+  // Browser loading hint. Use 'eager' for above-the-fold avatars (e.g. the
+  // active conversation header, call tiles). Defaults to 'lazy' so off-screen
+  // avatars (chat list rows, friends list, popovers) don't hammer Supabase
+  // Storage on initial render.
+  loading?: 'eager' | 'lazy';
 }
 
 export function Avatar({
@@ -19,6 +24,7 @@ export function Avatar({
   className = 'h-10 w-10',
   fallbackClass = 'bg-accent/20 text-accent',
   alt,
+  loading = 'lazy',
 }: Props) {
   const effectiveUrl = useCachedAvatarUrl(url);
   if (effectiveUrl) {
@@ -28,6 +34,7 @@ export function Avatar({
         alt={alt ?? displayName ?? ''}
         className={'shrink-0 rounded-full object-cover ' + className}
         draggable={false}
+        loading={loading}
       />
     );
   }

apps/desktop/src/components/CallParticipantTile.tsx

@@ -291,6 +291,7 @@ function AudioContent({
             src={avatarUrl}
             alt=""
             className="relative h-full w-full rounded-full object-cover"
+            loading="eager"
           />
         ) : (
           <span
@@ -366,7 +367,7 @@ function VideoStub({
         }
       >
         {avatarUrl ? (
-          <img src={avatarUrl} alt="" className="h-full w-full rounded-full object-cover" />
+          <img src={avatarUrl} alt="" className="h-full w-full rounded-full object-cover" loading="eager" />
         ) : (
           letter
         )}

apps/desktop/src/components/ConversationHeader.tsx

@@ -129,9 +129,9 @@ function HeaderBar({
         className="relative shrink-0 rounded-full text-left transition enabled:cursor-pointer enabled:hover:ring-2 enabled:hover:ring-accent/50 focus:outline-none focus-visible:ring-2 focus-visible:ring-accent/50 disabled:cursor-default"
       >
         {isDm ? (
-          <Avatar url={peerAvatar} displayName={title} className="h-10 w-10 text-base" />
+          <Avatar url={peerAvatar} displayName={title} className="h-10 w-10 text-base" loading="eager" />
         ) : peerAvatar ? (
-          <Avatar url={peerAvatar} displayName={title} className="h-10 w-10 text-base" />
+          <Avatar url={peerAvatar} displayName={title} className="h-10 w-10 text-base" loading="eager" />
         ) : (
           <div className="flex h-10 w-10 items-center justify-center rounded-full bg-accent/20 text-accent">
             <UsersIcon className="h-5 w-5" />

apps/desktop/src/context/AuthContext.tsx

@@ -204,6 +204,14 @@ export function AuthProvider({ children }: { children: ReactNode }) {
     void registerWebPush(installId);
   }, [session]);
 
+  // Pre-warm Supabase: fires the first round-trip in the background so the
+  // first user-triggered query (e.g. loading conversations) doesn't pay
+  // the cold-connection latency.
+  useEffect(() => {
+    if (!session) return;
+    void supabase.from('profiles').select('id').limit(1).then(() => undefined);
+  }, [session]);
+
   // Phase 3: ensure this install owns exactly one devices row. The row is
   // pure session-list telemetry — it does not carry any cryptographic
   // material since the per-user-key refactor. We re-use the row across