feat(call): introduce StageLayout discriminated union

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

apps/desktop/src/components/InCallPanel.tsx

@@ -294,12 +294,35 @@ export function InCallPanel({ conversation }: Props) {
             ? t('app:call.waiting_for_peers', { defaultValue: 'Warte auf andere…' })
             : t('app:call.connected');
 
-  // Screen shares no longer auto-promote — the user opts in by clicking the
-  // "Bildschirm anschauen" overlay, which also toggles whether the audio
-  // plays. Focus falls back to the first tile so focus-mode always has
-  // something to show when no tile was explicitly picked.
-  const effectiveFocusedId = focusedId ?? tiles[0]?.id ?? null;
-  const speaker = tiles.find((p) => p.id === effectiveFocusedId) ?? tiles[0];
+  // Discord-style precedence:
+  //   1. focusedId set         → 'focus', that tile is the stage.
+  //   2. ≥2 shares, no pin     → 'bento', shares fill the stage, webcams strip.
+  //   3. exactly 1 share, no pin → 'focus' (auto-promote share).
+  //   4. no shares, no pin     → 'equal-grid'.
+  type StageLayout =
+    | { kind: 'equal-grid' }
+    | { kind: 'focus'; bigTileId: string }
+    | { kind: 'bento'; shareIds: string[] };
+
+  const shareIds = tiles.filter((t) => t.kind === 'screen').map((t) => t.id);
+  const stageLayout: StageLayout = (() => {
+    if (focusedId !== null && tiles.some((t) => t.id === focusedId)) {
+      return { kind: 'focus', bigTileId: focusedId };
+    }
+    if (shareIds.length >= 2) return { kind: 'bento', shareIds };
+    if (shareIds.length === 1 && shareIds[0]) {
+      return { kind: 'focus', bigTileId: shareIds[0] };
+    }
+    return { kind: 'equal-grid' };
+  })();
+
+  // Tile that owns the big stage when layout is 'focus'. Resolved lazily by
+  // callers below — kept here just so the speaker prop on CallStage/Fullscreen
+  // stays consistent with the layout decision.
+  const bigTile =
+    stageLayout.kind === 'focus'
+      ? tiles.find((t) => t.id === stageLayout.bigTileId)
+      : undefined;
 
   const controls = (
     <CallControls
@@ -369,13 +392,6 @@ export function InCallPanel({ conversation }: Props) {
     }));
 
   if (callMode === 'fullscreen') {
-    // Discord-style: without an explicit pin, fullscreen stays as a stable
-    // equal-size grid. Focus only kicks in when the user pins a tile
-    // (focusedId !== null). Auto-promoting the latest speaker caused the
-    // whole layout to flip on every utterance, which is not what users
-    // expect from a "cinema" view.
-    const hasFocus = focusedId !== null;
-    const effectiveSpeaker = hasFocus ? speaker : undefined;
     return (
       <>
         {micError && (
@@ -391,7 +407,7 @@ export function InCallPanel({ conversation }: Props) {
         )}
         <FullscreenCall
           tiles={tiles}
-          speaker={effectiveSpeaker}
+          speaker={bigTile}
           remoteScreenShares={remoteScreenShares}
           conversationMembers={conversation.members}
           activeSpeakers={activeSpeakers}
@@ -540,7 +556,7 @@ export function InCallPanel({ conversation }: Props) {
 
       <CallStage
         tiles={tiles}
-        speaker={speaker}
+        speaker={bigTile}
         mode={callMode}
         activeSpeakers={activeSpeakers}
         e2ee={isE2EEActive}