refactor(deck): useDeckDetail + DeckDetailView (Brief 3)

Extract detail page state into useDeckDetail and layout into DeckDetailView;
pages/deck/[id].js is a thin loading/not-found gated composer.

Co-authored-by: Cursor <cursoragent@cursor.com>

components/DeckDetailView.js

@@ -0,0 +1,75 @@
+import Link from 'next/link';
+import DeckDetailCardList from './DeckDetailCardList';
+import DeckDetailStatsSidebar from './DeckDetailStatsSidebar';
+import { Button } from './ui';
+import { getDeckFormatIcon } from '../lib/deck-format-utils.js';
+
+export default function DeckDetailView({
+  deck,
+  groupBy,
+  groupedCards,
+  isOwner,
+  setGroupBy,
+  stats,
+}) {
+  return (
+    <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 py-8">
+      <div className="flex justify-between items-start mb-8">
+        <div>
+          <div className="flex items-center space-x-3 mb-2">
+            <Link
+              href="/decks"
+              className="hover:underline"
+              style={{ color: 'var(--accent-ember)' }}
+            >
+              ← Back to Decks
+            </Link>
+          </div>
+          <div className="flex items-center space-x-3 mb-2">
+            <span className="text-3xl">{getDeckFormatIcon(deck.format)}</span>
+            <h1 className="text-3xl font-bold" style={{ color: 'var(--text-primary)' }}>
+              {deck.name}
+            </h1>
+            {deck.is_public && (
+              <span
+                className="px-2 py-1 rounded-full text-xs font-medium"
+                style={{
+                  backgroundColor: 'var(--bg-tertiary)',
+                  color: 'var(--accent-ember)',
+                }}
+              >
+                Public
+              </span>
+            )}
+          </div>
+          <p className="mb-2" style={{ color: 'var(--text-secondary)' }}>
+            by {deck.creator_username} • {deck.format} • {stats.totalCards} cards
+          </p>
+          {deck.description && (
+            <p className="max-w-2xl" style={{ color: 'var(--text-secondary)' }}>
+              {deck.description}
+            </p>
+          )}
+        </div>
+
+        {isOwner && (
+          <div className="flex space-x-3">
+            <Link href={`/deck-builder?deck=${deck.id}`}>
+              <Button variant="primary">Edit Deck</Button>
+            </Link>
+          </div>
+        )}
+      </div>
+
+      <div className="grid grid-cols-1 lg:grid-cols-4 gap-6">
+        <DeckDetailStatsSidebar
+          deck={deck}
+          stats={stats}
+          groupBy={groupBy}
+          onGroupByChange={setGroupBy}
+        />
+        <DeckDetailCardList cards={deck.cards} groupedCards={groupedCards} />
+      </div>
+    </div>
+  );
+}

lib/use-deck-detail.js

@@ -0,0 +1,74 @@
+import { useState, useEffect, useMemo } from 'react';
+import { useRouter } from 'next/router';
+import { computeDeckStats } from './deck-builder-stats.js';
+import { groupDeckCards } from './deck-detail-grouping.js';
+
+/**
+ * Deck detail page state and derived data (god-component split).
+ */
+export function useDeckDetail({ user = null, authLoading = true } = {}) {
+  const router = useRouter();
+  const { id: deckId } = router.query;
+
+  const [deck, setDeck] = useState(null);
+  const [loading, setLoading] = useState(true);
+  const [groupBy, setGroupBy] = useState('type');
+
+  const fetchDeck = async () => {
+    try {
+      const token = localStorage.getItem('auth_token');
+      const headers = token ? { Authorization: `Bearer ${token}` } : {};
+
+      const response = await fetch(`/api/decks/${deckId}`, { headers });
+
+      if (response.ok) {
+        const data = await response.json();
+        setDeck(data);
+      } else {
+        console.error('Failed to fetch deck');
+        router.push('/decks');
+      }
+    } catch (error) {
+      console.error('Error fetching deck:', error);
+      router.push('/decks');
+    } finally {
+      setLoading(false);
+    }
+  };
+
+  useEffect(() => {
+    if (deckId) {
+      // eslint-disable-next-line react-hooks/set-state-in-effect -- load deck when route id changes
+      fetchDeck();
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps -- refetch when route deck id changes
+  }, [deckId]);
+
+  const stats = useMemo(
+    () => (deck ? computeDeckStats(deck.cards || []) : null),
+    [deck]
+  );
+
+  const groupedCards = useMemo(
+    () => (deck ? groupDeckCards(deck.cards, groupBy) : {}),
+    [deck, groupBy]
+  );
+
+  const isOwner = Boolean(user && deck && deck.user_id === user.userId);
+  const showDeckLoading = loading;
+  const showDeckNotFound = !loading && !deck;
+
+  return {
+    authLoading,
+    deck,
+    deckId,
+    groupBy,
+    groupedCards,
+    isOwner,
+    setGroupBy,
+    showDeckLoading,
+    showDeckNotFound,
+    stats,
+    user,
+  };
+}

pages/deck/[id].js

@@ -1,63 +1,14 @@
-import { useState, useEffect } from 'react';
-import { useRouter } from 'next/router';
 import Link from 'next/link';
 import Layout from '../../components/Layout';
-import DeckDetailCardList from '../../components/DeckDetailCardList';
+import DeckDetailView from '../../components/DeckDetailView';
-import DeckDetailStatsSidebar from '../../components/DeckDetailStatsSidebar';
-import { Button } from '../../components/ui';
-import { computeDeckStats } from '../../lib/deck-builder-stats.js';
-import { groupDeckCards } from '../../lib/deck-detail-grouping.js';
-import { getDeckFormatIcon } from '../../lib/deck-format-utils.js';
 import { useAuth } from '../../lib/use-auth';
-
+import { useDeckDetail } from '../../lib/use-deck-detail.js';
-/* 2026-06-04 design-sweep pass: this page used the broken Tailwind
-   token classes (bg-bg-*, text-text-*, bg-accent-ember,
-   hover:bg-accent-ember-dark, border-accent-ember) that don't
-   resolve in tailwind.config.js. Sweep replaces them with inline
-   CSS variables + Button primitive + glass-panel surface + the
-   nav-item-active / nav-item-hover utilities so the page renders
-   with the Liquid Glass design system. */
 
 export default function DeckDetail() {
-  const { user } = useAuth();
+  const { user, loading: authLoading } = useAuth();
-  const router = useRouter();
+  const detail = useDeckDetail({ user, authLoading });
-  const { id: deckId } = router.query;
 
-  const [deck, setDeck] = useState(null);
+  if (detail.showDeckLoading) {
-  const [loading, setLoading] = useState(true);
-  const [groupBy, setGroupBy] = useState('type');
-
-  const fetchDeck = async () => {
-    try {
-      const token = localStorage.getItem('auth_token');
-      const headers = token ? { 'Authorization': `Bearer ${token}` } : {};
-      
-      const response = await fetch(`/api/decks/${deckId}`, { headers });
-
-      if (response.ok) {
-        const data = await response.json();
-        setDeck(data);
-      } else {
-        console.error('Failed to fetch deck');
-        router.push('/decks');
-      }
-    } catch (error) {
-      console.error('Error fetching deck:', error);
-      router.push('/decks');
-    } finally {
-      setLoading(false);
-    }
-  }
-
-  useEffect(() => {
-    if (deckId) {
-      // eslint-disable-next-line react-hooks/set-state-in-effect -- load deck when route id changes
-      fetchDeck();
-    }
-    // eslint-disable-next-line react-hooks/exhaustive-deps -- refetch when route deck id changes
-  }, [deckId]);
-
-  if (loading) {
     return (
       <Layout user={user}>
         <div className="flex items-center justify-center min-h-screen">
@@ -70,15 +21,12 @@ export default function DeckDetail() {
     );
   }
 
-  if (!deck) {
+  if (detail.showDeckNotFound) {
     return (
       <Layout user={user}>
         <div className="flex items-center justify-center min-h-screen">
           <div className="text-center">
-            <h1
+            <h1 className="text-2xl font-bold mb-4" style={{ color: 'var(--text-primary)' }}>
-              className="text-2xl font-bold mb-4"
-              style={{ color: 'var(--text-primary)' }}
-            >
               Deck not found
             </h1>
             <Link
@@ -94,78 +42,9 @@ export default function DeckDetail() {
     );
   }
 
-  const stats = computeDeckStats(deck.cards || []);
-  const groupedCards = groupDeckCards(deck.cards, groupBy);
-  const isOwner = user && deck.user_id === user.userId;
-
   return (
     <Layout user={user}>
-      <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 py-8">
+      <DeckDetailView {...detail} />
-        {/* Header */}
-        <div className="flex justify-between items-start mb-8">
-          <div>
-            <div className="flex items-center space-x-3 mb-2">
-              <Link
-                href="/decks"
-                className="hover:underline"
-                style={{ color: 'var(--accent-ember)' }}
-              >
-                ← Back to Decks
-              </Link>
-            </div>
-            <div className="flex items-center space-x-3 mb-2">
-              <span className="text-3xl">{getDeckFormatIcon(deck.format)}</span>
-              <h1
-                className="text-3xl font-bold"
-                style={{ color: 'var(--text-primary)' }}
-              >
-                {deck.name}
-              </h1>
-              {deck.is_public && (
-                <span
-                  className="px-2 py-1 rounded-full text-xs font-medium"
-                  style={{
-                    backgroundColor: 'var(--bg-tertiary)',
-                    color: 'var(--accent-ember)',
-                  }}
-                >
-                  Public
-                </span>
-              )}
-            </div>
-            <p className="mb-2" style={{ color: 'var(--text-secondary)' }}>
-              by {deck.creator_username} • {deck.format} • {stats.totalCards} cards
-            </p>
-            {deck.description && (
-              <p
-                className="max-w-2xl"
-                style={{ color: 'var(--text-secondary)' }}
-              >
-                {deck.description}
-              </p>
-            )}
-          </div>
-
-          {isOwner && (
-            <div className="flex space-x-3">
-              <Link href={`/deck-builder?deck=${deck.id}`}>
-                <Button variant="primary">Edit Deck</Button>
-              </Link>
-            </div>
-          )}
-        </div>
-
-        <div className="grid grid-cols-1 lg:grid-cols-4 gap-6">
-          <DeckDetailStatsSidebar
-            deck={deck}
-            stats={stats}
-            groupBy={groupBy}
-            onGroupByChange={setGroupBy}
-          />
-
-          <DeckDetailCardList cards={deck.cards} groupedCards={groupedCards} />
-        </div>
-      </div>
     </Layout>
   );
 }