feat(contests): add GAME_24 contest to xDPC contest table group

.agents/skills/add-contest-table-provider/SKILL.md

@@ -8,6 +8,6 @@ Add a new contest table provider for: $ARGUMENTS
 
 > When in doubt at any step, use AskUserQuestion before proceeding.
 
-0. **Seed check** — grep `prisma/tasks.ts` for the contest_id(s); report count + task_ids; if absent or incomplete, ask the user to add missing rows (reference: `https://kenkoooo.com/atcoder/resources/problems.json`)
+0. **Seed check** — grep `prisma/tasks.ts` for the contest_id(s); report count + task_ids; if absent or incomplete, ask the user to paste the missing rows (source: `https://kenkoooo.com/atcoder/resources/problems.json`). Do not fetch it yourself: atcoder.jp is unreachable, and WebFetch truncates problems.json, so a miss there is not evidence of absence
 1. **Gather requirements** — infer the implementation pattern; confirm per [instructions.md §Requirements](instructions.md)
 2. **Implement** — follow [instructions.md](instructions.md) for the confirmed pattern across 5 layers (TDD)

.agents/skills/add-contest-table-provider/instructions.md

@@ -15,6 +15,7 @@ Step 0 (seed check) is already done. Confirm the following before touching code:
   - Pattern 2: single fixed contest_id (e.g. NDPC, TDPC, FPS_24)
   - Pattern 3: multiple contest_ids unified in one table (e.g. ABS, ABC-Like)
   - Pattern 4: one class instantiated N times via constructor parameter (e.g. ICPC by year)
+- task_id format? Do not derive it from contest_id (`game-24` → `game_a`, but `fps-24` → `fps_24_a`)
 - Nearest neighbor ContestType for insertion order in `contestTypePriorities`?
 - New group or merge into existing? If new: group name / `buttonLabel` / `ariaLabel`?
 
@@ -32,7 +33,7 @@ Step 0 (seed check) is already done. Confirm the following before touching code:
 
 > Skip when an existing ContestType already covers this contest family (e.g. `AOJ_JAG` for JAG Prelim).
 
-- [ ] Add to `prisma/schema.prisma` ContestType enum → `pnpm exec prisma generate`
+- [ ] Add to `prisma/schema.prisma` ContestType enum → `pnpm exec prisma migrate dev --name add_<type>_to_contest_type` (also regenerates the client)
 - [ ] Add to `ContestType` in `src/lib/contests/types/contest.ts` (same position as schema)
 - [ ] `pnpm check` — confirm error resolved
 
@@ -51,7 +52,7 @@ Step 0 (seed check) is already done. Confirm the following before touching code:
 - [ ] `CONTEST_TYPES_BY_ID` or `CLASSIFICATION_RULES` in `src/lib/contests/utils/classification.ts`
 - [ ] `contestTypePriorities` in `src/lib/contests/utils/priority.ts`
   - After priority insertion, all later entries shift +1 → **update JSDoc numeric ranges** (4 category names are immutable)
-  - Fix hardcoded priority-diff expected values in `src/test/lib/utils/task.test.ts` (-1 per shifted entry)
+  - Fix hardcoded priority-diff expected values in `src/test/lib/utils/task.test.ts` only when they involve a shifted entry (±1 each)
 - [ ] `LABEL_GENERATORS` in `src/lib/contests/utils/labels/index.ts` (add label generator, create per-type file if complex)
 - [ ] **GREEN**
 

docs/guides/agent-rules/prisma-db.md

@@ -13,6 +13,7 @@ paths:
 
 1. Edit `prisma/schema.prisma`
 2. Run `pnpm exec prisma migrate dev --name <snake_case_description>`
+3. Production needs no manual step: CI (`.github/workflows/ci.yml`) runs `prisma migrate deploy` on push to `main`, before deploying. Do not add a manual deploy step to plans
 
 ## Naming
 
@@ -21,7 +22,6 @@ paths:
 ## Server-Only Code
 
 - Import the DB client (`$lib/server/database`) only in `src/lib/server/**` and in server-only services under `src/lib/services/**` and `src/features/**/services/**`
-- Route handlers must not import the DB client directly — call service methods instead
 - Never import server-only code in client components
 
 ## Service Layer

docs/guides/agent-rules/svelte-components.md

@@ -26,6 +26,7 @@ Use `$props()`, `$state()`, `$derived()`, `$effect()` in all components:
 
 - Components: `PascalCase.svelte`
 - Stores: `snake_case.svelte.ts`; class-based with `$state()`, singleton export
+- Values persisted to `localStorage` or URL params are a contract: rename display labels freely, but changing a stored key/value (e.g. preset key `dps`) silently drops users' saved state
 
 ## Props & Reactivity
 
@@ -37,7 +38,7 @@ Use `$props()`, `$state()`, `$derived()`, `$effect()` in all components:
 ## `{#each}` Patterns
 
 - Always key: `(item.id)` or `(i)`
-- **Key MUST be unique per iteration** — if domain allows duplicates, use composite key (e.g. `contest_id + '-' + task_id`)
+- **Key MUST be unique per iteration** — if domain allows duplicates, use composite key. Trap: `task_id` alone repeats when a task appears in multiple contests; use `contest_id + '-' + task_id` (#3460, #3442)
 - `(i)` is only safe when the list's order and length never change (e.g. a fixed split of a string into lines). For a mutable list — reorderable, insertable, or deletable — use a persistent unique ID or composite key; `(i)` there causes Svelte to reuse DOM/state across the wrong items after a mutation.
 - Filter **before**, not inside with `{#if}`
 - Use `{:else}` for empty lists
@@ -50,8 +51,6 @@ Use `$props()`, `$state()`, `$derived()`, `$effect()` in all components:
 {/each}
 ```
 
-**Common Trap:** `task_id` alone is NOT unique when same task appears in multiple contests. Use `contest_id + '-' + task_id` as composite key (see issue #3460 & PR #3442).
-
 ## Snippets vs Components
 
 - **Snippet**: needs `$state` access, pure display, same-file; params require explicit type `{#snippet label(item: Item)}`

docs/guides/agent-rules/testing.md

@@ -37,7 +37,7 @@ paths:
 - Enum membership: `Object.hasOwn(Enum, value)`, not `in` (avoids prototype chain)
 - `Promise<void>`: use `await fn()` to assert no throw, or `.resolves.toBeUndefined()`. **Never** bare `.resolves` (false-positive)
 - **Stubs**: parameter types must match production signature — use domain types (`TaskGrade`), not `string`
-- **Test data**: realistic values (real task IDs, grade names). Extract shared fixtures to file/describe scope; inline for single-use
+- **Test data**: realistic values (real task IDs, grade names). Extract shared fixtures to file/describe scope; inline for single-use. When copying a neighbor's tests, grep each fixture/helper's usages first — do not replicate unreferenced ones
 - **Registry exhaustiveness**: `Record<string, T>` and `new Map([...])` give no compile-time enum coverage — assert it at runtime, with a named, commented exception list so deliberate gaps stay documented: `expect(Object.values(Enum).filter((key) => !REGISTRY.has(key))).toEqual(KNOWN_GAPS)` (`Record` registries: swap `REGISTRY.has(key)` for the `Object.hasOwn` form above)
 - **Test count as a proxy**: after a file split, compare counts (`--reporter=verbose`) — a drop means a describe block was lost in the move. A deliberate drop is valid only when mutation analysis shows detection is unchanged; record the evidence in the commit
 

docs/guides/how-to-add-contest-table-provider.md

@@ -115,12 +115,15 @@ AOJ/JAG 固有の詳細（`AOJ_LABEL_OVERRIDES`、`titleStyle`、同一年2回
 | TDPC                        | `'tdpc'`                | 26問   | A～Z         |
 | NDPC                        | `'ndpc'`                | 20問   | A～T         |
 | FPS_24                      | `'fps-24'`              | 24問   | A～X         |
+| GAME_24‡                    | `'game-24'`             | 24問   | A～X         |
 | ACL_PRACTICE                | `'practice2'`           | 12問   | A～L         |
 | ACL_BEGINNER / ACL_CONTEST1 | `'abl'`/`'acl1'`        | 6問    | A～F         |
 | AWC0100 / AWC0150†          | `'awc0100'`/`'awc0150'` | 15問   | A～O         |
 
 †注: ContestType.AWC を再利用し、section（`'0100'`, `'0150'`, `'0151Onwards'`）で provider key を一意化。ACL 系は `Acl` グループ、DP 系は `dps` グループで統一管理。
 
+‡注: task_id は `game_a`〜`game_x` で、contest_id の数字を含まない（`fps-24` は `fps_24_a`）。
+
 ### コンストラクタパラメータ型 / regex フィルタ型
 
 | コンテスト      | フィルタ方式    | 備考                                   |

e2e/problems_contest_table.spec.ts

@@ -0,0 +1,21 @@
+import { expect, test } from '@playwright/test';
+
+const XDPC_GROUP_ARIA_LABEL = 'xDPC and x 24 contests';
+const XDPC_GROUP_TABLE_TITLES = [
+  'Educational DP Contest / DP まとめコンテスト',
+  'Typical DP Contest',
+  'Next DP Contest',
+  'FPS 24 題',
+  '組合せゲーム 24 題',
+];
+
+test.describe('xDPC group in contest table', () => {
+  test('shows Game 24 table right after FPS 24 in the xDPC group', async ({ page }) => {
+    await page.goto('/problems');
+
+    await page.getByRole('button', { name: XDPC_GROUP_ARIA_LABEL }).click();
+
+    // Headings render even when the seed has no tasks for a provider, so this stays seed-independent.
+    await expect(page.getByRole('heading', { level: 2 })).toHaveText(XDPC_GROUP_TABLE_TITLES);
+  });
+});

prisma/migrations/20261006125938_add_game_24_to_contest_type/migration.sql

@@ -0,0 +1,2 @@
+-- AlterEnum
+ALTER TYPE "ContestType" ADD VALUE 'GAME_24';

prisma/schema.prisma

@@ -314,6 +314,7 @@ enum ContestType {
   AWC // AtCoder Weekday Contest
   UNIVERSITY // University Programming Contests in AtCoder (e.g., UTPC)
   FPS_24 // 24 Problems on Formal Power Series
+  GAME_24 // 24 Problems on Combinatorial Games
   ATCODER_MAIN_OFFICIAL_ONSITE // AtCoder World Tour Finals (official onsite finals)
   OTHERS // AtCoder (その他)
   AOJ_COURSES // AIZU ONLINE JUDGE Courses

prisma/tasks.ts

@@ -8809,6 +8809,174 @@ export const tasks = [
     name: 'Bacteria Growth Experiment',
     title: 'A. Bacteria Growth Experiment',
   },
+  {
+    id: 'game_x',
+    contest_id: 'game-24',
+    problem_index: 'X',
+    name: 'XOR Bag',
+    title: 'X. XOR Bag',
+  },
+  {
+    id: 'game_w',
+    contest_id: 'game-24',
+    problem_index: 'W',
+    name: 'Parity Game',
+    title: 'W. Parity Game',
+  },
+  {
+    id: 'game_v',
+    contest_id: 'game-24',
+    problem_index: 'V',
+    name: 'Delete Game',
+    title: 'V. Delete Game',
+  },
+  {
+    id: 'game_u',
+    contest_id: 'game-24',
+    problem_index: 'U',
+    name: 'Rectangle Flip Game',
+    title: 'U. Rectangle Flip Game',
+  },
+  {
+    id: 'game_t',
+    contest_id: 'game-24',
+    problem_index: 'T',
+    name: 'Consecutive Move Game',
+    title: 'T. Consecutive Move Game',
+  },
+  {
+    id: 'game_s',
+    contest_id: 'game-24',
+    problem_index: 'S',
+    name: 'Odd and Even',
+    title: 'S. Odd and Even',
+  },
+  {
+    id: 'game_r',
+    contest_id: 'game-24',
+    problem_index: 'R',
+    name: 'Delete and Divide',
+    title: 'R. Delete and Divide',
+  },
+  {
+    id: 'game_q',
+    contest_id: 'game-24',
+    problem_index: 'Q',
+    name: 'Moving Pieces on Graph',
+    title: 'Q. Moving Pieces on Graph',
+  },
+  {
+    id: 'game_p',
+    contest_id: 'game-24',
+    problem_index: 'P',
+    name: 'Game on Tree',
+    title: 'P. Game on Tree',
+  },
+  {
+    id: 'game_o',
+    contest_id: 'game-24',
+    problem_index: 'O',
+    name: 'Moving Pieces on Grid',
+    title: 'O. Moving Pieces on Grid',
+  },
+  {
+    id: 'game_n',
+    contest_id: 'game-24',
+    problem_index: 'N',
+    name: 'One and All',
+    title: 'N. One and All',
+  },
+  {
+    id: 'game_m',
+    contest_id: 'game-24',
+    problem_index: 'M',
+    name: 'LRUD Game',
+    title: 'M. LRUD Game',
+  },
+  {
+    id: 'game_l',
+    contest_id: 'game-24',
+    problem_index: 'L',
+    name: 'Unfair Nim',
+    title: 'L. Unfair Nim',
+  },
+  {
+    id: 'game_k',
+    contest_id: 'game-24',
+    problem_index: 'K',
+    name: 'Domino in Tetromino 2',
+    title: 'K. Domino in Tetromino 2',
+  },
+  {
+    id: 'game_j',
+    contest_id: 'game-24',
+    problem_index: 'J',
+    name: 'Restricted Nim 2',
+    title: 'J. Restricted Nim 2',
+  },
+  {
+    id: 'game_i',
+    contest_id: 'game-24',
+    problem_index: 'I',
+    name: 'Necklace 2',
+    title: 'I. Necklace 2',
+  },
+  {
+    id: 'game_h',
+    contest_id: 'game-24',
+    problem_index: 'H',
+    name: 'Lexicographic Order Game',
+    title: 'H. Lexicographic Order Game',
+  },
+  {
+    id: 'game_g',
+    contest_id: 'game-24',
+    problem_index: 'G',
+    name: 'Round Nim',
+    title: 'G. Round Nim',
+  },
+  {
+    id: 'game_f',
+    contest_id: 'game-24',
+    problem_index: 'F',
+    name: 'Necklace 1',
+    title: 'F. Necklace 1',
+  },
+  {
+    id: 'game_e',
+    contest_id: 'game-24',
+    problem_index: 'E',
+    name: 'Restricted Nim 1',
+    title: 'E. Restricted Nim 1',
+  },
+  {
+    id: 'game_d',
+    contest_id: 'game-24',
+    problem_index: 'D',
+    name: 'Parallel Nim',
+    title: 'D. Parallel Nim',
+  },
+  {
+    id: 'game_c',
+    contest_id: 'game-24',
+    problem_index: 'C',
+    name: 'Domino in Tetromino 1',
+    title: 'C. Domino in Tetromino 1',
+  },
+  {
+    id: 'game_b',
+    contest_id: 'game-24',
+    problem_index: 'B',
+    name: 'Chocolate',
+    title: 'B. Chocolate',
+  },
+  {
+    id: 'game_a',
+    contest_id: 'game-24',
+    problem_index: 'A',
+    name: 'Nim',
+    title: 'A. Nim',
+  },
   {
     id: 'fps_24_x',
     contest_id: 'fps-24',

src/features/tasks/utils/contest-table/contest_table_provider_groups.test.ts

@@ -168,21 +168,22 @@ describe('prepareContestProviderPresets', () => {
       }
     });
 
-    test('dps registers EDPC, TDPC, NDPC, and FPS 24 providers', () => {
+    test('dps registers EDPC, TDPC, NDPC, FPS 24, and Game 24 providers', () => {
       const group = presets.dps();
 
-      expect(group.getGroupName()).toBe('xDPC・FPS 24');
+      expect(group.getGroupName()).toBe('xDPC・x 24 題');
       expect(group.getMetadata()).toEqual({
-        buttonLabel: 'xDPC・FPS 24',
-        ariaLabel: 'xDPC and FPS 24 contests',
+        buttonLabel: 'xDPC・x 24 題',
+        ariaLabel: 'xDPC and x 24 contests',
       });
-      expect(group.getSize()).toBe(4);
+      expect(group.getSize()).toBe(5);
 
       const contestTypes = [
         ContestType.EDPC,
         ContestType.TDPC,
         ContestType.NDPC,
         ContestType.FPS_24,
+        ContestType.GAME_24,
       ];
 
       for (const contestType of contestTypes) {

src/features/tasks/utils/contest-table/contest_table_provider_groups.ts

@@ -25,6 +25,7 @@ import {
 import { MathAndAlgorithmProvider } from './math_and_algorithm_provider';
 import { EDPCProvider, TDPCProvider, NDPCProvider } from './dp_providers';
 import { FPS24Provider } from './fps24_provider';
+import { Game24Provider } from './game24_provider';
 import { ACLPracticeProvider, ACLBeginnerProvider, ACLProvider } from './acl_providers';
 import {
   JOIFirstQualRoundProvider,
@@ -239,17 +240,18 @@ export const prepareContestProviderPresets = () => {
       }).addProvider(new MathAndAlgorithmProvider(ContestType.MATH_AND_ALGORITHM)),
 
     /**
-     * DP group (EDPC, TDPC, NDPC, and FPS 24)
+     * DP group (EDPC, TDPC, NDPC, FPS 24, and Game 24)
      */
     dps: () =>
-      new ContestTableProviderGroup(`xDPC・FPS 24`, {
-        buttonLabel: 'xDPC・FPS 24',
-        ariaLabel: 'xDPC and FPS 24 contests',
+      new ContestTableProviderGroup(`xDPC・x 24 題`, {
+        buttonLabel: 'xDPC・x 24 題',
+        ariaLabel: 'xDPC and x 24 contests',
       }).addProviders(
         new EDPCProvider(ContestType.EDPC),
         new TDPCProvider(ContestType.TDPC),
         new NDPCProvider(ContestType.NDPC),
         new FPS24Provider(ContestType.FPS_24),
+        new Game24Provider(ContestType.GAME_24),
       ),
 
     /**