feat: store problem letters as task_table_index for AOJ ICPC / JAG Prelim

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

@@ -81,8 +81,8 @@ Step 0 (seed check) is already done. Confirm the following before touching code:
 - [ ] Export `OLDEST_YEAR` / `LATEST_YEAR` constants. Use `super(contestType, String(param))` for unique provider key
 - [ ] Tests: `getSize() === LATEST - OLDEST + 1`, etc.
 - [ ] **RED** → implement → **GREEN**
-- [ ] If display label needed: use `getTaskLabels` — do NOT mutate title inside `generateTable` (optimistic update + `$derived` re-run causes prefix accumulation)
-- [ ] For AOJ-specific options (`getTaskLabels` / override map / `titleStyle` / `columnWrapThreshold`), see `aoj_icpc_providers.ts` / `aoj_jag_providers.ts`
+- [ ] If cells need an index prefix (e.g. `A. title`): set `isShownTaskIndex: true` so the cell builds it from `task_table_index` — do NOT mutate title inside `generateTable` (optimistic update + `$derived` re-run causes prefix accumulation)
+- [ ] For AOJ-specific options (`titleStyle` / `columnWrapThreshold`), see `aoj_icpc_providers.ts` / `aoj_jag_providers.ts`
 
 ---
 

.agents/skills/add-tasks/instructions.md

@@ -17,6 +17,7 @@
 - Source: `https://kenkoooo.com/atcoder/resources/problems.json`
 - atcoder.jp is unreachable and WebFetch truncates problems.json, so a miss there is not evidence of absence — ask the user to paste the rows
 - Use `id` / `problem_index` / `name` / `title` verbatim; do not derive `id` from contest_id
+- ICPC Prelim / ICPC Regional / JAG Prelim: set `problem_index` to the problem letter, not the AOJ problem id — A, B, C... in ascending problem id within the contest, as `assignProblemLetters` does on import. `seed_problem_letters.test.ts` checks this
 
 ## Tests
 

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

@@ -80,7 +80,7 @@ protected setFilterCondition(): (taskResult: TaskResult) => boolean {
 - 年度範囲定数（`OLDEST_YEAR` / `LATEST_YEAR`）を `export` してテストでも参照
 - グループ登録は最新年→古い年の降順（`addProvider` 順 = 表示順、先 = 上）
 
-AOJ/JAG 固有の詳細（`AOJ_LABEL_OVERRIDES`、`titleStyle`、同一年2回開催の `suffix` 分割など）は `aoj_icpc_providers.ts` / `aoj_jag_providers.ts` を参照。
+AOJ/JAG 固有の詳細（`titleStyle`、同一年2回開催の `suffix` 分割など）は `aoj_icpc_providers.ts` / `aoj_jag_providers.ts` を参照。
 
 ### 補足: 固定セクションによる同一 ContestType 内の共存
 

prisma/migrations/20261024033928_update_aoj_task_table_index/migration.sql

@@ -0,0 +1,33 @@
+-- Replace the AOJ problem id in task_table_index with the problem letter (A, B, C...)
+-- for ICPC Prelim / ICPC Regional / JAG Prelim.
+-- Basic rule: letters follow ascending problem id within each contest.
+-- JAG training camps (also AOJ_JAG) are out of scope and excluded by contest_id.
+
+-- (1) Build a task_id -> problem letter lookup table.
+WITH letters AS (
+  SELECT task_id,
+         chr(64 + row_number() OVER (
+           PARTITION BY contest_id      -- Restart numbering for each contest.
+           ORDER BY task_id::int        -- AOJ problem ids are numeric.
+         )::int) AS letter
+  FROM "task"
+  WHERE contest_type = 'AOJ_ICPC'
+     -- AOJ_JAG also covers training camps, so narrow it by contest_id.
+     OR (contest_type = 'AOJ_JAG' AND contest_id LIKE 'JAGPrelim%')
+)
+-- (2) Apply the lookup table to the task rows.
+UPDATE "task" AS t
+SET "task_table_index" = letters.letter
+FROM letters
+WHERE t."task_id" = letters.task_id
+  -- Redundant with the CTE filter, but keeps the blast radius fixed.
+  AND (
+    t."contest_type" = 'AOJ_ICPC'
+    OR (t."contest_type" = 'AOJ_JAG' AND t."contest_id" LIKE 'JAGPrelim%')
+  );
+
+-- Align the AOJ-KUPC2011 title with the plain AOJ title format.
+UPDATE "task"
+SET "title" = 'Mountain'
+WHERE "task_id" = '2279'
+  AND "title" = 'I. Mountain';