diff --git a/docs/tools/office.md b/docs/tools/office.md
index a72f0c9..2b810a6 100644
--- a/docs/tools/office.md
+++ b/docs/tools/office.md
@@ -65,12 +65,53 @@ ReadPdf({ path: "input/spec.pdf", query: "第\\d+条", query_mode: "regex" })
 ### ReadExcel
 
 ```js
-ReadExcel({ file_path: "input/data.xlsx" })
+ReadExcel({ path: "input/data.xlsx" })
 // → 全シートのセル内容をテキスト形式で返す
 ```
 
 巨大な Excel は token を食うので、シートを絞る場合は SplitExcelSheets を使う。
 
+#### include_styles — セル装飾の取得（オプション）
+
+```js
+ReadExcel({ path: "input/report.xlsx", include_styles: true })
+// → 値テーブルの後に ### Styles セクションが追記される
+```
+
+デフォルトは `false`（後方互換）。`include_styles: true` を指定すると、値テーブルの直後に各シートの `### Styles` セクションが出力される。
+
+**出力形式 — dedup legend + range map:**
+
+```
+### Styles — Sheet1
+s1 = fill:#FFF2CC;font:bold
+s2 = border:top(thin),bottom(double,#808080);numFmt:"0.00%"
+
+s1: A1:D1,A5:D5
+s2: B2
+merges: B2:D4
+```
+
+- **legend**: スタイル ID (`s1`, `s2`, ...) とそのシグネチャを列挙。シグネチャは `fill` / `font` / `border` / `numFmt` / `align` のうち非デフォルト部分を `;` 区切りで結合した文字列。
+- **range map**: 同一スタイルを持つセルを矩形にまとめて `A1:D3` 形式で列挙。単一セルは `A1`。
+- **merges**: 結合セル範囲の一覧（`ws.model.merges` から取得）。
+- **conditionalFormatting**: 条件付き書式が存在する場合 `present (effective styles not evaluated)` と表示（実際の表示色は評価しない）。
+- **装飾のみ・値なしセルも捕捉**: スタイルスキャンは `includeEmpty:true` で実行するため、値がなく書式だけ設定されたセルも対象に含まれる。
+- **`sheet`/`range` フィルタを尊重**: `include_styles` は値テーブルと同じ `sheet`/`range` フィルタでスキャン範囲を限定する。指定した範囲外のセルのスタイルと、範囲に交差しない結合セルは結果に含まれない。
+- **デフォルト色の省略**: デフォルト色 (theme index 1 = 通常黒) に明示設定したフォント色はデフォルト扱いで省略される。同様に border の theme index 0（自動色）も省略される。
+
+**テーマカラーの解決（ベストエフォート）:**
+
+テーマカラーはファイルの `theme1.xml` から読み取り、OOXML の lt/dk スワップを適用して `#RRGGBB` に解決する。解決できた場合は `theme(N,resolved=#RRGGBB)` の形式で表示し、`resolved=` は近似値であることに注意。テーマ XML が解析できない場合は `theme(N,tint=T)` のように生の参照のまま出力する。
+
+**max_style_ranges — range 数の上限:**
+
+`max_style_ranges`（デフォルト 250）で全シートを通じた range 出力数を制限する。上限に達した場合は `[styles truncated: max_style_ranges=N reached]` を表示し、以降のスタイルは省略される。値テーブルが先に出力されるため、スタイルセクションがトークン上限で切り捨てられても値は失われない。
+
+**編集には python + openpyxl を推奨:**
+
+ReadExcel はスタイルを読むだけで、書き込みは行わない。既存スタイルを保持したまま値を編集する場合は `Bash` ツールで python + openpyxl を使うこと（openpyxl は触れていないセルのスタイルを保持する）。
+
 ### ReadDocx
 
 ```js
diff --git a/pieces/game-tweet-generator.yaml b/pieces/game-tweet-generator.yaml
deleted file mode 100644
index ca692a1..0000000
--- a/pieces/game-tweet-generator.yaml
+++ /dev/null
@@ -1,86 +0,0 @@
-name: game-tweet-generator
-description: |
-  指定したゲームアカウントの X (Twitter) 投稿を調査し、その情報を元に特定の SNS アカウント（例: NFTGamerJP）風のツイート文章を生成する。
-  選ぶべき場合: 「ゲームの最新情報を調べて、こんな風にツイートして」と指示されたとき
-  選ぶべきでない場合: 一般的な SNS 調査のみ、またはツイート生成以外の目的
-triggers:
-  keywords:
-    - ゲームツイート作成
-    - ゲーム調査ツイート
-    - アカウント風ツイート
-    - ゲームアップデート調査
-    - ツイート文案作成
-max_movements: 1
-initial_movement: generate
-movements:
-  - name: generate
-    edit: true
-    persona: researcher_and_writer
-    instruction: |
-      AVAX に関連するゲームアカウントの X (Twitter) 投稿を調査し、その情報を元にターゲットアカウント（例: NFTGamerJP）風のツイート文章を生成する。
-
-      ## 関係するアカウント
-
-      - Off The Grid
-      - DeFi Kingdoms
-      - The Grotto
-      - Fort Block Games
-      - Beam
-
-      ## ワークフロー
-
-      1. **ゲームアカウントの特定**
-         - Task instruction から対象となるゲームアカウントを抽出する
-         - 複数アカウント指定がある場合は主要なアカウントを優先
-
-      2. **最新投稿の調査**
-         - XUserPosts で対象アカウントの最新投稿を取得し、直近 1 週間以内を重点的に確認
-         - アップデート情報・イベント告知・コミュニティ反応などを選定
-
-      3. **詳細調査**
-         - 重要な投稿は XPostDetail でスレッド文脈・リプライを確認
-         - ゲームの最新動向が不足する場合は WebSearch で補完
-
-      4. **ターゲットアカウントのスタイル分析**
-         - 指定されたターゲットアカウントの過去投稿を XUserPosts で取得し、以下を分析:
-           - 使用する絵文字の種類と配置
-           - 文中の装飾（改行・区切り線等）とハッシュタグのパターン
-           - 情報提供とエンターテインメントのバランス
-           - 投稿の長さと構成
-
-      5. **ツイート文章の生成**
-         - 調査したゲーム情報を元に、ターゲットアカウントのスタイルに合わせた文章を作成
-         - 重要なアップデート・イベント情報の要約、適切な絵文字、関連ハッシュタグを含める
-         - 短め（簡潔版）と詳細版など複数バリエーションを提示する
-
-      ## 原則
-
-      - 【必須】モデルの内部知識だけで情報を書かないこと。必ず実際のツイートデータを収集する
-      - 調査が一部失敗しても、取得できた情報で最善の提案を行う
-      - ターゲットアカウントのスタイルを参考にしつつ、情報に基づいた独自の文章を作ること（単なるコピーは不可）
-
-      ## 完了方法
-      この piece は単一 movement のため、終了は必ず `complete` ツールで行う。`transition` は使わない。
-
-      - **ツイート文章を生成できた場合**: `complete({status: "success", result: "生成したツイート文章（複数バリエーション含む）と、根拠となった調査結果のサマリ"})`
-        - `result` がそのままユーザーに表示される最終出力。短いメモではなく完成形を入れる
-      - **調査対象や目的が曖昧で確認が必要**: `complete({status: "needs_user_input", missing_info: "確認したい内容", why_no_default: "デフォルトで進められない理由"})`
-      - **技術的失敗で打ち切り**: `complete({status: "aborted", abort_reason: "失敗の理由"})`
-
-    allowed_tools:
-      - XSearch
-      - XUserPosts
-      - XPostDetail
-      - XFetchCardMedia
-      - WebSearch
-      - WebFetch
-      - Read
-      - Write
-      - Edit
-      - Glob
-      - Grep
-      - Bash
-      - 'mcp__*'
-    # default_next is the engine-internal fallback. Not exposed to the LLM.
-    default_next: COMPLETE
-    rules: []
diff --git a/src/bridge/local-tasks-api.test.ts b/src/bridge/local-tasks-api.test.ts
index 52e7783..1186afa 100644
--- a/src/bridge/local-tasks-api.test.ts
+++ b/src/bridge/local-tasks-api.test.ts
@@ -1,7 +1,7 @@
 import { describe, expect, it, beforeEach, afterEach } from 'vitest';
 import express from 'express';
 import request from 'supertest';
-import { mkdtempSync, rmSync } from 'fs';
+import { existsSync, mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'fs';
 import { join } from 'path';
 import { tmpdir } from 'os';
 import { Repository, localTaskRepoName } from '../db/repository.js';
@@ -911,3 +911,120 @@ describe('POST /api/local/tasks/:id/continue', () => {
     }
   });
 });
+
+// ---------------------------------------------------------------------------
+// Regression: /continue must accept pieces that exist ONLY in the task
+// owner's per-user dir.  The old pieceExists(name) callback never checked
+// that dir and always returned false → 400 piece_not_found for user-custom
+// pieces even though the worker would have loaded them successfully.
+// ---------------------------------------------------------------------------
+describe('POST /api/local/tasks/:id/continue — user-custom piece resolution', () => {
+  let tempDir = '';
+  let repo: Repository;
+  let app: express.Application;
+  let aliceUser: Express.User;
+
+  beforeEach(() => {
+    tempDir = mkdtempSync(join(tmpdir(), 'lt-ucpiece-'));
+    repo = new Repository(join(tempDir, 'db.sqlite'));
+    const real = repo.createUser({ email: 'uc@x.com', name: 'uc', role: 'user', status: 'active' });
+    aliceUser = {
+      ...real,
+      orgIds: [],
+      defaultVisibility: 'private',
+      defaultVisibilityOrgId: null,
+    };
+    app = express();
+    app.use(express.json());
+    app.use((req, _res, next) => {
+      (req as unknown as { user: Express.User }).user = aliceUser;
+      next();
+    });
+
+    // Simulate the server.ts pieceExists implementation:
+    //   per-user dir → (global-custom skipped here) → builtin dir.
+    const builtinDir = join(tempDir, 'pieces');
+    const userFolderRoot = join(tempDir, 'users');
+    mkdirSync(builtinDir, { recursive: true });
+    // 'manual-writer' only exists in the builtin dir (used for the starter job).
+    writeFileSync(
+      join(builtinDir, 'manual-writer.yaml'),
+      'name: manual-writer\nmovements: []\n',
+    );
+    // 'my-custom-piece' exists ONLY in Alice's per-user dir.
+    const userPiecesPath = join(userFolderRoot, aliceUser.id, 'pieces');
+    mkdirSync(userPiecesPath, { recursive: true });
+    writeFileSync(
+      join(userPiecesPath, 'my-custom-piece.yaml'),
+      'name: my-custom-piece\nmovements: []\n',
+    );
+
+    mountLocalTasksApi(app, {
+      repo,
+      worktreeDir: join(tempDir, 'workspaces'),
+      pieceExists: (name: string, ownerId?: string) => {
+        // Check owner's per-user dir first (mirrors worker resolution).
+        if (ownerId) {
+          if (existsSync(join(userFolderRoot, ownerId, 'pieces', `${name}.yaml`))) return true;
+        }
+        // Fall back to builtin dir.
+        return existsSync(join(builtinDir, `${name}.yaml`));
+      },
+    });
+  });
+
+  afterEach(() => {
+    repo.close();
+    rmSync(tempDir, { recursive: true, force: true });
+  });
+
+  it('accepts a piece that exists only in the owner per-user dir (regression: was 400)', async () => {
+    // Set up a task owned by alice with a terminal starter job.
+    const task = await repo.createLocalTask({
+      title: 't',
+      body: 'b',
+      pieceName: 'manual-writer',
+      ownerId: aliceUser.id,
+    });
+    const prev = await repo.createJob({
+      repo: localTaskRepoName(task.id),
+      issueNumber: task.id,
+      instruction: 'go',
+      pieceName: 'manual-writer',
+      ownerId: aliceUser.id,
+    });
+    await repo.updateJob(prev.id, { status: 'succeeded' });
+
+    // 'my-custom-piece' is ONLY in alice's per-user dir — should succeed.
+    const res = await request(app)
+      .post(`/api/local/tasks/${task.id}/continue`)
+      .send({ piece: 'my-custom-piece', instruction: 'continue with user-custom piece' });
+    expect(res.status).toBe(201);
+    expect(res.body.jobId).toBeTruthy();
+    const newJob = await repo.getJob(res.body.jobId);
+    expect(newJob?.pieceName).toBe('my-custom-piece');
+  });
+
+  it('rejects a piece that exists in neither builtin nor user-custom dir', async () => {
+    const task = await repo.createLocalTask({
+      title: 't',
+      body: 'b',
+      pieceName: 'manual-writer',
+      ownerId: aliceUser.id,
+    });
+    const prev = await repo.createJob({
+      repo: localTaskRepoName(task.id),
+      issueNumber: task.id,
+      instruction: 'go',
+      pieceName: 'manual-writer',
+      ownerId: aliceUser.id,
+    });
+    await repo.updateJob(prev.id, { status: 'succeeded' });
+
+    const res = await request(app)
+      .post(`/api/local/tasks/${task.id}/continue`)
+      .send({ piece: 'nonexistent-piece', instruction: 'go' });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toBe('piece_not_found');
+  });
+});
diff --git a/src/bridge/local-tasks-api.ts b/src/bridge/local-tasks-api.ts
index 20a4d4c..b72ee2b 100644
--- a/src/bridge/local-tasks-api.ts
+++ b/src/bridge/local-tasks-api.ts
@@ -18,8 +18,12 @@ export interface LocalTasksApiOptions {
    * Server-side validator for piece names accepted by the
    * /continue endpoint. Returns true if the piece is loadable.
    * When unset, /continue rejects all requests with 500 (misconfiguration).
+   *
+   * `ownerId` is the task owner's user id; when provided the implementation
+   * MUST also check the owner's per-user piece dir so that user-custom pieces
+   * are accepted (matching the resolution order the worker uses at run time).
    */
-  pieceExists?: (name: string) => boolean;
+  pieceExists?: (name: string, ownerId?: string) => boolean;
   /**
    * Optional. When set, accepting browserSessionProfileId on task create
    * verifies the profile belongs to the requesting user. Without it, the
@@ -506,7 +510,7 @@ export function mountLocalTasksApi(app: Application, opts: LocalTasksApiOptions)
         res.status(500).json({ error: 'piece_validation_unavailable' });
         return;
       }
-      if (!opts.pieceExists(piece)) {
+      if (!opts.pieceExists(piece, task?.ownerId ?? undefined)) {
         res.status(400).json({ error: 'piece_not_found', piece });
         return;
       }
diff --git a/src/bridge/pieces-api.test.ts b/src/bridge/pieces-api.test.ts
index 525d8db..b866873 100644
--- a/src/bridge/pieces-api.test.ts
+++ b/src/bridge/pieces-api.test.ts
@@ -1,7 +1,7 @@
 import { describe, it, expect, beforeEach } from 'vitest';
 import express from 'express';
 import request from 'supertest';
-import { mkdtempSync, writeFileSync, mkdirSync, existsSync } from 'fs';
+import { mkdtempSync, writeFileSync, mkdirSync, existsSync, readFileSync } from 'fs';
 import { join } from 'path';
 import { tmpdir } from 'os';
 import { mountPiecesApi } from './pieces-api.js';
@@ -295,13 +295,16 @@ describe('Pieces API (no auth — legacy behavior)', () => {
     expect(res.status).toBe(201);
   });
 
-  it('DELETE /api/pieces/:name deletes piece', async () => {
+  it('DELETE /api/pieces/:name — legacy no-auth pieces land in piecesDir (builtin source) and are non-deletable', async () => {
+    // In legacy no-auth mode with no customPiecesDir, POST writes to piecesDir.
+    // Those files are resolved as source='builtin' and are non-deletable.
     await request(app).post('/api/pieces').send({
       name: 'deleteme', description: 'x', max_movements: 1, initial_movement: 'a',
-      movements: [{ name: 'a', edit: false, persona: 'x', instruction: 'x', allowed_tools: [], rules: [] }],
+      movements: [{ name: 'a', edit: false, persona: 'x', instruction: 'x', allowed_tools: [], default_next: 'COMPLETE', rules: [] }],
     });
     const res = await request(app).delete('/api/pieces/deleteme');
-    expect(res.status).toBe(200);
+    expect(res.status).toBe(403);
+    expect(res.body.error).toMatch(/cannot delete a built-in/i);
   });
 
   it('DELETE /api/pieces/general is forbidden', async () => {
@@ -371,16 +374,21 @@ describe('Pieces API (auth-aware: per-user custom + write authz)', () => {
     expect(byName['bob-tool']).toBeUndefined();
   });
 
-  it("GET /api/pieces — user-custom shadows built-in with the same name", async () => {
+  it("GET /api/pieces — user-custom and built-in both appear when same name (no hiding)", async () => {
     mkdirSync(join(userPiecesRootDir, 'alice', 'pieces'), { recursive: true });
     writeFileSync(join(userPiecesRootDir, 'alice', 'pieces', 'general.yaml'), makeMinimalPieceYaml('general', 'alice override'));
 
     const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'alice', role: 'user' }))
       .get('/api/pieces');
     expect(res.status).toBe(200);
-    const general = res.body.pieces.find((p: any) => p.name === 'general');
-    expect(general.source).toBe('user-custom');
-    expect(general.description).toBe('alice override');
+    const generals = res.body.pieces.filter((p: any) => p.name === 'general');
+    // Both builtin and user-custom should appear
+    expect(generals).toHaveLength(2);
+    const customGeneral = generals.find((p: any) => p.source === 'user-custom');
+    const builtinGeneral = generals.find((p: any) => p.source === 'builtin');
+    expect(customGeneral).toBeDefined();
+    expect(customGeneral.description).toBe('alice override');
+    expect(builtinGeneral).toBeDefined();
   });
 
   it('POST /api/pieces creates a user-custom piece for non-admin caller', async () => {
@@ -399,7 +407,9 @@ describe('Pieces API (auth-aware: per-user custom + write authz)', () => {
     expect(existsSync(join(piecesDir, 'alice-custom.yaml'))).toBe(false);
   });
 
-  it('POST /api/pieces by admin writes to piecesDir (legacy behavior)', async () => {
+  it('POST /api/pieces by admin writes to user-custom dir (not piecesDir)', async () => {
+    // POST always targets user-custom dir regardless of admin role.
+    // Admins edit built-ins via PUT on existing ones.
     const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'admin1', role: 'admin' }))
       .post('/api/pieces')
       .send({
@@ -410,7 +420,9 @@ describe('Pieces API (auth-aware: per-user custom + write authz)', () => {
         movements: [{ name: 'only', edit: false, persona: 'p', instruction: 'i', allowed_tools: ['Read'], default_next: 'COMPLETE', rules: [] }],
       });
     expect(res.status).toBe(201);
-    expect(existsSync(join(piecesDir, 'admin-piece.yaml'))).toBe(true);
+    // Piece lands in admin's user-custom dir, NOT in piecesDir.
+    expect(existsSync(join(userPiecesRootDir, 'admin1', 'pieces', 'admin-piece.yaml'))).toBe(true);
+    expect(existsSync(join(piecesDir, 'admin-piece.yaml'))).toBe(false);
   });
 
   it('PUT /api/pieces/:name on built-in by non-admin returns 403', async () => {
@@ -479,10 +491,11 @@ describe('Pieces API (auth-aware: per-user custom + write authz)', () => {
     expect(existsSync(join(userPiecesRootDir, 'alice', 'pieces', 'goner.yaml'))).toBe(false);
   });
 
-  it('admin can edit and delete built-in pieces', async () => {
+  it('admin can edit built-in pieces (PUT 200) but NOT delete them (DELETE 403)', async () => {
     writeFileSync(join(piecesDir, 'admin-target.yaml'), makeMinimalPieceYaml('admin-target', 'before'));
     const adminApp = makeAuthApp(piecesDir, userPiecesRootDir, { id: 'admin1', role: 'admin' });
 
+    // Admin CAN edit (PUT) a built-in
     const putRes = await request(adminApp).put('/api/pieces/admin-target').send({
       name: 'admin-target',
       description: 'after',
@@ -492,8 +505,538 @@ describe('Pieces API (auth-aware: per-user custom + write authz)', () => {
     });
     expect(putRes.status).toBe(200);
 
+    // Admin CANNOT delete a built-in — 403 for everyone
     const delRes = await request(adminApp).delete('/api/pieces/admin-target');
-    expect(delRes.status).toBe(200);
-    expect(existsSync(join(piecesDir, 'admin-target.yaml'))).toBe(false);
+    expect(delRes.status).toBe(403);
+    expect(delRes.body.ok).toBe(false);
+    expect(delRes.body.error).toMatch(/cannot delete a built-in/i);
+    // File must still exist
+    expect(existsSync(join(piecesDir, 'admin-target.yaml'))).toBe(true);
+  });
+
+  // --- Task 2A: built-in must not be hidden by same-named custom ---
+  it("GET /api/pieces — built-in is NOT hidden when user has a same-named custom", async () => {
+    mkdirSync(join(userPiecesRootDir, 'alice', 'pieces'), { recursive: true });
+    writeFileSync(join(userPiecesRootDir, 'alice', 'pieces', 'chat.yaml'), makeMinimalPieceYaml('chat', 'alice chat override'));
+
+    const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'alice', role: 'user' }))
+      .get('/api/pieces');
+    expect(res.status).toBe(200);
+    // Both the user-custom AND the builtin should appear
+    const chatPieces = res.body.pieces.filter((p: any) => p.name === 'chat');
+    expect(chatPieces).toHaveLength(2);
+    const sources = chatPieces.map((p: any) => p.source).sort();
+    expect(sources).toEqual(['builtin', 'user-custom']);
+    // Custom has the custom description, builtin has the original
+    const customChat = chatPieces.find((p: any) => p.source === 'user-custom');
+    const builtinChat = chatPieces.find((p: any) => p.source === 'builtin');
+    expect(customChat.description).toBe('alice chat override');
+    expect(builtinChat.description).toBe('built-in chat');
+  });
+
+  // --- Task 2B: CreatePiece rejects name collision with built-in ---
+  it('POST /api/pieces rejects custom creation with a built-in name', async () => {
+    // 'general' and 'chat' are in piecesDir (built-in)
+    const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'alice', role: 'user' }))
+      .post('/api/pieces')
+      .send({
+        name: 'chat',
+        description: 'my chat',
+        max_movements: 1,
+        initial_movement: 'only',
+        movements: [{ name: 'only', edit: false, persona: 'p', instruction: 'i', allowed_tools: ['Read'], default_next: 'COMPLETE', rules: [] }],
+      });
+    expect(res.status).toBe(409);
+    expect(res.body.error).toMatch(/built-in/i);
+  });
+
+  it('POST /api/pieces with a fresh custom name still works for non-admin', async () => {
+    const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'alice', role: 'user' }))
+      .post('/api/pieces')
+      .send({
+        name: 'fresh-custom',
+        description: 'fresh',
+        max_movements: 1,
+        initial_movement: 'only',
+        movements: [{ name: 'only', edit: false, persona: 'p', instruction: 'i', allowed_tools: ['Read'], default_next: 'COMPLETE', rules: [] }],
+      });
+    expect(res.status).toBe(201);
+  });
+
+  // --- Task 2C: regression — non-admin DELETE of built-in → 403 ---
+  it('non-admin DELETE of built-in returns 403', async () => {
+    writeFileSync(join(piecesDir, 'deletable-builtin.yaml'), makeMinimalPieceYaml('deletable-builtin', 'del'));
+    const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'alice', role: 'user' }))
+      .delete('/api/pieces/deletable-builtin');
+    expect(res.status).toBe(403);
+    expect(existsSync(join(piecesDir, 'deletable-builtin.yaml'))).toBe(true);
+  });
+
+  // --- Fix 2: GET /api/pieces/:name?source=builtin fetches the specific source ---
+  it('GET /api/pieces/:name?source=builtin returns builtin even when user-custom exists with same name', async () => {
+    // Alice has a user-custom 'chat' that overrides by default priority
+    mkdirSync(join(userPiecesRootDir, 'alice', 'pieces'), { recursive: true });
+    writeFileSync(join(userPiecesRootDir, 'alice', 'pieces', 'chat.yaml'), makeMinimalPieceYaml('chat', 'alice custom chat'));
+
+    const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'alice', role: 'user' }))
+      .get('/api/pieces/chat?source=builtin');
+    expect(res.status).toBe(200);
+    expect(res.body.source).toBe('builtin');
+    expect(res.body.piece.description).toBe('built-in chat');
+  });
+
+  it('GET /api/pieces/:name without ?source uses priority resolution (user-custom first)', async () => {
+    mkdirSync(join(userPiecesRootDir, 'alice', 'pieces'), { recursive: true });
+    writeFileSync(join(userPiecesRootDir, 'alice', 'pieces', 'chat.yaml'), makeMinimalPieceYaml('chat', 'alice custom chat'));
+
+    const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'alice', role: 'user' }))
+      .get('/api/pieces/chat');
+    expect(res.status).toBe(200);
+    expect(res.body.source).toBe('user-custom');
+    expect(res.body.piece.description).toBe('alice custom chat');
+  });
+
+  // --- Fix 3: DELETE of a user-custom named 'chat' by its owner must succeed ---
+  it("DELETE /api/pieces/chat on owner's user-custom named 'chat' returns 200 (guard only blocks builtin)", async () => {
+    mkdirSync(join(userPiecesRootDir, 'alice', 'pieces'), { recursive: true });
+    writeFileSync(join(userPiecesRootDir, 'alice', 'pieces', 'chat.yaml'), makeMinimalPieceYaml('chat', 'alice custom chat'));
+
+    const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'alice', role: 'user' }))
+      .delete('/api/pieces/chat');
+    expect(res.status).toBe(200);
+    // User-custom file removed; built-in chat still present
+    expect(existsSync(join(userPiecesRootDir, 'alice', 'pieces', 'chat.yaml'))).toBe(false);
+    expect(existsSync(join(piecesDir, 'chat.yaml'))).toBe(true);
+  });
+
+  it('DELETE /api/pieces/chat on builtin by non-admin returns 403', async () => {
+    // No user-custom for alice, so findPieceForCaller resolves to builtin
+    const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'alice', role: 'user' }))
+      .delete('/api/pieces/chat');
+    expect(res.status).toBe(403);
+    expect(existsSync(join(piecesDir, 'chat.yaml'))).toBe(true);
+  });
+
+  // --- Fix source param for PUT/DELETE (P1-b) ---
+
+  it('PUT /api/pieces/chat?source=builtin by admin updates the builtin, not a same-named custom', async () => {
+    // Alice (admin) has a user-custom chat AND there is a builtin chat.
+    mkdirSync(join(userPiecesRootDir, 'admin1', 'pieces'), { recursive: true });
+    writeFileSync(join(userPiecesRootDir, 'admin1', 'pieces', 'chat.yaml'), makeMinimalPieceYaml('chat', 'admin custom chat'));
+    const adminApp = makeAuthApp(piecesDir, userPiecesRootDir, { id: 'admin1', role: 'admin' });
+
+    const res = await request(adminApp).put('/api/pieces/chat?source=builtin').send({
+      name: 'chat',
+      description: 'builtin updated',
+      max_movements: 1,
+      initial_movement: 'only',
+      movements: [{ name: 'only', edit: false, persona: 'p', instruction: 'i', allowed_tools: ['Read'], default_next: 'COMPLETE', rules: [] }],
+    });
+    expect(res.status).toBe(200);
+    // Builtin was updated
+    const builtinContent = readFileSync(join(piecesDir, 'chat.yaml'), 'utf-8');
+    expect(builtinContent).toContain('builtin updated');
+    // Custom is untouched
+    const customContent = readFileSync(join(userPiecesRootDir, 'admin1', 'pieces', 'chat.yaml'), 'utf-8');
+    expect(customContent).toContain('admin custom chat');
+  });
+
+  it('DELETE /api/pieces/chat?source=builtin by admin deletes the builtin, not same-named custom', async () => {
+    // admin1 has a user-custom chat AND builtin chat
+    mkdirSync(join(userPiecesRootDir, 'admin1', 'pieces'), { recursive: true });
+    writeFileSync(join(userPiecesRootDir, 'admin1', 'pieces', 'chat.yaml'), makeMinimalPieceYaml('chat', 'admin custom'));
+    const adminApp = makeAuthApp(piecesDir, userPiecesRootDir, { id: 'admin1', role: 'admin' });
+
+    const res = await request(adminApp).delete('/api/pieces/chat?source=builtin');
+    // Built-in pieces are non-deletable for everyone (including admins)
+    expect(res.status).toBe(403);
+    // Both still intact
+    expect(existsSync(join(piecesDir, 'chat.yaml'))).toBe(true);
+    expect(existsSync(join(userPiecesRootDir, 'admin1', 'pieces', 'chat.yaml'))).toBe(true);
+  });
+
+  it('DELETE /api/pieces/extra?source=user-custom targets user-custom, not builtin', async () => {
+    writeFileSync(join(piecesDir, 'extra.yaml'), makeMinimalPieceYaml('extra', 'builtin extra'));
+    mkdirSync(join(userPiecesRootDir, 'alice', 'pieces'), { recursive: true });
+    writeFileSync(join(userPiecesRootDir, 'alice', 'pieces', 'extra.yaml'), makeMinimalPieceYaml('extra', 'alice extra'));
+
+    const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'alice', role: 'user' }))
+      .delete('/api/pieces/extra?source=user-custom');
+    expect(res.status).toBe(200);
+    // User-custom removed
+    expect(existsSync(join(userPiecesRootDir, 'alice', 'pieces', 'extra.yaml'))).toBe(false);
+    // Builtin untouched
+    expect(existsSync(join(piecesDir, 'extra.yaml'))).toBe(true);
+  });
+
+  // P2 fix: GET /api/pieces/:name (no ?source) includes source in response body
+  // so the UI can derive the correct read-only state regardless of URL params.
+  it('GET /api/pieces/general (no ?source) returns source: builtin in the body', async () => {
+    const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'alice', role: 'user' }))
+      .get('/api/pieces/general');
+    expect(res.status).toBe(200);
+    expect(res.body.piece.name).toBe('general');
+    expect(res.body.source).toBe('builtin');
+    expect(res.body.custom).toBe(false);
+  });
+
+  it('POST /api/pieces creates in user-custom dir for admin (not piecesDir)', async () => {
+    // Regression for P2: POST always targets user-custom, admin is no exception.
+    const res = await request(makeAuthApp(piecesDir, userPiecesRootDir, { id: 'admin1', role: 'admin' }))
+      .post('/api/pieces')
+      .send({
+        name: 'admin-new-custom',
+        description: 'admin custom piece',
+        max_movements: 1,
+        initial_movement: 'only',
+        movements: [{ name: 'only', edit: false, persona: 'p', instruction: 'i', allowed_tools: ['Read'], default_next: 'COMPLETE', rules: [] }],
+      });
+    expect(res.status).toBe(201);
+    expect(existsSync(join(userPiecesRootDir, 'admin1', 'pieces', 'admin-new-custom.yaml'))).toBe(true);
+    expect(existsSync(join(piecesDir, 'admin-new-custom.yaml'))).toBe(false);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Finding 2 regression: authenticated POST with userPiecesRootDir UNSET → 503
+// Never falls through to shared/builtin dirs for an authenticated user.
+// ---------------------------------------------------------------------------
+
+describe('Pieces API (Finding 2: POST auth fallback hole)', () => {
+  let piecesDir: string;
+
+  function makeAppWithAuthButNoUserPiecesRoot(user: UserShape | null): express.Application {
+    const app = express();
+    app.use(express.json());
+    app.use((req, _res, next) => {
+      if (user) (req as any).user = user;
+      next();
+    });
+    // Intentionally: no userPiecesRootDir configured, no customPiecesDir.
+    mountPiecesApi(app, { piecesDir });
+    return app;
+  }
+
+  beforeEach(() => {
+    const tempDir = mkdtempSync(join(tmpdir(), 'pieces-api-f2-'));
+    piecesDir = join(tempDir, 'pieces');
+    mkdirSync(piecesDir);
+    writeFileSync(join(piecesDir, 'general.yaml'), makeGeneralPieceYaml());
+  });
+
+  it('authenticated non-admin POST with userPiecesRootDir unset returns 503 (does not write shared/builtin)', async () => {
+    const app = makeAppWithAuthButNoUserPiecesRoot({ id: 'alice', role: 'user' });
+    const res = await request(app)
+      .post('/api/pieces')
+      .send({
+        name: 'should-not-exist',
+        description: 'fallback hole test',
+        max_movements: 1,
+        initial_movement: 'only',
+        movements: [{ name: 'only', edit: false, persona: 'p', instruction: 'i', allowed_tools: ['Read'], default_next: 'COMPLETE', rules: [] }],
+      });
+    expect(res.status).toBe(503);
+    expect(res.body.ok).toBe(false);
+    expect(res.body.error).toMatch(/not configured/i);
+    // Must NOT have written anything to the builtin dir.
+    expect(existsSync(join(piecesDir, 'should-not-exist.yaml'))).toBe(false);
+  });
+
+  it('authenticated admin POST with userPiecesRootDir unset also returns 503', async () => {
+    const app = makeAppWithAuthButNoUserPiecesRoot({ id: 'admin1', role: 'admin' });
+    const res = await request(app)
+      .post('/api/pieces')
+      .send({
+        name: 'admin-fallback-hole',
+        description: 'admin hole test',
+        max_movements: 1,
+        initial_movement: 'only',
+        movements: [{ name: 'only', edit: false, persona: 'p', instruction: 'i', allowed_tools: ['Read'], default_next: 'COMPLETE', rules: [] }],
+      });
+    expect(res.status).toBe(503);
+    expect(res.body.ok).toBe(false);
+    // Must NOT have written anything to the builtin dir.
+    expect(existsSync(join(piecesDir, 'admin-fallback-hole.yaml'))).toBe(false);
+  });
+
+  it('unauthenticated POST with no userPiecesRootDir falls back to piecesDir (legacy no-auth mode)', async () => {
+    // No user: genuine no-auth legacy mode — should still work (existing behavior).
+    const app = makeAppWithAuthButNoUserPiecesRoot(null);
+    const res = await request(app)
+      .post('/api/pieces')
+      .send({
+        name: 'legacy-fallback',
+        description: 'legacy',
+        max_movements: 1,
+        initial_movement: 'only',
+        movements: [{ name: 'only', edit: false, persona: 'p', instruction: 'i', allowed_tools: ['Read'], default_next: 'COMPLETE', rules: [] }],
+      });
+    expect(res.status).toBe(201);
+    expect(existsSync(join(piecesDir, 'legacy-fallback.yaml'))).toBe(true);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Fix 1: invalid ?source param → 400 (no fallback to priority resolution)
+// ---------------------------------------------------------------------------
+
+describe('Pieces API (Fix 1: invalid ?source → 400, no destructive fallback)', () => {
+  let piecesDir: string;
+  let userPiecesRootDir: string;
+
+  beforeEach(() => {
+    const tempDir = mkdtempSync(join(tmpdir(), 'pieces-api-fix1-'));
+    piecesDir = join(tempDir, 'pieces');
+    userPiecesRootDir = join(tempDir, 'users');
+    mkdirSync(piecesDir);
+    mkdirSync(userPiecesRootDir);
+    // A builtin and a user-custom with the same name
+    writeFileSync(join(piecesDir, 'chat.yaml'), makeMinimalPieceYaml('chat', 'builtin chat'));
+    // Alice has a user-custom 'chat'
+    mkdirSync(join(userPiecesRootDir, 'alice', 'pieces'), { recursive: true });
+    writeFileSync(join(userPiecesRootDir, 'alice', 'pieces', 'chat.yaml'), makeMinimalPieceYaml('chat', 'alice custom chat'));
+  });
+
+  function makeApp(user: UserShape | null) {
+    const app = express();
+    app.use(express.json());
+    app.use((req, _res, next) => {
+      if (user) (req as any).user = user;
+      next();
+    });
+    mountPiecesApi(app, { piecesDir, userPiecesRootDir });
+    return app;
+  }
+
+  it('GET /api/pieces/:name?source=builtinn (typo) → 400 (not priority-fallback)', async () => {
+    const res = await request(makeApp({ id: 'alice', role: 'user' }))
+      .get('/api/pieces/chat?source=builtinn');
+    expect(res.status).toBe(400);
+    expect(res.body.ok).toBe(false);
+    expect(res.body.error).toMatch(/invalid source/i);
+  });
+
+  it('DELETE /api/pieces/chat?source=builtinn (typo) → 400, does NOT delete user-custom', async () => {
+    const res = await request(makeApp({ id: 'alice', role: 'user' }))
+      .delete('/api/pieces/chat?source=builtinn');
+    expect(res.status).toBe(400);
+    expect(res.body.ok).toBe(false);
+    expect(res.body.error).toMatch(/invalid source/i);
+    // User-custom must be untouched
+    expect(existsSync(join(userPiecesRootDir, 'alice', 'pieces', 'chat.yaml'))).toBe(true);
+  });
+
+  it('PUT /api/pieces/chat?source=user_custom (underscore typo) → 400, does NOT mutate user-custom', async () => {
+    const res = await request(makeApp({ id: 'alice', role: 'user' }))
+      .put('/api/pieces/chat?source=user_custom')
+      .send({
+        name: 'chat',
+        description: 'hijacked',
+        max_movements: 1,
+        initial_movement: 'only',
+        movements: [{ name: 'only', edit: false, persona: 'p', instruction: 'i', allowed_tools: ['Read'], default_next: 'COMPLETE', rules: [] }],
+      });
+    expect(res.status).toBe(400);
+    expect(res.body.ok).toBe(false);
+    expect(res.body.error).toMatch(/invalid source/i);
+    // User-custom description must be unchanged
+    const content = readFileSync(join(userPiecesRootDir, 'alice', 'pieces', 'chat.yaml'), 'utf-8');
+    expect(content).toContain('alice custom chat');
+    expect(content).not.toContain('hijacked');
+  });
+
+  it('valid ?source=builtin still works (not rejected)', async () => {
+    const res = await request(makeApp({ id: 'alice', role: 'user' }))
+      .get('/api/pieces/chat?source=builtin');
+    expect(res.status).toBe(200);
+    expect(res.body.source).toBe('builtin');
+  });
+
+  it('absent ?source still does priority resolution (not rejected)', async () => {
+    const res = await request(makeApp({ id: 'alice', role: 'user' }))
+      .get('/api/pieces/chat');
+    expect(res.status).toBe(200);
+    // priority: user-custom wins
+    expect(res.body.source).toBe('user-custom');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Fix 2: POST /api/pieces returns actual source in response body
+// ---------------------------------------------------------------------------
+
+describe('Pieces API (Fix 2: POST returns actual source)', () => {
+  let piecesDir: string;
+  let userPiecesRootDir: string;
+
+  function minimalPieceBody(name: string) {
+    return {
+      name,
+      description: 'test',
+      max_movements: 1,
+      initial_movement: 'only',
+      movements: [{ name: 'only', edit: false, persona: 'p', instruction: 'i', allowed_tools: ['Read'], default_next: 'COMPLETE', rules: [] }],
+    };
+  }
+
+  beforeEach(() => {
+    const tempDir = mkdtempSync(join(tmpdir(), 'pieces-api-fix2-'));
+    piecesDir = join(tempDir, 'pieces');
+    userPiecesRootDir = join(tempDir, 'users');
+    mkdirSync(piecesDir);
+    mkdirSync(userPiecesRootDir);
+  });
+
+  it('authenticated POST returns source: user-custom', async () => {
+    const app = express();
+    app.use(express.json());
+    app.use((req, _res, next) => { (req as any).user = { id: 'alice', role: 'user' }; next(); });
+    mountPiecesApi(app, { piecesDir, userPiecesRootDir });
+    const res = await request(app).post('/api/pieces').send(minimalPieceBody('my-piece'));
+    expect(res.status).toBe(201);
+    expect(res.body.ok).toBe(true);
+    expect(res.body.source).toBe('user-custom');
+  });
+
+  it('legacy (no-auth) POST with customPiecesDir returns source: global-custom', async () => {
+    const tempDir = mkdtempSync(join(tmpdir(), 'pieces-api-fix2-gc-'));
+    const gcDir = join(tempDir, 'custom');
+    mkdirSync(join(tempDir, 'pieces'));
+    mkdirSync(gcDir);
+    const app = express();
+    app.use(express.json());
+    // No user set — legacy no-auth mode
+    mountPiecesApi(app, { piecesDir: join(tempDir, 'pieces'), customPiecesDir: gcDir });
+    const res = await request(app).post('/api/pieces').send(minimalPieceBody('gc-piece'));
+    expect(res.status).toBe(201);
+    expect(res.body.ok).toBe(true);
+    expect(res.body.source).toBe('global-custom');
+  });
+
+  it('legacy (no-auth) POST without customPiecesDir returns source: builtin', async () => {
+    const app = express();
+    app.use(express.json());
+    // No user, no customPiecesDir
+    mountPiecesApi(app, { piecesDir });
+    const res = await request(app).post('/api/pieces').send(minimalPieceBody('legacy-piece'));
+    expect(res.status).toBe(201);
+    expect(res.body.ok).toBe(true);
+    expect(res.body.source).toBe('builtin');
+  });
+
+  it('no-auth POST with userPiecesRootDir returns source: user-custom (regression fix)', async () => {
+    const app = express();
+    app.use(express.json());
+    // No user, but userPiecesRootDir is configured (the fixed path)
+    mountPiecesApi(app, { piecesDir, userPiecesRootDir });
+    const res = await request(app).post('/api/pieces').send(minimalPieceBody('noauth-custom'));
+    expect(res.status).toBe(201);
+    expect(res.body.ok).toBe(true);
+    expect(res.body.source).toBe('user-custom');
+    // Piece is in data/users/local/pieces, NOT in piecesDir
+    expect(existsSync(join(userPiecesRootDir, 'local', 'pieces', 'noauth-custom.yaml'))).toBe(true);
+    expect(existsSync(join(piecesDir, 'noauth-custom.yaml'))).toBe(false);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Regression fix: no-auth + userPiecesRootDir → 'local' user-custom namespace
+// ---------------------------------------------------------------------------
+
+describe('Pieces API (regression: no-auth uses local user-custom, not piecesDir)', () => {
+  let piecesDir: string;
+  let userPiecesRootDir: string;
+
+  function minimalPieceBody(name: string) {
+    return {
+      name,
+      description: 'test',
+      max_movements: 1,
+      initial_movement: 'only',
+      movements: [{ name: 'only', edit: false, persona: 'p', instruction: 'i', allowed_tools: ['Read'], default_next: 'COMPLETE', rules: [] }],
+    };
+  }
+
+  beforeEach(() => {
+    const tempDir = mkdtempSync(join(tmpdir(), 'pieces-noauth-local-'));
+    piecesDir = join(tempDir, 'pieces');
+    userPiecesRootDir = join(tempDir, 'users');
+    mkdirSync(piecesDir);
+    mkdirSync(userPiecesRootDir);
+    writeFileSync(join(piecesDir, 'general.yaml'), makeGeneralPieceYaml());
+  });
+
+  function makeNoAuthApp() {
+    const app = express();
+    app.use(express.json());
+    // No user middleware — simulates no-auth mode
+    mountPiecesApi(app, { piecesDir, userPiecesRootDir });
+    return app;
+  }
+
+  it('no-auth POST creates under local user-custom dir, NOT in piecesDir', async () => {
+    const app = makeNoAuthApp();
+    const res = await request(app).post('/api/pieces').send(minimalPieceBody('my-noauth-piece'));
+    expect(res.status).toBe(201);
+    expect(res.body.source).toBe('user-custom');
+    // Must be in the 'local' user-custom dir
+    expect(existsSync(join(userPiecesRootDir, 'local', 'pieces', 'my-noauth-piece.yaml'))).toBe(true);
+    // Must NOT be in bundled piecesDir
+    expect(existsSync(join(piecesDir, 'my-noauth-piece.yaml'))).toBe(false);
+  });
+
+  it('no-auth created piece (with userPiecesRootDir) is DELETABLE — DELETE returns 200', async () => {
+    const app = makeNoAuthApp();
+    // Create it first
+    await request(app).post('/api/pieces').send(minimalPieceBody('deletable-noauth'));
+    expect(existsSync(join(userPiecesRootDir, 'local', 'pieces', 'deletable-noauth.yaml'))).toBe(true);
+
+    // Now delete — must succeed (not 403)
+    const delRes = await request(app).delete('/api/pieces/deletable-noauth');
+    expect(delRes.status).toBe(200);
+    expect(delRes.body.ok).toBe(true);
+    expect(existsSync(join(userPiecesRootDir, 'local', 'pieces', 'deletable-noauth.yaml'))).toBe(false);
+  });
+
+  it('bundled built-in piece is still non-deletable (403) for no-auth callers', async () => {
+    const app = makeNoAuthApp();
+    const res = await request(app).delete('/api/pieces/general');
+    expect(res.status).toBe(403);
+    expect(res.body.error).toMatch(/cannot delete a built-in/i);
+    expect(existsSync(join(piecesDir, 'general.yaml'))).toBe(true);
+  });
+
+  it('no-auth LIST includes the local user-custom piece (source=user-custom)', async () => {
+    // Pre-create a piece in the 'local' user-custom dir
+    mkdirSync(join(userPiecesRootDir, 'local', 'pieces'), { recursive: true });
+    writeFileSync(
+      join(userPiecesRootDir, 'local', 'pieces', 'local-custom.yaml'),
+      makeMinimalPieceYaml('local-custom', 'no-auth local piece'),
+    );
+
+    const app = makeNoAuthApp();
+    const res = await request(app).get('/api/pieces');
+    expect(res.status).toBe(200);
+    const byName = Object.fromEntries(res.body.pieces.map((p: any) => [p.name, p]));
+    expect(byName['local-custom']).toBeDefined();
+    expect(byName['local-custom'].source).toBe('user-custom');
+    expect(byName['local-custom'].ownerId).toBe('local');
+    // Built-in also visible
+    expect(byName['general']).toBeDefined();
+    expect(byName['general'].source).toBe('builtin');
+  });
+
+  it('no-auth GET resolves user-custom piece from local dir by priority', async () => {
+    mkdirSync(join(userPiecesRootDir, 'local', 'pieces'), { recursive: true });
+    writeFileSync(
+      join(userPiecesRootDir, 'local', 'pieces', 'my-piece.yaml'),
+      makeMinimalPieceYaml('my-piece', 'local custom'),
+    );
+
+    const app = makeNoAuthApp();
+    const res = await request(app).get('/api/pieces/my-piece');
+    expect(res.status).toBe(200);
+    expect(res.body.source).toBe('user-custom');
+    expect(res.body.ownerId).toBe('local');
   });
 });
diff --git a/src/bridge/pieces-api.ts b/src/bridge/pieces-api.ts
index ce8edbe..9f8d055 100644
--- a/src/bridge/pieces-api.ts
+++ b/src/bridge/pieces-api.ts
@@ -100,6 +100,19 @@ function validateName(name: string): boolean {
   return VALID_PIECE_NAME.test(name);
 }
 
+const VALID_SOURCES = new Set<string>(['builtin', 'user-custom', 'global-custom']);
+
+/**
+ * Returns true when `source` is absent (caller wants priority resolution).
+ * Returns false when `source` is a known valid value.
+ * Returns a 400 error string when `source` is present but unrecognised.
+ */
+function parseSourceParam(source: string | undefined): { valid: true; value: PieceSource | undefined } | { valid: false; error: string } {
+  if (source === undefined) return { valid: true, value: undefined };
+  if (VALID_SOURCES.has(source)) return { valid: true, value: source as PieceSource };
+  return { valid: false, error: 'Invalid source' };
+}
+
 export function findPieceFile(name: string, piecesDir: string, customPiecesDir?: string): { path: string; custom: boolean } | null {
   if (customPiecesDir) {
     const customPath = join(customPiecesDir, `${name}.yaml`);
@@ -122,6 +135,9 @@ export interface PiecesApiOptions {
   userPiecesRootDir?: string;
 }
 
+/** Canonical owner id for no-auth / legacy mode. Mirrors worker-bootstrap and piece-catalog default. */
+const LOCAL_OWNER = 'local';
+
 type AuthedUser = { id: string; role?: string };
 
 function getUser(req: Request): AuthedUser | undefined {
@@ -137,6 +153,7 @@ function isAdminOrLegacy(user: AuthedUser | undefined): boolean {
 /**
  * Lookup priority for a given caller:
  *   1. Caller's own user-custom dir (overrides everything below).
+ *      No-auth callers use the 'local' owner id.
  *   2. Global custom dir (admin-managed, all users see).
  *   3. Built-in dir.
  */
@@ -145,9 +162,10 @@ function findPieceForCaller(
   user: AuthedUser | undefined,
   name: string,
 ): { path: string; source: PieceSource; ownerId?: string } | null {
-  if (opts.userPiecesRootDir && user) {
-    const ucPath = join(userPiecesDir(opts.userPiecesRootDir, user.id), `${name}.yaml`);
-    if (existsSync(ucPath)) return { path: ucPath, source: 'user-custom', ownerId: user.id };
+  if (opts.userPiecesRootDir) {
+    const ownerId = user?.id ?? LOCAL_OWNER;
+    const ucPath = join(userPiecesDir(opts.userPiecesRootDir, ownerId), `${name}.yaml`);
+    if (existsSync(ucPath)) return { path: ucPath, source: 'user-custom', ownerId };
   }
   if (opts.customPiecesDir) {
     const gcPath = join(opts.customPiecesDir, `${name}.yaml`);
@@ -178,30 +196,31 @@ export function mountPiecesApi(
   app.get('/api/pieces', (req: Request, res: Response) => {
     try {
       const user = getUser(req);
-      const seen = new Set<string>();
       const pieces: PieceSummary[] = [];
 
-      // Order matters: user-custom overrides global-custom, which overrides built-in.
-      const sources: Array<{ dir: string; source: PieceSource; ownerId?: string }> = [];
-      if (opts.userPiecesRootDir && user) {
-        const ucDir = userPiecesDir(opts.userPiecesRootDir, user.id);
-        if (existsSync(ucDir)) sources.push({ dir: ucDir, source: 'user-custom', ownerId: user.id });
+      // Build custom sources (user-custom first, then global-custom).
+      // Within custom umbrella: dedup by name so user-custom wins over global-custom.
+      // Built-ins are ALWAYS emitted separately — they are never hidden by a same-named custom.
+      const customSources: Array<{ dir: string; source: PieceSource; ownerId?: string }> = [];
+      if (opts.userPiecesRootDir) {
+        // No-auth callers use the 'local' owner id, mirroring worker and piece-catalog defaults.
+        const ownerId = user?.id ?? LOCAL_OWNER;
+        const ucDir = userPiecesDir(opts.userPiecesRootDir, ownerId);
+        if (existsSync(ucDir)) customSources.push({ dir: ucDir, source: 'user-custom', ownerId });
       }
       if (opts.customPiecesDir && existsSync(opts.customPiecesDir)) {
-        sources.push({ dir: opts.customPiecesDir, source: 'global-custom' });
-      }
-      if (existsSync(opts.piecesDir)) {
-        sources.push({ dir: opts.piecesDir, source: 'builtin' });
+        customSources.push({ dir: opts.customPiecesDir, source: 'global-custom' });
       }
 
-      for (const { dir, source, ownerId } of sources) {
+      // Emit custom pieces (dedup within custom umbrella only).
+      const seenCustom = new Set<string>();
+      for (const { dir, source, ownerId } of customSources) {
         for (const f of listPieceFiles(dir)) {
           try {
             const p = loadPieceFile(f);
             const name = p.name ?? f.replace(/.*\//, '').replace('.yaml', '');
-            if (seen.has(name)) continue;
-            seen.add(name);
-            // Drift is meaningful only for global-custom that shadows a built-in.
+            if (seenCustom.has(name)) continue;
+            seenCustom.add(name);
             let drift: DriftStatus | undefined;
             if (source === 'global-custom' && existsSync(opts.piecesDir)) {
               const builtinPath = join(opts.piecesDir, `${name}.yaml`);
@@ -212,7 +231,7 @@ export function mountPiecesApi(
               description: p.description,
               triggers: p.triggers,
               requiredMcp: Array.isArray(p.required_mcp) ? p.required_mcp.filter((v: unknown): v is string => typeof v === 'string') : undefined,
-              custom: source !== 'builtin',
+              custom: true,
               source,
               ownerId,
               drift,
@@ -222,6 +241,27 @@ export function mountPiecesApi(
           }
         }
       }
+
+      // Always emit ALL built-ins (never hidden by custom pieces of the same name).
+      if (existsSync(opts.piecesDir)) {
+        for (const f of listPieceFiles(opts.piecesDir)) {
+          try {
+            const p = loadPieceFile(f);
+            const name = p.name ?? f.replace(/.*\//, '').replace('.yaml', '');
+            pieces.push({
+              name,
+              description: p.description,
+              triggers: p.triggers,
+              requiredMcp: Array.isArray(p.required_mcp) ? p.required_mcp.filter((v: unknown): v is string => typeof v === 'string') : undefined,
+              custom: false,
+              source: 'builtin',
+            });
+          } catch {
+            // skip malformed piece files
+          }
+        }
+      }
+
       res.json({ pieces });
     } catch (e) {
       res.status(500).json({ error: `Failed to list pieces: ${e}` });
@@ -232,7 +272,31 @@ export function mountPiecesApi(
     if (!validateName(req.params.name)) { res.status(400).json({ error: 'Invalid piece name' }); return; }
     try {
       const user = getUser(req);
-      const found = findPieceForCaller(opts, user, req.params.name);
+      const sourceParsed = parseSourceParam(req.query.source as string | undefined);
+      if (!sourceParsed.valid) { res.status(400).json({ ok: false, error: sourceParsed.error }); return; }
+      const requestedSource = sourceParsed.value;
+
+      let found: { path: string; source: PieceSource; ownerId?: string } | null = null;
+
+      if (requestedSource === 'builtin') {
+        const biPath = join(opts.piecesDir, `${req.params.name}.yaml`);
+        if (existsSync(biPath)) found = { path: biPath, source: 'builtin' };
+      } else if (requestedSource === 'user-custom') {
+        if (opts.userPiecesRootDir) {
+          const ownerId = user?.id ?? LOCAL_OWNER;
+          const ucPath = join(userPiecesDir(opts.userPiecesRootDir, ownerId), `${req.params.name}.yaml`);
+          if (existsSync(ucPath)) found = { path: ucPath, source: 'user-custom', ownerId };
+        }
+      } else if (requestedSource === 'global-custom') {
+        if (opts.customPiecesDir) {
+          const gcPath = join(opts.customPiecesDir, `${req.params.name}.yaml`);
+          if (existsSync(gcPath)) found = { path: gcPath, source: 'global-custom' };
+        }
+      } else {
+        // No source param: priority resolution (user-custom > global-custom > builtin).
+        found = findPieceForCaller(opts, user, req.params.name);
+      }
+
       if (!found) { res.status(404).json({ error: 'Piece not found' }); return; }
       const piece = loadPieceFile(found.path);
       res.json({
@@ -253,7 +317,29 @@ export function mountPiecesApi(
     if (!validateName(req.params.name)) { res.status(400).json({ error: 'Invalid piece name' }); return; }
     try {
       const user = getUser(req);
-      const found = findPieceForCaller(opts, user, req.params.name);
+      const sourceParsed = parseSourceParam(req.query.source as string | undefined);
+      if (!sourceParsed.valid) { res.status(400).json({ ok: false, error: sourceParsed.error }); return; }
+      const requestedSource = sourceParsed.value;
+
+      let found: { path: string; source: PieceSource; ownerId?: string } | null = null;
+      if (requestedSource === 'builtin') {
+        const biPath = join(opts.piecesDir, `${req.params.name}.yaml`);
+        if (existsSync(biPath)) found = { path: biPath, source: 'builtin' };
+      } else if (requestedSource === 'user-custom') {
+        if (opts.userPiecesRootDir) {
+          const ownerId = user?.id ?? LOCAL_OWNER;
+          const ucPath = join(userPiecesDir(opts.userPiecesRootDir, ownerId), `${req.params.name}.yaml`);
+          if (existsSync(ucPath)) found = { path: ucPath, source: 'user-custom', ownerId };
+        }
+      } else if (requestedSource === 'global-custom') {
+        if (opts.customPiecesDir) {
+          const gcPath = join(opts.customPiecesDir, `${req.params.name}.yaml`);
+          if (existsSync(gcPath)) found = { path: gcPath, source: 'global-custom' };
+        }
+      } else {
+        found = findPieceForCaller(opts, user, req.params.name);
+      }
+
       if (!found) { res.status(404).json({ error: 'Piece not found' }); return; }
 
       // Authz: built-in / global-custom → admin (or legacy no-auth); user-custom → owner (or admin).
@@ -262,7 +348,7 @@ export function mountPiecesApi(
           res.status(403).json({ ok: false, error: 'Only admins can modify built-in or global-custom pieces' });
           return;
         }
-      } else if (found.ownerId !== user?.id && !isAdminOrLegacy(user)) {
+      } else if (found.ownerId !== (user?.id ?? LOCAL_OWNER) && !isAdminOrLegacy(user)) {
         // Different user's user-custom — and not admin. Should be unreachable since
         // findPieceForCaller scopes user-custom to the caller, but guard anyway.
         res.status(403).json({ ok: false, error: "Cannot modify another user's custom piece" });
@@ -293,33 +379,55 @@ export function mountPiecesApi(
       if (error) { res.status(400).json({ ok: false, error }); return; }
 
       const user = getUser(req);
-      const adminOrLegacy = isAdminOrLegacy(user);
 
-      // Determine destination dir:
-      //   - admin / legacy → preserve existing behavior (write to piecesDir).
-      //   - non-admin user → write to their user-custom dir.
+      // POST always creates in user-custom dir. "+" is always Create Custom.
+      // Admins edit built-ins via PUT on existing ones, not by POST-creating new built-ins.
+      // No-auth / legacy with userPiecesRootDir: use the 'local' owner id so pieces are
+      // user-custom (deletable) and never pollute piecesDir.
+      // No-auth / legacy WITHOUT userPiecesRootDir: fall back to global customPiecesDir or piecesDir.
       let destDir: string;
-      if (adminOrLegacy) {
-        destDir = opts.piecesDir;
-      } else {
-        if (!opts.userPiecesRootDir) {
-          res.status(503).json({ ok: false, error: 'User pieces directory not configured on this server' });
-          return;
-        }
-        destDir = userPiecesDir(opts.userPiecesRootDir, user!.id);
+      let createdSource: PieceSource;
+      if (opts.userPiecesRootDir) {
+        // Both authenticated and no-auth go to user-custom dir when userPiecesRootDir is set.
+        // Authenticated users: 503 guard below is only needed when root is NOT set.
+        const ownerId = user?.id ?? LOCAL_OWNER;
+        destDir = userPiecesDir(opts.userPiecesRootDir, ownerId);
         mkdirSync(destDir, { recursive: true });
+        createdSource = 'user-custom';
+      } else if (user) {
+        // Authenticated caller but userPiecesRootDir is not configured — cannot safely write.
+        res.status(503).json({ ok: false, error: 'User piece storage not configured' });
+        return;
+      } else if (opts.customPiecesDir) {
+        // Legacy (no-auth) with global custom dir configured.
+        destDir = opts.customPiecesDir;
+        mkdirSync(destDir, { recursive: true });
+        createdSource = 'global-custom';
+      } else {
+        // Pure legacy single-user: fall back to piecesDir (existing behavior).
+        destDir = opts.piecesDir;
+        createdSource = 'builtin';
       }
 
-      // Reject if any visible-to-caller piece with this name already exists
-      // (built-in, global-custom, or caller's user-custom).
+      // Always reject if the name collides with a built-in — Custom and Default are
+      // separate namespaces. (This also covers the admin case, since admins should
+      // use PUT to update an existing built-in, not POST to create a duplicate.)
+      const builtinPath = join(opts.piecesDir, `${req.body.name}.yaml`);
+      if (existsSync(builtinPath) && destDir !== opts.piecesDir) {
+        res.status(409).json({ ok: false, error: `"${req.body.name}" は組み込み (built-in) Piece と同名です。Custom Piece には別名を付けてください。` });
+        return;
+      }
+
+      // Reject if the caller's visible piece with this name already exists
+      // (global-custom or caller's own user-custom).
       if (findPieceForCaller(opts, user, req.body.name)) {
         res.status(409).json({ ok: false, error: 'Piece already exists' }); return;
       }
 
       const filePath = join(destDir, `${req.body.name}.yaml`);
       writeFileSync(filePath, stringify(req.body, { lineWidth: 120 }), 'utf-8');
-      logger.info(`[pieces-api] created piece=${req.body.name} dest=${destDir} actor=${user?.id ?? 'legacy'}`);
-      res.status(201).json({ ok: true });
+      logger.info(`[pieces-api] created piece=${req.body.name} dest=${destDir} source=${createdSource} actor=${user?.id ?? 'legacy'}`);
+      res.status(201).json({ ok: true, source: createdSource });
     } catch (e) {
       res.status(500).json({ error: `Failed to create piece: ${e}` });
     }
@@ -327,23 +435,51 @@ export function mountPiecesApi(
 
   app.delete('/api/pieces/:name', (req: Request, res: Response) => {
     if (!validateName(req.params.name)) { res.status(400).json({ error: 'Invalid piece name' }); return; }
-    if (req.params.name === 'general' || req.params.name === 'chat') {
-      res.status(403).json({ ok: false, error: 'Cannot delete general piece' }); return;
-    }
     try {
       const user = getUser(req);
-      const found = findPieceForCaller(opts, user, req.params.name);
+      const sourceParsed = parseSourceParam(req.query.source as string | undefined);
+      if (!sourceParsed.valid) { res.status(400).json({ ok: false, error: sourceParsed.error }); return; }
+      const requestedSource = sourceParsed.value;
+
+      let found: { path: string; source: PieceSource; ownerId?: string } | null = null;
+      if (requestedSource === 'builtin') {
+        const biPath = join(opts.piecesDir, `${req.params.name}.yaml`);
+        if (existsSync(biPath)) found = { path: biPath, source: 'builtin' };
+      } else if (requestedSource === 'user-custom') {
+        if (opts.userPiecesRootDir) {
+          const ownerId = user?.id ?? LOCAL_OWNER;
+          const ucPath = join(userPiecesDir(opts.userPiecesRootDir, ownerId), `${req.params.name}.yaml`);
+          if (existsSync(ucPath)) found = { path: ucPath, source: 'user-custom', ownerId };
+        }
+      } else if (requestedSource === 'global-custom') {
+        if (opts.customPiecesDir) {
+          const gcPath = join(opts.customPiecesDir, `${req.params.name}.yaml`);
+          if (existsSync(gcPath)) found = { path: gcPath, source: 'global-custom' };
+        }
+      } else {
+        found = findPieceForCaller(opts, user, req.params.name);
+      }
+
       if (!found) { res.status(404).json({ error: 'Piece not found' }); return; }
 
-      // Authz mirrors PUT: built-in / global-custom → admin; user-custom → owner.
-      if (found.source !== 'user-custom') {
+      // Built-in (Default) pieces are non-deletable for everyone — including admins.
+      // This covers general/chat and all other built-ins. Admins may still EDIT
+      // built-ins via PUT; only deletion is prohibited.
+      if (found.source === 'builtin') {
+        res.status(403).json({ ok: false, error: 'Cannot delete a built-in (Default) piece' }); return;
+      }
+
+      // Authz for non-builtin sources: global-custom → admin; user-custom → owner.
+      if (found.source === 'global-custom') {
         if (!isAdminOrLegacy(user)) {
-          res.status(403).json({ ok: false, error: 'Only admins can delete built-in or global-custom pieces' });
+          res.status(403).json({ ok: false, error: 'Only admins can delete global-custom pieces' });
+          return;
+        }
+      } else if (found.source === 'user-custom') {
+        if (found.ownerId !== (user?.id ?? LOCAL_OWNER) && !isAdminOrLegacy(user)) {
+          res.status(403).json({ ok: false, error: "Cannot delete another user's custom piece" });
           return;
         }
-      } else if (found.ownerId !== user?.id && !isAdminOrLegacy(user)) {
-        res.status(403).json({ ok: false, error: "Cannot delete another user's custom piece" });
-        return;
       }
 
       unlinkSync(found.path);
diff --git a/src/bridge/server.ts b/src/bridge/server.ts
index 5a45399..61fbfd8 100644
--- a/src/bridge/server.ts
+++ b/src/bridge/server.ts
@@ -43,6 +43,7 @@ import { createWorkerMetrics, type WorkerMetrics } from '../metrics/worker-metri
 import { createMetricsHandler } from '../metrics/http-handler.js';
 import { buildDirectProbe, buildProxyProbe } from '../engine/backend-probes.js';
 import { startTrashCleanup } from '../user-folder/trash-cleanup.js';
+import { userPiecesDir } from '../user-folder/paths.js';
 import { startReflectionRetentionSweep } from '../engine/reflection/retention.js';
 import type { AuthConfig } from '../config.js';
 import { isKeyConfigured } from '../mcp/crypto.js';
@@ -777,7 +778,16 @@ export function createCoreServer(opts: CoreServerOptions): {
     generateTitle: opts.generateTitle,
     selectPiece: opts.selectPiece,
     pieceExists: opts.piecesDir
-      ? (name: string) => findPieceFile(name, opts.piecesDir!, opts.customPiecesDir) !== null
+      ? (name: string, ownerId?: string) => {
+          // Mirror the worker's per-user → global-custom → builtin resolution order.
+          // 1. Owner's per-user dir (matches what worker uses at job run time).
+          // No-auth tasks (ownerId null) fall back to 'local', mirroring the worker.
+          const ufl = loadConfig().userFolderRoot ?? './data/users';
+          const ownerForPieces = ownerId ?? 'local';
+          if (existsSync(join(userPiecesDir(ufl, ownerForPieces), `${name}.yaml`))) return true;
+          // 2. Global-custom + builtin via existing helper.
+          return findPieceFile(name, opts.piecesDir!, opts.customPiecesDir) !== null;
+        }
       : undefined,
     sessRepo,
     getMaxUploadMb: opts.configManager
diff --git a/src/engine/piece-runner.test.ts b/src/engine/piece-runner.test.ts
index 334e427..78a0a3c 100644
--- a/src/engine/piece-runner.test.ts
+++ b/src/engine/piece-runner.test.ts
@@ -396,9 +396,9 @@ movements:
     expect(() => loadPiece('multi', 'pieces', tempDir)).not.toThrow();
   });
 
-  it('all 13 bundled pieces load without validation errors', () => {
+  it('all 12 bundled pieces load without validation errors', () => {
     const piecesDir = join(process.cwd(), 'pieces');
-    const names = ['brainstorming', 'chat', 'data-process', 'game-tweet-generator', 'general',
+    const names = ['brainstorming', 'chat', 'data-process', 'general',
                    'office-process', 'piece-builder', 'research', 'slide', 'sns-research',
                    'ssh-console', 'ssh-ops', 'x-ai-digest'];
     for (const name of names) {
@@ -1111,3 +1111,50 @@ describe('allowed_ssh_connections validation (Phase 4)', () => {
     expect(() => validatePieceDef(piece)).toThrow(/Piece "ssh-test" has invalid allowed_ssh_connections/);
   });
 });
+
+// --- Task 1: loadPiece multi-dir support ---
+describe('loadPiece multi-dir (string | string[])', () => {
+  it('resolves from a list of custom dirs (per-user wins over builtin name miss)', () => {
+    const dirA = mkdtempSync(join(tmpdir(), 'pa-')); // empty
+    const dirB = mkdtempSync(join(tmpdir(), 'pb-'));
+    writeFileSync(
+      join(dirB, 'mycustom.yaml'),
+      `name: mycustom\ndescription: d\nmax_movements: 1\ninitial_movement: go\nmovements:\n  - name: go\n    edit: false\n    persona: w\n    instruction: x\n    allowed_tools: []\n    rules: []\n    default_next: COMPLETE\n`,
+    );
+    // array form: searches dirA then dirB then builtin
+    const p = loadPiece('mycustom', 'pieces', [dirA, dirB]);
+    expect(p.name).toBe('mycustom');
+    // builtin still resolvable when not in any custom dir
+    expect(() => loadPiece('chat', 'pieces', [dirA, dirB])).not.toThrow();
+    rmSync(dirA, { recursive: true });
+    rmSync(dirB, { recursive: true });
+  });
+
+  it('first dir wins when same name appears in two custom dirs', () => {
+    const dirA = mkdtempSync(join(tmpdir(), 'pa-'));
+    const dirB = mkdtempSync(join(tmpdir(), 'pb-'));
+    writeFileSync(
+      join(dirA, 'dup.yaml'),
+      `name: dup\ndescription: from-a\nmax_movements: 1\ninitial_movement: go\nmovements:\n  - name: go\n    edit: false\n    persona: w\n    instruction: x\n    allowed_tools: []\n    rules: []\n    default_next: COMPLETE\n`,
+    );
+    writeFileSync(
+      join(dirB, 'dup.yaml'),
+      `name: dup\ndescription: from-b\nmax_movements: 1\ninitial_movement: go\nmovements:\n  - name: go\n    edit: false\n    persona: w\n    instruction: x\n    allowed_tools: []\n    rules: []\n    default_next: COMPLETE\n`,
+    );
+    const p = loadPiece('dup', 'pieces', [dirA, dirB]);
+    expect(p.description).toBe('from-a');
+    rmSync(dirA, { recursive: true });
+    rmSync(dirB, { recursive: true });
+  });
+
+  it('string form still works (backward compat)', () => {
+    const dir = mkdtempSync(join(tmpdir(), 'pc-'));
+    writeFileSync(
+      join(dir, 'strcompat.yaml'),
+      `name: strcompat\ndescription: str\nmax_movements: 1\ninitial_movement: go\nmovements:\n  - name: go\n    edit: false\n    persona: w\n    instruction: x\n    allowed_tools: []\n    rules: []\n    default_next: COMPLETE\n`,
+    );
+    const p = loadPiece('strcompat', 'pieces', dir);
+    expect(p.name).toBe('strcompat');
+    rmSync(dir, { recursive: true });
+  });
+});
diff --git a/src/engine/piece-runner.ts b/src/engine/piece-runner.ts
index fde8ee3..ce92ab3 100644
--- a/src/engine/piece-runner.ts
+++ b/src/engine/piece-runner.ts
@@ -209,29 +209,22 @@ export function validateAllowedSshConnections(piece: PieceDef): string[] {
 }
 
 // pieces/ ディレクトリから piece 定義を読み込む（customPiecesDir を優先探索）
-export function loadPiece(pieceName: string, piecesDir: string = 'pieces', customPiecesDir?: string): PieceDef {
+// customPiecesDir は string | string[] を受け付ける（配列の場合は先頭から順に探索）
+export function loadPiece(pieceName: string, piecesDir: string = 'pieces', customPiecesDir?: string | string[]): PieceDef {
   let raw: string;
   let source: string;
-  if (customPiecesDir) {
-    const customPath = join(customPiecesDir, `${pieceName}.yaml`);
-    if (existsSync(customPath)) {
-      logger.debug(`[piece-runner] loadPiece piece=${pieceName} source=custom path=${customPath}`);
-      raw = readFileSync(customPath, 'utf-8');
-      source = 'custom';
-    } else {
-      const filePath = join(piecesDir, `${pieceName}.yaml`);
-      if (!existsSync(filePath)) {
-        logger.warn(`[piece-runner] loadPiece piece=${pieceName} not found dirs=[${customPiecesDir}, ${piecesDir}]`);
-        throw new Error(`Piece not found: ${pieceName}`);
-      }
-      logger.debug(`[piece-runner] loadPiece piece=${pieceName} source=builtin path=${filePath}`);
-      raw = readFileSync(filePath, 'utf-8');
-      source = 'builtin';
-    }
+  const customDirs = customPiecesDir == null ? [] : (Array.isArray(customPiecesDir) ? customPiecesDir : [customPiecesDir]);
+  const found = customDirs
+    .map((d) => join(d, `${pieceName}.yaml`))
+    .find((p) => existsSync(p));
+  if (found) {
+    logger.debug(`[piece-runner] loadPiece piece=${pieceName} source=custom path=${found}`);
+    raw = readFileSync(found, 'utf-8');
+    source = 'custom';
   } else {
     const filePath = join(piecesDir, `${pieceName}.yaml`);
     if (!existsSync(filePath)) {
-      logger.warn(`[piece-runner] loadPiece piece=${pieceName} not found dirs=[${piecesDir}]`);
+      logger.warn(`[piece-runner] loadPiece piece=${pieceName} not found dirs=[${[...customDirs, piecesDir].join(', ')}]`);
       throw new Error(`Piece not found: ${pieceName}`);
     }
     logger.debug(`[piece-runner] loadPiece piece=${pieceName} source=builtin path=${filePath}`);
@@ -252,11 +245,12 @@ export function loadPiece(pieceName: string, piecesDir: string = 'pieces', custo
 /**
  * pieces/ ディレクトリ内の全 Piece から triggers を読み込む（customPiecesDir があれば優先、同名は custom が勝つ）
  */
-export function loadAllPieceTriggers(piecesDir: string = 'pieces', customPiecesDir?: string): Array<{ name: string; keywords: string[] }> {
+export function loadAllPieceTriggers(piecesDir: string = 'pieces', customPiecesDir?: string | string[]): Array<{ name: string; keywords: string[] }> {
   const triggers: Array<{ name: string; keywords: string[] }> = [];
   const seen = new Set<string>();
 
-  const dirs = customPiecesDir ? [customPiecesDir, piecesDir] : [piecesDir];
+  const customDirsArr = Array.isArray(customPiecesDir) ? customPiecesDir : (customPiecesDir ? [customPiecesDir] : []);
+  const dirs = [...customDirsArr, piecesDir];
   logger.info(`[piece-runner] loadAllPieceTriggers scanning dirs=[${dirs.join(', ')}]`);
   for (const dir of dirs) {
     if (!existsSync(dir)) {
@@ -299,7 +293,7 @@ export async function runPiece(
     abortController?: AbortController;
     safetyConfig?: { maxIterations?: number; maxRevisits?: number; bashUnrestricted?: boolean; bashSandbox?: 'auto' | 'always' | 'off' };
     searchFilter?: SearchFilterConfig;
-    customPiecesDir?: string;
+    customPiecesDir?: string | string[];
     contextManager?: ContextManager;
     vlmEnabled?: boolean;
     /** Phase 5: parent's job id, used to populate MemoryHandoff.parentJobId
@@ -657,7 +651,7 @@ function prepareMovementContext(
   options?: {
     spawnSubTask?: (params: { title: string; instruction: string; piece?: string }) => Promise<{ jobId: string; subtaskIndex: number; workspacePath: string }>;
     searchFilter?: SearchFilterConfig;
-    customPiecesDir?: string;
+    customPiecesDir?: string | string[];
     vlmEnabled?: boolean;
     /** Traceability T-1: per-run event logger threaded into ToolContext. */
     eventLogger?: EventLogger;
@@ -724,6 +718,9 @@ function prepareMovementContext(
     toolsConfig,
     eventLogger: options?.eventLogger,
     searchFilter: options?.searchFilter,
+    // Pass the full array so in-agent reads (ListPieces/GetPiece) can see ALL
+    // custom dirs (per-user + global-custom). CreatePiece writes to dirs[0]
+    // (the per-user dir) — handled inside pieces.ts.
     customPiecesDir: options?.customPiecesDir,
     spawnSubTask: options?.spawnSubTask,
     missionBrief: options?.missionBrief,
diff --git a/src/engine/tools/excel-styles.test.ts b/src/engine/tools/excel-styles.test.ts
new file mode 100644
index 0000000..bcc7578
--- /dev/null
+++ b/src/engine/tools/excel-styles.test.ts
@@ -0,0 +1,142 @@
+import { describe, expect, it } from 'vitest';
+import ExcelJS from 'exceljs';
+import { mkdtempSync } from 'fs';
+import { tmpdir } from 'os';
+import { join } from 'path';
+import { resolveThemePalette, applyTint, extractSheetStyles } from './excel-styles.js';
+
+async function roundTrip(build: (ws: ExcelJS.Worksheet) => void): Promise<ExcelJS.Worksheet> {
+  const wb = new ExcelJS.Workbook(); const ws = wb.addWorksheet('S'); build(ws);
+  const p = join(mkdtempSync(join(tmpdir(), 'xls-')), 't.xlsx');
+  await wb.xlsx.writeFile(p);
+  const wb2 = new ExcelJS.Workbook(); await wb2.xlsx.readFile(p);
+  return wb2.getWorksheet('S')!;
+}
+
+describe('resolveThemePalette', () => {
+  it('parses srgbClr + sysClr and applies the lt/dk swap', () => {
+    const xml = `<a:theme><a:themeElements><a:clrScheme name="x">
+      <a:dk1><a:sysClr val="windowText" lastClr="000000"/></a:dk1>
+      <a:lt1><a:sysClr val="window" lastClr="FFFFFF"/></a:lt1>
+      <a:dk2><a:srgbClr val="44546A"/></a:dk2>
+      <a:lt2><a:srgbClr val="E7E6E6"/></a:lt2>
+      <a:accent1><a:srgbClr val="4472C4"/></a:accent1>
+      <a:accent2><a:srgbClr val="ED7D31"/></a:accent2>
+      <a:accent3><a:srgbClr val="A5A5A5"/></a:accent3>
+      <a:accent4><a:srgbClr val="FFC000"/></a:accent4>
+      <a:accent5><a:srgbClr val="5B9BD5"/></a:accent5>
+      <a:accent6><a:srgbClr val="70AD47"/></a:accent6>
+      <a:hlink><a:srgbClr val="0563C1"/></a:hlink>
+      <a:folHlink><a:srgbClr val="954F72"/></a:folHlink>
+    </a:clrScheme></a:themeElements></a:theme>`;
+    const pal = resolveThemePalette(xml);
+    expect(pal[0]).toBe('#FFFFFF'); // theme idx 0 = Light1 = lt1
+    expect(pal[1]).toBe('#000000'); // theme idx 1 = Dark1 = dk1
+    expect(pal[4]).toBe('#4472C4'); // accent1
+  });
+  it('returns [] on missing scheme', () => { expect(resolveThemePalette(undefined)).toEqual([]); });
+});
+
+describe('applyTint', () => {
+  it('lightens with positive tint and darkens with negative', () => {
+    const lighter = applyTint('#4472C4', 0.4);
+    const darker = applyTint('#4472C4', -0.4);
+    expect(lighter).not.toBe('#4472C4');
+    expect(darker).not.toBe('#4472C4');
+    // positive tint raises luminance
+    const lum = (h: string) => parseInt(h.slice(1,3),16)+parseInt(h.slice(3,5),16)+parseInt(h.slice(5,7),16);
+    expect(lum(lighter)).toBeGreaterThan(lum('#4472C4'));
+    expect(lum(darker)).toBeLessThan(lum('#4472C4'));
+  });
+});
+
+describe('extractSheetStyles', () => {
+  it('dedups identical fills into one legend entry with a merged range', async () => {
+    const ws = await roundTrip((ws) => {
+      for (const a of ['A1','B1','C1','D1']) ws.getCell(a).fill = { type:'pattern', pattern:'solid', fgColor:{ argb:'FFFFF2CC' } };
+    });
+    const r = extractSheetStyles(ws, [], 250);
+    expect(r.legend.length).toBe(1);
+    expect(r.legend[0].sig).toContain('#FFF2CC');
+    expect(r.assignments[0].ranges).toEqual(['A1:D1']); // horizontal run merged
+  });
+  it('captures a decorated but EMPTY cell', async () => {
+    const ws = await roundTrip((ws) => { ws.getCell('B5').fill = { type:'pattern', pattern:'solid', fgColor:{ argb:'FFFF0000' } }; });
+    const r = extractSheetStyles(ws, [], 250);
+    expect(r.assignments.some(a => a.ranges.includes('B5'))).toBe(true);
+  });
+  it('reports font bold + color', async () => {
+    const ws = await roundTrip((ws) => { ws.getCell('A1').value='x'; ws.getCell('A1').font={ bold:true, color:{ argb:'FF9C0006' } }; });
+    const r = extractSheetStyles(ws, [], 250);
+    expect(r.legend[0].sig).toMatch(/font:.*bold/);
+    expect(r.legend[0].sig).toContain('#9C0006');
+  });
+  it('merges vertically-adjacent identical column-runs into a rectangle', async () => {
+    const ws = await roundTrip((ws) => {
+      for (let row=2; row<=20; row++) ws.getCell(`B${row}`).fill={ type:'pattern', pattern:'solid', fgColor:{ argb:'FF00FF00' } };
+    });
+    const r = extractSheetStyles(ws, [], 250);
+    expect(r.assignments[0].ranges).toEqual(['B2:B20']);
+  });
+  it('respects max_style_ranges cap', async () => {
+    const ws = await roundTrip((ws) => {
+      // 5 disjoint single cells with distinct fills (no merge possible)
+      const colors=['FFAA0000','FF00AA00','FF0000AA','FFAAAA00','FF00AAAA'];
+      colors.forEach((c,i)=>{ ws.getCell(`A${i*2+1}`).fill={type:'pattern',pattern:'solid',fgColor:{argb:c}}; });
+    });
+    const r = extractSheetStyles(ws, [], 2);
+    expect(r.truncated).toBe(true);
+  });
+
+  // Fix 4 (M-1): merges
+  it('includes merged cell range in result merges', async () => {
+    const ws = await roundTrip((ws) => {
+      ws.getCell('A1').value = 'merged';
+      ws.mergeCells('A1:C2');
+    });
+    const r = extractSheetStyles(ws, [], 250);
+    expect(r.merges).toContain('A1:C2');
+  });
+
+  // Fix 4 (M-2): conditional formatting — round-trip keeps conditionalFormattings
+  it('detects conditional formatting', async () => {
+    const ws = await roundTrip((ws) => {
+      ws.addConditionalFormatting({
+        ref: 'A1:A10',
+        rules: [{ type: 'expression', formulae: ['TRUE'], style: { fill: { type: 'pattern', pattern: 'solid', bgColor: { argb: 'FFFF0000' } } } }],
+      });
+    });
+    // ExcelJS preserves conditionalFormattings after round-trip (empirically verified)
+    const r = extractSheetStyles(ws, [], 250);
+    expect(r.conditionalFormatting).toBe(true);
+  });
+
+  // Fix 4 (M-3): border + numFmt + alignment
+  it('captures border, numFmt, and alignment in cell signature', async () => {
+    const ws = await roundTrip((ws) => {
+      const cell = ws.getCell('B2');
+      cell.value = 0.42;
+      cell.border = { bottom: { style: 'thin' } };
+      cell.numFmt = '0.00%';
+      cell.alignment = { horizontal: 'center' };
+    });
+    const r = extractSheetStyles(ws, [], 250);
+    expect(r.legend.length).toBeGreaterThan(0);
+    const sig = r.legend[0]!.sig;
+    expect(sig).toContain('border:');
+    expect(sig).toContain('numFmt:"0.00%"');
+    expect(sig).toContain('align:');
+  });
+
+  // Fix 4 (I-1 range honoring): rangeBounds filters cells
+  it('honors rangeBounds — includes A1 but excludes Z99', async () => {
+    const ws = await roundTrip((ws) => {
+      ws.getCell('A1').fill = { type: 'pattern', pattern: 'solid', fgColor: { argb: 'FF0000FF' } };
+      ws.getCell('Z99').fill = { type: 'pattern', pattern: 'solid', fgColor: { argb: 'FF00FF00' } };
+    });
+    const r = extractSheetStyles(ws, [], 250, { minRow: 1, maxRow: 5, minCol: 1, maxCol: 5 });
+    const allRanges = r.assignments.flatMap(a => a.ranges);
+    expect(allRanges.some(rng => rng === 'A1' || rng.startsWith('A1:'))).toBe(true);
+    expect(allRanges.every(rng => !rng.includes('Z99') && !rng.startsWith('Z'))).toBe(true);
+  });
+});
diff --git a/src/engine/tools/excel-styles.ts b/src/engine/tools/excel-styles.ts
new file mode 100644
index 0000000..91f179c
--- /dev/null
+++ b/src/engine/tools/excel-styles.ts
@@ -0,0 +1,515 @@
+/**
+ * excel-styles.ts — Pure helper for ExcelJS style extraction.
+ * No dependency on office.ts internals; only imports exceljs types + stdlib.
+ */
+
+import type ExcelJS from 'exceljs';
+
+// --- Public API ---
+
+export interface SheetStyleResult {
+  legend: Array<{ id: string; sig: string }>;           // s1 = "fill:#FFF2CC;font:bold,#9C0006"
+  assignments: Array<{ id: string; ranges: string[] }>; // s1: ['A1:D1','A10:D10']
+  merges: string[];                                      // ['A1:D1']
+  conditionalFormatting: boolean;
+  truncated: boolean;                                    // true if range count hit the cap
+}
+
+/**
+ * Parse <a:clrScheme> from a theme1 XML string into a theme-index→'#RRGGBB' map.
+ * Returns [] if themeXml is missing/unparseable (caller then emits raw theme refs).
+ */
+export function resolveThemePalette(themeXml: string | undefined): string[] {
+  if (!themeXml) return [];
+
+  // Extract the clrScheme block
+  const schemeMatch = themeXml.match(/<a:clrScheme[^>]*>([\s\S]*?)<\/a:clrScheme>/);
+  if (!schemeMatch) return [];
+  const schemeXml = schemeMatch[1]!;
+
+  // The 12 entries in XML order: dk1, lt1, dk2, lt2, accent1-6, hlink, folHlink
+  const tagNames = ['dk1', 'lt1', 'dk2', 'lt2', 'accent1', 'accent2', 'accent3', 'accent4', 'accent5', 'accent6', 'hlink', 'folHlink'];
+
+  const scheme: string[] = [];
+  for (const tag of tagNames) {
+    const tagMatch = schemeXml.match(new RegExp(`<a:${tag}>[\\s\\S]*?</a:${tag}>`));
+    if (!tagMatch) {
+      // Missing entry
+      return [];
+    }
+    const block = tagMatch[0]!;
+
+    // Try srgbClr first
+    const srgbMatch = block.match(/<a:srgbClr[^>]*val="([0-9A-Fa-f]{6})"/);
+    if (srgbMatch) {
+      scheme.push('#' + srgbMatch[1]!.toUpperCase());
+      continue;
+    }
+
+    // Try sysClr with lastClr
+    const sysMatch = block.match(/<a:sysClr[^>]*lastClr="([0-9A-Fa-f]{6})"/);
+    if (sysMatch) {
+      scheme.push('#' + sysMatch[1]!.toUpperCase());
+      continue;
+    }
+
+    // Unrecognized
+    return [];
+  }
+
+  if (scheme.length < 12) return [];
+
+  // Apply the well-known lt/dk swap:
+  // themeIndex 0=Light1=lt1=scheme[1], 1=Dark1=dk1=scheme[0],
+  // 2=Light2=lt2=scheme[3], 3=Dark2=dk2=scheme[2],
+  // 4-9=accent1-6=scheme[4..9], 10=hlink=scheme[10], 11=folHlink=scheme[11]
+  return [
+    scheme[1]!,   // 0: Light1 (lt1)
+    scheme[0]!,   // 1: Dark1  (dk1)
+    scheme[3]!,   // 2: Light2 (lt2)
+    scheme[2]!,   // 3: Dark2  (dk2)
+    scheme[4]!,   // 4: accent1
+    scheme[5]!,   // 5: accent2
+    scheme[6]!,   // 6: accent3
+    scheme[7]!,   // 7: accent4
+    scheme[8]!,   // 8: accent5
+    scheme[9]!,   // 9: accent6
+    scheme[10]!,  // 10: hlink
+    scheme[11]!,  // 11: folHlink
+  ];
+}
+
+/**
+ * OOXML tint applied to a '#RRGGBB' hex. tint in [-1,1]. Best-effort (HSL lum).
+ * if (tint < 0) L = L * (1 + tint); else L = L * (1 - tint) + tint
+ */
+export function applyTint(hexRgb: string, tint: number): string {
+  if (tint === 0) return hexRgb;
+
+  // Parse hex to [0,1]
+  const r = parseInt(hexRgb.slice(1, 3), 16) / 255;
+  const g = parseInt(hexRgb.slice(3, 5), 16) / 255;
+  const b = parseInt(hexRgb.slice(5, 7), 16) / 255;
+
+  // RGB to HSL
+  const max = Math.max(r, g, b);
+  const min = Math.min(r, g, b);
+  let h = 0;
+  let s = 0;
+  let l = (max + min) / 2;
+
+  if (max !== min) {
+    const d = max - min;
+    s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
+    switch (max) {
+      case r: h = ((g - b) / d + (g < b ? 6 : 0)) / 6; break;
+      case g: h = ((b - r) / d + 2) / 6; break;
+      case b: h = ((r - g) / d + 4) / 6; break;
+    }
+  }
+
+  // Apply tint to luminance
+  if (tint < 0) {
+    l = l * (1 + tint);
+  } else {
+    l = l * (1 - tint) + tint;
+  }
+  l = Math.max(0, Math.min(1, l));
+
+  // HSL back to RGB
+  function hue2rgb(p: number, q: number, t: number): number {
+    if (t < 0) t += 1;
+    if (t > 1) t -= 1;
+    if (t < 1/6) return p + (q - p) * 6 * t;
+    if (t < 1/2) return q;
+    if (t < 2/3) return p + (q - p) * (2/3 - t) * 6;
+    return p;
+  }
+
+  let rOut: number, gOut: number, bOut: number;
+  if (s === 0) {
+    rOut = gOut = bOut = l;
+  } else {
+    const q = l < 0.5 ? l * (1 + s) : l + s - l * s;
+    const p = 2 * l - q;
+    rOut = hue2rgb(p, q, h + 1/3);
+    gOut = hue2rgb(p, q, h);
+    bOut = hue2rgb(p, q, h - 1/3);
+  }
+
+  const toHex = (v: number) => Math.round(v * 255).toString(16).padStart(2, '0').toUpperCase();
+  return '#' + toHex(rOut) + toHex(gOut) + toHex(bOut);
+}
+
+// --- Internal helpers ---
+
+// Standard 56-color indexed palette (BIFF8/OOXML standard colors)
+// Index 64 = system fg, 65 = system bg → omit (return undefined)
+const INDEXED_COLORS: (string | undefined)[] = [
+  '#000000', '#FFFFFF', '#FF0000', '#00FF00', '#0000FF', '#FFFF00', '#FF00FF', '#00FFFF',
+  '#000000', '#FFFFFF', '#FF0000', '#00FF00', '#0000FF', '#FFFF00', '#FF00FF', '#00FFFF',
+  '#800000', '#008000', '#000080', '#808000', '#800080', '#008080', '#C0C0C0', '#808080',
+  '#9999FF', '#993366', '#FFFFCC', '#CCFFFF', '#660066', '#FF8080', '#0066CC', '#CCCCFF',
+  '#000080', '#FF00FF', '#FFFF00', '#00FFFF', '#800080', '#800000', '#008080', '#0000FF',
+  '#00CCFF', '#CCFFFF', '#CCFFCC', '#FFFF99', '#99CCFF', '#FF99CC', '#CC99FF', '#FFCC99',
+  '#3366FF', '#33CCCC', '#99CC00', '#FFCC00', '#FF9900', '#FF6600', '#666699', '#969696',
+  '#003366', '#339966', '#003300', '#333300', '#993300', '#993366', '#333399', '#333333',
+  undefined, // 64 = system fg
+  undefined, // 65 = system bg
+];
+
+type ExcelJSColor = { argb?: string; theme?: number; tint?: number; indexed?: number };
+
+function renderColor(color: ExcelJSColor | undefined, palette: string[]): string | null {
+  if (!color) return null;
+
+  if (color.argb) {
+    // ARGB: 'FFRRGGBB' → '#RRGGBB'
+    const argb = color.argb;
+    if (argb.length === 8) {
+      return '#' + argb.slice(2).toUpperCase();
+    }
+    return null;
+  }
+
+  if (color.theme !== undefined) {
+    const tint = color.tint ?? 0;
+    if (palette.length > 0 && palette[color.theme]) {
+      const resolved = applyTint(palette[color.theme]!, tint);
+      if (tint !== 0) {
+        return `theme(${color.theme},tint=${tint.toFixed(4)},resolved=${resolved})`;
+      }
+      return `theme(${color.theme},resolved=${resolved})`;
+    }
+    // Palette empty or missing this index — raw only
+    if (tint !== 0) {
+      return `theme(${color.theme},tint=${tint.toFixed(4)})`;
+    }
+    return `theme(${color.theme})`;
+  }
+
+  if (color.indexed !== undefined) {
+    const hex = INDEXED_COLORS[color.indexed];
+    if (!hex) return null; // system fg/bg
+    return `indexed(${color.indexed},${hex})`;
+  }
+
+  return null;
+}
+
+/**
+ * Returns true if a rendered color token represents the default color for the given theme index.
+ * Handles both `theme(N)` (no palette) and `theme(N,resolved=...)` (palette resolved) forms.
+ * Used to suppress the default font color (theme 1 = Dark1 ≈ black) and default border color
+ * (theme 0 = Light1 ≈ white/auto) from style signatures.
+ */
+function isDefaultColorToken(token: string, defaultThemeIndex: number): boolean {
+  // Exact bare form: "theme(N)"
+  if (token === `theme(${defaultThemeIndex})`) return true;
+  // Resolved form: "theme(N,resolved=#RRGGBB)" — tint variants are NOT default
+  if (token.startsWith(`theme(${defaultThemeIndex},resolved=`) && !token.includes(',tint=')) return true;
+  return false;
+}
+
+/**
+ * Build a canonical style signature string from non-default cell parts.
+ * Returns null if the cell has no non-default styling.
+ */
+function cellStyleSignature(
+  cell: ExcelJS.Cell,
+  palette: string[],
+): string | null {
+  const parts: string[] = [];
+
+  // Fill: only pattern=solid (or other patterns) with fgColor
+  const fill = cell.fill as ExcelJS.Fill | undefined;
+  if (fill && (fill.type === 'pattern' || fill.type === 'gradient')) {
+    if (fill.type === 'pattern' && fill.pattern && fill.pattern !== 'none') {
+      const pf = fill as ExcelJS.FillPattern;
+      if (pf.fgColor) {
+        const colorStr = renderColor(pf.fgColor as ExcelJSColor, palette);
+        if (colorStr) {
+          parts.push(`fill:${colorStr}`);
+        }
+      }
+    } else if (fill.type === 'gradient') {
+      parts.push('fill:gradient');
+    }
+  }
+
+  // Font: only explicit flags + explicit color
+  const font = cell.font as ExcelJS.Font | undefined;
+  if (font) {
+    const fontParts: string[] = [];
+    if (font.bold === true) fontParts.push('bold');
+    if (font.italic === true) fontParts.push('italic');
+    if (font.underline) fontParts.push('underline');
+
+    // Color: only include if explicitly set (not the default theme 1 / auto-color)
+    const fontColor = renderColor(font.color as ExcelJSColor | undefined, palette);
+    if (fontColor && !isDefaultColorToken(fontColor, 1)) {
+      fontParts.push(fontColor);
+    }
+
+    if (fontParts.length > 0) {
+      parts.push(`font:${fontParts.join(',')}`);
+    }
+  }
+
+  // Border: for each side with a style
+  const border = cell.border as ExcelJS.Borders | undefined;
+  if (border) {
+    const sides: string[] = [];
+    for (const side of ['top', 'bottom', 'left', 'right', 'diagonal'] as const) {
+      const edge = border[side] as ExcelJS.Border | undefined;
+      if (edge?.style) {
+        const colorStr = renderColor(edge.color as ExcelJSColor | undefined, palette);
+        if (colorStr && !isDefaultColorToken(colorStr, 0)) {
+          sides.push(`${side}(${edge.style},${colorStr})`);
+        } else {
+          sides.push(`${side}(${edge.style})`);
+        }
+      }
+    }
+    if (sides.length > 0) {
+      parts.push(`border:${sides.join(',')}`);
+    }
+  }
+
+  // numFmt
+  const numFmt = cell.numFmt as string | undefined;
+  if (numFmt && numFmt !== 'General' && numFmt !== '') {
+    parts.push(`numFmt:"${numFmt}"`);
+  }
+
+  // Alignment
+  const alignment = cell.alignment as ExcelJS.Alignment | undefined;
+  if (alignment) {
+    const alignParts: string[] = [];
+    if (alignment.horizontal) alignParts.push(alignment.horizontal);
+    if (alignment.vertical) alignParts.push(alignment.vertical);
+    if (alignment.wrapText) alignParts.push('wrap');
+    if (alignParts.length > 0) {
+      parts.push(`align:${alignParts.join(',')}`);
+    }
+  }
+
+  if (parts.length === 0) return null;
+  return parts.join(';');
+}
+
+/** Parse an Excel range like "A1:C3" into 1-based row/col bounds. Returns null on parse failure. */
+function parseRange(rangeStr: string): { minRow: number; maxRow: number; minCol: number; maxCol: number } | null {
+  const match = rangeStr.match(/^([A-Z]+)(\d+):([A-Z]+)(\d+)$/i);
+  if (!match) return null;
+  function letterToCol(letters: string): number {
+    let col = 0;
+    for (const ch of letters.toUpperCase()) {
+      col = col * 26 + (ch.charCodeAt(0) - 64);
+    }
+    return col;
+  }
+  return {
+    minRow: parseInt(match[2]!, 10),
+    maxRow: parseInt(match[4]!, 10),
+    minCol: letterToCol(match[1]!),
+    maxCol: letterToCol(match[3]!),
+  };
+}
+
+/** Convert 1-based column index to Excel column letter(s). */
+function colIndexToLetter(colIdx: number): string {
+  let s = '';
+  let n = colIdx;
+  while (n > 0) {
+    const rem = (n - 1) % 26;
+    s = String.fromCharCode(65 + rem) + s;
+    n = Math.floor((n - 1) / 26);
+  }
+  return s;
+}
+
+/**
+ * Scan a worksheet (includeEmpty:true so decorated-but-empty cells count) and
+ * produce the dedup legend + range map. `palette` from resolveThemePalette.
+ *
+ * @param rangeBounds - When provided, only cells within [minRow..maxRow] x [minCol..maxCol]
+ *   are scanned, and merges are filtered to those intersecting this region. This must match
+ *   the same range filter applied to the values table so styles and values cover the same cells.
+ */
+export function extractSheetStyles(
+  ws: ExcelJS.Worksheet,
+  palette: string[],
+  maxRanges: number,
+  rangeBounds?: { minRow: number; maxRow: number; minCol: number; maxCol: number },
+): SheetStyleResult {
+  // Step 1: Scan all cells, build sig→id map and per-sig cell list
+  const sigToId = new Map<string, string>();
+  const cellsBySig = new Map<string, Array<[number, number]>>();
+  let counter = 0;
+
+  ws.eachRow({ includeEmpty: true }, (row, r) => {
+    if (rangeBounds && (r < rangeBounds.minRow || r > rangeBounds.maxRow)) return;
+    row.eachCell({ includeEmpty: true }, (cell, c) => {
+      if (rangeBounds && (c < rangeBounds.minCol || c > rangeBounds.maxCol)) return;
+      const sig = cellStyleSignature(cell, palette);
+      if (!sig) return;
+
+      if (!sigToId.has(sig)) {
+        sigToId.set(sig, `s${++counter}`);
+        cellsBySig.set(sig, []);
+      }
+      cellsBySig.get(sig)!.push([r, c]);
+    });
+  });
+
+  // Step 2: Build legend in id order
+  const idOrder: Array<{ id: string; sig: string }> = [];
+  for (const [sig, id] of sigToId) {
+    idOrder.push({ id, sig });
+  }
+  idOrder.sort((a, b) => {
+    const na = parseInt(a.id.slice(1), 10);
+    const nb = parseInt(b.id.slice(1), 10);
+    return na - nb;
+  });
+
+  // Step 3: For each sig, group cells into rectangles
+  const assignments: Array<{ id: string; ranges: string[] }> = [];
+  let totalRanges = 0;
+  let truncated = false;
+
+  for (const { id, sig } of idOrder) {
+    if (truncated) break;
+
+    const cells = cellsBySig.get(sig)!;
+
+    // Bucket by row
+    const byRow = new Map<number, number[]>();
+    for (const [r, c] of cells) {
+      if (!byRow.has(r)) byRow.set(r, []);
+      byRow.get(r)!.push(c);
+    }
+
+    // For each row, sort and split into contiguous horizontal runs
+    // A run is (row, colStart, colEnd)
+    const allRuns: Array<{ r: number; c1: number; c2: number }> = [];
+    for (const [r, cols] of byRow) {
+      cols.sort((a, b) => a - b);
+      let start = cols[0]!;
+      let prev = cols[0]!;
+      for (let i = 1; i < cols.length; i++) {
+        if (cols[i]! !== prev + 1) {
+          allRuns.push({ r, c1: start, c2: prev });
+          start = cols[i]!;
+        }
+        prev = cols[i]!;
+      }
+      allRuns.push({ r, c1: start, c2: prev });
+    }
+
+    // Sort runs by row, then c1
+    allRuns.sort((a, b) => a.r !== b.r ? a.r - b.r : a.c1 - b.c1);
+
+    // Merge vertically: greedy - open rectangles extended when next row has same c1,c2.
+    // O(K) implementation: openRects is keyed by (c1,c2); after finishing each row r,
+    // any rect not extended this row (r2 !== r) is flushed to closedRects immediately.
+    type Rect = { r1: number; r2: number; c1: number; c2: number };
+    // Key: `${c1},${c2}` → open rect
+    const openMap = new Map<string, Rect>();
+    const closedRects: Rect[] = [];
+
+    // Group runs by row so we can flush after each row
+    const runsByRow = new Map<number, Array<{ c1: number; c2: number }>>();
+    for (const run of allRuns) {
+      if (!runsByRow.has(run.r)) runsByRow.set(run.r, []);
+      runsByRow.get(run.r)!.push({ c1: run.c1, c2: run.c2 });
+    }
+
+    // Process rows in ascending order
+    const sortedRows = [...runsByRow.keys()].sort((a, b) => a - b);
+    for (const r of sortedRows) {
+      const runs = runsByRow.get(r)!;
+      const extendedKeys = new Set<string>();
+
+      for (const { c1, c2 } of runs) {
+        const key = `${c1},${c2}`;
+        const existing = openMap.get(key);
+        if (existing && existing.r2 === r - 1) {
+          // Extend the open rect into this row
+          existing.r2 = r;
+          extendedKeys.add(key);
+        } else {
+          // If there was a stale open rect with this key, close it first
+          if (existing) {
+            closedRects.push(existing);
+          }
+          // Open a new rect
+          openMap.set(key, { r1: r, r2: r, c1, c2 });
+          extendedKeys.add(key);
+        }
+      }
+
+      // Flush any open rects that were NOT extended this row (r2 !== r)
+      for (const [key, rect] of openMap) {
+        if (rect.r2 !== r) {
+          closedRects.push(rect);
+          openMap.delete(key);
+        }
+      }
+    }
+
+    // Close all remaining open rects
+    for (const rect of openMap.values()) {
+      closedRects.push(rect);
+    }
+
+    // Emit ranges
+    const ranges: string[] = [];
+    for (const rect of closedRects) {
+      if (totalRanges >= maxRanges) {
+        truncated = true;
+        break;
+      }
+      let rangeStr: string;
+      if (rect.r1 === rect.r2 && rect.c1 === rect.c2) {
+        rangeStr = `${colIndexToLetter(rect.c1)}${rect.r1}`;
+      } else {
+        rangeStr = `${colIndexToLetter(rect.c1)}${rect.r1}:${colIndexToLetter(rect.c2)}${rect.r2}`;
+      }
+      ranges.push(rangeStr);
+      totalRanges++;
+    }
+
+    if (ranges.length > 0) {
+      assignments.push({ id, ranges });
+    }
+    if (truncated) break;
+  }
+
+  // Step 4: Merges from ws.model.merges (filtered to rangeBounds when provided)
+  const allMerges: string[] = (ws.model.merges as string[] | undefined) ?? [];
+  const merges: string[] = rangeBounds
+    ? allMerges.filter((m) => {
+        // Parse merge range "A1:C3" and check for intersection with rangeBounds
+        const mp = parseRange(m);
+        if (!mp) return true; // unparseable: keep it
+        // Two rectangles intersect if NOT (one is completely to the side/above/below the other)
+        return !(mp.maxRow < rangeBounds.minRow || mp.minRow > rangeBounds.maxRow ||
+                 mp.maxCol < rangeBounds.minCol || mp.minCol > rangeBounds.maxCol);
+      })
+    : allMerges;
+
+  // Step 5: Conditional formatting
+  const conditionalFormatting = Boolean(
+    ((ws as unknown) as { conditionalFormattings?: unknown[] }).conditionalFormattings?.length
+  );
+
+  return {
+    legend: idOrder,
+    assignments,
+    merges,
+    conditionalFormatting,
+    truncated,
+  };
+}
diff --git a/src/engine/tools/office.test.ts b/src/engine/tools/office.test.ts
index 2364211..37b24cf 100644
--- a/src/engine/tools/office.test.ts
+++ b/src/engine/tools/office.test.ts
@@ -358,4 +358,27 @@ describe('Read* tools — format mismatch rejection (issue #246)', () => {
     expect(result?.isError).toBe(false);
     expect(result?.output).toContain('Sheet1');
   });
+
+  it('ReadExcel includes a Styles section only when include_styles=true', async () => {
+    workspacePath = makeWorkspace();
+    fs.mkdirSync(path.join(workspacePath, 'input'), { recursive: true });
+
+    const ExcelJS = (await import('exceljs')).default;
+    const wb = new ExcelJS.Workbook();
+    const ws = wb.addWorksheet('Sheet1');
+    ws.getCell('A1').value = 'Header';
+    ws.getCell('A1').fill = { type: 'pattern', pattern: 'solid', fgColor: { argb: 'FFFFF2CC' } };
+    ws.getCell('A1').font = { bold: true };
+    await wb.xlsx.writeFile(path.join(workspacePath, 'input', 'styled.xlsx'));
+
+    // Without include_styles: no Styles section (backward compat)
+    const plain = await executeTool('ReadExcel', { path: 'input/styled.xlsx' }, makeContext(workspacePath));
+    expect(plain!.output).not.toContain('### Styles');
+
+    // With include_styles: Styles section present with fill color and font bold
+    const styled = await executeTool('ReadExcel', { path: 'input/styled.xlsx', include_styles: true }, makeContext(workspacePath));
+    expect(styled!.output).toContain('### Styles');
+    expect(styled!.output).toContain('#FFF2CC');
+    expect(styled!.output).toMatch(/bold/);
+  });
 });
diff --git a/src/engine/tools/office.ts b/src/engine/tools/office.ts
index 140372e..4ff64a5 100644
--- a/src/engine/tools/office.ts
+++ b/src/engine/tools/office.ts
@@ -9,6 +9,7 @@ import { PDFParse } from 'pdf-parse';
 import { ToolDef } from '../../llm/openai-compat.js';
 import type { ToolContext, ToolResult } from './core.js';
 import { resolveAndGuard, resolveOutputPathWithin, truncateToBudget, getToolOutputBudgetTokens } from './core.js';
+import { resolveThemePalette, extractSheetStyles } from './excel-styles.js';
 import { logger } from '../../logger.js';
 import { callVisionModel, resolveImagePath } from './image.js';
 import type {
@@ -204,7 +205,7 @@ const READ_EXCEL_DEF: ToolDef = {
   type: 'function',
   function: {
     name: 'ReadExcel',
-    description: 'Excel (.xlsx) を読み取りテキストで返す。詳細は ReadToolDoc({ name: "ReadExcel" })。',
+    description: 'Excel (.xlsx) を読み取りテキストで返す。include_styles:true でセル装飾も取得可。詳細は ReadToolDoc({ name: "ReadExcel" })。',
     parameters: {
       type: 'object',
       properties: {
@@ -212,6 +213,8 @@ const READ_EXCEL_DEF: ToolDef = {
         sheet: { type: 'string', description: 'シート名（省略時は全シート）' },
         range: { type: 'string', description: 'セル範囲（例: A1:D10、省略時はシート全体）' },
         max_cells: { type: 'number', description: '最大セル数（デフォルト: 1000）' },
+        include_styles: { type: 'boolean', description: 'true でセル装飾(背景色/フォント/罫線/書式/結合)を ### Styles として追記。デフォルト false' },
+        max_style_ranges: { type: 'number', description: 'include_styles 時に出力する style range の上限（デフォルト 250）' },
       },
       required: ['path'],
     },
@@ -538,6 +541,8 @@ async function executeReadExcel(
   const sheetFilter = typeof input['sheet'] === 'string' ? input['sheet'] : undefined;
   const rangeFilter = typeof input['range'] === 'string' ? input['range'] : undefined;
   const maxCells = typeof input['max_cells'] === 'number' ? input['max_cells'] : 1000;
+  const includeStyles = input['include_styles'] === true;
+  const maxStyleRanges = typeof input['max_style_ranges'] === 'number' ? input['max_style_ranges'] : 250;
 
   let resolved: string;
   try {
@@ -583,6 +588,9 @@ async function executeReadExcel(
       return { output: `Failed to read Excel file: ${(e as Error).message}`, isError: true };
     }
 
+    const themeXml = includeStyles ? ((wb.model as unknown as { themes?: { theme1?: string } }).themes?.theme1) : undefined;
+    const palette = includeStyles ? resolveThemePalette(themeXml) : [];
+
     const filename = path.basename(resolved);
     const sheetBlocks: ExcelSheetBlock[] = [];
     let totalCells = 0;
@@ -697,6 +705,26 @@ async function executeReadExcel(
       parts.push('');
     }
 
+    if (includeStyles) {
+      let rangeBudget = maxStyleRanges;
+      for (const ws of wb.worksheets) {
+        if (sheetFilter && ws.name !== sheetFilter) continue;
+        const styleBounds = rangeFilter ? parseRange(rangeFilter) : null;
+        const styles = extractSheetStyles(ws, palette, rangeBudget, styleBounds ?? undefined);
+        rangeBudget -= styles.assignments.reduce((n, a) => n + a.ranges.length, 0);
+        if (styles.legend.length === 0 && styles.merges.length === 0 && !styles.conditionalFormatting) continue;
+        parts.push(`### Styles — ${ws.name}`);
+        for (const { id, sig } of styles.legend) parts.push(`${id} = ${sig}`);
+        parts.push('');
+        for (const { id, ranges } of styles.assignments) parts.push(`${id}: ${ranges.join(',')}`);
+        if (styles.merges.length) parts.push(`merges: ${styles.merges.join(',')}`);
+        if (styles.conditionalFormatting) parts.push('conditionalFormatting: present (effective styles not evaluated)');
+        if (styles.truncated || rangeBudget <= 0) parts.push(`[styles truncated: max_style_ranges=${maxStyleRanges} reached]`);
+        parts.push('');
+        if (rangeBudget <= 0) break;
+      }
+    }
+
     if (doc.warnings.length > 0) {
       parts.push('### Warnings');
       for (const w of doc.warnings) {
diff --git a/src/engine/tools/orchestration.ts b/src/engine/tools/orchestration.ts
index 9d3b3a5..7602d3b 100644
--- a/src/engine/tools/orchestration.ts
+++ b/src/engine/tools/orchestration.ts
@@ -52,8 +52,11 @@ export async function executeTool(
   }
 
   const builtinPath = join('pieces', `${piece}.yaml`);
-  const customPath = ctx.customPiecesDir ? join(ctx.customPiecesDir, `${piece}.yaml`) : null;
-  if (!existsSync(builtinPath) && !(customPath && existsSync(customPath))) {
+  const customDirs = ctx.customPiecesDir
+    ? (Array.isArray(ctx.customPiecesDir) ? ctx.customPiecesDir : [ctx.customPiecesDir])
+    : [];
+  const customExists = customDirs.some(d => existsSync(join(d, `${piece}.yaml`)));
+  if (!existsSync(builtinPath) && !customExists) {
     return {
       output: `指定されたピース "${piece}" が見つかりません。利用可能なピースを確認してください。`,
       isError: true,
diff --git a/src/engine/tools/pieces.test.ts b/src/engine/tools/pieces.test.ts
index 3e4aeef..c97af86 100644
--- a/src/engine/tools/pieces.test.ts
+++ b/src/engine/tools/pieces.test.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect, beforeEach, afterEach } from 'vitest';
-import { mkdtempSync, rmSync, existsSync, readFileSync, writeFileSync, cpSync } from 'fs';
+import { mkdtempSync, mkdirSync, rmSync, existsSync, readFileSync, writeFileSync, cpSync } from 'fs';
 import { join } from 'path';
 import { tmpdir } from 'os';
 import { executeTool } from './pieces.js';
@@ -87,6 +87,111 @@ movements:
   });
 });
 
+describe('customPiecesDir as array — P1-a regression', () => {
+  /**
+   * When worker passes customPiecesDir=[userDir, globalDir] to ToolContext,
+   * ListPieces and GetPiece must see pieces from BOTH dirs.
+   * CreatePiece must write to dirs[0] (per-user dir, not global).
+   */
+  let userDir: string;
+  let globalDir: string;
+
+  beforeEach(() => {
+    userDir = mkdtempSync(join(tmpdir(), 'pieces-user-'));
+    globalDir = mkdtempSync(join(tmpdir(), 'pieces-global-'));
+  });
+
+  afterEach(() => {
+    rmSync(userDir, { recursive: true, force: true });
+    rmSync(globalDir, { recursive: true, force: true });
+  });
+
+  const userPiece = `name: user-only-piece
+description: user piece
+max_movements: 1
+initial_movement: do
+movements:
+  - name: do
+    edit: false
+    persona: p
+    instruction: i
+    allowed_tools: []
+    rules:
+      - condition: done
+        next: do
+`;
+
+  const globalPiece = `name: global-only-piece
+description: global piece
+max_movements: 1
+initial_movement: do
+movements:
+  - name: do
+    edit: false
+    persona: p
+    instruction: i
+    allowed_tools: []
+    rules:
+      - condition: done
+        next: do
+`;
+
+  function arrayCtx(): ToolContext {
+    return { workspacePath: '/tmp/dummy', editAllowed: false, customPiecesDir: [userDir, globalDir] };
+  }
+
+  it('ListPieces returns pieces from BOTH per-user and global-custom dirs', async () => {
+    writeFileSync(join(userDir, 'user-only-piece.yaml'), userPiece, 'utf-8');
+    writeFileSync(join(globalDir, 'global-only-piece.yaml'), globalPiece, 'utf-8');
+
+    const result = await executeTool('ListPieces', {}, arrayCtx());
+    expect(result?.isError).toBe(false);
+    expect(result?.output).toContain('user-only-piece');
+    expect(result?.output).toContain('global-only-piece');
+  });
+
+  it('GetPiece finds a piece in the second custom dir (global-custom)', async () => {
+    writeFileSync(join(globalDir, 'global-only-piece.yaml'), globalPiece, 'utf-8');
+
+    const result = await executeTool('GetPiece', { name: 'global-only-piece' }, arrayCtx());
+    expect(result?.isError).toBe(false);
+    expect(result?.output).toContain('global piece');
+  });
+
+  it('GetPiece prefers dirs[0] (per-user) over dirs[1] (global) for same name', async () => {
+    const userVersion = userPiece.replace('description: user piece', 'description: per-user version');
+    writeFileSync(join(userDir, 'global-only-piece.yaml'), userVersion, 'utf-8');
+    writeFileSync(join(globalDir, 'global-only-piece.yaml'), globalPiece, 'utf-8');
+
+    const result = await executeTool('GetPiece', { name: 'global-only-piece' }, arrayCtx());
+    expect(result?.isError).toBe(false);
+    expect(result?.output).toContain('per-user version');
+  });
+
+  it('CreatePiece writes to dirs[0] (per-user dir), not global dir', async () => {
+    const newPiece = `name: brand-new-piece
+description: new
+max_movements: 5
+initial_movement: do
+movements:
+  - name: do
+    edit: false
+    persona: p
+    instruction: i
+    allowed_tools: []
+    rules:
+      - condition: done
+        next: do
+`;
+    const result = await executeTool('CreatePiece', { yaml_content: newPiece }, arrayCtx());
+    expect(result?.isError).toBe(false);
+    // Must land in userDir (dirs[0])
+    expect(existsSync(join(userDir, 'brand-new-piece.yaml'))).toBe(true);
+    // Must NOT land in globalDir (dirs[1])
+    expect(existsSync(join(globalDir, 'brand-new-piece.yaml'))).toBe(false);
+  });
+});
+
 describe('UpdatePiece', () => {
   // Uses the real bundled `chat.yaml` to exercise the built-in guard. The
   // file's pre-update content is captured up-front so we can detect any
diff --git a/src/engine/tools/pieces.ts b/src/engine/tools/pieces.ts
index 4933135..1870c34 100644
--- a/src/engine/tools/pieces.ts
+++ b/src/engine/tools/pieces.ts
@@ -7,10 +7,20 @@ import type { ToolContext, ToolResult } from './core.js';
 const BUILTIN_PIECES_DIR = resolve(process.cwd(), 'pieces');
 const VALID_NAME = /^[a-z0-9-]+$/;
 
-function findPiecePath(name: string, customDir: string | undefined): string | null {
-  if (customDir) {
-    const customPath = join(customDir, `${name}.yaml`);
-    if (existsSync(customPath)) return customPath;
+/** Normalise `string | string[] | undefined` → `string[]` (may be empty). */
+function toCustomDirs(customDir: string | string[] | undefined): string[] {
+  if (!customDir) return [];
+  return Array.isArray(customDir) ? customDir : [customDir];
+}
+
+/**
+ * Search all custom dirs in order, then fall back to built-in.
+ * Returns the first path that exists, or null.
+ */
+function findPiecePath(name: string, customDir: string | string[] | undefined): string | null {
+  for (const d of toCustomDirs(customDir)) {
+    const p = join(d, `${name}.yaml`);
+    if (existsSync(p)) return p;
   }
   const builtinPath = join(BUILTIN_PIECES_DIR, `${name}.yaml`);
   if (existsSync(builtinPath)) return builtinPath;
@@ -19,17 +29,16 @@ function findPiecePath(name: string, customDir: string | undefined): string | nu
 
 /**
  * A piece is "built-in" when it lives only under the bundled BUILTIN_PIECES_DIR
- * (no override in customDir). Built-ins are git-tracked and shipped with the
+ * (no override in any custom dir). Built-ins are git-tracked and shipped with the
  * app — letting the LLM rewrite them in place corrupts the install (a real
  * incident: the agent silently replaced game-tweet-generator with a version
  * missing max_movements, making every subsequent run abort instantly). The
  * LLM should use CreatePiece with a new name to derive a customized variant
  * instead.
  */
-function isBuiltinOnly(name: string, customDir: string | undefined): boolean {
-  if (customDir) {
-    const customPath = join(customDir, `${name}.yaml`);
-    if (existsSync(customPath)) return false;
+function isBuiltinOnly(name: string, customDir: string | string[] | undefined): boolean {
+  for (const d of toCustomDirs(customDir)) {
+    if (existsSync(join(d, `${name}.yaml`))) return false;
   }
   const builtinPath = join(BUILTIN_PIECES_DIR, `${name}.yaml`);
   return existsSync(builtinPath);
@@ -156,7 +165,9 @@ function executeListPieces(ctx: ToolContext): ToolResult {
     const seen = new Set<string>();
     const pieces: Array<{ name: string; description: string; keywords: string[]; custom: boolean }> = [];
     const dirs: Array<{ dir: string; custom: boolean }> = [];
-    if (ctx.customPiecesDir && existsSync(ctx.customPiecesDir)) dirs.push({ dir: ctx.customPiecesDir, custom: true });
+    for (const d of toCustomDirs(ctx.customPiecesDir)) {
+      if (existsSync(d)) dirs.push({ dir: d, custom: true });
+    }
     dirs.push({ dir: BUILTIN_PIECES_DIR, custom: false });
 
     for (const { dir, custom } of dirs) {
@@ -231,8 +242,9 @@ function executeCreatePiece(input: Record<string, unknown>, ctx: ToolContext): T
     return { output: `Piece "${piece.name}" already exists. Use UpdatePiece to modify it.`, isError: true };
   }
 
-  // カスタムディレクトリがあればそこに、なければ builtin に書き込み
-  const targetDir = ctx.customPiecesDir ?? BUILTIN_PIECES_DIR;
+  // Write to the FIRST custom dir (per-user dir), or fall back to builtin if no custom dirs.
+  const customDirs = toCustomDirs(ctx.customPiecesDir);
+  const targetDir = customDirs[0] ?? BUILTIN_PIECES_DIR;
   mkdirSync(targetDir, { recursive: true });
   const filePath = join(targetDir, `${piece.name}.yaml`);
   try {
diff --git a/src/worker.test.ts b/src/worker.test.ts
index 456da81..e0545d7 100644
--- a/src/worker.test.ts
+++ b/src/worker.test.ts
@@ -3,6 +3,8 @@ import { existsSync, mkdirSync, readFileSync, writeFileSync, mkdtempSync } from
 import { join } from 'path';
 import { tmpdir } from 'os';
 import { buildRetryHandoffSummary, Worker } from './worker.js';
+import { userPiecesDir } from './user-folder/paths.js';
+import { loadPiece } from './engine/piece-runner.js';
 import type { AppConfig } from './config.js';
 import type { Job } from './db/repository.js';
 
@@ -358,3 +360,53 @@ describe('Worker', () => {
     void worker; // worker インスタンスを参照して lint 警告を回避
   });
 });
+
+// ---------------------------------------------------------------------------
+// Regression: null-ownerId job resolves pieces from data/users/local/pieces
+// ---------------------------------------------------------------------------
+
+describe('Worker piece resolution for null-ownerId job', () => {
+  it('a no-auth job (ownerId null) can load a piece from data/users/local/pieces', () => {
+    const tempDir = mkdtempSync(join(tmpdir(), 'worker-piece-res-'));
+    const piecesDir = join(tempDir, 'pieces');
+    const userFolderRoot = join(tempDir, 'users');
+    mkdirSync(piecesDir);
+
+    // Write a piece under local user-custom dir (where no-auth POST now writes)
+    const localPiecesDir = userPiecesDir(userFolderRoot, 'local');
+    mkdirSync(localPiecesDir, { recursive: true });
+    writeFileSync(join(localPiecesDir, 'local-piece.yaml'), [
+      'name: local-piece',
+      'description: local custom piece',
+      'max_movements: 1',
+      'initial_movement: only',
+      'movements:',
+      '  - name: only',
+      '    edit: false',
+      '    persona: p',
+      '    instruction: i',
+      '    allowed_tools: [Read]',
+      '    default_next: COMPLETE',
+      '    rules: []',
+    ].join('\n'));
+
+    // Simulate what worker.ts does: ownerForPieces = job.ownerId ?? 'local'
+    const ownerForPieces = (null as string | null) ?? 'local';
+    const customPieceDirs = [userPiecesDir(userFolderRoot, ownerForPieces)].filter(Boolean);
+
+    // loadPiece should find the piece in the local user-custom dir
+    const piece = loadPiece('local-piece', piecesDir, customPieceDirs);
+    expect(piece.name).toBe('local-piece');
+    expect(piece.description).toBe('local custom piece');
+  });
+
+  it('a null-ownerId job resolves the local user-custom dir path consistently', () => {
+    const userFolderRoot = '/data/users';
+    // The fixed worker uses: job.ownerId ?? 'local'
+    const ownerForNullJob = (null as string | null) ?? 'local';
+    const resolvedDir = userPiecesDir(userFolderRoot, ownerForNullJob);
+    expect(resolvedDir).toContain('local');
+    // Same dir that no-auth POST writes to
+    expect(resolvedDir).toBe(userPiecesDir(userFolderRoot, 'local'));
+  });
+});
diff --git a/src/worker.ts b/src/worker.ts
index 817e0f0..20c003e 100644
--- a/src/worker.ts
+++ b/src/worker.ts
@@ -1,4 +1,5 @@
 import { Repository, Job, localTaskRepoName, type JobRole } from './db/repository.js';
+import { userPiecesDir } from './user-folder/paths.js';
 import { BrowserSessionRepo } from './db/browser-session-repo.js';
 import { assertProfileOwner } from './engine/browser-session-auth.js';
 import { initMasterKey, decryptUserDek, decryptStateBlob } from './crypto/sessions.js';
@@ -922,9 +923,17 @@ export class Worker {
     // watchdog 誤検知防止: runPiece 実行中に updated_at を定期更新
     let heartbeatTimer: ReturnType<typeof setInterval> | undefined;
     try {
-      // Piece 読み込み
-      logger.info(`[worker:${this.workerId}] job ${jobId} loadPiece piece=${job.pieceName} customPiecesDir=${this.config.customPiecesDir ?? 'none'} piecesDir=pieces`);
-      const piece = loadPiece(job.pieceName, 'pieces', this.config.customPiecesDir);
+      // Piece 読み込み: per-user カスタムディレクトリ → global カスタムディレクトリ → builtin の順に探索
+      // No-auth jobs (ownerId null) resolve pieces from data/users/local/pieces, matching
+      // where no-auth POST now writes (LOCAL_OWNER='local' in pieces-api.ts).
+      const userFolderRoot = this.config.userFolderRoot ?? './data/users';
+      const ownerForPieces = job.ownerId ?? 'local';
+      const customPieceDirs = [
+        userPiecesDir(userFolderRoot, ownerForPieces),
+        this.config.customPiecesDir,
+      ].filter((d): d is string => !!d);
+      logger.info(`[worker:${this.workerId}] job ${jobId} loadPiece piece=${job.pieceName} customDirs=[${customPieceDirs.join(', ') || 'none'}] piecesDir=pieces`);
+      const piece = loadPiece(job.pieceName, 'pieces', customPieceDirs);
       if (
         piece.model &&
         this.availableModels.size > 0 &&
@@ -1283,7 +1292,7 @@ export class Worker {
         abortController: jobAbortController,
         safetyConfig: this.config.safety,
         searchFilter: this.config.searchFilter,
-        customPiecesDir: this.config.customPiecesDir,
+        customPiecesDir: customPieceDirs,
         contextManager,
         vlmEnabled: workerDef.vlm === true,
         jobId,                  // Phase 5: subtask handoff parent identity
diff --git a/ui/src/App.tsx b/ui/src/App.tsx
index f50b237..8b33201 100644
--- a/ui/src/App.tsx
+++ b/ui/src/App.tsx
@@ -399,7 +399,7 @@ function AppInner({ isAdmin, authEnabled, user }: { isAdmin: boolean; authEnable
       </div>
 
       {page === 'settings' && <div className="flex-1 min-h-0 overflow-hidden"><SettingsPage isAdmin={isAdmin} /></div>}
-      {page === 'pieces' && isAdmin && <div className="flex-1 min-h-0 overflow-hidden"><PiecesPage showToast={showToast} /></div>}
+      {page === 'pieces' && <div className="flex-1 min-h-0 overflow-hidden"><PiecesPage showToast={showToast} isAdmin={isAdmin} /></div>}
       {page === 'schedules' && <div className="flex-1 min-h-0 overflow-hidden"><SchedulesPage showToast={showToast} /></div>}
       {page === 'users' && isAdmin && authEnabled && <div className="flex-1 min-h-0 overflow-hidden"><UsersPage /></div>}
       {page === 'captcha' && <div className="flex-1 min-h-0 overflow-hidden"><AdminCaptchaPage isAdmin={isAdmin} /></div>}
diff --git a/ui/src/api.ts b/ui/src/api.ts
index 72a7328..362b016 100644
--- a/ui/src/api.ts
+++ b/ui/src/api.ts
@@ -358,8 +358,10 @@ export async function reloadConfig(): Promise<void> {
 
 // --- Pieces ---
 export interface DriftStatus { drifted: boolean; forkedFromCommit: string | null; latestCommit: string | null }
-export interface PieceSummary { name: string; description: string; triggers?: { keywords: string[] }; custom?: boolean; drift?: DriftStatus; requiredMcp?: string[] }
+export interface PieceSummary { name: string; description: string; triggers?: { keywords: string[] }; custom?: boolean; source?: 'builtin' | 'user-custom' | 'global-custom'; ownerId?: string; drift?: DriftStatus; requiredMcp?: string[] }
 export interface PieceDef { name: string; description: string; max_movements: number; initial_movement: string; triggers?: { keywords: string[] }; movements: any[]; requiredMcp?: string[] }
+/** Full response from GET /api/pieces/:name — includes the server-resolved source. */
+export interface PieceFetchResult { piece: PieceDef; source: 'builtin' | 'user-custom' | 'global-custom'; ownerId?: string }
 
 export async function fetchPieces(): Promise<PieceSummary[]> {
   const res = await fetch(`${BASE}/pieces`);
@@ -368,15 +370,17 @@ export async function fetchPieces(): Promise<PieceSummary[]> {
   return data.pieces;
 }
 
-export async function fetchPiece(name: string): Promise<PieceDef> {
-  const res = await fetch(`${BASE}/pieces/${name}`);
+export async function fetchPiece(name: string, source?: 'builtin' | 'user-custom' | 'global-custom'): Promise<PieceFetchResult> {
+  const url = source ? `${BASE}/pieces/${name}?source=${source}` : `${BASE}/pieces/${name}`;
+  const res = await fetch(url);
   const data = await res.json();
   if (!res.ok) throw new Error(data?.error ?? 'Failed to fetch piece');
-  return data.piece;
+  return { piece: data.piece, source: data.source, ownerId: data.ownerId };
 }
 
-export async function updatePiece(name: string, piece: PieceDef): Promise<void> {
-  const res = await fetch(`${BASE}/pieces/${name}`, {
+export async function updatePiece(name: string, piece: PieceDef, source?: 'builtin' | 'user-custom' | 'global-custom'): Promise<void> {
+  const url = source ? `${BASE}/pieces/${name}?source=${source}` : `${BASE}/pieces/${name}`;
+  const res = await fetch(url, {
     method: 'PUT',
     headers: { 'Content-Type': 'application/json' },
     body: JSON.stringify(piece),
@@ -384,17 +388,22 @@ export async function updatePiece(name: string, piece: PieceDef): Promise<void>
   if (!res.ok) { const d = await res.json(); throw new Error(d?.error ?? 'Failed to update piece'); }
 }
 
-export async function createPiece(piece: PieceDef): Promise<void> {
+export interface PieceCreateResult { source: 'builtin' | 'user-custom' | 'global-custom' }
+
+export async function createPiece(piece: PieceDef): Promise<PieceCreateResult> {
   const res = await fetch(`${BASE}/pieces`, {
     method: 'POST',
     headers: { 'Content-Type': 'application/json' },
     body: JSON.stringify(piece),
   });
   if (!res.ok) { const d = await res.json(); throw new Error(d?.error ?? 'Failed to create piece'); }
+  const d = await res.json();
+  return { source: d.source ?? 'user-custom' };
 }
 
-export async function deletePiece(name: string): Promise<void> {
-  const res = await fetch(`${BASE}/pieces/${name}`, { method: 'DELETE' });
+export async function deletePiece(name: string, source?: 'builtin' | 'user-custom' | 'global-custom'): Promise<void> {
+  const url = source ? `${BASE}/pieces/${name}?source=${source}` : `${BASE}/pieces/${name}`;
+  const res = await fetch(url, { method: 'DELETE' });
   if (!res.ok) { const d = await res.json(); throw new Error(d?.error ?? 'Failed to delete piece'); }
 }
 
diff --git a/ui/src/components/create/CreateTaskDialog.tsx b/ui/src/components/create/CreateTaskDialog.tsx
index 6dcde59..debf7f6 100644
--- a/ui/src/components/create/CreateTaskDialog.tsx
+++ b/ui/src/components/create/CreateTaskDialog.tsx
@@ -5,6 +5,7 @@ import { CreateLocalTaskInput, fetchMyOrgs, Visibility, listBrowserSessionProfil
 import { AttachmentDropzone } from './AttachmentDropzone';
 import { ScheduleFields } from './ScheduleFields';
 import { usePieceList } from '../../hooks/usePieces';
+import { resolvePieceOptions } from '../../lib/splitPieces';
 import { useAuthState } from '../../App';
 
 interface CreateTaskDialogProps {
@@ -80,7 +81,8 @@ export function CreateTaskDialog({ onClose, onSubmit, initialPiece, initialBody,
     scheduledAt: '',
   });
 
-  const selectedPiece = (pieces ?? []).find(p => p.name === form.piece);
+  const resolvedPieces = resolvePieceOptions(pieces ?? []);
+  const selectedPiece = resolvedPieces.find(p => p.name === form.piece);
   const missingMcp = selectedPiece?.requiredMcp
     ? selectedPiece.requiredMcp.filter(
         (id) => !(connections ?? []).find((c) => c.serverId === id && c.connected),
@@ -241,7 +243,7 @@ export function CreateTaskDialog({ onClose, onSubmit, initialPiece, initialBody,
                         className="w-full px-2.5 py-1.5 border border-slate-200 rounded-lg text-xs outline-none focus:border-accent"
                       >
                         <option value="auto">自動選択</option>
-                        {(pieces ?? []).map(p => (
+                        {resolvedPieces.map(p => (
                           <option key={p.name} value={p.name}>{p.name}</option>
                         ))}
                       </select>
diff --git a/ui/src/components/detail/ContinueWithPieceDialog.tsx b/ui/src/components/detail/ContinueWithPieceDialog.tsx
index 5726312..4487e39 100644
--- a/ui/src/components/detail/ContinueWithPieceDialog.tsx
+++ b/ui/src/components/detail/ContinueWithPieceDialog.tsx
@@ -2,6 +2,7 @@ import { useState } from 'react';
 import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
 import { continueTaskWithPiece, fetchLocalTaskComments } from '../../api';
 import { usePieceList } from '../../hooks/usePieces';
+import { resolvePieceOptions } from '../../lib/splitPieces';
 import { MarkdownText } from '../../lib/markdown-text';
 
 interface PrevJobInfo {
@@ -123,7 +124,7 @@ export function ContinueWithPieceDialog({
               disabled={piecesQuery.isLoading}
               className="px-3 py-2 rounded-md border border-hairline text-[13px] focus:outline-none focus:ring-2 focus:ring-accent/30 focus:border-accent"
             >
-              {(piecesQuery.data ?? []).map(p => (
+              {resolvePieceOptions(piecesQuery.data ?? []).map(p => (
                 <option key={p.name} value={p.name}>
                   {p.name}
                   {p.name === prevJob.pieceName ? ' (現在)' : ''}
diff --git a/ui/src/components/layout/TopBar.tsx b/ui/src/components/layout/TopBar.tsx
index 38eaba3..b5ba0bb 100644
--- a/ui/src/components/layout/TopBar.tsx
+++ b/ui/src/components/layout/TopBar.tsx
@@ -18,7 +18,7 @@ interface TopBarProps {
 export const NAV_ITEMS: Array<{ id: PageId; label: string; adminOnly: boolean; requiresAuth: boolean }> = [
   { id: 'tasks', label: 'タスク', adminOnly: false, requiresAuth: false },
   { id: 'schedules', label: 'スケジュール', adminOnly: false, requiresAuth: false },
-  { id: 'pieces', label: 'Pieces', adminOnly: true, requiresAuth: false },
+  { id: 'pieces', label: 'Pieces', adminOnly: false, requiresAuth: false },
   { id: 'captcha', label: 'CAPTCHA', adminOnly: true, requiresAuth: false },
   { id: 'settings', label: '設定', adminOnly: false, requiresAuth: false },
   { id: 'users', label: 'ユーザー', adminOnly: true, requiresAuth: true },
diff --git a/ui/src/components/settings/MovementAccordion.tsx b/ui/src/components/settings/MovementAccordion.tsx
index 59d3f4a..ff4ba30 100644
--- a/ui/src/components/settings/MovementAccordion.tsx
+++ b/ui/src/components/settings/MovementAccordion.tsx
@@ -7,9 +7,10 @@ export interface MovementAccordionProps {
   onAdd: () => void;
   onRemove: (index: number) => void;
   onMove: (index: number, direction: 'up' | 'down') => void;
+  disabled?: boolean;
 }
 
-export function MovementAccordion({ movements, onChange, onAdd, onRemove, onMove }: MovementAccordionProps) {
+export function MovementAccordion({ movements, onChange, onAdd, onRemove, onMove, disabled = false }: MovementAccordionProps) {
   const [expandedIndex, setExpandedIndex] = useState<number | null>(null);
   const movementNames = movements.map((m) => m.name ?? '');
 
@@ -49,40 +50,42 @@ export function MovementAccordion({ movements, onChange, onAdd, onRemove, onMove
                 {/* Spacer */}
                 <div className="flex-1" />
 
-                {/* Controls */}
-                <div className="flex items-center gap-1" onClick={(e) => e.stopPropagation()}>
-                  <button
-                    type="button"
-                    onClick={() => onMove(i, 'up')}
-                    disabled={i === 0}
-                    className="text-slate-400 hover:text-slate-600 disabled:opacity-30 text-sm px-1"
-                    title="Move up"
-                  >
-                    &#9650;
-                  </button>
-                  <button
-                    type="button"
-                    onClick={() => onMove(i, 'down')}
-                    disabled={i === movements.length - 1}
-                    className="text-slate-400 hover:text-slate-600 disabled:opacity-30 text-sm px-1"
-                    title="Move down"
-                  >
-                    &#9660;
-                  </button>
-                  <button
-                    type="button"
-                    onClick={() => {
-                      if (confirm(`Movement "${movement.name}" を削除しますか？`)) {
-                        onRemove(i);
-                        if (expandedIndex === i) setExpandedIndex(null);
-                      }
-                    }}
-                    className="text-slate-400 hover:text-red-500 text-sm px-1"
-                    title="Delete"
-                  >
-                    &times;
-                  </button>
-                </div>
+                {/* Controls — hidden in read-only mode */}
+                {!disabled && (
+                  <div className="flex items-center gap-1" onClick={(e) => e.stopPropagation()}>
+                    <button
+                      type="button"
+                      onClick={() => onMove(i, 'up')}
+                      disabled={i === 0}
+                      className="text-slate-400 hover:text-slate-600 disabled:opacity-30 text-sm px-1"
+                      title="Move up"
+                    >
+                      &#9650;
+                    </button>
+                    <button
+                      type="button"
+                      onClick={() => onMove(i, 'down')}
+                      disabled={i === movements.length - 1}
+                      className="text-slate-400 hover:text-slate-600 disabled:opacity-30 text-sm px-1"
+                      title="Move down"
+                    >
+                      &#9660;
+                    </button>
+                    <button
+                      type="button"
+                      onClick={() => {
+                        if (confirm(`Movement "${movement.name}" を削除しますか？`)) {
+                          onRemove(i);
+                          if (expandedIndex === i) setExpandedIndex(null);
+                        }
+                      }}
+                      className="text-slate-400 hover:text-red-500 text-sm px-1"
+                      title="Delete"
+                    >
+                      &times;
+                    </button>
+                  </div>
+                )}
               </div>
 
               {/* Expanded form */}
@@ -92,6 +95,7 @@ export function MovementAccordion({ movements, onChange, onAdd, onRemove, onMove
                     movement={movement}
                     movementNames={movementNames}
                     onChange={(field, value) => onChange(i, field, value)}
+                    disabled={disabled}
                   />
                 </div>
               )}
@@ -100,13 +104,15 @@ export function MovementAccordion({ movements, onChange, onAdd, onRemove, onMove
         })}
       </div>
 
-      <button
-        type="button"
-        onClick={onAdd}
-        className="mt-3 text-sm text-blue-600 hover:text-blue-700"
-      >
-        + Add Movement
-      </button>
+      {!disabled && (
+        <button
+          type="button"
+          onClick={onAdd}
+          className="mt-3 text-sm text-blue-600 hover:text-blue-700"
+        >
+          + Add Movement
+        </button>
+      )}
     </div>
   );
 }
diff --git a/ui/src/components/settings/MovementForm.tsx b/ui/src/components/settings/MovementForm.tsx
index 4978924..a433540 100644
--- a/ui/src/components/settings/MovementForm.tsx
+++ b/ui/src/components/settings/MovementForm.tsx
@@ -8,10 +8,12 @@ export interface MovementFormProps {
   movement: any;
   movementNames: string[];
   onChange: (field: string, value: any) => void;
+  disabled?: boolean;
 }
 
-export function MovementForm({ movement, movementNames, onChange }: MovementFormProps) {
+export function MovementForm({ movement, movementNames, onChange, disabled = false }: MovementFormProps) {
   const nextOptions = [...movementNames.filter((n) => n !== movement.name), ...SPECIAL_TARGETS];
+  const disabledClass = disabled ? 'bg-slate-50 text-slate-500 cursor-not-allowed' : '';
 
   return (
     <div className="space-y-4">
@@ -22,7 +24,8 @@ export function MovementForm({ movement, movementNames, onChange }: MovementForm
           type="text"
           value={movement.name ?? ''}
           onChange={(e) => onChange('name', e.target.value)}
-          className="w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none"
+          disabled={disabled}
+          className={`w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none ${disabledClass}`}
         />
       </div>
 
@@ -33,7 +36,8 @@ export function MovementForm({ movement, movementNames, onChange }: MovementForm
           type="text"
           value={movement.persona ?? ''}
           onChange={(e) => onChange('persona', e.target.value)}
-          className="w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none"
+          disabled={disabled}
+          className={`w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none ${disabledClass}`}
         />
       </div>
 
@@ -43,7 +47,8 @@ export function MovementForm({ movement, movementNames, onChange }: MovementForm
         <select
           value={movement.default_next ?? 'COMPLETE'}
           onChange={(e) => onChange('default_next', e.target.value)}
-          className="w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none bg-white"
+          disabled={disabled}
+          className={`w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none bg-white ${disabledClass}`}
         >
           {nextOptions.map((opt) => (
             <option key={opt} value={opt}>{opt}</option>
@@ -58,7 +63,8 @@ export function MovementForm({ movement, movementNames, onChange }: MovementForm
           id={`edit-${movement.name}`}
           checked={movement.edit ?? false}
           onChange={(e) => onChange('edit', e.target.checked)}
-          className="rounded border-slate-300"
+          disabled={disabled}
+          className="rounded border-slate-300 disabled:cursor-not-allowed"
         />
         <label htmlFor={`edit-${movement.name}`} className="text-xs font-medium text-slate-600">edit</label>
         <HelpText>有効にすると Write / Edit ツールが LLM に提示されます</HelpText>
@@ -71,7 +77,8 @@ export function MovementForm({ movement, movementNames, onChange }: MovementForm
           value={movement.instruction ?? ''}
           onChange={(e) => onChange('instruction', e.target.value)}
           rows={6}
-          className="w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none font-mono"
+          disabled={disabled}
+          className={`w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none font-mono ${disabledClass}`}
         />
         <HelpText>LLM に渡される指示文。Markdown 記法が使えます</HelpText>
       </div>
@@ -80,6 +87,7 @@ export function MovementForm({ movement, movementNames, onChange }: MovementForm
       <ToolTagInput
         value={movement.allowed_tools ?? []}
         onChange={(tools) => onChange('allowed_tools', tools)}
+        disabled={disabled}
       />
 
       {/* rules */}
@@ -87,6 +95,7 @@ export function MovementForm({ movement, movementNames, onChange }: MovementForm
         rules={movement.rules ?? []}
         movementNames={movementNames.filter((n) => n !== movement.name)}
         onChange={(rules) => onChange('rules', rules)}
+        disabled={disabled}
       />
     </div>
   );
diff --git a/ui/src/components/settings/PieceEditor.tsx b/ui/src/components/settings/PieceEditor.tsx
index 7614877..e04a327 100644
--- a/ui/src/components/settings/PieceEditor.tsx
+++ b/ui/src/components/settings/PieceEditor.tsx
@@ -9,10 +9,22 @@ import { MovementAccordion } from './MovementAccordion';
 
 export interface PieceEditorProps {
   name: string;
+  /** Whether the current user has admin role. Controls edit access for built-in/global-custom pieces. */
+  isAdmin?: boolean;
+  /**
+   * Source hint from URL / list selection — used for the targeted GET request.
+   * The read-only gate uses the SOURCE the API actually resolved (authoritative),
+   * so a deep link without pieceSource still renders correctly for non-admins.
+   */
+  source?: 'builtin' | 'user-custom' | 'global-custom';
 }
 
-export function PieceEditor({ name }: PieceEditorProps) {
-  const { data: piece, isLoading, error } = usePiece(name);
+export function PieceEditor({ name, isAdmin = true, source }: PieceEditorProps) {
+  const { data: fetchResult, isLoading, error } = usePiece(name, source);
+  // Use the server-resolved source as the authoritative value; fall back to the
+  // prop only while the fetch hasn't completed yet (avoids flicker on known paths).
+  const piece = fetchResult?.piece ?? null;
+  const effectiveSource = fetchResult?.source ?? source;
   const queryClient = useQueryClient();
   const { setUrlState } = useUrlState();
 
@@ -33,7 +45,7 @@ export function PieceEditor({ name }: PieceEditorProps) {
       setEditMode('visual');
       setYamlError(null);
     }
-  }, [piece]);
+  }, [piece]); // piece is derived from fetchResult above
 
   const showToast = (msg: string, duration = 2000) => {
     setToast(msg);
@@ -159,7 +171,7 @@ export function PieceEditor({ name }: PieceEditorProps) {
 
     setSaving(true);
     try {
-      await updatePiece(name, saveData);
+      await updatePiece(name, saveData, effectiveSource);
       await queryClient.invalidateQueries({ queryKey: ['piece', name] });
       await queryClient.invalidateQueries({ queryKey: ['pieces'] });
       setIsDirty(false);
@@ -177,7 +189,7 @@ export function PieceEditor({ name }: PieceEditorProps) {
   const handleDelete = async () => {
     if (!confirm(`Piece "${name}" を削除しますか？この操作は取り消せません。`)) return;
     try {
-      await deletePiece(name);
+      await deletePiece(name, effectiveSource);
       await queryClient.invalidateQueries({ queryKey: ['pieces'] });
       setUrlState((prev) => ({ ...prev, piece: undefined, section: 'provider' as any }));
     } catch (e: any) {
@@ -189,6 +201,12 @@ export function PieceEditor({ name }: PieceEditorProps) {
   if (error) return <div className="text-sm text-red-500">Piece の読み込みに失敗しました</div>;
   if (!draft) return null;
 
+  // Non-admins cannot edit built-in or global-custom pieces — read-only view.
+  // user-custom stays editable for its owner. Admins can edit all sources.
+  // Use the SERVER-RESOLVED source (effectiveSource) as the authoritative value so
+  // that deep links without a ?pieceSource param still render read-only for non-admins.
+  const readonly = !isAdmin && (effectiveSource === 'builtin' || effectiveSource === 'global-custom');
+
   const movementNames = (draft.movements ?? []).map((m: any) => m.name ?? '');
 
   return (
@@ -201,13 +219,21 @@ export function PieceEditor({ name }: PieceEditorProps) {
             <p className="text-sm text-slate-500 mt-0.5 line-clamp-2">{String(draft.description).split('\n')[0]}</p>
           )}
         </div>
-        <button
-          type="button"
-          onClick={handleDelete}
-          className="px-3 py-1.5 text-xs text-red-600 hover:bg-red-50 rounded-lg border border-red-200"
-        >
-          Delete
-        </button>
+        {/* Delete is hidden for ALL built-in pieces (non-deletable by everyone, including admins). */}
+        {!readonly && effectiveSource !== 'builtin' && (
+          <button
+            type="button"
+            onClick={handleDelete}
+            className="px-3 py-1.5 text-xs text-red-600 hover:bg-red-50 rounded-lg border border-red-200"
+          >
+            Delete
+          </button>
+        )}
+        {readonly && (
+          <span className="px-2 py-1 text-xs text-slate-400 bg-slate-100 rounded border border-slate-200">
+            読み取り専用
+          </span>
+        )}
       </div>
 
       {/* Mode toggle */}
@@ -242,6 +268,7 @@ export function PieceEditor({ name }: PieceEditorProps) {
               piece={draft}
               onChange={handleMetaChange}
               movementNames={movementNames}
+              disabled={readonly}
             />
           </div>
 
@@ -253,6 +280,7 @@ export function PieceEditor({ name }: PieceEditorProps) {
               onAdd={handleAddMovement}
               onRemove={handleRemoveMovement}
               onMove={handleMoveMovement}
+              disabled={readonly}
             />
           </div>
         </>
@@ -268,7 +296,9 @@ export function PieceEditor({ name }: PieceEditorProps) {
             value={yamlText}
             onChange={(e) => handleYamlChange(e.target.value)}
             spellCheck={false}
-            className="w-full px-4 py-3 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none font-mono bg-slate-50 leading-relaxed resize-y"
+            readOnly={readonly}
+            disabled={readonly}
+            className={`w-full px-4 py-3 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none font-mono leading-relaxed resize-y ${readonly ? 'bg-slate-100 text-slate-500 cursor-not-allowed' : 'bg-slate-50'}`}
             style={{ minHeight: '500px', tabSize: 2 }}
           />
           <p className="text-xs text-slate-400 mt-1">
@@ -278,27 +308,29 @@ export function PieceEditor({ name }: PieceEditorProps) {
       )}
 
       {/* Footer */}
-      <div className="flex items-center justify-end gap-3 pt-4 mt-6 border-t border-slate-200">
-        {toast && (
-          <span className={`text-xs mr-auto ${toast.startsWith('エラー') ? 'text-red-500' : 'text-green-600'}`}>
-            {toast}
-          </span>
-        )}
-        <button
-          onClick={handleDiscard}
-          disabled={!isDirty}
-          className="px-4 py-2 text-sm text-slate-600 hover:bg-slate-100 rounded-lg disabled:opacity-50"
-        >
-          Discard Changes
-        </button>
-        <button
-          onClick={handleSave}
-          disabled={!isDirty || saving}
-          className="px-4 py-2 text-sm bg-accent text-accent-fg rounded-lg hover:bg-accent-deep disabled:opacity-50"
-        >
-          {saving ? 'Saving...' : 'Save'}
-        </button>
-      </div>
+      {!readonly && (
+        <div className="flex items-center justify-end gap-3 pt-4 mt-6 border-t border-slate-200">
+          {toast && (
+            <span className={`text-xs mr-auto ${toast.startsWith('エラー') ? 'text-red-500' : 'text-green-600'}`}>
+              {toast}
+            </span>
+          )}
+          <button
+            onClick={handleDiscard}
+            disabled={!isDirty}
+            className="px-4 py-2 text-sm text-slate-600 hover:bg-slate-100 rounded-lg disabled:opacity-50"
+          >
+            Discard Changes
+          </button>
+          <button
+            onClick={handleSave}
+            disabled={!isDirty || saving}
+            className="px-4 py-2 text-sm bg-accent text-accent-fg rounded-lg hover:bg-accent-deep disabled:opacity-50"
+          >
+            {saving ? 'Saving...' : 'Save'}
+          </button>
+        </div>
+      )}
     </div>
   );
 }
diff --git a/ui/src/components/settings/PieceMetaForm.tsx b/ui/src/components/settings/PieceMetaForm.tsx
index 6d7da42..7cee7ed 100644
--- a/ui/src/components/settings/PieceMetaForm.tsx
+++ b/ui/src/components/settings/PieceMetaForm.tsx
@@ -4,10 +4,12 @@ export interface PieceMetaFormProps {
   piece: any;
   onChange: (field: string, value: any) => void;
   movementNames: string[];
+  disabled?: boolean;
 }
 
-export function PieceMetaForm({ piece, onChange, movementNames }: PieceMetaFormProps) {
+export function PieceMetaForm({ piece, onChange, movementNames, disabled = false }: PieceMetaFormProps) {
   const triggersText = (piece.triggers?.keywords ?? []).join(', ');
+  const disabledClass = disabled ? 'bg-slate-50 text-slate-500 cursor-not-allowed' : '';
 
   return (
     <div className="space-y-4">
@@ -30,7 +32,8 @@ export function PieceMetaForm({ piece, onChange, movementNames }: PieceMetaFormP
           type="text"
           value={piece.description ?? ''}
           onChange={(e) => onChange('description', e.target.value)}
-          className="w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none"
+          disabled={disabled}
+          className={`w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none ${disabledClass}`}
         />
       </div>
 
@@ -42,7 +45,8 @@ export function PieceMetaForm({ piece, onChange, movementNames }: PieceMetaFormP
           value={piece.max_movements ?? 10}
           onChange={(e) => onChange('max_movements', parseInt(e.target.value, 10) || 0)}
           min={1}
-          className="w-32 px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none"
+          disabled={disabled}
+          className={`w-32 px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none ${disabledClass}`}
         />
         <HelpText>1 ジョブで実行できる movement の最大回数。ループ防止のため</HelpText>
       </div>
@@ -53,7 +57,8 @@ export function PieceMetaForm({ piece, onChange, movementNames }: PieceMetaFormP
         <select
           value={piece.initial_movement ?? ''}
           onChange={(e) => onChange('initial_movement', e.target.value)}
-          className="w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none bg-white"
+          disabled={disabled}
+          className={`w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none bg-white ${disabledClass}`}
         >
           {movementNames.length === 0 && <option value="">--</option>}
           {movementNames.map((name) => (
@@ -77,7 +82,8 @@ export function PieceMetaForm({ piece, onChange, movementNames }: PieceMetaFormP
             onChange('triggers', { ...piece.triggers, keywords });
           }}
           placeholder="keyword1, keyword2, ..."
-          className="w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none"
+          disabled={disabled}
+          className={`w-full px-3 py-2 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none ${disabledClass}`}
         />
         <HelpText>タスク本文にこれらのキーワードが含まれると、この piece が自動選択されます</HelpText>
       </div>
diff --git a/ui/src/components/settings/RulesTable.tsx b/ui/src/components/settings/RulesTable.tsx
index cebd256..f0a0371 100644
--- a/ui/src/components/settings/RulesTable.tsx
+++ b/ui/src/components/settings/RulesTable.tsx
@@ -6,10 +6,12 @@ export interface RulesTableProps {
   rules: Array<{ condition: string; next: string }>;
   movementNames: string[];
   onChange: (rules: Array<{ condition: string; next: string }>) => void;
+  disabled?: boolean;
 }
 
-export function RulesTable({ rules, movementNames, onChange }: RulesTableProps) {
+export function RulesTable({ rules, movementNames, onChange, disabled = false }: RulesTableProps) {
   const nextOptions = [...movementNames, ...SPECIAL_TARGETS];
+  const disabledClass = disabled ? 'bg-slate-50 text-slate-500 cursor-not-allowed' : '';
 
   const updateRule = (index: number, field: 'condition' | 'next', value: string) => {
     const updated = rules.map((r, i) => (i === index ? { ...r, [field]: value } : r));
@@ -33,7 +35,7 @@ export function RulesTable({ rules, movementNames, onChange }: RulesTableProps)
             <tr className="text-xs text-slate-500">
               <th className="text-left font-medium pb-1 pr-2">condition</th>
               <th className="text-left font-medium pb-1 pr-2 w-44">next</th>
-              <th className="w-8" />
+              {!disabled && <th className="w-8" />}
             </tr>
           </thead>
           <tbody>
@@ -44,7 +46,8 @@ export function RulesTable({ rules, movementNames, onChange }: RulesTableProps)
                     type="text"
                     value={rule.condition}
                     onChange={(e) => updateRule(i, 'condition', e.target.value)}
-                    className="w-full px-3 py-1.5 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none"
+                    disabled={disabled}
+                    className={`w-full px-3 py-1.5 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none ${disabledClass}`}
                     placeholder="条件..."
                   />
                 </td>
@@ -52,34 +55,39 @@ export function RulesTable({ rules, movementNames, onChange }: RulesTableProps)
                   <select
                     value={rule.next}
                     onChange={(e) => updateRule(i, 'next', e.target.value)}
-                    className="w-full px-3 py-1.5 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none bg-white"
+                    disabled={disabled}
+                    className={`w-full px-3 py-1.5 text-sm border border-slate-300 rounded-lg focus:ring-2 focus:ring-accent-ring focus:border-accent outline-none bg-white ${disabledClass}`}
                   >
                     {nextOptions.map((opt) => (
                       <option key={opt} value={opt}>{opt}</option>
                     ))}
                   </select>
                 </td>
-                <td className="pb-1">
-                  <button
-                    type="button"
-                    onClick={() => removeRule(i)}
-                    className="text-slate-400 hover:text-red-500 text-sm px-1"
-                  >
-                    &times;
-                  </button>
-                </td>
+                {!disabled && (
+                  <td className="pb-1">
+                    <button
+                      type="button"
+                      onClick={() => removeRule(i)}
+                      className="text-slate-400 hover:text-red-500 text-sm px-1"
+                    >
+                      &times;
+                    </button>
+                  </td>
+                )}
               </tr>
             ))}
           </tbody>
         </table>
       )}
-      <button
-        type="button"
-        onClick={addRule}
-        className="text-xs text-blue-600 hover:text-blue-700"
-      >
-        + Add Rule
-      </button>
+      {!disabled && (
+        <button
+          type="button"
+          onClick={addRule}
+          className="text-xs text-blue-600 hover:text-blue-700"
+        >
+          + Add Rule
+        </button>
+      )}
       <HelpText>LLM が transition ツールで遷移先を選ぶ際の条件です</HelpText>
     </div>
   );
diff --git a/ui/src/components/settings/ToolTagInput.tsx b/ui/src/components/settings/ToolTagInput.tsx
index cf7c6e9..376e235 100644
--- a/ui/src/components/settings/ToolTagInput.tsx
+++ b/ui/src/components/settings/ToolTagInput.tsx
@@ -6,6 +6,7 @@ import { HelpText } from './HelpText';
 export interface ToolTagInputProps {
   value: string[];
   onChange: (tools: string[]) => void;
+  disabled?: boolean;
 }
 
 /**
@@ -24,7 +25,7 @@ export interface ToolTagInputProps {
  *  - Selecting an unavailable catalog tool is still allowed (the user might be
  *    preparing for a server that's about to come back online).
  */
-export function ToolTagInput({ value, onChange }: ToolTagInputProps) {
+export function ToolTagInput({ value, onChange, disabled = false }: ToolTagInputProps) {
   const { data: catalog } = useToolList();
   const [input, setInput] = useState('');
   const [showDropdown, setShowDropdown] = useState(false);
@@ -127,24 +128,27 @@ export function ToolTagInput({ value, onChange }: ToolTagInputProps) {
                 name={tool}
                 entry={entry}
                 onRemove={() => removeTool(tool)}
+                readOnly={disabled}
               />
             );
           })}
-          <input
-            ref={inputRef}
-            type="text"
-            value={input}
-            onChange={(e) => {
-              setInput(e.target.value);
-              setShowDropdown(true);
-            }}
-            onFocus={() => setShowDropdown(true)}
-            onKeyDown={handleKeyDown}
-            placeholder={value.length === 0 ? 'ツール名を入力...' : ''}
-            className="flex-1 min-w-[120px] text-sm outline-none bg-transparent"
-          />
+          {!disabled && (
+            <input
+              ref={inputRef}
+              type="text"
+              value={input}
+              onChange={(e) => {
+                setInput(e.target.value);
+                setShowDropdown(true);
+              }}
+              onFocus={() => setShowDropdown(true)}
+              onKeyDown={handleKeyDown}
+              placeholder={value.length === 0 ? 'ツール名を入力...' : ''}
+              className="flex-1 min-w-[120px] text-sm outline-none bg-transparent"
+            />
+          )}
         </div>
-        {showDropdown && groupedSuggestions.length > 0 && (
+        {!disabled && showDropdown && groupedSuggestions.length > 0 && (
           <div className="absolute z-10 mt-1 w-full max-h-72 overflow-y-auto bg-white border border-slate-200 rounded-lg shadow-lg">
             {groupedSuggestions.map((g) => (
               <div key={g.key}>
@@ -202,10 +206,12 @@ function SelectedToolChip({
   name,
   entry,
   onRemove,
+  readOnly = false,
 }: {
   name: string;
   entry: ToolCatalogEntry | undefined;
   onRemove: () => void;
+  readOnly?: boolean;
 }) {
   const isUnknown = !entry;
   const isUnavailable = entry ? !entry.available : false;
@@ -231,14 +237,16 @@ function SelectedToolChip({
       {entry && <ScopeBadge scope={entry.scope} dim />}
       {isUnknown && <Badge color="amber">unknown</Badge>}
       {!isUnknown && isUnavailable && <Badge color="amber">{entry?.reason ?? 'offline'}</Badge>}
-      <button
-        type="button"
-        onClick={onRemove}
-        className="text-current opacity-60 hover:opacity-100"
-        aria-label={`remove ${name}`}
-      >
-        &times;
-      </button>
+      {!readOnly && (
+        <button
+          type="button"
+          onClick={onRemove}
+          className="text-current opacity-60 hover:opacity-100"
+          aria-label={`remove ${name}`}
+        >
+          &times;
+        </button>
+      )}
     </span>
   );
 }
diff --git a/ui/src/content/help/05-pieces.md b/ui/src/content/help/05-pieces.md
index e2508b9..e4d6f99 100644
--- a/ui/src/content/help/05-pieces.md
+++ b/ui/src/content/help/05-pieces.md
@@ -49,19 +49,37 @@ Piece は「タスクの種類ごとの実行手順」を定義したもので
 
 > このほか組織が独自に追加した Piece もここに加わります。利用可能なツールの一覧は [ツール一覧](16-tools.md) を参照。
 
-## カスタム Piece を作る（admin / パワーユーザー）
+## Default Pieces と Custom Pieces
+
+Pieces ページでは「**Default Pieces**」と「**Custom Pieces**」の 2 つのセクションが表示されます。
+
+**Default Pieces（組み込み）**
+
+- システムに同梱され、git で管理されている Piece です
+- **削除は非 admin ユーザーには禁止**されています（削除は admin のみ）
+- **編集は admin のみ** 可能です（非 admin ユーザーは読み取り専用）
+- 非 admin ユーザーは `⎘` ボタンで **「Custom に複製」** でき、別名の Custom Piece として自分用にカスタマイズできます
+
+**Custom Pieces（ユーザー作成）**
+
+- ユーザーが作成した Piece で、自分のユーザーフォルダ配下に保存されます
+- 自分で作った Custom Piece は編集・削除できます
+- Custom Piece は **Default Piece と同名にできません**（別名を付けてください）
+- タスク実行時、Custom Piece はそのオーナーのユーザーフォルダから読み込まれ、正しく実行されます
+
+## カスタム Piece を作る
 
 ### 方法 1: piece-builder に依頼する
 
 タスクを作成し、「○○用の Piece を作って」と書きます。`piece-builder` が選ばれ、要件をヒアリングしながら movement 構成・ツール選定・遷移ルールを設計して Piece を保存します。既存 Piece の改良で済む場合はそれを優先します。
 
-### 方法 2: Pieces ページで手動編集する
+### 方法 2: Pieces ページで手動作成する
 
-admin は TopBar → Pieces から Piece の一覧・閲覧・新規作成・編集ができます。YAML を直接編集して保存すると `pieces/{name}.yaml` に反映されます。
+TopBar → Pieces → Custom Pieces セクションの `+` から新規作成できます。YAML を直接編集して保存できます。**Default Piece と同名の名前は使えません**（別名を付けてください）。
 
-### 方法 3: 自分専用に fork する
+### 方法 3: Default Piece を複製してカスタマイズする
 
-組み込み Piece を少しだけ変えたい場合、ユーザーフォルダ配下に同名の Piece を置くと、自分のタスクではそちらが優先されます。組み込み定義はそのまま残ります。
+Default Piece の行にある `⎘` ボタンをクリックすると「複製名」の入力ダイアログが開きます。別名を入力して複製すると、Custom Pieces セクションに追加されます。元の Default Piece はそのまま残ります。複製後の Custom Piece は自分で自由に編集できます。
 
 ## Piece を編集するときの勘所
 
diff --git a/ui/src/hooks/usePieces.ts b/ui/src/hooks/usePieces.ts
index 1e53bda..61b5a7d 100644
--- a/ui/src/hooks/usePieces.ts
+++ b/ui/src/hooks/usePieces.ts
@@ -6,10 +6,15 @@ export function usePieceList() {
   return useQuery({ queryKey: ['pieces'], queryFn: fetchPieces, staleTime: STALE_TIME.SEMI_STATIC });
 }
 
-export function usePiece(name: string | undefined) {
+/**
+ * Fetches a single piece by name (and optional source).
+ * Returns the full PieceFetchResult so callers can use the server-resolved source
+ * for authorization decisions (e.g. read-only gate in PieceEditor).
+ */
+export function usePiece(name: string | undefined, source?: 'builtin' | 'user-custom' | 'global-custom') {
   return useQuery({
-    queryKey: ['piece', name],
-    queryFn: () => fetchPiece(name!),
+    queryKey: ['piece', name, source],
+    queryFn: () => fetchPiece(name!, source),
     enabled: !!name,
     staleTime: STALE_TIME.SEMI_STATIC,
   });
diff --git a/ui/src/lib/splitPieces.test.ts b/ui/src/lib/splitPieces.test.ts
new file mode 100644
index 0000000..79c807d
--- /dev/null
+++ b/ui/src/lib/splitPieces.test.ts
@@ -0,0 +1,125 @@
+import { describe, it, expect } from 'vitest';
+import { splitPieces, resolvePieceOptions } from './splitPieces';
+import type { PieceSummary } from '../api';
+
+function makePiece(name: string, source?: PieceSummary['source']): PieceSummary {
+  return { name, description: 'test', source };
+}
+
+describe('splitPieces', () => {
+  it('puts builtin pieces in defaults', () => {
+    const pieces = [makePiece('chat', 'builtin'), makePiece('general', 'builtin')];
+    const { defaults, customs } = splitPieces(pieces);
+    expect(defaults).toHaveLength(2);
+    expect(customs).toHaveLength(0);
+  });
+
+  it('puts user-custom pieces in customs', () => {
+    const pieces = [makePiece('my-piece', 'user-custom')];
+    const { defaults, customs } = splitPieces(pieces);
+    expect(defaults).toHaveLength(0);
+    expect(customs).toHaveLength(1);
+    expect(customs[0].name).toBe('my-piece');
+  });
+
+  it('puts global-custom pieces in customs', () => {
+    const pieces = [makePiece('global-piece', 'global-custom')];
+    const { defaults, customs } = splitPieces(pieces);
+    expect(defaults).toHaveLength(0);
+    expect(customs).toHaveLength(1);
+  });
+
+  it('splits mixed list correctly', () => {
+    const pieces = [
+      makePiece('chat', 'builtin'),
+      makePiece('general', 'builtin'),
+      makePiece('my-chat', 'user-custom'),
+      makePiece('chat', 'user-custom'), // same name as builtin, but still custom
+    ];
+    const { defaults, customs } = splitPieces(pieces);
+    expect(defaults).toHaveLength(2);
+    expect(customs).toHaveLength(2);
+    expect(defaults.map(p => p.name)).toEqual(['chat', 'general']);
+    expect(customs.map(p => p.name)).toEqual(['my-chat', 'chat']);
+  });
+
+  it('handles pieces with undefined source as custom', () => {
+    const pieces = [makePiece('legacy')]; // no source
+    const { defaults, customs } = splitPieces(pieces);
+    expect(defaults).toHaveLength(0);
+    expect(customs).toHaveLength(1);
+  });
+
+  it('returns empty arrays for empty input', () => {
+    const { defaults, customs } = splitPieces([]);
+    expect(defaults).toHaveLength(0);
+    expect(customs).toHaveLength(0);
+  });
+});
+
+describe('resolvePieceOptions', () => {
+  it('returns unique names with no duplicates when all sources differ', () => {
+    const pieces = [makePiece('chat', 'builtin'), makePiece('my-tool', 'user-custom')];
+    const result = resolvePieceOptions(pieces);
+    expect(result).toHaveLength(2);
+    expect(result.map(p => p.name).sort()).toEqual(['chat', 'my-tool']);
+  });
+
+  it('user-custom wins over builtin for the same name', () => {
+    const pieces = [makePiece('chat', 'builtin'), makePiece('chat', 'user-custom')];
+    const result = resolvePieceOptions(pieces);
+    expect(result).toHaveLength(1);
+    expect(result[0].source).toBe('user-custom');
+  });
+
+  it('user-custom wins over global-custom for the same name', () => {
+    const pieces = [makePiece('chat', 'global-custom'), makePiece('chat', 'user-custom')];
+    const result = resolvePieceOptions(pieces);
+    expect(result).toHaveLength(1);
+    expect(result[0].source).toBe('user-custom');
+  });
+
+  it('global-custom wins over builtin for the same name', () => {
+    const pieces = [makePiece('chat', 'builtin'), makePiece('chat', 'global-custom')];
+    const result = resolvePieceOptions(pieces);
+    expect(result).toHaveLength(1);
+    expect(result[0].source).toBe('global-custom');
+  });
+
+  it('user-custom wins over both global-custom and builtin', () => {
+    const pieces = [
+      makePiece('chat', 'builtin'),
+      makePiece('chat', 'global-custom'),
+      makePiece('chat', 'user-custom'),
+    ];
+    const result = resolvePieceOptions(pieces);
+    expect(result).toHaveLength(1);
+    expect(result[0].source).toBe('user-custom');
+  });
+
+  it('de-duplicates only same-name entries, keeps different names', () => {
+    const pieces = [
+      makePiece('chat', 'builtin'),
+      makePiece('general', 'builtin'),
+      makePiece('chat', 'user-custom'),
+      makePiece('my-tool', 'user-custom'),
+    ];
+    const result = resolvePieceOptions(pieces);
+    expect(result).toHaveLength(3);
+    const byName = Object.fromEntries(result.map(p => [p.name, p]));
+    expect(byName['chat'].source).toBe('user-custom');
+    expect(byName['general'].source).toBe('builtin');
+    expect(byName['my-tool'].source).toBe('user-custom');
+  });
+
+  it('returns empty array for empty input', () => {
+    expect(resolvePieceOptions([])).toHaveLength(0);
+  });
+
+  it('undefined source is treated as builtin priority (lowest)', () => {
+    const pieces = [makePiece('chat', 'global-custom'), makePiece('chat', undefined)];
+    const result = resolvePieceOptions(pieces);
+    expect(result).toHaveLength(1);
+    expect(result[0].source).toBe('global-custom');
+  });
+});
diff --git a/ui/src/lib/splitPieces.ts b/ui/src/lib/splitPieces.ts
new file mode 100644
index 0000000..5cd1e82
--- /dev/null
+++ b/ui/src/lib/splitPieces.ts
@@ -0,0 +1,57 @@
+import type { PieceSummary } from '../api';
+
+export interface SplitPieces {
+  defaults: PieceSummary[];
+  customs: PieceSummary[];
+}
+
+/**
+ * Split a flat list of PieceSummary into Default (built-in) and Custom sections.
+ * Pieces with source === 'builtin' go to defaults; all others go to customs.
+ */
+export function splitPieces(pieces: PieceSummary[]): SplitPieces {
+  const defaults: PieceSummary[] = [];
+  const customs: PieceSummary[] = [];
+  for (const p of pieces) {
+    if (p.source === 'builtin') {
+      defaults.push(p);
+    } else {
+      customs.push(p);
+    }
+  }
+  return { defaults, customs };
+}
+
+/**
+ * De-duplicate a flat list of PieceSummary by name, keeping the highest-priority
+ * source for each name — mirroring the executor's resolution order:
+ *   user-custom  >  global-custom  >  builtin
+ *
+ * Use this wherever a piece is SELECTED TO RUN (task creation, scheduled tasks,
+ * continue-with-piece dialogs). The result matches what the executor will actually
+ * run, so the user sees exactly one "chat" entry rather than two.
+ *
+ * Do NOT use this in the management/PiecesPage view — that view intentionally
+ * shows both the builtin and any same-named custom side-by-side.
+ */
+export function resolvePieceOptions(pieces: PieceSummary[]): PieceSummary[] {
+  const PRIORITY: Record<string, number> = {
+    'user-custom': 0,
+    'global-custom': 1,
+    builtin: 2,
+  };
+  const seen = new Map<string, PieceSummary>();
+  for (const p of pieces) {
+    const existing = seen.get(p.name);
+    const pPrio = PRIORITY[p.source ?? 'builtin'] ?? 2;
+    if (!existing) {
+      seen.set(p.name, p);
+    } else {
+      const existingPrio = PRIORITY[existing.source ?? 'builtin'] ?? 2;
+      if (pPrio < existingPrio) {
+        seen.set(p.name, p);
+      }
+    }
+  }
+  return Array.from(seen.values());
+}
diff --git a/ui/src/lib/urlState.ts b/ui/src/lib/urlState.ts
index adecdf3..ade8367 100644
--- a/ui/src/lib/urlState.ts
+++ b/ui/src/lib/urlState.ts
@@ -78,6 +78,8 @@ export interface UiUrlState {
   taskId: number | null;
   section?: SettingsSection;
   piece?: string;
+  /** Source of the currently-selected piece ('builtin' | 'user-custom' | 'global-custom'). */
+  pieceSource?: 'builtin' | 'user-custom' | 'global-custom';
   /** Active SideInfoPanel widget slug. Default: 'worker-status'. */
   dashboardWidget?: string;
   /** Selected help section id. Only meaningful when page === 'help'. */
@@ -107,6 +109,11 @@ export function readUiUrlState(): UiUrlState {
   const taskId = Number(params.get('task') ?? '');
   const section = params.get('section');
   const piece = params.get('piece');
+  const pieceSourceRaw = params.get('pieceSource');
+  const PIECE_SOURCES = ['builtin', 'user-custom', 'global-custom'] as const;
+  const pieceSource = PIECE_SOURCES.includes(pieceSourceRaw as any)
+    ? (pieceSourceRaw as UiUrlState['pieceSource'])
+    : undefined;
   const dashboardWidget = params.get('dashboardWidget');
   const help = params.get('help');
 
@@ -127,6 +134,7 @@ export function readUiUrlState(): UiUrlState {
     taskId: Number.isFinite(taskId) && taskId > 0 ? taskId : null,
     section: section && SETTINGS_SECTIONS.includes(section as SettingsSection) ? section as SettingsSection : undefined,
     piece: piece || undefined,
+    ...(pieceSource ? { pieceSource } : {}),
     ...(dashboardWidget ? { dashboardWidget } : {}),
     ...(help ? { help } : {}),
   };
@@ -144,6 +152,7 @@ export function buildUiUrlStateSearch(state: UiUrlState): string {
   if (state.taskId) params.set('task', String(state.taskId));
   if (state.section) params.set('section', state.section);
   if (state.piece) params.set('piece', state.piece);
+  if (state.pieceSource) params.set('pieceSource', state.pieceSource);
   if (state.help) params.set('help', state.help);
   if (state.dashboardWidget && state.dashboardWidget !== 'worker-status') {
     params.set('dashboardWidget', state.dashboardWidget);
diff --git a/ui/src/pages/PiecesPage.tsx b/ui/src/pages/PiecesPage.tsx
index e87383f..b5848ca 100644
--- a/ui/src/pages/PiecesPage.tsx
+++ b/ui/src/pages/PiecesPage.tsx
@@ -2,8 +2,15 @@ import { useEffect, useRef, useState } from 'react';
 import { useQueryClient } from '@tanstack/react-query';
 import { useUrlState } from '../hooks/useUrlState';
 import { usePieceList } from '../hooks/usePieces';
-import { createPiece, fetchPiece, PieceDef, DriftStatus } from '../api';
+import { createPiece, fetchPiece, PieceDef, DriftStatus, PieceSummary } from '../api';
 import { PieceEditor } from '../components/settings/PieceEditor';
+import { splitPieces } from '../lib/splitPieces';
+
+type PieceSource = 'builtin' | 'user-custom' | 'global-custom';
+
+/** Composite selection key so same-named builtin and custom rows are independently selectable. */
+type SelectionKey = string; // `${name}::${source}`
+function makeKey(name: string, source: PieceSource): SelectionKey { return `${name}::${source}`; }
 
 function shortSha(sha: string | null): string {
   return sha ? sha.slice(0, 7) : '???????';
@@ -64,13 +71,57 @@ function DriftBadge({ drift }: { drift: DriftStatus }) {
 
 type ShowToast = (message: string, variant?: 'success' | 'error') => void;
 
+interface PieceRowProps {
+  p: PieceSummary;
+  activeKey?: SelectionKey;
+  isBuiltin: boolean;
+  isAdmin: boolean;
+  onSelectPiece: (name: string, source: PieceSource) => void;
+  startDuplicate: (name: string, source: PieceSource) => void;
+}
+
+function PieceRow({ p, activeKey, isBuiltin, isAdmin, onSelectPiece, startDuplicate }: PieceRowProps) {
+  // For Default pieces:
+  //   - admins: show Duplicate (hover)
+  //   - non-admins: show Duplicate always (it's their only action)
+  // For Custom pieces: existing behavior (Duplicate on hover)
+  const duplicateAlwaysVisible = isBuiltin && !isAdmin;
+  const src = (p.source ?? (isBuiltin ? 'builtin' : 'user-custom')) as PieceSource;
+  const thisKey = makeKey(p.name, src);
+
+  return (
+    <div key={thisKey} className="group flex items-center mb-0.5 gap-1 pr-1">
+      <button onClick={() => onSelectPiece(p.name, src)}
+        className={`flex-1 text-left px-2 py-1 rounded text-xs transition-colors min-w-0 truncate ${
+          activeKey === thisKey
+            ? 'bg-accent-soft text-accent font-semibold'
+            : 'text-slate-700 hover:bg-surface'
+        }`}>
+        {p.name}
+      </button>
+      {p.drift?.drifted && <DriftBadge drift={p.drift} />}
+      <button
+        onClick={(e) => { e.stopPropagation(); startDuplicate(p.name, src); }}
+        className={`text-slate-400 hover:text-slate-700 text-xs px-1.5 transition-opacity flex-shrink-0 ${
+          duplicateAlwaysVisible ? 'opacity-100' : 'opacity-0 group-hover:opacity-100'
+        }`}
+        title="複製"
+      >
+        &#x2398;
+      </button>
+    </div>
+  );
+}
+
 function PiecesSidebar({
-  activePiece,
+  activeKey,
   onSelectPiece,
+  isAdmin,
   showToast,
 }: {
-  activePiece?: string;
-  onSelectPiece: (name: string) => void;
+  activeKey?: SelectionKey;
+  onSelectPiece: (name: string, source: PieceSource) => void;
+  isAdmin: boolean;
   showToast?: ShowToast;
 }) {
   const { data: pieces } = usePieceList();
@@ -79,8 +130,9 @@ function PiecesSidebar({
   const [newName, setNewName] = useState('');
   const [creating, setCreating] = useState(false);
 
-  // Inline duplicate dialog state — replaces window.prompt
-  const [duplicateSource, setDuplicateSource] = useState<string | null>(null);
+  // Inline duplicate dialog state — replaces window.prompt.
+  // Track both the name and source of the piece being duplicated.
+  const [duplicateTarget, setDuplicateTarget] = useState<{ name: string; source: PieceSource } | null>(null);
   const [duplicateName, setDuplicateName] = useState('');
   const [duplicateError, setDuplicateError] = useState<string | null>(null);
   const [duplicating, setDuplicating] = useState(false);
@@ -111,11 +163,11 @@ function PiecesSidebar({
     };
     try {
       setCreating(true);
-      await createPiece(defaultPiece);
+      const { source } = await createPiece(defaultPiece);
       await queryClient.invalidateQueries({ queryKey: ['pieces'] });
       setIsCreating(false);
       setNewName('');
-      onSelectPiece(name);
+      onSelectPiece(name, source);
     } catch (e) {
       notifyError('Piece の作成に失敗', e);
     } finally {
@@ -123,20 +175,20 @@ function PiecesSidebar({
     }
   };
 
-  const startDuplicate = (sourceName: string) => {
-    setDuplicateSource(sourceName);
-    setDuplicateName(`${sourceName}-copy`);
+  const startDuplicate = (name: string, source: PieceSource) => {
+    setDuplicateTarget({ name, source });
+    setDuplicateName(`${name}-copy`);
     setDuplicateError(null);
   };
 
   const cancelDuplicate = () => {
-    setDuplicateSource(null);
+    setDuplicateTarget(null);
     setDuplicateName('');
     setDuplicateError(null);
   };
 
   const submitDuplicate = async () => {
-    if (!duplicateSource || duplicating) return;
+    if (!duplicateTarget || duplicating) return;
     const name = duplicateName.trim();
     if (!name) {
       setDuplicateError('複製名を入力してください');
@@ -149,11 +201,12 @@ function PiecesSidebar({
     try {
       setDuplicating(true);
       setDuplicateError(null);
-      const source = await fetchPiece(duplicateSource);
-      await createPiece({ ...source, name });
+      // Pass the source so we fetch from the SPECIFIC source (Fix 2).
+      const { piece: pieceData } = await fetchPiece(duplicateTarget.name, duplicateTarget.source);
+      const { source } = await createPiece({ ...pieceData, name });
       await queryClient.invalidateQueries({ queryKey: ['pieces'] });
       cancelDuplicate();
-      onSelectPiece(name);
+      onSelectPiece(name, source);
     } catch (e) {
       const msg = e instanceof Error ? e.message : 'Failed to duplicate piece';
       setDuplicateError(msg);
@@ -162,10 +215,32 @@ function PiecesSidebar({
     }
   };
 
+  const { defaults, customs } = splitPieces(pieces ?? []);
+
   return (
     <div className="h-full overflow-y-auto border-r border-hairline bg-white p-3">
+      {/* Default Pieces section */}
       <div className="flex items-center justify-between mb-2 px-2">
-        <span className="section-label">Pieces</span>
+        <span className="section-label">Default Pieces</span>
+      </div>
+      {defaults.length === 0 && (
+        <div className="px-2 text-xs text-slate-400 mb-2">(none)</div>
+      )}
+      {defaults.map(p => (
+        <PieceRow
+          key={`builtin-${p.name}`}
+          p={p}
+          activeKey={activeKey}
+          isBuiltin={true}
+          isAdmin={isAdmin}
+          onSelectPiece={onSelectPiece}
+          startDuplicate={startDuplicate}
+        />
+      ))}
+
+      {/* Custom Pieces section */}
+      <div className="flex items-center justify-between mt-3 mb-2 px-2">
+        <span className="section-label">Custom Pieces</span>
         <button
           onClick={() => setIsCreating(true)}
           className="w-5 h-5 flex items-center justify-center rounded text-slate-500 hover:bg-surface-2 hover:text-slate-900 text-sm leading-none transition-colors"
@@ -190,27 +265,22 @@ function PiecesSidebar({
           />
         </div>
       )}
-      {(pieces ?? []).map(p => (
-        <div key={p.name} className="group flex items-center mb-0.5 gap-1 pr-1">
-          <button onClick={() => onSelectPiece(p.name)}
-            className={`flex-1 text-left px-2 py-1 rounded text-xs transition-colors min-w-0 truncate ${
-              activePiece === p.name
-                ? 'bg-accent-soft text-accent font-semibold'
-                : 'text-slate-700 hover:bg-surface'
-            }`}>
-            {p.name}
-          </button>
-          {p.drift?.drifted && <DriftBadge drift={p.drift} />}
-          <button
-            onClick={(e) => { e.stopPropagation(); startDuplicate(p.name); }}
-            className="opacity-0 group-hover:opacity-100 text-slate-400 hover:text-slate-700 text-xs px-1.5 transition-opacity flex-shrink-0"
-            title="複製"
-          >
-            &#x2398;
-          </button>
-        </div>
+      {customs.length === 0 && !isCreating && (
+        <div className="px-2 text-xs text-slate-400">(none)</div>
+      )}
+      {customs.map(p => (
+        <PieceRow
+          key={`custom-${p.name}`}
+          p={p}
+          activeKey={activeKey}
+          isBuiltin={false}
+          isAdmin={isAdmin}
+          onSelectPiece={onSelectPiece}
+          startDuplicate={startDuplicate}
+        />
       ))}
-      {duplicateSource && (
+
+      {duplicateTarget && (
         <div
           role="dialog"
           aria-modal="true"
@@ -223,7 +293,7 @@ function PiecesSidebar({
             onClick={e => e.stopPropagation()}
           >
             <div id="dup-piece-label" className="text-[13px] font-semibold text-slate-800 mb-2">
-              "{duplicateSource}" を複製
+              "{duplicateTarget.name}" を複製
             </div>
             <label className="block text-2xs font-medium text-slate-500 mb-1">複製名</label>
             <input
@@ -267,11 +337,14 @@ function PiecesSidebar({
 
 interface PiecesPageProps {
   showToast?: ShowToast;
+  isAdmin?: boolean;
 }
 
-export function PiecesPage({ showToast }: PiecesPageProps = {}) {
+export function PiecesPage({ showToast, isAdmin = true }: PiecesPageProps = {}) {
   const { urlState, setUrlState } = useUrlState();
   const piece = urlState.piece;
+  // pieceSource is persisted in the URL so reload correctly restores both name+source.
+  const selectedSource: PieceSource | undefined = urlState.pieceSource;
 
   // モバイルでは list / detail のどちらかを全幅で表示。
   // URL に piece が指定されていれば detail から、そうでなければ list から。
@@ -282,17 +355,26 @@ export function PiecesPage({ showToast }: PiecesPageProps = {}) {
     if (piece) setMobileView('detail');
   }, [piece]);
 
-  const handleSelectPiece = (name: string) => {
-    setUrlState(prev => ({ ...prev, piece: name }));
+  const handleSelectPiece = (name: string, source: PieceSource) => {
+    setUrlState(prev => ({ ...prev, piece: name, pieceSource: source }));
     setMobileView('detail');
   };
 
+  // Composite key for sidebar highlight.
+  const activeKey: SelectionKey | undefined =
+    piece && selectedSource ? makeKey(piece, selectedSource) : undefined;
+
   return (
     <div className="flex h-full">
       <div
         className={`${mobileView === 'list' ? 'block' : 'hidden'} md:block w-full md:w-52 flex-shrink-0`}
       >
-        <PiecesSidebar activePiece={piece} onSelectPiece={handleSelectPiece} showToast={showToast} />
+        <PiecesSidebar
+          activeKey={activeKey}
+          onSelectPiece={handleSelectPiece}
+          isAdmin={isAdmin}
+          showToast={showToast}
+        />
       </div>
       <div
         className={`${mobileView === 'detail' ? 'flex' : 'hidden'} md:flex flex-1 flex-col overflow-y-auto`}
@@ -309,7 +391,7 @@ export function PiecesPage({ showToast }: PiecesPageProps = {}) {
         )}
         <div className="flex-1 p-6">
           {piece ? (
-            <PieceEditor name={piece} />
+            <PieceEditor name={piece} isAdmin={isAdmin} source={selectedSource} />
           ) : (
             <div className="text-sm text-slate-400">左から Piece を選択してください。</div>
           )}
diff --git a/ui/src/pages/SchedulesPage.tsx b/ui/src/pages/SchedulesPage.tsx
index bd2e02b..435e68b 100644
--- a/ui/src/pages/SchedulesPage.tsx
+++ b/ui/src/pages/SchedulesPage.tsx
@@ -4,6 +4,7 @@ import { POLLING } from '../lib/constants.js';
 import { EmptyState } from '../components/shared/EmptyState';
 import { StatChip } from '../components/shared/StatChip';
 import { usePieceList } from '../hooks/usePieces';
+import { resolvePieceOptions } from '../lib/splitPieces';
 import { fetchMyOrgs, listBrowserSessionProfiles, type Visibility } from '../api';
 import { useAuthState } from '../App';
 
@@ -846,7 +847,7 @@ function ScheduleEditor({ mode, initialTask, onCancel, onSaved }: ScheduleEditor
 
   const pieceOptions = useMemo(() => {
     const opts = [{ value: 'auto', label: 'auto', description: 'LLM が自動選択' }];
-    for (const p of pieces) {
+    for (const p of resolvePieceOptions(pieces)) {
       if (p.name === 'auto') continue;
       opts.push({ value: p.name, label: p.name, description: p.description ?? '' });
     }