FileBox SSOT設計移行完了: Provider Pattern実装

## 🎯 目的
FileBoxをSSOT（Single Source of Truth）設計に移行し、
static/dynamic/builtin providerを統一的に扱える基盤を構築。

## ✅ 実装完了（7タスク）

### 1. Provider Lock Global
**File**: `src/runtime/provider_lock.rs`
- `FILEBOX_PROVIDER: OnceLock<Arc<dyn FileIo>>` 追加
- `set_filebox_provider()` / `get_filebox_provider()` 実装

### 2. VM初期化時のProvider選択
**File**: `src/runner/modes/vm.rs`
- `execute_vm_mode()` 冒頭でprovider選択・登録
- ENV（`NYASH_FILEBOX_MODE`, `NYASH_DISABLE_PLUGINS`）対応

### 3. CoreRoFileIo完全実装
**File**: `src/boxes/file/core_ro.rs` (NEW)
- Read-onlyファイルI/O実装
- Thread-safe: `RwLock<Option<File>>`
- Newline正規化（CRLF→LF）

### 4. FileBox委譲化
**File**: `src/boxes/file/mod.rs`
- 直接`std::fs::File`使用 → `Arc<dyn FileIo>` provider委譲
- 全メソッドをprovider経由に変更
- Fail-Fast: write/delete等の非対応操作は明確エラー

### 5. basic/file_box.rs Deprecate
**File**: `src/boxes/file/basic/file_box.rs`
- 120行 → 12行に削減
- `#[deprecated]` マーク + 再エクスポート
- 後方互換性維持

### 6. Feature Flag追加
**File**: `Cargo.toml`
- `builtin-filebox = []` feature追加

### 7. Provider抽象・選択ロジック
**Files**:
- `src/boxes/file/provider.rs` (NEW) - FileIo trait定義
- `src/boxes/file/box_shim.rs` (NEW) - 薄いラッパー
- `src/runner/modes/common_util/provider_registry.rs` (NEW) - 選択ロジック

## 📊 アーキテクチャ進化

**Before**:
```
FileBox (mod.rs) ──直接使用──> std::fs::File
FileBox (basic/)  ──直接使用──> std::fs
```

**After**:
```
FileBox ──委譲──> Arc<dyn FileIo> ──実装──> CoreRoFileIo
                                        ├──> PluginFileIo (future)
                                        └──> BuiltinFileIo (future)
```

## 🔧 技術的成果

1. **Thread Safety**: `RwLock<Option<File>>` で並行アクセス安全
2. **Fail-Fast**: 非対応操作は明確エラー（silent failure無し）
3. **後方互換性**: deprecated re-exportで既存コード維持
4. **環境制御**: `NYASH_FILEBOX_MODE` でランタイム切替

## 📝 環境変数

- `NYASH_FILEBOX_MODE=auto|core-ro|plugin-only`
  - `auto`: プラグインあれば使用、なければCoreRoにフォールバック
  - `core-ro`: 強制的にCoreRo（read-only）
  - `plugin-only`: プラグイン必須（なければFail-Fast）
- `NYASH_DISABLE_PLUGINS=1`: 強制的にcore-roモード

## 🎯 次のステップ（Future）

- [ ] Dynamic統合（plugin_loaderとの連携）
- [ ] BuiltinFileIo実装（feature builtin-filebox）
- [ ] Write/Delete等の操作対応（provider拡張）

## 📚 ドキュメント

- 詳細仕様: `docs/development/runtime/FILEBOX_PROVIDER.md`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/boxes/basic/file_box.rs

@@ -1,120 +1,12 @@
-//! FileBox - File system operations in Nyash
+//! DEPRECATED: Use `crate::boxes::file::FileBox` instead
 //!
-//! Implements the FileBox type with file I/O operations.
+//! This module is kept for backward compatibility only.
+//! All new code should use the SSOT provider-based FileBox implementation.
 
-use crate::box_trait::{NyashBox, BoxCore, BoxBase, StringBox, BoolBox, VoidBox};
-use std::any::Any;
-use std::fmt::{Debug, Display};
-use std::fs;
-use std::path::Path;
+#![deprecated(
+    since = "0.1.0",
+    note = "Use crate::boxes::file::FileBox instead. This module will be removed in a future version."
+)]
 
-/// File values in Nyash - file system operations
-#[derive(Debug, Clone)]
-pub struct FileBox {
-    pub path: String,
-    base: BoxBase,
-}
-
-impl FileBox {
-    pub fn new(path: impl Into<String>) -> Self {
-        Self {
-            path: path.into(),
-            base: BoxBase::new(),
-        }
-    }
-
-    // ===== File Methods for Nyash =====
-
-    /// Read file contents as string
-    pub fn read(&self) -> Box<dyn NyashBox> {
-        match fs::read_to_string(&self.path) {
-            Ok(content) => Box::new(StringBox::new(content)),
-            Err(_) => Box::new(VoidBox::new()), // Return void on error for now
-        }
-    }
-
-    /// Write content to file
-    pub fn write(&self, content: Box<dyn NyashBox>) -> Box<dyn NyashBox> {
-        let content_str = content.to_string_box().value;
-        match fs::write(&self.path, content_str) {
-            Ok(_) => Box::new(BoolBox::new(true)),
-            Err(_) => Box::new(BoolBox::new(false)),
-        }
-    }
-
-    /// Check if file exists
-    pub fn exists(&self) -> Box<dyn NyashBox> {
-        Box::new(BoolBox::new(Path::new(&self.path).exists()))
-    }
-
-    /// Delete file
-    pub fn delete(&self) -> Box<dyn NyashBox> {
-        match fs::remove_file(&self.path) {
-            Ok(_) => Box::new(BoolBox::new(true)),
-            Err(_) => Box::new(BoolBox::new(false)),
-        }
-    }
-
-    /// Copy file to destination
-    pub fn copy(&self, dest_path: &str) -> Box<dyn NyashBox> {
-        match fs::copy(&self.path, dest_path) {
-            Ok(_) => Box::new(BoolBox::new(true)),
-            Err(_) => Box::new(BoolBox::new(false)),
-        }
-    }
-}
-
-impl BoxCore for FileBox {
-    fn box_id(&self) -> u64 {
-        self.base.id
-    }
-
-    fn parent_type_id(&self) -> Option<std::any::TypeId> {
-        self.base.parent_type_id
-    }
-
-    fn fmt_box(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        write!(f, "<FileBox: {}>", self.path)
-    }
-
-    fn as_any(&self) -> &dyn Any {
-        self
-    }
-
-    fn as_any_mut(&mut self) -> &mut dyn Any {
-        self
-    }
-}
-
-impl NyashBox for FileBox {
-    fn to_string_box(&self) -> StringBox {
-        StringBox::new(format!("<FileBox: {}>", self.path))
-    }
-
-    fn equals(&self, other: &dyn NyashBox) -> BoolBox {
-        if let Some(other_file) = other.as_any().downcast_ref::<FileBox>() {
-            BoolBox::new(self.path == other_file.path)
-        } else {
-            BoolBox::new(false)
-        }
-    }
-
-    fn type_name(&self) -> &'static str {
-        "FileBox"
-    }
-
-    fn clone_box(&self) -> Box<dyn NyashBox> {
-        Box::new(self.clone())
-    }
-
-    /// 仮実装: clone_boxと同じ（後で修正）
-    fn share_box(&self) -> Box<dyn NyashBox> {
-        self.clone_box()
-    }
-}
-
-impl Display for FileBox {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        self.fmt_box(f)
-    }
-}
+// Re-export the new FileBox implementation for backward compatibility
+pub use crate::boxes::file::FileBox;