feat(phase21.5): Stage-B parser loop fix + delegate path stabilization

## 修正内容

### 1. Stage-B パーサー修正（偶然の回避）
- **ファイル**:
  - `lang/src/compiler/parser/expr/parser_expr_box.hako`
  - `lang/src/compiler/parser/stmt/parser_control_box.hako`
- **問題**: ネストループで gpos が正しく進まず、loop の cond/body が壊れる
- **回避策**: new 式のメソッドチェーン処理追加で別ループを導入
- **結果**: MIR 生成が変わって VM gpos バグを回避

### 2. delegate パス動作確認
- **テスト**: `/tmp/loop_min.hako` → rc=10 ✅
- **MIR構造**: 正しい PHI/compare/binop を生成
- **チェーン**: hakorune parser → Rust delegate → LLVM EXE 完動

### 3. ドキュメント追加
- `docs/development/analysis/` - delegate 分析
- `docs/development/guides/` - ループテストガイド
- `docs/development/testing/` - Stage-B 検証報告

### 4. カナリーテスト追加
- `tools/smokes/v2/profiles/quick/core/phase2100/` 配下に複数追加
- emit_boxcall_length_canary_vm.sh
- stageb_parser_loop_json_canary_vm.sh
- 他

### 受け入れ基準
- ✅ delegate パス: rc=10 返す
- ✅ FORCE パス: rc=10 返す（既存）
- ✅ MIR 構造: 正しい PHI incoming と compare
- ✅ 既定挙動: 不変（dev トグルのみ）

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

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

crates/nyash_kernel/src/lib.rs

@@ -36,6 +36,21 @@ pub extern "C" fn nyash_string_len_h(handle: i64) -> i64 {
     0
 }
 
+// FAST-path helper: compute string length from raw pointer (i8*) with mode (reserved)
+// Exported as both legacy name (nyash.string.length_si) and neutral name (nyrt_string_length)
+#[export_name = "nyrt_string_length"]
+pub extern "C" fn nyrt_string_length(ptr: *const i8, _mode: i64) -> i64 {
+    use std::ffi::CStr;
+    if ptr.is_null() {
+        return 0;
+    }
+    // Safety: pointer is expected to point to a null-terminated UTF-8 byte string
+    let c = unsafe { CStr::from_ptr(ptr) };
+    match c.to_bytes().len() {
+        n => n as i64,
+    }
+}
+
 // String.charCodeAt_h(handle, idx) -> i64 (byte-based; -1 if OOB)
 #[export_name = "nyash.string.charCodeAt_h"]
 pub extern "C" fn nyash_string_charcode_at_h_export(handle: i64, idx: i64) -> i64 {
@@ -62,6 +77,22 @@ pub extern "C" fn nyash_string_charcode_at_h_export(handle: i64, idx: i64) -> i6
     -1
 }
 
+// Build ArrayBox from process argv (excluding program name)
+// Exported as: nyash.env.argv_get() -> i64 (ArrayBox handle)
+#[export_name = "nyash.env.argv_get"]
+pub extern "C" fn nyash_env_argv_get() -> i64 {
+    use nyash_rust::{box_trait::{NyashBox, StringBox}, boxes::array::ArrayBox, runtime::host_handles as handles};
+    let mut arr = ArrayBox::new();
+    // Skip argv[0] (program name), collect the rest
+    for (i, a) in std::env::args().enumerate() {
+        if i == 0 { continue; }
+        let sb: Box<dyn NyashBox> = Box::new(StringBox::new(a));
+        let _ = arr.push(sb);
+    }
+    let arc: std::sync::Arc<dyn NyashBox> = std::sync::Arc::new(arr);
+    handles::to_handle_arc(arc) as i64
+}
+
 // String.concat_hh(lhs_h, rhs_h) -> handle
 #[export_name = "nyash.string.concat_hh"]
 pub extern "C" fn nyash_string_concat_hh_export(a_h: i64, b_h: i64) -> i64 {