feat(mir): Phase 25.1f完了 - Conservative PHI + ControlForm観測レイヤー

🎉 Conservative PHI Box理論による完全SSA構築

**Phase 7-B: Conservative PHI実装**
- 片方branchのみ定義変数に対応（emit_void使用）
- 全変数にPHI生成（Conservative Box理論）
- Stage-1 resolver全テスト緑化（3/3 PASS）

**Phase 25.1f: ControlForm観測レイヤー**
- LoopShape/IfShape/ControlForm構造定義
- Loop/If統一インターフェース実装
- debug_dump/debug_validate機能追加
- NYASH_CONTROL_FORM_TRACE環境変数対応

**主な変更**:
- src/mir/builder/phi.rs: Conservative PHI実装
- src/mir/control_form.rs: ControlForm構造（NEW）
- src/mir/loop_builder.rs: LoopForm v2デフォルト化

**テスト結果**:
✅ mir_stage1_using_resolver_min_fragment_verifies
✅ mir_stage1_using_resolver_full_collect_entries_verifies
✅ mir_parserbox_parse_program2_harness_parses_minimal_source

🤖 Generated with Claude Code
Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: ChatGPT <chatgpt@openai.com>

src/mir/builder/rewrite/known.rs

@@ -19,6 +19,7 @@ fn rewrite_enabled() -> bool {
 
 /// Try Known‑route instance→function rewrite.
 /// 既存の安全ガード（user_defined/存在確認/ENV）を尊重して関数化する。
+#[allow(dead_code)]
 pub(crate) fn try_known_rewrite(
     builder: &mut MirBuilder,
     object_value: ValueId,
@@ -119,6 +120,7 @@ pub(crate) fn try_known_rewrite_to_dst(
 
 /// Fallback: when exactly one user-defined method matches by name/arity across the module,
 /// resolve to that even if class inference failed. Deterministic via uniqueness and user-box prefix.
+#[allow(dead_code)]
 pub(crate) fn try_unique_suffix_rewrite(
     builder: &mut MirBuilder,
     object_value: ValueId,
@@ -183,7 +185,7 @@ pub(crate) fn try_unique_suffix_rewrite_to_dst(
     if cands.len() != 1 { return None; }
     let fname = cands.remove(0);
     if let Some((bx, _)) = fname.split_once('.') { if !builder.user_defined_boxes.contains(bx) { return None; } } else { return None; }
-    let name_const = match crate::mir::builder::name_const::make_name_const_result(builder, &fname) {
+    let _name_const = match crate::mir::builder::name_const::make_name_const_result(builder, &fname) {
         Ok(v) => v,
         Err(e) => return Some(Err(e)),
     };
@@ -212,6 +214,7 @@ pub(crate) fn try_unique_suffix_rewrite_to_dst(
 }
 
 /// Unified entry: try Known rewrite first, then unique-suffix fallback.
+#[allow(dead_code)]
 pub(crate) fn try_known_or_unique(
     builder: &mut MirBuilder,
     object_value: ValueId,

src/mir/builder/rewrite/special.rs

@@ -2,6 +2,7 @@ use super::super::MirBuilder;
 
 /// Early special-case: toString/stringify → str（互換）を処理。
 /// 戻り値: Some(result_id) なら処理済み。None なら通常経路へ委譲。
+#[allow(dead_code)]
 pub(crate) fn try_early_str_like(
     builder: &mut MirBuilder,
     object_value: super::super::ValueId,
@@ -104,6 +105,7 @@ pub(crate) fn try_early_str_like(
 
 /// Special-case for equals/1: prefer Known rewrite; otherwise allow unique-suffix fallback
 /// when it is deterministic (single candidate). This centralizes equals handling.
+#[allow(dead_code)]
 pub(crate) fn try_special_equals(
     builder: &mut MirBuilder,
     object_value: super::super::ValueId,
@@ -151,7 +153,7 @@ pub(crate) fn try_early_str_like_to_dst(
                 "certainty": "Known",
             });
             super::super::observe::resolve::emit_choose(builder, meta);
-            let name_const = match crate::mir::builder::name_const::make_name_const_result(builder, &chosen) {
+            let _name_const = match crate::mir::builder::name_const::make_name_const_result(builder, &chosen) {
                 Ok(v) => v,
                 Err(e) => return Some(Err(e)),
             };
@@ -182,7 +184,7 @@ pub(crate) fn try_early_str_like_to_dst(
             "certainty": "Heuristic",
         });
         super::super::observe::resolve::emit_choose(builder, meta);
-        let name_const = match crate::mir::builder::name_const::make_name_const_result(builder, &fname) {
+        let _name_const = match crate::mir::builder::name_const::make_name_const_result(builder, &fname) {
             Ok(v) => v,
             Err(e) => return Some(Err(e)),
         };
@@ -209,7 +211,7 @@ pub(crate) fn try_early_str_like_to_dst(
                 "certainty": "Heuristic",
             });
             super::super::observe::resolve::emit_choose(builder, meta);
-            let name_const = match crate::mir::builder::name_const::make_name_const_result(builder, &fname) {
+            let _name_const = match crate::mir::builder::name_const::make_name_const_result(builder, &fname) {
                 Ok(v) => v,
                 Err(e) => return Some(Err(e)),
             };