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/runner/json_v0_bridge/lowering.rs

@@ -2,7 +2,7 @@ use super::ast::{ProgramV0, StmtV0, ExprV0};
 use crate::mir::Callee;
 use crate::mir::{
     BasicBlockId, ConstValue, EffectMask, FunctionSignature, MirFunction, MirInstruction, MirModule,
-    MirPrinter, MirType, ValueId, BinaryOp,
+    MirPrinter, MirType, ValueId,
 };
 use std::collections::HashMap;
 use std::cell::RefCell;
@@ -103,6 +103,7 @@ pub(super) struct BridgeEnv {
 }
 
 impl BridgeEnv {
+    #[allow(dead_code)]
     pub(super) fn load() -> Self {
         Self::with_imports(HashMap::new())
     }

src/runner/json_v0_bridge/lowering/expr.rs

@@ -3,7 +3,7 @@ use super::BridgeEnv;
 use super::ternary;
 use super::match_expr;
 use crate::mir::{
-    BasicBlockId, BinaryOp, ConstValue, EffectMask, MirFunction, MirInstruction, ValueId,
+    BasicBlockId, ConstValue, EffectMask, MirFunction, MirInstruction, ValueId,
 };
 use std::collections::HashMap;
 

src/runner/json_v0_bridge/lowering/if_else.rs

@@ -1,5 +1,5 @@
 use super::{lower_stmt_list_with_vars, merge_var_maps, new_block, BridgeEnv, LoopContext};
-use crate::mir::{BasicBlockId, MirFunction, MirInstruction, ValueId};
+use crate::mir::{BasicBlockId, MirFunction, ValueId};
 use std::collections::HashMap;
 use super::super::ast::StmtV0;
 use super::super::ast::ExprV0;

src/runner/json_v0_bridge/lowering/ternary.rs

@@ -5,7 +5,7 @@
 
 use super::merge::new_block;
 use super::BridgeEnv;
-use crate::mir::{BasicBlockId, MirFunction, MirInstruction, ValueId};
+use crate::mir::{BasicBlockId, MirFunction, ValueId};
 use super::super::ast::ExprV0;
 
 use super::expr::{lower_expr_with_scope, VarScope};
@@ -35,7 +35,7 @@ pub(super) fn lower_ternary_expr_with_scope<S: VarScope>(
     }
     let out = f.next_value_id();
     // フェーズM.2: PHI統一処理（no_phi分岐削除）
-    let mut inputs = vec![(tend, tval), (eend, eval)];
+    let inputs = vec![(tend, tval), (eend, eval)];
     crate::mir::ssot::cf_common::insert_phi_at_head(f, merge_bb, out, inputs);
     Ok((out, merge_bb))
 }

src/runner/json_v0_bridge/lowering/throw_ctx.rs

@@ -1,4 +1,4 @@
-use crate::mir::{BasicBlockId, MirFunction, MirInstruction, ValueId};
+use crate::mir::{BasicBlockId, MirFunction, ValueId};
 use std::cell::RefCell;
 
 thread_local! {