refactor(plan): Phase 273 P3+ - Legacy code removal

Phase 273 P3+ 完成: レガシーコード削除 + 未使用 import 整理

Removed Legacy Items:
1. emit_scan_with_init_edgecfg() - Pattern6 固有の emission 関数
   - File deleted: src/mir/builder/emission/loop_scan_with_init.rs (~144 lines)
   - Replaced by: generalized Frag API (Phase 273 P2)

2. CoreCarrierInfo struct - Legacy carrier representation
   - Removed from: src/mir/builder/control_flow/plan/mod.rs (~15 lines)
   - Replaced by: CorePhiInfo (generalized PHI representation)

3. verify_carrier() function - CoreCarrierInfo validator
   - Removed from: src/mir/builder/control_flow/plan/verifier.rs (~15 lines)
   - Replaced by: generalized PHI verification (V7-V9)

Code Cleanup:
- cargo fix applied: unused imports removed (~30 files)
- Verifier invariants updated: V1→V2-V9 (carrier→PHI model)
- Module declaration cleanup in emission/mod.rs

Impact:
- Total lines removed: ~174 lines (net reduction)
- Pattern-agnostic architecture strengthened
- All legacy Pattern6 references eliminated

Tests:
- ✅ VM tests PASS (phase254/256/258)
- ✅ LLVM tests PASS (phase256/258)

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/development/current/main/phases/phase-273/README.md

@@ -1,6 +1,6 @@
 # Phase 273: Plan Extractor (Pure) + PlanLowerer SSOT
 
-Status: ✅ P0/P1 completed (2025-12-22)
+Status: ✅ P0/P1/P2 completed (2025-12-22)
 
 Goal:
 - pattern 列挙の裾広がりを止める。
@@ -9,6 +9,15 @@ Goal:
 
 ---
 
+## P2 完了 (2025-12-22)
+
+P2 では Pattern7（split scan）を Plan ラインへ移行し、P1 の CorePlan を保ったまま “収束圧” を上げた。
+
+- ✅ Pattern7: Extractor → DomainPlan → Normalizer → CorePlan → Lowerer（MIR/Frag/emit_frag）へ統一
+- ✅ CoreLoopPlan: `block_effects / phis / frag / final_values` で一般化（Pattern6/7 が同一 CorePlan に収束）
+- ✅ CoreEffectPlan: `dst: Option<ValueId>` + `effects: EffectMask` で副作用（例: `push`）を表現可能にした
+- ✅ Lowerer: “split” の知識を持たず、CorePlan のみを処理（pattern-agnostic 維持）
+
 ## P1 完了 (2025-12-22)
 
 ### アーキテクチャ
@@ -52,7 +61,7 @@ pub enum CorePlan {
 }
 
 pub enum CoreEffectPlan {
-    MethodCall { dst, object, method, args },
+    MethodCall { dst, object, method, args, effects },
     BinOp { dst, lhs, op, rhs },
     Compare { dst, lhs, op, rhs },
     Const { dst, value },
@@ -111,6 +120,16 @@ AOT ランタイム（nyrt）は `ny_main()` の返り値が **raw i64** か **h
 
 - P0 Claude Code: `docs/development/current/main/phases/phase-273/P0-CLAUDE.md`
 - P1 Claude Code: `docs/development/current/main/phases/phase-273/P1-CLAUDE.md`
+- P2 Completion: `docs/development/current/main/phases/phase-273/P2-COMPLETION.md`
+
+## Next (P3 proposal)
+
+P2 で追加した “legacy fallback” を残したままだと、Lowerer の中に `emit_scan_with_init_edgecfg()` 等の旧経路が残り続ける。
+収束を完成させるには、次を P3 で行うのが良い：
+
+- Pattern6 を generalized CoreLoopPlan（`frag/block_effects/phis/final_values`）に移行
+- `lower_loop_legacy()` を撤去し、generalized 経路を SSOT 化（Fail-Fast）
+- CoreLoopPlan の `Option<...>` フィールドを必須化（構造で “揺れ” を消す）
 
 ## Future Work (P2+)