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>

src/mir/builder/control_flow/plan/mod.rs

@@ -192,21 +192,7 @@ pub(in crate::mir::builder) struct CoreLoopPlan {
     pub final_values: Vec<(String, ValueId)>,
 }
 
-/// Phase 273 P1: Loop carrier (PHI variable)
-#[derive(Debug, Clone)]
-pub(in crate::mir::builder) struct CoreCarrierInfo {
-    /// Variable name (for variable_map update)
-    pub name: String,
-
-    /// Initial value (from preheader)
-    pub init_value: ValueId,
-
-    /// Step value (from step block, back-edge)
-    pub step_value: ValueId,
-
-    /// PHI destination (loop variable inside loop)
-    pub phi_dst: ValueId,
-}
+// Phase 273 P3: CoreCarrierInfo removed (replaced by CorePhiInfo)
 
 /// Phase 273 P1: Conditional plan
 #[derive(Debug, Clone)]

src/mir/builder/control_flow/plan/normalizer.rs

@@ -12,7 +12,7 @@
 //! Lowerer processes CorePlan without any pattern knowledge.
 
 use super::{
-    CoreCarrierInfo, CoreEffectPlan, CoreLoopPlan, CorePhiInfo, CorePlan, DomainPlan,
+    CoreEffectPlan, CoreLoopPlan, CorePhiInfo, CorePlan, DomainPlan,
     ScanWithInitPlan, SplitScanPlan,
 };
 use crate::mir::builder::control_flow::joinir::patterns::router::LoopPatternContext;

src/mir/builder/control_flow/plan/verifier.rs

@@ -1,4 +1,4 @@
-//! Phase 273 P1: PlanVerifier - CorePlan 不変条件検証 (fail-fast)
+//! Phase 273 P3: PlanVerifier - CorePlan 不変条件検証 (fail-fast)
 //!
 //! # Responsibilities
 //!
@@ -6,16 +6,20 @@
 //! - Fail fast on close-but-unsupported patterns
 //! - Prevent silent miscompilation
 //!
-//! # Invariants (V1-V6)
+//! # Invariants (V2-V9)
 //!
-//! - V1: Carrier completeness (name/init_value/step_value present)
 //! - V2: Condition validity (valid ValueId)
 //! - V3: Exit validity (Return in function, Break/Continue in loop)
 //! - V4: Seq non-empty
 //! - V5: If completeness (then_plans non-empty)
 //! - V6: ValueId validity (all ValueIds pre-generated)
+//! - V7: PHI non-empty (loops require at least one carrier)
+//! - V8: Frag entry matches header_bb
+//! - V9: block_effects contains header_bb
+//!
+//! Phase 273 P3: V1 (Carrier completeness) removed with CoreCarrierInfo
 
-use super::{CoreCarrierInfo, CoreEffectPlan, CoreExitPlan, CoreIfPlan, CoreLoopPlan, CorePlan};
+use super::{CoreEffectPlan, CoreExitPlan, CoreIfPlan, CoreLoopPlan, CorePlan};
 use crate::mir::ValueId;
 
 /// Phase 273 P1: PlanVerifier - CorePlan 不変条件検証 (fail-fast)
@@ -132,21 +136,7 @@ impl PlanVerifier {
         Ok(())
     }
 
-    /// V1: Carrier completeness
-    fn verify_carrier(carrier: &CoreCarrierInfo, depth: usize, index: usize) -> Result<(), String> {
-        if carrier.name.is_empty() {
-            return Err(format!(
-                "[V1] Carrier[{}] at depth {} has empty name",
-                index, depth
-            ));
-        }
-
-        Self::verify_value_id_basic(carrier.init_value, depth, &format!("carrier[{}].init_value", index))?;
-        Self::verify_value_id_basic(carrier.step_value, depth, &format!("carrier[{}].step_value", index))?;
-        Self::verify_value_id_basic(carrier.phi_dst, depth, &format!("carrier[{}].phi_dst", index))?;
-
-        Ok(())
-    }
+    // Phase 273 P3: verify_carrier() removed (CoreCarrierInfo replaced by CorePhiInfo)
 
     /// V5: If completeness
     fn verify_if(if_plan: &CoreIfPlan, depth: usize, in_loop: bool) -> Result<(), String> {