feat(llvm): Phase 131-11-H/12 - ループキャリアPHI型修正 & vmap snapshot SSOT

## Phase 131-11-H: ループキャリアPHI型修正
- PHI生成時に初期値（entry block）の型のみ使用
- backedge の値を型推論に使わない（循環依存回避）
- NYASH_CARRIER_PHI_DEBUG=1 でトレース

## Phase 131-12-P0: def_blocks 登録 & STRICT エラー化
- safe_vmap_write() で PHI 上書き保護
- resolver miss を STRICT でエラー化（フォールバック 0 禁止）
- def_blocks 自動登録

## Phase 131-12-P1: vmap_cur スナップショット実装
- DeferredTerminator 構造体（block, term_ops, vmap_snapshot）
- Pass A で vmap_cur をスナップショット
- Pass C でスナップショット復元（try-finally）
- STRICT モード assert

## 結果
- ✅ MIR PHI型: Integer（正しい）
- ✅ VM: Result: 3
- ✅ vmap snapshot 機構: 動作確認
- ⚠️ LLVM: Result: 0（別のバグ、次Phase で調査）

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

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

src/llvm_py/resolver.py

@@ -88,7 +88,20 @@ class Resolver:
         Creates PHI at block start if needed, caches the result.
         """
         cache_key = (current_block.name, value_id)
-        
+
+        import os
+        if os.environ.get('NYASH_LLVM_PHI_DEBUG') == '1':
+            try:
+                bid = int(str(current_block.name).replace('bb',''))
+                in_def_blocks = value_id in self.def_blocks
+                if in_def_blocks:
+                    def_in_blocks = list(self.def_blocks.get(value_id, set()))
+                else:
+                    def_in_blocks = []
+                trace_phi(f"[resolve_i64/entry] bb{bid} v{value_id} in_def_blocks={in_def_blocks} def_in={def_in_blocks}")
+            except Exception as e:
+                trace_phi(f"[resolve_i64/entry] ERROR: {e}")
+
         # Check cache
         if cache_key in self.i64_cache:
             return self.i64_cache[cache_key]
@@ -158,10 +171,18 @@ class Resolver:
             defined_here = False
         if defined_here:
             existing = vmap.get(value_id)
+            import os
+            if os.environ.get('NYASH_LLVM_PHI_DEBUG') == '1':
+                existing_type = type(existing).__name__ if existing is not None else "None"
+                trace_phi(f"[resolve/def_here] bb{bid} v{value_id} existing={existing_type} in vmap={value_id in vmap}")
             if existing is not None and hasattr(existing, 'type') and isinstance(existing.type, ir.IntType) and existing.type.width == 64:
                 trace_values(f"[resolve] local reuse: bb{bid} v{value_id}")
                 self.i64_cache[cache_key] = existing
                 return existing
+            elif existing is not None:
+                if os.environ.get('NYASH_LLVM_PHI_DEBUG') == '1':
+                    existing_llvm_type = str(existing.type) if hasattr(existing, 'type') else "no_type"
+                    trace_phi(f"[resolve/def_here] bb{bid} v{value_id} existing has wrong type: {existing_llvm_type}")
         else:
             # Do NOT blindly reuse vmap across blocks: it may reference values defined
             # in non-dominating predecessors (e.g., other branches). Only reuse when
@@ -235,6 +256,24 @@ class Resolver:
                 result = placeholder if (placeholder is not None and hasattr(placeholder, 'add_incoming')) else ir.Constant(self.i64, 0)
             else:
                 # No declared PHI and multi-pred: do not synthesize; fallback to zero
+                import os
+                if os.environ.get('NYASH_LLVM_STRICT') == '1':
+                    # P0-2: STRICT mode - fail fast on undeclared PHI in multi-pred context
+                    def_blocks_info = "not_in_def_blocks"
+                    try:
+                        if value_id in self.def_blocks:
+                            def_blocks_info = f"def_blocks={sorted(list(self.def_blocks[value_id]))}"
+                    except Exception:
+                        pass
+
+                    raise RuntimeError(
+                        f"[LLVM_PY/STRICT] Undeclared PHI in multi-pred block:\n"
+                        f"  ValueId: {value_id}\n"
+                        f"  Block: bb{cur_bid}\n"
+                        f"  Predecessors: {pred_ids}\n"
+                        f"  {def_blocks_info}\n"
+                        f"  Hint: Value needs PHI but not declared in block_phi_incomings"
+                    )
                 result = ir.Constant(self.i64, 0)
         
         # Cache and return
@@ -342,6 +381,31 @@ class Resolver:
 
         preds_s = ','.join(str(x) for x in pred_ids)
         trace_phi(f"[resolve] end_i64 miss: bb{block_id} v{value_id} preds=[{preds_s}] → 0")
+
+        # P0-2: STRICT mode - fail fast on resolution miss
+        import os
+        if os.environ.get('NYASH_LLVM_STRICT') == '1':
+            # Collect diagnostic information
+            def_blocks_info = "not_in_def_blocks"
+            try:
+                if value_id in self.def_blocks:
+                    def_blocks_info = f"def_blocks={sorted(list(self.def_blocks[value_id]))}"
+            except Exception:
+                pass
+
+            # Build search path for diagnostics
+            search_path = [block_id] + pred_ids
+
+            raise RuntimeError(
+                f"[LLVM_PY/STRICT] PHI resolution miss:\n"
+                f"  ValueId: {value_id}\n"
+                f"  Target block: {block_id}\n"
+                f"  Predecessors: [{preds_s}]\n"
+                f"  Search path: {search_path}\n"
+                f"  {def_blocks_info}\n"
+                f"  Hint: PHI dst may not be registered in def_blocks, or dominance issue"
+            )
+
         z = ir.Constant(self.i64, 0)
         self._end_i64_cache[key] = z
         return z