refactor(llvm): Phase 131-12-P2 - block_end_values SSOT 化（WIP）

## 実装内容
- get_end_values() API 追加
- _value_at_end_i64() を snapshot-only に変更
- def_blocks 即時更新
- PHI incoming を snapshot から取得

## 発見された問題
- 同一ブロック内の def→use が predecessor snapshot を見てしまう
- これは次フェーズで resolve_cur / resolve_incoming 分離で修正

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

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

src/llvm_py/instructions/phi.py

@@ -58,39 +58,42 @@ def lower_phi(
         # Fallback: use blocks in incoming list
         actual_preds = [b for _, b in incoming]
 
-    # Collect incoming values
+    # P1: Collect incoming values from corresponding snapshots (SSOT)
     incoming_pairs: List[Tuple[ir.Block, ir.Value]] = []
     used_default_zero = False
+
+    import os
+    strict_mode = os.environ.get('NYASH_LLVM_STRICT') == '1'
+
     for block_id in actual_preds:
         block = bb_map.get(block_id)
         vid = incoming_map.get(block_id)
         if block is None:
             continue
-        # Prefer resolver-driven localization per predecessor block to satisfy dominance
-        if vid is not None and resolver is not None and bb_map is not None:
-            try:
-                pred_block_obj = bb_map.get(block_id)
-                if pred_block_obj is not None and hasattr(resolver, 'resolve_i64'):
-                    val = resolver.resolve_i64(vid, pred_block_obj, preds_map or {}, block_end_values or {}, vmap, bb_map)
-                else:
-                    val = None
-            except Exception:
-                val = None
-            if val is None:
-                # Missing incoming for this predecessor → default 0
-                val = ir.Constant(phi_type, 0)
-                used_default_zero = True
+
+        # P1: Get value from pred_bid's snapshot (SSOT - no global search)
+        if block_end_values is not None:
+            pred_snapshot = block_end_values.get(block_id, {})
+            val = pred_snapshot.get(vid) if vid is not None else None
+        else:
+            val = None
+
+        if val is None:
+            # P1: STRICT mode - fail fast on snapshot miss
+            if strict_mode:
+                available_keys = sorted(list(pred_snapshot.keys())) if block_end_values is not None else []
+                raise RuntimeError(
+                    f"[LLVM_PY/STRICT] PHI incoming miss:\n"
+                    f"  Source ValueId: v{vid}\n"
+                    f"  Predecessor Block: bb{block_id}\n"
+                    f"  PHI destination: v{dst_vid}\n"
+                    f"  Available in snapshot: {available_keys}\n"
+                    f"  Hint: Value v{vid} should be in block_end_values[{block_id}]"
+                )
+            # Non-STRICT: fallback to 0
+            val = ir.Constant(phi_type, 0)
+            used_default_zero = True
         else:
-            # Snapshot fallback
-            if block_end_values is not None:
-                snap = block_end_values.get(block_id, {})
-                val = snap.get(vid) if vid is not None else None
-            else:
-                val = vmap.get(vid) if vid is not None else None
-            if not val:
-                # Missing incoming for this predecessor → default 0
-                val = ir.Constant(phi_type, 0)
-                used_default_zero = True
             # Coerce pointer to i64 at predecessor end
             if hasattr(val, 'type') and val.type != phi_type:
                 pb = ir.IRBuilder(block)