diff --git a/docs/development/current/main/phase131-3-llvm-lowering-inventory.md b/docs/development/current/main/phase131-3-llvm-lowering-inventory.md
index baf30116..4c7820fe 100644
--- a/docs/development/current/main/phase131-3-llvm-lowering-inventory.md
+++ b/docs/development/current/main/phase131-3-llvm-lowering-inventory.md
@@ -27,6 +27,16 @@
   - Investigation: [phase132-llvm-exit-phi-wrong-result.md](investigations/phase132-llvm-exit-phi-wrong-result.md)
   - Phase summary: [phases/phase-132/README.md](phases/phase-132/README.md)
 
+## Phase 132-P1 Update (2025-12-15)
+
+✅ **STRUCTURAL FIX**: Function-local state isolation in LLVM Python backend
+
+- **Issue**: block id / value id が “関数をまたいで” 衝突し得る（snapshot / cache / PHI state の漏洩）
+- **Fix**: `FunctionLowerContext` Box で function-scoped state を隔離し、tuple-key workaround を不要化
+- **Code**:
+  - `src/llvm_py/context/function_lower_context.py`
+  - `src/llvm_py/builders/function_lower.py`
+
 ## Root Causes Identified
 
 ### 1. TAG-EMIT: Loop PHI → Invalid LLVM IR (Case B) ✅ FIXED (Phase 131-10)
diff --git a/docs/development/current/main/phases/phase-132/README.md b/docs/development/current/main/phases/phase-132/README.md
index 514412e5..50d978ac 100644
--- a/docs/development/current/main/phases/phase-132/README.md
+++ b/docs/development/current/main/phases/phase-132/README.md
@@ -110,3 +110,24 @@ JoinIR merge の契約検証（debug build）で **早期に Fail-Fast** する
 期待される振る舞い:
 - debug build では compile/run 中に panic で即停止（原因と修正案が出る）
 - release build の既定挙動は変えない（検証は `debug_assertions` のみ）
+
+---
+
+## 追加: Phase 132-P1（LLVM Python）FunctionLowerContext Box
+
+Phase 131–132 で顕在化した「関数間の状態漏洩（block id / value id の衝突）」を、
+tuple-key の小手先ではなく **構造で根治**するために、関数ローカル状態を 1 箱に隔離した。
+
+- 実装: `src/llvm_py/context/function_lower_context.py`
+- 統合: `src/llvm_py/builders/function_lower.py`
+
+箱の責務（SSOT）:
+- `block_end_values`（snapshot）
+- `def_blocks`
+- `jump_only_blocks`
+- `phi_manager`
+- resolver caches（i64/ptr/f64/end_i64 など）
+
+狙い:
+- 関数単位で state を自動破棄し、cross-function collision を “起こせない構造” にする
+- 追加の手動クリアや tuple-key を不要にする
diff --git a/src/llvm_py/builders/function_lower.py b/src/llvm_py/builders/function_lower.py
index 16c33b3e..c7bb6fb3 100644
--- a/src/llvm_py/builders/function_lower.py
+++ b/src/llvm_py/builders/function_lower.py
@@ -51,6 +51,14 @@ def lower_function(builder, func_data: Dict[str, Any]):
         builder.bb_map.clear()
     except Exception:
         builder.bb_map = {}
+    # Phase 132-P1: Clear per-function predeclared PHI placeholders (avoid cross-function leakage)
+    try:
+        builder.predeclared_ret_phis.clear()
+    except Exception:
+        try:
+            builder.predeclared_ret_phis = {}
+        except Exception:
+            pass
 
     # Phase 132-P1: Create function-local context Box
     # This automatically isolates all function-scoped state
@@ -63,6 +71,7 @@ def lower_function(builder, func_data: Dict[str, Any]):
     builder.phi_manager = context.phi_manager
     builder.block_phi_incomings = context.block_phi_incomings
     builder.def_blocks = context.def_blocks
+    builder.block_end_values = context.block_end_values
 
     # Bind resolver to context (redirects caches to context storage)
     builder.resolver.bind_context(context)
@@ -311,7 +320,7 @@ def lower_function(builder, func_data: Dict[str, Any]):
             vmap=builder.vmap,
             bb_map=builder.bb_map,
             preds=builder.preds,
-            block_end_values=builder.block_end_values,
+            block_end_values=context.block_end_values,
             resolver=builder.resolver,
             trace_phi=os.environ.get('NYASH_LLVM_TRACE_PHI') == '1',
             verbose=os.environ.get('NYASH_CLI_VERBOSE') == '1',