feat(llvm): Phase 132 - Pattern 1 exit value parity fix + Box-First refactoring

## Phase 132: Exit PHI Value Parity Fix

### Problem
Pattern 1 (Simple While) returned 0 instead of final loop variable value (3)
- VM: RC: 3 ✅ (correct)
- LLVM: Result: 0 ❌ (wrong)

### Root Cause (Two Layers)
1. **JoinIR/Boundary**: Missing exit_bindings → ExitLineReconnector not firing
2. **LLVM Python**: block_end_values snapshot dropping PHI values

### Fix
**JoinIR** (simple_while_minimal.rs):
- Jump(k_exit, [i_param]) passes exit value

**Boundary** (pattern1_minimal.rs):
- Added LoopExitBinding with carrier_name="i", role=LoopState
- Enables ExitLineReconnector to update variable_map

**LLVM** (block_lower.py):
- Use predeclared_ret_phis for reliable PHI filtering
- Protect builder.vmap PHIs from overwrites (SSOT principle)

### Result
- ✅ VM: RC: 3
- ✅ LLVM: Result: 3
- ✅ VM/LLVM parity achieved

## Phase 132-Post: Box-First Refactoring

### Rust Side
**JoinModule::require_function()** (mod.rs):
- Encapsulate function search logic
- 10 lines → 1 line (90% reduction)
- Reusable for Pattern 2-5

### Python Side
**PhiManager Box** (phi_manager.py - new):
- Centralized PHI lifecycle management
- 47 lines → 8 lines (83% reduction)
- SSOT: builder.vmap owns PHIs
- Fail-Fast: No silent overwrites

**Integration**:
- LLVMBuilder: Added phi_manager
- block_lower.py: Delegated to PhiManager
- tagging.py: Register PHIs with manager

### Documentation
**New Files**:
- docs/development/architecture/exit-phi-design.md
- docs/development/current/main/investigations/phase132-llvm-exit-phi-wrong-result.md
- docs/development/current/main/phases/phase-132/

**Updated**:
- docs/development/current/main/10-Now.md
- docs/development/current/main/phase131-3-llvm-lowering-inventory.md

### Design Principles
- Box-First: Logic encapsulated in classes/methods
- SSOT: Single Source of Truth (builder.vmap for PHIs)
- Fail-Fast: Early explicit failures, no fallbacks
- Separation of Concerns: 3-layer architecture

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

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

docs/development/current/main/phase131-3-llvm-lowering-inventory.md

@@ -12,9 +12,24 @@
 | B2 | `/tmp/case_b_simple.hako` | ✅ | ✅ | ✅ | **PASS** - Simple print(42) without loop works |
 | C | `apps/tests/llvm_stage3_loop_only.hako` | ✅ | ✅ | ⚠️ | **TAG-RUN** - Loop ok; print/concat path segfaults |
 
+## Phase 132 Update (2025-12-15)
+
+✅ **MAJOR FIX**: Exit PHI wrong result bug fixed!
+- **Issue**: Pattern 1 の `return i` が LLVM だけ 0 を返す（VM は 3）
+- **Test**: `/tmp/p1_return_i.hako` が VM/LLVM ともに 3 を返すようになった
+- **Root Cause (two-layer)**:
+  - JoinIR/Boundary: exit 値が境界を通っていなかった（exit_bindings / Jump args）
+  - LLVM Python: builder.vmap の PHI placeholder が上書きされ、`ret` が 0 を参照
+- **Fix**:
+  - JoinIR/Boundary: Pattern 1 で exit 値を明示的に渡す + LoopExitBinding を境界へ設定
+  - LLVM Python: `predeclared_ret_phis` で PHI 所有を追跡し、PHI placeholder を上書きしない
+- **Details**:
+  - 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)
+
 ## Root Causes Identified
 
-### 1. TAG-EMIT: Loop PHI → Invalid LLVM IR (Case B)
+### 1. TAG-EMIT: Loop PHI → Invalid LLVM IR (Case B) ✅ FIXED (Phase 131-10)
 
 **File**: `apps/tests/loop_min_while.hako`