diff --git a/src/llvm_py/builders/function_lower.py b/src/llvm_py/builders/function_lower.py
index 4b87449e..65e1aac1 100644
--- a/src/llvm_py/builders/function_lower.py
+++ b/src/llvm_py/builders/function_lower.py
@@ -11,6 +11,74 @@ from phi_wiring import (
 )
 
 
+def _clear_function_local_state(builder):
+    """
+    Phase 132-P1: Clear all function-local state at function boundary.
+
+    Box-First Principle: Prevents cross-function ValueId/BlockId collisions
+    by clearing all function-scoped state when entering a new function.
+
+    Cleared state:
+    1. PhiManager.predeclared - (bid, vid) -> phi_value
+    2. Resolver caches - i64_cache, ptr_cache, f64_cache, _end_i64_cache
+    3. Jump-only blocks - _jump_only_blocks
+    4. PHI incomings - block_phi_incomings, def_blocks
+    5. String/NewBox caches - function-local string handling
+    """
+    try:
+        # 1. PhiManager predeclared PHIs (bid, vid) -> phi_value
+        if hasattr(builder, 'phi_manager') and hasattr(builder.phi_manager, 'predeclared'):
+            builder.phi_manager.predeclared.clear()
+    except Exception:
+        pass
+
+    try:
+        # 2. Resolver caches (all keyed by block/value IDs)
+        builder.resolver.i64_cache.clear()
+        builder.resolver.ptr_cache.clear()
+        builder.resolver.f64_cache.clear()
+        if hasattr(builder.resolver, '_end_i64_cache'):
+            builder.resolver._end_i64_cache.clear()
+
+        # 3. String-related caches (function-local)
+        if hasattr(builder.resolver, 'string_ids'):
+            builder.resolver.string_ids.clear()
+        if hasattr(builder.resolver, 'string_literals'):
+            builder.resolver.string_literals.clear()
+        if hasattr(builder.resolver, 'string_ptrs'):
+            builder.resolver.string_ptrs.clear()
+        if hasattr(builder.resolver, 'length_cache'):
+            builder.resolver.length_cache.clear()
+
+        # 4. NewBox→string-arg hints (function-local)
+        if hasattr(builder.resolver, 'newbox_string_args') and isinstance(builder.resolver.newbox_string_args, dict):
+            builder.resolver.newbox_string_args.clear()
+    except Exception:
+        pass
+
+    try:
+        # 5. Jump-only blocks (bid -> pred_bid)
+        if hasattr(builder, '_jump_only_blocks'):
+            builder._jump_only_blocks.clear()
+    except Exception:
+        pass
+
+    try:
+        # 6. PHI incomings and def_blocks (function-local)
+        if hasattr(builder, 'block_phi_incomings'):
+            builder.block_phi_incomings.clear()
+        if hasattr(builder, 'def_blocks'):
+            builder.def_blocks.clear()
+
+        # Also clear resolver's references to these
+        if hasattr(builder.resolver, 'block_phi_incomings'):
+            builder.resolver.block_phi_incomings = {}
+        if hasattr(builder.resolver, 'def_blocks'):
+            builder.resolver.def_blocks.clear()
+    except Exception:
+        pass
+
+
 def lower_function(builder, func_data: Dict[str, Any]):
     """Lower a single MIR function to LLVM IR using the given builder context.
     This is a faithful extraction of NyashLLVMBuilder.lower_function.
@@ -49,35 +117,8 @@ def lower_function(builder, func_data: Dict[str, Any]):
         builder.bb_map.clear()
     except Exception:
         builder.bb_map = {}
-    # Phase 132-P0: Clear phi_manager per-function to avoid ValueId collisions
-    try:
-        if hasattr(builder, 'phi_manager') and hasattr(builder.phi_manager, 'predeclared'):
-            builder.phi_manager.predeclared.clear()
-    except Exception:
-        pass
-    try:
-        # Reset resolver caches keyed by block names
-        builder.resolver.i64_cache.clear()
-        builder.resolver.ptr_cache.clear()
-        builder.resolver.f64_cache.clear()
-        if hasattr(builder.resolver, '_end_i64_cache'):
-            builder.resolver._end_i64_cache.clear()
-        if hasattr(builder.resolver, 'string_ids'):
-            builder.resolver.string_ids.clear()
-        if hasattr(builder.resolver, 'string_literals'):
-            builder.resolver.string_literals.clear()
-        if hasattr(builder.resolver, 'string_ptrs'):
-            builder.resolver.string_ptrs.clear()
-        if hasattr(builder.resolver, 'length_cache'):
-            builder.resolver.length_cache.clear()
-        # Also clear newbox→string-arg hints per function to avoid leakage
-        try:
-            if hasattr(builder.resolver, 'newbox_string_args') and isinstance(builder.resolver.newbox_string_args, dict):
-                builder.resolver.newbox_string_args.clear()
-        except Exception:
-            pass
-    except Exception:
-        pass
+    # Phase 132-P1: Clear all function-local state (prevent cross-function collision)
+    _clear_function_local_state(builder)
 
     # Phase 131-15-P1: Load value_types metadata from JSON into resolver
     try: