Phase 25.1b: Step2完了（FuncBodyBasicLowerBox導入）

Step2実装内容:
- FuncBodyBasicLowerBox導入（defs専用下請けモジュール）
- _try_lower_local_if_return実装（Local+単純if）
- _inline_local_ints実装（軽い正規化）
- minimal lowers統合（Return/BinOp/IfCompare/MethodArray系）

Fail-Fast体制確立:
- MirBuilderBox: defs_onlyでも必ずタグ出力
- [builder/selfhost-first:unsupported:defs_only]
- [builder/selfhost-first:unsupported:no_match]

Phase構造整備:
- Phase 25.1b README新設（Step0-3計画）
- Phase 25.2b README新設（次期計画）
- UsingResolverBox追加（using system対応準備）

スモークテスト:
- stage1_launcher_program_to_mir_canary_vm.sh追加

Next: Step3 LoopForm対応

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

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

lang/src/shared/mir/loop_form_box.hako

@@ -12,7 +12,7 @@ static box LoopFormBox {
   //   i = i + 1;
   // }
   // Builds LoopForm structure with Header/Latch PHI + Exit PHI (continue/break aware)
-  loop_counter(limit, skip_value, break_value) {
+  method loop_counter(limit, skip_value, break_value) {
     if skip_value == null { skip_value = 2 }
     if break_value == null { break_value = limit }
 
@@ -109,7 +109,7 @@ static box LoopFormBox {
   //   body:      r12 = i + step, jump latch
   //   latch:     jump header (PHI incoming from body)
   //   exit:      ret r10
-  loop_count(limit) {
+  method loop_count(limit) {
     // Preheader
     local pre = new ArrayBox()
     pre.push(MirSchemaBox.inst_const(1, 0))
@@ -148,10 +148,10 @@ static box LoopFormBox {
 
   // loop_count_param — counting loop with init/step parameters
   // Returns final i value, starting from init, incremented by step while i < limit
-  loop_count_param(init, limit, step) {
+  method build_loop_count_param(start_value, limit, step) {
     // Preheader
     local pre = new ArrayBox()
-    pre.push(MirSchemaBox.inst_const(1, init))
+    pre.push(MirSchemaBox.inst_const(1, start_value))
     pre.push(MirSchemaBox.inst_const(2, limit))
     pre.push(MirSchemaBox.inst_const(3, step))
     pre.push(MirSchemaBox.inst_jump(1))
@@ -185,13 +185,13 @@ static box LoopFormBox {
 
   // Extended param variant: allow custom compare op ("Lt"/"Le"/"Gt"/"Ge") via opts
   // and negative step (handled by passing negative string for step)
-  loop_count_param_ex(init, limit, step, cmp) {
+  method build_loop_count_param_ex(start_value, limit, step, cmp) {
     local cmpop = "" + cmp
     if cmpop == null || cmpop == "" { cmpop = "Lt" }
 
     // Preheader
     local pre = new ArrayBox()
-    pre.push(MirSchemaBox.inst_const(1, init))
+    pre.push(MirSchemaBox.inst_const(1, start_value))
     pre.push(MirSchemaBox.inst_const(2, limit))
     pre.push(MirSchemaBox.inst_const(3, step))
     pre.push(MirSchemaBox.inst_jump(1))
@@ -227,18 +227,18 @@ static box LoopFormBox {
   // mode:
   //   - "count"   : counting loop that returns final i (uses loop_count)
   //   - "sum_bc"  : sum with break/continue sentinels (uses loop_counter)
-  build(mode, limit, skip_value, break_value) {
+  method build(mode, limit, skip_value, break_value) {
     local m = "" + mode
     if m == "count" {
       return me.loop_count(limit)
     }
     if m == "count_param" {
       // Here, skip_value carries init and break_value carries step (temporary param slots)
-      local init = skip_value
+      local start_value = skip_value
       local step = break_value
-      if init == null { init = 0 }
+      if start_value == null { start_value = 0 }
       if step == null { step = 1 }
-      return me.loop_count_param(init, limit, step)
+      return me.build_loop_count_param(start_value, limit, step)
     }
     if m == "sum_bc" {
       if skip_value == null { skip_value = 2 }
@@ -250,20 +250,20 @@ static box LoopFormBox {
   }
 
   // Map-based builder: build2({ mode, init, limit, step, skip, break })
-  build2(opts) {
+  method build2(opts) {
     if opts == null { return null }
     local mode = "" + opts.get("mode")
-    local init = opts.get("init")
+    local start_value = opts.get("init")
     local limit = opts.get("limit")
     local step = opts.get("step")
     local skip_v = opts.get("skip")
     local break_v = opts.get("break")
     if mode == "count" {
-      if init == null { init = 0 }
+      if start_value == null { start_value = 0 }
       if step == null { step = 1 }
       local cmp = opts.get("cmp") // optional: "Lt"/"Le"/"Gt"/"Ge"
       if cmp == null { cmp = "Lt" }
-      return me.loop_count_param_ex(init, limit, step, cmp)
+      return me.build_loop_count_param_ex(start_value, limit, step, cmp)
     }
     if mode == "sum_bc" { return me.loop_counter(limit, skip_v, break_v) }
     print("[loopform/unsupported-mode] " + mode)