fix(mir): PHI検証panic修正 - update_cfg()を検証前に呼び出し

A案実装: debug_verify_phi_inputs呼び出し前にCFG predecessorを更新

修正箇所（7箇所）:
- src/mir/builder/phi.rs:50, 73, 132, 143
- src/mir/builder/ops.rs:273, 328, 351

根本原因:
- Branch/Jump命令でsuccessorは即座に更新
- predecessorはupdate_cfg()で遅延再構築
- PHI検証が先に実行されてpredecessor未更新でpanic

解決策:
- 各debug_verify_phi_inputs呼び出し前に
  if let Some(func) = self.current_function.as_mut() {
      func.update_cfg();
  }
  を挿入してCFGを同期

影響: if/else文、論理演算子(&&/||)のPHI生成が正常動作

lang/src/compiler/entry/compiler.hako

@@ -30,7 +30,8 @@ static box Main {
 
   _collect_flags(args) {
     // Stage-A flags: emit/source/return only
-    local flags = { emit: 0, ret: null, source: null, stage_b: 0 }
+    // Stage-B flags: prefer_cfg/stage3/v1_compat
+    local flags = { emit: 0, ret: null, source: null, stage_b: 0, prefer_cfg: 1, stage3: 0, v1_compat: 0 }
     if args == null { return flags }
 
     local i = 0
@@ -48,6 +49,14 @@ static box Main {
         local parsed = me._parse_signed_int(args.get(i + 1))
         if parsed != null { flags.ret = parsed }
         i = i + 1
+      } else if token == "--prefer-cfg" && i + 1 < n {
+        local parsed = me._parse_signed_int(args.get(i + 1))
+        if parsed != null { flags.prefer_cfg = parsed }
+        i = i + 1
+      } else if token == "--stage3" {
+        flags.stage3 = 1
+      } else if token == "--v1-compat" {
+        flags.v1_compat = 1
       }
       i = i + 1
     }
@@ -469,7 +478,9 @@ static box Main {
   main(args) {
     local flags = me._collect_flags(args)
     if flags.stage_b == 1 {
-      return StageBMain.main(args)
+      local json = StageBMain._do_compile_stage_b(flags.source, flags.prefer_cfg, flags.stage3, flags.v1_compat)
+      print(json)
+      return 0
     }
     if flags.emit == 1 {
       local json = me._compile_source_to_json_v0(flags.source)
@@ -489,4 +500,5 @@ static box Main {
     me._emit_program_json(ret)
     return 0
   }
+
 }

lang/src/compiler/entry/compiler_stageb.hako

@@ -1,9 +1,13 @@
 // Stage-B compiler entry — ParserBox → FlowEntry emit-only
 
-using "lang/src/compiler/parser/parser_box.hako" as ParserBox
-using "lang/src/compiler/pipeline_v2/flow_entry.hako" as FlowEntryBox
+using lang.compiler.parser.box as ParserBox
+using lang.compiler.pipeline_v2.flow_entry as FlowEntryBox
 
 static box StageBMain {
+  _fallback_program() {
+    return "{\"version\":0,\"kind\":\"Program\",\"body\":[{\"type\":\"Return\",\"expr\":{\"type\":\"Int\",\"value\":0}}]}"
+  }
+
   _parse_signed_int(raw) {
     if raw == null { return null }
     local text = "" + raw
@@ -52,23 +56,20 @@ static box StageBMain {
     return flags
   }
 
-  main(args) {
-    local flags = me._collect_flags(args)
-    local src = flags.source
+  _do_compile_stage_b(src, prefer_cfg, stage3, v1_compat) {
     if src == null || src == "" {
-      print("{\"version\":0,\"kind\":\"Program\",\"body\":[{\"type\":\"Return\",\"expr\":{\"type\":\"Int\",\"value\":0}}]}")
-      return 0
+      return me._fallback_program()
     }
     local p = new ParserBox()
-    if flags.stage3 == 1 { p.stage3_enable(1) }
+    if stage3 == 1 { p.stage3_enable(1) }
     p.extract_usings(src)
     local usings_json = p.get_usings_json()
     p.extract_externs(src)
     local externs_json = p.get_externs_json()
     local ast_json = p.parse_program2(src)
-    local prefer = flags.prefer_cfg
+    local prefer = prefer_cfg
     local jv0 = null
-    if flags.v1_compat == 1 {
+    if v1_compat == 1 {
       jv0 = FlowEntryBox.emit_v1_compat_from_ast_with_meta(ast_json, prefer, externs_json)
     }
     if jv0 == null || jv0 == "" {
@@ -77,9 +78,21 @@ static box StageBMain {
     if jv0 == null || jv0 == "" {
       jv0 = FlowEntryBox.emit_v0_from_ast(ast_json, prefer)
     }
-    // Attach usings metadata when available（Stage-B pipeline consumes via resolver）
-    if jv0 == null || jv0 == "" { jv0 = "{\"version\":0,\"kind\":\"Program\",\"body\":[{\"type\":\"Return\",\"expr\":{\"type\":\"Int\",\"value\":0}}]}" }
-    print(jv0)
+    if jv0 == null || jv0 == "" {
+      jv0 = me._fallback_program()
+    }
+    return jv0
+  }
+
+  main(args) {
+    local flags = me._collect_flags(args)
+    local src = flags.source
+    local prefer = flags.prefer_cfg
+    local stage3 = flags.stage3
+    local v1_compat = flags.v1_compat
+    local json = me._do_compile_stage_b(src, prefer, stage3, v1_compat)
+    if json == null || json == "" { json = me._fallback_program() }
+    print(json)
     return 0
   }
 }