Phase 25.1b: Step3完了（LoopForm対応）

Step3実装内容（LoopForm → MIR導線確立）:
- FuncBodyBasicLowerBox._try_lower_loop追加:
  - Loop判定 → LowerLoopSumBcBox → LowerLoopSimpleBox の順に試行
  - 成功時は_rebindで関数名をBox.method/arityに付け替え
  - 失敗時は[builder/funcs:unsupported:loopform]でFail-Fast
- lowerメソッド冒頭でLoop優先処理:
  - Loop含む場合は_try_lower_loopを呼び、成功/失敗で明確に分岐
  - Loopが無い場合のみ既存のLocal/If/Return処理に進む
- PHI地獄防止ポリシー徹底:
  - FuncBodyBasicLowerBox/FuncLowering側でPHIやキャリアを直接いじらない
  - LoopForm制約外は必ずタグ付きでFail-Fast（Rust providerに退避可能）

ドキュメント更新:
- Phase 25.1b README: Step3をinitial-implementedに更新
- builder README: [builder/funcs:unsupported:loopform]タグ追加
- CURRENT_TASK.md: Step3進捗記録

スモークテスト:
- selfhost_mir_loopform_basic_vm.sh追加（基本構造実装済み）
- defs生成経路の詳細調整は継続タスク

Next: Step4（MethodCall/ExternCall対応）

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

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

tools/smokes/v2/profiles/quick/core/phase251/selfhost_mir_loopform_basic_vm.sh

@@ -0,0 +1,58 @@
+#!/usr/bin/env bash
+# selfhost_mir_loopform_basic_vm.sh
+# - Canary for Phase 25.1b Step3: ensure FuncBodyBasicLowerBox can delegate
+#   LoopForm-normalized loops to LowerLoopSimpleBox/LowerLoopSumBcBox.
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+ROOT_DIR="$(git -C "$SCRIPT_DIR" rev-parse --show-toplevel 2>/dev/null || (cd "$SCRIPT_DIR/../../../../../../.." && pwd))"
+
+# Create a minimal .hako file with a simple counting loop
+TEST_HAKO="$(mktemp --suffix .hako)"
+cat > "$TEST_HAKO" <<'HAKO'
+static box TestBox {
+  count() {
+    local i = 0
+    loop(i < 10) {
+      i = i + 1
+    }
+    return i
+  }
+}
+
+static box Main {
+  main() {
+    return 0
+  }
+}
+HAKO
+
+OUT_MIR="$(mktemp --suffix .json)"
+LOG_OUT="$(mktemp --suffix .log)"
+trap 'rm -f "$TEST_HAKO" "$OUT_MIR" "$LOG_OUT" || true' EXIT
+
+set +e
+HAKO_SELFHOST_BUILDER_FIRST=1 HAKO_MIR_BUILDER_FUNCS=1 HAKO_SELFHOST_TRACE=1 NYASH_JSON_ONLY=1 \
+  bash "$ROOT_DIR/tools/hakorune_emit_mir.sh" "$TEST_HAKO" "$OUT_MIR" >"$LOG_OUT" 2>&1
+rc=$?
+set -e
+
+# Check logs for LoopForm lower tags
+if ! grep -q "\[funcs/basic:loop\." "$LOG_OUT"; then
+  echo "[FAIL] selfhost_mir_loopform_basic_vm (no [funcs/basic:loop.*] tag found)" >&2
+  echo "=== LOG OUTPUT ===" >&2
+  cat "$LOG_OUT" >&2
+  exit 1
+fi
+
+# Check MIR(JSON) was generated
+if [ $rc -ne 0 ] || [ ! -s "$OUT_MIR" ]; then
+  echo "[FAIL] selfhost_mir_loopform_basic_vm (MIR generation failed rc=$rc)" >&2
+  echo "=== LOG OUTPUT ===" >&2
+  cat "$LOG_OUT" >&2
+  exit 1
+fi
+
+echo "[PASS] selfhost_mir_loopform_basic_vm (LoopForm lower delegated successfully)"
+exit 0