Phase 21.7 normalization: optimization pre-work + bench harness expansion

- Add opt-in optimizations (defaults OFF)
  - Ret purity verifier: NYASH_VERIFY_RET_PURITY=1
  - strlen FAST enhancement for const handles
  - FAST_INT gate for same-BB SSA optimization
  - length cache for string literals in llvmlite
- Expand bench harness (tools/perf/microbench.sh)
  - Add branch/call/stringchain/arraymap/chip8/kilo cases
  - Auto-calculate ratio vs C reference
  - Document in benchmarks/README.md
- Compiler health improvements
  - Unify PHI insertion to insert_phi_at_head()
  - Add NYASH_LLVM_SKIP_BUILD=1 for build reuse
- Runtime & safety enhancements
  - Clarify Rust/Hako ownership boundaries
  - Strengthen receiver localization (LocalSSA/pin/after-PHIs)
  - Stop excessive PluginInvoke→BoxCall rewrites
- Update CURRENT_TASK.md, docs, and canaries

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

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

tools/perf/dump_mir.sh

@@ -0,0 +1,81 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# dump_mir.sh — Stable helper to emit MIR(JSON) and print a quick histogram
+#
+# Usage:
+#   tools/perf/dump_mir.sh <input.hako> [--out out.json] [--mode {provider|jsonfrag}]
+#
+# Notes:
+#   - provider: 普通の MirBuilder ルート（失敗する環境では自動で jsonfrag にフォールバック）
+#   - jsonfrag : ループを while-form に純化した最小 MIR（構造検証用）
+
+INPUT="${1:-}"
+OUT=""
+MODE="provider"
+shift || true
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --out) OUT="$2"; shift 2;;
+    --mode) MODE="$2"; shift 2;;
+    -h|--help) echo "Usage: $0 <input.hako> [--out out.json] [--mode {provider|jsonfrag}]"; exit 0;;
+    *) echo "Unknown arg: $1"; exit 2;;
+  esac
+done
+
+if [[ -z "$INPUT" || ! -f "$INPUT" ]]; then
+  echo "[FAIL] input .hako not found: $INPUT" >&2; exit 2
+fi
+
+ROOT="$(git -C "$(dirname "$0")" rev-parse --show-toplevel 2>/dev/null || true)"
+[[ -z "$ROOT" ]] && ROOT="$(cd "$(dirname "$0")/../.." && pwd)"
+
+TMP_OUT=$(mktemp --suffix .mir.json)
+trap 'rm -f "$TMP_OUT" >/dev/null 2>&1 || true' EXIT
+
+emit_provider() {
+  # Provider/selfhost-first with min fallback; keep plugins ON to satisfy core boxes
+  set +e
+  NYASH_SKIP_TOML_ENV=1 NYASH_DISABLE_PLUGINS=0 NYASH_ENABLE_USING=1 HAKO_ENABLE_USING=1 \
+  HAKO_SELFHOST_BUILDER_FIRST=1 HAKO_SELFHOST_TRY_MIN=1 HAKO_MIR_NORMALIZE_PROVIDER=0 NYASH_JSON_ONLY=1 \
+  "$ROOT/tools/hakorune_emit_mir.sh" "$INPUT" "$TMP_OUT" >/dev/null 2>&1
+  local rc=$?
+  set -e
+  return $rc
+}
+
+emit_jsonfrag() {
+  NYASH_SKIP_TOML_ENV=1 NYASH_DISABLE_PLUGINS=1 \
+  HAKO_SELFHOST_BUILDER_FIRST=1 HAKO_MIR_BUILDER_LOOP_JSONFRAG=1 HAKO_MIR_BUILDER_LOOP_FORCE_JSONFRAG=1 \
+  HAKO_MIR_BUILDER_JSONFRAG_PURIFY=1 NYASH_JSON_ONLY=1 \
+  "$ROOT/tools/hakorune_emit_mir.sh" "$INPUT" "$TMP_OUT" >/dev/null
+}
+
+if [[ "$MODE" = "provider" ]]; then
+  if ! emit_provider; then
+    echo "[WARN] provider emit failed; falling back to jsonfrag" >&2
+    emit_jsonfrag
+  fi
+else
+  emit_jsonfrag
+fi
+
+if [[ -n "$OUT" ]]; then
+  cp -f "$TMP_OUT" "$OUT"
+  echo "[OK] MIR JSON -> $OUT"
+fi
+
+# Print a quick histogram
+python3 - "$TMP_OUT" <<'PY'
+import json,sys
+p=sys.argv[1]
+j=json.load(open(p))
+for f in j.get('functions',[]):
+  print('Function:', f.get('name'))
+  for b in (f.get('blocks') or []):
+    ops=[(i or {}).get('op') for i in (b.get('instructions') or [])]
+    if not ops: continue
+    from collections import Counter
+    c=Counter(ops)
+    print('  bb', b.get('id'), dict(c))
+PY