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/smokes/v2/lib/crate_exec.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+# crate_exec.sh — tiny helpers to build and run ny-llvmc EXE reps with bounded time
+
+set -euo pipefail
+
+: "${HAKO_BUILD_TIMEOUT:=10}"
+: "${HAKO_EXE_TIMEOUT:=5}"
+
+crate_build_exe() {
+  # Args: in_json out_exe [nyrt_dir]
+  local in_json="$1"; shift
+  local out_exe="$1"; shift
+  local nyrt_dir="${1:-$NYASH_ROOT/target/release}"
+  local bin_nyllvmc="${NYASH_NY_LLVM_COMPILER:-$NYASH_ROOT/target/release/ny-llvmc}"
+  timeout "$HAKO_BUILD_TIMEOUT" "$bin_nyllvmc" --in "$in_json" --emit exe --nyrt "$nyrt_dir" --out "$out_exe" >/dev/null 2>&1
+}
+
+crate_run_exe() {
+  # Args: exe_path
+  local exe="$1"
+  timeout "$HAKO_EXE_TIMEOUT" "$exe" >/dev/null 2>&1
+}
+