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>

examples/plugins/autoload_sample/README.md

@@ -0,0 +1,12 @@
+Plugins Autoload Sample
+
+How to run (from repo root):
+- Build core: `cargo build --release`
+- Enable autoload and run:
+  `NYASH_USING_DYLIB_AUTOLOAD=1 ./target/release/hakorune examples/plugins/autoload_sample/main.hako`
+
+Notes
+- The plugin path in nyash.toml points to `plugins/nyash-counter-plugin/*`. Ensure the shared library exists.
+- If missing, build plugins with `cargo build --release -p nyash-counter-plugin`.
+- Autoload is guarded; respects `NYASH_DISABLE_PLUGINS=1`.
+

examples/plugins/autoload_sample/main.hako

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+using counter
+
+static box Main {
+  main() {
+    // Minimal plugin usage example (CounterBox from nyash-counter-plugin)
+    local c = new CounterBox()
+    c.inc()
+    c.inc()
+    print("Counter value: " + c.get())
+    return 0
+  }
+}
+

examples/plugins/autoload_sample/nyash.toml

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+[using.counter]
+kind = "dylib"
+# Adjust the path if running from another directory
+path = "../../plugins/nyash-counter-plugin/libnyash_counter_plugin.so"
+bid = "CounterBox"
+
+[using]
+paths = ["lib"]
+