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>

src/runner_plugin_init.rs

@@ -63,6 +63,45 @@ pub fn init_bid_plugins() {
                 eprintln!("✅ plugin host fully configured");
             }
         }
+
+        // Optional autoload for [using.*] kind="dylib" packages
+        if std::env::var("NYASH_USING_DYLIB_AUTOLOAD").ok().as_deref() == Some("1")
+            && std::env::var("NYASH_DISABLE_PLUGINS").ok().as_deref() != Some("1")
+        {
+            if plugin_debug || cli_verbose { eprintln!("[using.dylib/autoload] scanning nyash.toml packages …"); }
+            let mut using_paths: Vec<String> = Vec::new();
+            let mut pending_modules: std::vec::Vec<(String, String)> = Vec::new();
+            let mut aliases: std::collections::HashMap<String, String> = std::collections::HashMap::new();
+            let mut packages: std::collections::HashMap<String, crate::using::spec::UsingPackage> = std::collections::HashMap::new();
+            let _ = crate::using::resolver::populate_from_toml(
+                &mut using_paths,
+                &mut pending_modules,
+                &mut aliases,
+                &mut packages,
+            );
+            for (name, pkg) in packages.iter() {
+                if let crate::using::spec::PackageKind::Dylib = pkg.kind {
+                    // Build library name from file stem (best-effort)
+                    let lib_name = std::path::Path::new(&pkg.path)
+                        .file_name()
+                        .and_then(|s| s.to_str())
+                        .unwrap_or(name)
+                        .to_string();
+                    let host = get_global_plugin_host();
+                    let res = host
+                        .read()
+                        .unwrap()
+                        .load_library_direct(&lib_name, &pkg.path, &[]);
+                    if let Err(e) = res {
+                        if plugin_debug || cli_verbose {
+                            eprintln!("[using.dylib/autoload] failed '{}': {}", lib_name, e);
+                        }
+                    } else if plugin_debug || cli_verbose {
+                        eprintln!("[using.dylib/autoload] loaded '{}' from {}", lib_name, pkg.path);
+                    }
+                }
+            }
+        }
     } else if plugin_debug || cli_verbose {
         eprintln!("⚠️ Failed to load plugin config (hakorune.toml/nyash.toml) - plugins disabled");
     }