phase: 20.49 COMPLETE; 20.50 Flow+String minimal reps; 20.51 selfhost v0/v1 minimal (Option A/B); hv1-inline binop/unop/copy; docs + run_all + CURRENT_TASK -> 21.0

examples/string_plugin_concat_demo.hako

@@ -0,0 +1,16 @@
+// StringBox plugin concat demo
+// Build plugin: (cd plugins/nyash-string-plugin && cargo build --release)
+
+static box Main {
+  main() {
+    local s, t
+    s = new StringBox()
+    // concat with literal
+    t = s.concat("hello")
+    // concat again (handle)
+    t = t.concat(" world")
+    // return length of resulting string
+    return t.length()
+  }
+}
+