Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: simongdavies

src/js-host-api/README.md

@@ -98,7 +98,7 @@ A sandbox with the JavaScript runtime loaded, ready for handlers and modules.
 - `clearModules()` — Remove all registered modules (sync)
 
 **Other Methods:**
-- `getLoadedSandbox()` → `Promise<LoadedJSSandbox>` — Compiles all modules and handlers into the guest. Modules are registered first, then handlers.
+- `getLoadedSandbox()` → `Promise<LoadedJSSandbox>` — Registers all module sources and compiles/loads handlers into the guest; modules are compiled on-demand when first imported.
 
 ```javascript
 // Add a module (sync)

src/js-host-api/src/lib.rs

@@ -862,6 +862,7 @@ impl JSSandboxWrapper {
         validate_napi_module_identifier(&module_name, "Module name")?;
         if let Some(ref ns) = namespace {
             validate_napi_module_identifier(ns, "Module namespace")?;
+            validate_napi_namespace_not_reserved(ns)?;
         }
         self.with_inner_mut(|sandbox| {
             match namespace {