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

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

Author: simongdavies

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

@@ -412,13 +412,16 @@ impl SandboxBuilderWrapper {
     ) -> napi::Result<&Self> {
         self.with_inner(|b| {
             // Blocking mode is intentional: the guest's print/console.log call
-            // is synchronous — the guest must wait for the print to complete
-            // before continuing execution. Unlike host functions (which use
-            // NonBlocking + oneshot channel for async Promise resolution),
-            // print is fire-and-forget with no return value to await.
+            // blocks until the print has been dispatched to JS via the
+            // ThreadsafeFunction. However, the current JS/TS wrapper may invoke
+            // the user-provided callback via a Promise microtask, so user code
+            // can still run *after* guest execution resumes. From the guest's
+            // perspective, print is effectively fire-and-forget with no return
+            // value to await, unlike host functions (which use NonBlocking +
+            // oneshot channel for async Promise resolution).
             //
-            // **Reentrancy note:** The print callback runs while the sandbox
-            // Mutex is held (inside `call_handler`'s `spawn_blocking`).
+            // **Reentrancy note:** The print callback ultimately runs while the
+            // sandbox Mutex is held (inside `call_handler`'s `spawn_blocking`).
             // Calling Hyperlight APIs that acquire the same lock from within
             // the callback (e.g. `snapshot()`, `restore()`, `unload()`) will
             // deadlock. Keep print callbacks simple — logging only.