Fix race condition by making window.complete() async and awaiting it

- window.complete() was fire-and-forget, causing execution-complete to arrive before console messages
- This caused sandbox to unregister before console message responses arrived
- Made complete() async and await sendRuntimeMessage()
- SandboxedIframe wrapper now awaits window.complete()
- Ensures all messages are processed before cleanup/unregister
- Fixes 30-second timeout on javascript_repl

packages/web-ui/src/components/SandboxedIframe.ts

@@ -339,7 +339,7 @@ export class SandboxIframe extends LitElement {
 					}
 				}
 
-				window.complete();
+				await window.complete();
 			} catch (error) {
 				console.error(error?.stack || error?.message || String(error));
 
@@ -352,7 +352,7 @@ export class SandboxIframe extends LitElement {
 					}
 				}
 
-				window.complete({
+				await window.complete({
 					message: error?.message || String(error),
 					stack: error?.stack || new Error().stack
 				});

packages/web-ui/src/components/sandbox/ConsoleRuntimeProvider.ts

@@ -120,7 +120,7 @@ export class ConsoleRuntimeProvider implements SandboxRuntimeProvider {
 
 			// Expose complete() method for user code to call
 			let completionSent = false;
-			(window as any).complete = (error?: { message: string; stack: string }) => {
+			(window as any).complete = async (error?: { message: string; stack: string }) => {
 				if (completionSent) return;
 				completionSent = true;
 
@@ -128,18 +128,14 @@ export class ConsoleRuntimeProvider implements SandboxRuntimeProvider {
 
 				if ((window as any).sendRuntimeMessage) {
 					if (finalError) {
-						(window as any)
-							.sendRuntimeMessage({
-								type: "execution-error",
-								error: finalError,
-							})
-							.catch(() => {});
+						await (window as any).sendRuntimeMessage({
+							type: "execution-error",
+							error: finalError,
+						});
 					} else {
-						(window as any)
-							.sendRuntimeMessage({
-								type: "execution-complete",
-							})
-							.catch(() => {});
+						await (window as any).sendRuntimeMessage({
+							type: "execution-complete",
+						});
 					}
 				}
 			};