fix: ensure onCompleted callback finishes before using persistedResult

- Update RooTerminalCallbacks.onCompleted type to allow async callbacks (void | Promise<void>)
- Track onCompleted completion with a promise and await it before using persistedResult
- This fixes a race condition where exitDetails could be set before the async finalize() completes
- Fix test callback to not return assignment value

src/core/tools/ExecuteCommandTool.ts

@@ -210,6 +210,7 @@ export async function executeCommandInTerminal(
 	// Bound accumulated output buffer size to prevent unbounded memory growth for long-running commands.
 	// The interceptor preserves full output; this buffer is only for UI display (100KB limit).
 	const maxAccumulatedOutputSize = 100_000
+
 	// Track when onCompleted callback finishes to avoid race condition.
 	// The callback is async but Terminal/ExecaTerminal don't await it, so we track completion
 	// explicitly to ensure persistedResult is set before we use it.