fix(tui): fail fast on invalid session startup (#23837)

packages/opencode/src/util/error.ts

@@ -26,6 +26,15 @@ export function errorMessage(error: unknown): string {
     return error.message
   }
 
+  if (
+    isRecord(error) &&
+    isRecord(error.data) &&
+    typeof error.data.message === "string" &&
+    error.data.message
+  ) {
+    return error.data.message
+  }
+
   const text = String(error)
   if (text && text !== "[object Object]") return text