fix(app): support text attachments (#17335)

packages/opencode/src/util/data-url.ts

@@ -0,0 +1,9 @@
+export function decodeDataUrl(url: string) {
+  const idx = url.indexOf(",")
+  if (idx === -1) return ""
+
+  const head = url.slice(0, idx)
+  const body = url.slice(idx + 1)
+  if (head.includes(";base64")) return Buffer.from(body, "base64").toString("utf8")
+  return decodeURIComponent(body)
+}