fix cursor stream-json multiplexed output handling

packages/adapters/cursor-local/src/shared/stream.ts

@@ -0,0 +1,16 @@
+export function normalizeCursorStreamLine(rawLine: string): {
+  stream: "stdout" | "stderr" | null;
+  line: string;
+} {
+  const trimmed = rawLine.trim();
+  if (!trimmed) return { stream: null, line: "" };
+
+  const prefixed = trimmed.match(/^(stdout|stderr)\s*[:=]?\s*([\[{].*)$/i);
+  if (!prefixed) {
+    return { stream: null, line: trimmed };
+  }
+
+  const stream = prefixed[1]?.toLowerCase() === "stderr" ? "stderr" : "stdout";
+  const line = (prefixed[2] ?? "").trim();
+  return { stream, line };
+}