refactor(media-understanding): share gemini output extract

src/media-understanding/output-extract.ts

@@ -0,0 +1,26 @@
+export function extractLastJsonObject(raw: string): unknown {
+  const trimmed = raw.trim();
+  const start = trimmed.lastIndexOf("{");
+  if (start === -1) {
+    return null;
+  }
+  const slice = trimmed.slice(start);
+  try {
+    return JSON.parse(slice);
+  } catch {
+    return null;
+  }
+}
+
+export function extractGeminiResponse(raw: string): string | null {
+  const payload = extractLastJsonObject(raw);
+  if (!payload || typeof payload !== "object") {
+    return null;
+  }
+  const response = (payload as { response?: unknown }).response;
+  if (typeof response !== "string") {
+    return null;
+  }
+  const trimmed = response.trim();
+  return trimmed || null;
+}