refactor(core): Extract thought parsing logic into a dedicated utility (#9503)

packages/core/src/utils/thoughtUtils.ts

@@ -0,0 +1,54 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+export type ThoughtSummary = {
+  subject: string;
+  description: string;
+};
+
+const START_DELIMITER = '**';
+const END_DELIMITER = '**';
+
+/**
+ * Parses a raw thought string into a structured ThoughtSummary object.
+ *
+ * Thoughts are expected to have a bold "subject" part enclosed in double
+ * asterisks (e.g., **Subject**). The rest of the string is considered
+ * the description. This function only parses the first valid subject found.
+ *
+ * @param rawText The raw text of the thought.
+ * @returns A ThoughtSummary object. If no valid subject is found, the entire
+ * string is treated as the description.
+ */
+export function parseThought(rawText: string): ThoughtSummary {
+  const startIndex = rawText.indexOf(START_DELIMITER);
+  if (startIndex === -1) {
+    // No start delimiter found, the whole text is the description.
+    return { subject: '', description: rawText.trim() };
+  }
+
+  const endIndex = rawText.indexOf(
+    END_DELIMITER,
+    startIndex + START_DELIMITER.length,
+  );
+  if (endIndex === -1) {
+    // Start delimiter found but no end delimiter, so it's not a valid subject.
+    // Treat the entire string as the description.
+    return { subject: '', description: rawText.trim() };
+  }
+
+  const subject = rawText
+    .substring(startIndex + START_DELIMITER.length, endIndex)
+    .trim();
+
+  // The description is everything before the start delimiter and after the end delimiter.
+  const description = (
+    rawText.substring(0, startIndex) +
+    rawText.substring(endIndex + END_DELIMITER.length)
+  ).trim();
+
+  return { subject, description };
+}