fix: invalid tool call ID recovery and system-reminder tag centralization (#627)

Co-authored-by: Letta <noreply@letta.com>

src/constants.ts

@@ -17,6 +17,13 @@ export const DEFAULT_AGENT_NAME = "Nameless Agent";
  */
 export const INTERRUPTED_BY_USER = "Interrupted by user";
 
+/**
+ * XML tag used to wrap system reminder content injected into messages
+ */
+export const SYSTEM_REMINDER_TAG = "system-reminder";
+export const SYSTEM_REMINDER_OPEN = `<${SYSTEM_REMINDER_TAG}>`;
+export const SYSTEM_REMINDER_CLOSE = `</${SYSTEM_REMINDER_TAG}>`;
+
 /**
  * Status bar thresholds - only show indicators when values exceed these
  */