feat: add cache-ttl pruning mode

src/config/types.agent-defaults.ts

@@ -23,7 +23,9 @@ export type AgentModelListConfig = {
 };
 
 export type AgentContextPruningConfig = {
-  mode?: "off" | "adaptive" | "aggressive";
+  mode?: "off" | "cache-ttl";
+  /** TTL to consider cache expired (duration string, default unit: minutes). */
+  ttl?: string;
   keepLastAssistants?: number;
   softTrimRatio?: number;
   hardClearRatio?: number;