Implement simple persistent cache with automatic saving on status changes

agent/src/config/validation.rs

@@ -112,14 +112,8 @@ pub fn validate_config(config: &AgentConfig) -> Result<()> {
     }
 
     // Validate cache configuration
-    if config.cache.enabled {
-        if config.cache.default_ttl_seconds == 0 {
-            bail!("Cache TTL cannot be 0");
-        }
-
-        if config.cache.max_entries == 0 {
-            bail!("Cache max entries cannot be 0");
-        }
+    if config.cache.persist_path.is_empty() {
+        bail!("Cache persist path cannot be empty");
     }
 
     Ok(())