fix: update Composio API endpoint from v2 to v3

Fixes #309 - Composio v2 endpoint has been discontinued. Updated to v3
endpoint which is the current supported version.

Composio v2 API is no longer available, causing all Composio tool
executions to fail. This updates the base URL to use v3.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/tools/composio.rs

@@ -852,4 +852,66 @@ mod tests {
         );
         assert_eq!(extract_api_error_message("not-json"), None);
     }
+
+    #[test]
+    fn composio_action_with_null_fields() {
+        let json_str = r#"{"name": "TEST_ACTION", "appName": null, "description": null, "enabled": false}"#;
+        let action: ComposioAction = serde_json::from_str(json_str).unwrap();
+        assert_eq!(action.name, "TEST_ACTION");
+        assert!(action.app_name.is_none());
+        assert!(action.description.is_none());
+        assert!(!action.enabled);
+    }
+
+    #[test]
+    fn composio_action_with_special_characters() {
+        let json_str = r#"{"name": "GMAIL_SEND_EMAIL_WITH_ATTACHMENT", "appName": "gmail", "description": "Send email with attachment & special chars: <>'\"\"", "enabled": true}"#;
+        let action: ComposioAction = serde_json::from_str(json_str).unwrap();
+        assert_eq!(action.name, "GMAIL_SEND_EMAIL_WITH_ATTACHMENT");
+        assert!(action.description.as_ref().unwrap().contains("&"));
+        assert!(action.description.as_ref().unwrap().contains("<"));
+    }
+
+    #[test]
+    fn composio_action_with_unicode() {
+        let json_str = r#"{"name": "SLACK_SEND_MESSAGE", "appName": "slack", "description": "Send message with emoji 🎉 and unicode 中文", "enabled": true}"#;
+        let action: ComposioAction = serde_json::from_str(json_str).unwrap();
+        assert!(action.description.as_ref().unwrap().contains("🎉"));
+        assert!(action.description.as_ref().unwrap().contains("中文"));
+    }
+
+    #[test]
+    fn composio_malformed_json_returns_error() {
+        let json_str = r#"{"name": "TEST_ACTION", "appName": "gmail", }"#;
+        let result: Result<ComposioAction, _> = serde_json::from_str(json_str);
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn composio_empty_json_string_returns_error() {
+        let json_str = r#" ""#;
+        let result: Result<ComposioAction, _> = serde_json::from_str(json_str);
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn composio_large_actions_list() {
+        let mut items = Vec::new();
+        for i in 0..100 {
+            items.push(json!({
+                "name": format!("ACTION_{i}"),
+                "appName": "test",
+                "description": "Test action",
+                "enabled": true
+            }));
+        }
+        let json_str = json!({"items": items}).to_string();
+        let resp: ComposioActionsResponse = serde_json::from_str(&json_str).unwrap();
+        assert_eq!(resp.items.len(), 100);
+    }
+
+    #[test]
+    fn composio_api_base_url_is_v3() {
+        assert_eq!(COMPOSIO_API_BASE_V3, "https://backend.composio.dev/api/v3");
+    }
 }