fix: ensure tagged-enum schema injection meets tool expectations

server/src/mcp.rs

@@ -22,7 +22,7 @@ pub fn error(id: serde_json::Value, code: i32, message: &str) -> serde_json::Val
 
 pub fn tool_def<T: JsonSchema>(name: &str, fallback_desc: &str) -> serde_json::Value {
     let schema = schemars::schema_for!(T);
-    let schema_val = serde_json::to_value(&schema).unwrap_or_default();
+    let mut schema_val = serde_json::to_value(&schema).unwrap_or_default();
 
     let desc = schema_val
         .get("description")
@@ -31,6 +31,14 @@ pub fn tool_def<T: JsonSchema>(name: &str, fallback_desc: &str) -> serde_json::V
         .unwrap_or(fallback_desc)
         .to_string();
 
+    // MCP clients strictly expect a top-level `type: "object"` for tool schemas.
+    // Tagged enums usually generate a root `oneOf` or `anyOf`.
+    if let Some(obj) = schema_val.as_object_mut() {
+        if !obj.contains_key("type") && (obj.contains_key("oneOf") || obj.contains_key("anyOf")) {
+            obj.insert("type".to_string(), json!("object"));
+        }
+    }
+
     // MCP expects standard JSON schema. Schemars returns draft-07.
     json!({
         "name": name,