fix(mcp): prevent internal handler serialization errors from being silently discarded or defaulting to empty strings

server/src/handlers/env.rs

@@ -61,7 +61,7 @@ impl McpTool for ReadEnvFingerprintHandler {
             .env_fingerprints
             .read_with(|fps| fps.get(&req.namespace).cloned());
         if let Some(fp) = data {
-            let data = serde_json::to_string(&fp).unwrap_or_default();
+            let data = serde_json::to_string(&fp).map_err(|e| e.to_string())?;
             Ok(data)
         } else {
             Ok("{}".to_string())