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

server/src/handlers/graph.rs

@@ -353,7 +353,7 @@ impl McpTool for ReadGraphHandler {
 
     async fn execute(&self, args: Value, state: Arc<MemoryState>) -> Result<String, String> {
         let req: ReadGraphTool = serde_json::from_value(args).map_err(|e| e.to_string())?;
-        let data = state.read_graph(|full| {
+        let data = state.read_graph(|full| -> Result<String, String> {
             if let Some(ns) = req.namespace {
                 let mut filtered = BorrowedGraph::default();
                 for (k, v) in &full.entities {
@@ -366,11 +366,11 @@ impl McpTool for ReadGraphHandler {
                         filtered.relations.push(r);
                     }
                 }
-                serde_json::to_string(&filtered).unwrap_or_default()
+                serde_json::to_string(&filtered).map_err(|e| e.to_string())
             } else {
-                serde_json::to_string(full).unwrap_or_default()
+                serde_json::to_string(full).map_err(|e| e.to_string())
             }
-        });
+        })?;
         Ok(data)
     }
 }
@@ -396,7 +396,7 @@ impl McpTool for SearchNodesHandler {
             vec![]
         };
 
-        let data = state.read_graph(|full| {
+        let data = state.read_graph(|full| -> Result<String, String> {
             let mut result = BorrowedGraph::default();
             for (id, doc_type, _, _, _) in &matches {
                 if doc_type == "entity"
@@ -425,7 +425,7 @@ impl McpTool for OpenNodesHandler {
 
     async fn execute(&self, args: Value, state: Arc<MemoryState>) -> Result<String, String> {
         let req: OpenNodesTool = serde_json::from_value(args).map_err(|e| e.to_string())?;
-        let data = state.read_graph(|full| {
+        let data = state.read_graph(|full| -> Result<String, String> {
             let targets: HashSet<&str> = req.names.iter().map(|s| s.as_str()).collect();
             let mut result = BorrowedGraph::default();
             let mut connected: HashSet<&str> = HashSet::new();
@@ -650,7 +650,7 @@ impl McpTool for FindOrphansHandler {
                 .cloned()
                 .collect::<Vec<String>>()
         });
-        let data = serde_json::to_string(&orphans).unwrap_or_default();
+        let data = serde_json::to_string(&orphans).map_err(|e| e.to_string())?;
         Ok(data)
     }
 }