feat(handlers): enrich semantic error messages with prescriptive tool hints to prevent LLM hallucination traps

server/src/handlers/graph.rs

@@ -230,7 +230,7 @@ impl McpTool for DeleteEntitiesHandler {
         });
 
         if !missing.is_empty() {
-            return Err(format!("Error: Entities not found: {}", missing.join(", ")));
+            return Err(format!("Error: Entities not found: {}. Please use the search_nodes or read_graph tools to verify the exact entity names.", missing.join(", ")));
         }
 
         let idx = state.get_search_index();
@@ -271,7 +271,7 @@ impl McpTool for DeleteObservationsHandler {
             }
         });
         if !missing.is_empty() {
-            return Err(format!("Error: Entities not found: {}", missing.join(", ")));
+            return Err(format!("Error: Entities not found: {}. Please use the search_nodes or read_graph tools to verify the exact entity names.", missing.join(", ")));
         }
         Ok("Observations deleted".to_string())
     }
@@ -299,7 +299,7 @@ impl McpTool for DeleteRelationsHandler {
             missing_count = to_rem.len() - (initial_len - master.relations.len());
         });
         if missing_count > 0 {
-            return Err(format!("Error: {} relation(s) not found in graph", missing_count));
+            return Err(format!("Error: {} relation(s) not found in graph. Please verify exact relation properties using read_graph.", missing_count));
         }
         Ok("Relations deleted".to_string())
     }
@@ -527,7 +527,7 @@ impl McpTool for CondenseEntityHandler {
             }
         });
         if missing {
-            return Err(format!("Error: Entity '{}' not found", req.entity_name));
+            return Err(format!("Error: Entity '{}' not found. Please verify the exact entity name using search_nodes.", req.entity_name));
         }
         Ok("Entity condensed".to_string())
     }
@@ -579,7 +579,7 @@ impl McpTool for MergeEntitiesHandler {
             });
         });
         if missing {
-            return Err(format!("Error: Source entity '{}' not found", req.source_entity));
+            return Err(format!("Error: Source entity '{}' not found. Please verify the exact entity name using search_nodes.", req.source_entity));
         }
         Ok("Entities merged".to_string())
     }