fix(mcp): return explicit JSON-RPC errors instead of misleading Ok strings for missing entities and silent graph modification drops

server/src/handlers/graph.rs

@@ -169,7 +169,7 @@ impl McpTool for CreateRelationsHandler {
         });
         if !missing_nodes.is_empty() {
             let missing: Vec<_> = missing_nodes.into_iter().collect();
-            return Ok(format!("Warning: Relations dropped due to missing entities: {}", missing.join(", ")));
+            return Err(format!("Error: Relations dropped due to missing entities: {}", missing.join(", ")));
         }
         Ok("Relations created".to_string())
     }
@@ -200,7 +200,7 @@ impl McpTool for AddObservationsHandler {
             }
         });
         if !missing_entities.is_empty() {
-            return Ok(format!("Warning: Observations dropped for missing entities: {}", missing_entities.join(", ")));
+            return Err(format!("Error: Observations dropped for missing entities: {}", missing_entities.join(", ")));
         }
         Ok("Observations added".to_string())
     }
@@ -260,14 +260,20 @@ impl McpTool for DeleteObservationsHandler {
     async fn execute(&self, args: Value, state: Arc<MemoryState>) -> Result<String, String> {
         let req: DeleteObservationsTool =
             serde_json::from_value(args).map_err(|e| e.to_string())?;
+        let mut missing = Vec::new();
         state.modify_graph(|master| {
             for d in req.deletions {
                 if let Some(e) = master.entities.get_mut(&d.entity_name) {
                     let to_rem: HashSet<_> = d.observations.into_iter().collect();
                     e.observations.retain(|o| !to_rem.contains(o));
+                } else {
+                    missing.push(d.entity_name);
                 }
             }
         });
+        if !missing.is_empty() {
+            return Err(format!("Error: Entities not found: {}", missing.join(", ")));
+        }
         Ok("Observations deleted".to_string())
     }
 }
@@ -507,11 +513,17 @@ impl McpTool for CondenseEntityHandler {
 
     async fn execute(&self, args: Value, state: Arc<MemoryState>) -> Result<String, String> {
         let req: CondenseEntityTool = serde_json::from_value(args).map_err(|e| e.to_string())?;
+        let mut missing = false;
         state.modify_graph(|master| {
             if let Some(e) = master.entities.get_mut(&req.entity_name) {
                 e.observations = req.summarized_observations;
+            } else {
+                missing = true;
             }
         });
+        if missing {
+            return Err(format!("Error: Entity '{}' not found", req.entity_name));
+        }
         Ok("Entity condensed".to_string())
     }
 }
@@ -530,6 +542,7 @@ impl McpTool for MergeEntitiesHandler {
 
     async fn execute(&self, args: Value, state: Arc<MemoryState>) -> Result<String, String> {
         let req: MergeEntitiesTool = serde_json::from_value(args).map_err(|e| e.to_string())?;
+        let mut missing = false;
         state.modify_graph(|master| {
             if let Some(src) = master.entities.remove(&req.source_entity) {
                 if let Some(tgt) = master.entities.get_mut(&req.target_entity) {
@@ -541,6 +554,8 @@ impl McpTool for MergeEntitiesHandler {
                     new_tgt.name = req.target_entity.clone();
                     master.entities.insert(req.target_entity.clone(), new_tgt);
                 }
+            } else {
+                missing = true;
             }
             let mut seen = std::collections::HashSet::new();
             master.relations.retain_mut(|r| {
@@ -558,6 +573,9 @@ impl McpTool for MergeEntitiesHandler {
                 }
             });
         });
+        if missing {
+            return Err(format!("Error: Source entity '{}' not found", req.source_entity));
+        }
         Ok("Entities merged".to_string())
     }
 }