refactor: UI

internal/backend/forwarder/service.go

@@ -1736,6 +1736,13 @@ func (service *Service) handleToolInvocation(stream *ActiveStream, invocation ru
 	stream.ToolInvocationCount++
 	stream.UpdatedAt = time.Now().UTC()
 	stream.mu.Unlock()
+	if !isKnownToolName(trimmedToolName) {
+		displayToolName := trimmedToolName
+		if displayToolName == "" {
+			displayToolName = "<empty>"
+		}
+		return service.completePreDispatchToolError(stream, invocation, nil, false, false, fmt.Errorf("Model hallucination: attempted to invoke a nonexistent tool: %s", displayToolName))
+	}
 	if !isToolAllowedInMode(mode, subagentTypeName, trimmedToolName) {
 		return service.completePreDispatchToolError(stream, invocation, nil, false, false, fmt.Errorf("tool invocation is not enabled in mode %s: %s", mode.String(), invocation.ToolName))
 	}

internal/backend/forwarder/tool_catalog.go

@@ -181,6 +181,25 @@ func supportedToolNamesForMode(mode agentv1.AgentMode) map[string]struct{} {
 	}
 }
 
+func isKnownToolName(toolName string) bool {
+	trimmedToolName := strings.TrimSpace(toolName)
+	if trimmedToolName == "" {
+		return false
+	}
+	for _, supported := range []map[string]struct{}{
+		agentModeToolNames,
+		askModeToolNames,
+		planModeToolNames,
+		debugModeToolNames,
+		multitaskModeToolNames,
+	} {
+		if _, ok := supported[trimmedToolName]; ok {
+			return true
+		}
+	}
+	return false
+}
+
 func isToolAllowedInMode(mode agentv1.AgentMode, subagentTypeName string, toolName string) bool {
 	trimmedToolName := strings.TrimSpace(toolName)
 	if trimmedToolName == "" {