feat(server): place generated images beside the reference anchor node

Read a "reference anchor node:" agent directive and lay newly generated
image nodes immediately to the right of that node, inheriting its row and
falling back to its size, for planned, follow-up, and incremental flows.
Generalize the directive parser shared with the image-generator target.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/application/design_service.go

@@ -696,6 +696,7 @@ func (s *DesignService) AgentChat(ctx context.Context, projectID string, req des
 	now := s.now()
 	actionID := newID()
 	targetNodeID := imageGeneratorTargetNodeID(req.Messages)
+	referenceAnchorID := referenceAnchorNodeID(req.Messages)
 	isolatedImageGenerator := isImageGeneratorRequest(mode, targetNodeID)
 	directImageMode := isDirectImageGenerationMode(mode, isolatedImageGenerator)
 	enableWebSearch := req.EnableWebSearch || toolConfigEnablesSearch(req.ToolConfig)
@@ -792,7 +793,8 @@ func (s *DesignService) AgentChat(ctx context.Context, projectID string, req des
 		if targetNodeID != "" {
 			project.Nodes = markImageGeneratorTargetGenerating(project.Nodes, targetNodeID, prompt, req.ImageSize, plannedImageCount(taskPlan))
 		} else {
-			project.Nodes = append(project.Nodes, newGeneratingImageNodesForPlan(prompt, len(project.Nodes), taskPlan, req.ImageSize)...)
+			placeholders := newGeneratingImageNodesForPlan(prompt, len(project.Nodes), taskPlan, req.ImageSize)
+			project.Nodes = append(project.Nodes, positionGeneratedNodesBesideReference(project.Nodes, referenceAnchorID, placeholders)...)
 		}
 	}
 	project.Connections = nil
@@ -3114,6 +3116,7 @@ func (s *DesignService) completeFollowupGeneration(ctx context.Context, projectI
 	var plan design.AgentPlan
 	var incremental bool
 	targetNodeID := imageGeneratorTargetNodeID(messages)
+	referenceAnchorID := referenceAnchorNodeID(messages)
 	if isolated {
 		plan, incremental, err = s.planWithIncrementalImages(ctx, projectID, threadID, prompt, targetNodeID, false, request)
 	} else {
@@ -3139,6 +3142,7 @@ func (s *DesignService) completeFollowupGeneration(ctx context.Context, projectI
 			}
 			return s.markAgentGenerationFailed(detachedUserContext(ctx), projectID, threadID, err)
 		}
+		plan.GeneratedNodes = positionGeneratedNodesBesideReference(project.Nodes, referenceAnchorID, plan.GeneratedNodes)
 	} else if err := incompleteIncrementalGenerationError(plan, taskPlan); err != nil {
 		if isolated {
 			return s.markIsolatedGenerationFailed(detachedUserContext(ctx), projectID, targetNodeID, err)
@@ -3241,6 +3245,10 @@ func (s *DesignService) planWithIncrementalImages(ctx context.Context, projectID
 			return fmt.Errorf("image generation returned empty image")
 		}
 		node := nodes[0]
+		positioned := positionGeneratedNodesBesideReference(req.Project.Nodes, referenceAnchorNodeID(req.Messages), append(persistedNodes, node))
+		if len(positioned) > 0 {
+			node = positioned[len(positioned)-1]
+		}
 		persistedNodes = append(persistedNodes, node)
 		return s.applyIncrementalGeneratedNode(ctx, projectID, threadID, prompt, targetNodeID, node, result.Index, appendArtifacts)
 	})
@@ -4710,7 +4718,15 @@ func isImageGeneratorRequest(mode string, targetNodeID string) bool {
 }
 
 func imageGeneratorTargetNodeID(messages []design.AgentChatMessage) string {
-	const targetPrefix = "image generator target node:"
+	return agentDirectiveNodeID(messages, "image generator target node:")
+}
+
+func referenceAnchorNodeID(messages []design.AgentChatMessage) string {
+	return agentDirectiveNodeID(messages, "reference anchor node:")
+}
+
+func agentDirectiveNodeID(messages []design.AgentChatMessage, prefix string) string {
+	prefix = strings.ToLower(strings.TrimSpace(prefix))
 	for _, message := range messages {
 		for _, content := range message.Contents {
 			if strings.ToLower(strings.TrimSpace(content.Type)) != "text" {
@@ -4718,8 +4734,8 @@ func imageGeneratorTargetNodeID(messages []design.AgentChatMessage) string {
 			}
 			for _, line := range strings.Split(content.Text, "\n") {
 				line = strings.TrimSpace(line)
-				if strings.HasPrefix(strings.ToLower(line), targetPrefix) {
-					return strings.TrimSpace(line[len(targetPrefix):])
+				if strings.HasPrefix(strings.ToLower(line), prefix) {
+					return strings.TrimSpace(line[len(prefix):])
 				}
 			}
 		}
@@ -4727,6 +4743,29 @@ func imageGeneratorTargetNodeID(messages []design.AgentChatMessage) string {
 	return ""
 }
 
+func positionGeneratedNodesBesideReference(nodes []design.Node, referenceNodeID string, generated []design.Node) []design.Node {
+	positioned := append([]design.Node(nil), generated...)
+	referenceIndex := findNodeIndex(nodes, strings.TrimSpace(referenceNodeID))
+	if referenceIndex < 0 || len(positioned) == 0 {
+		return positioned
+	}
+	reference := nodes[referenceIndex]
+	gap := math.Max(48, math.Min(120, reference.Width*0.08))
+	nextX := reference.X + reference.Width + gap
+	for index := range positioned {
+		if positioned[index].Width <= 0 {
+			positioned[index].Width = reference.Width
+		}
+		if positioned[index].Height <= 0 {
+			positioned[index].Height = reference.Height
+		}
+		positioned[index].X = nextX
+		positioned[index].Y = reference.Y
+		nextX += positioned[index].Width + gap
+	}
+	return positioned
+}
+
 func mergeGeneratedNodesIntoTarget(nodes []design.Node, generated []design.Node, targetNodeID string) []design.Node {
 	if strings.TrimSpace(targetNodeID) == "" || len(generated) == 0 {
 		return append(nodes, completedImageGeneratorNodes(generated)...)