feat(server): persist node semantic context and retain CAD agent context

Add a semantic_context column to canvas_nodes (schema, sqlc queries,
generated models, repository upserts) and thread SemanticContext through the
domain node, API type, and mappers so CAD-derived context survives canvas
saves.

Treat agent text parts with textSource "cad-context" like settings: keep
them for planning, memory, and image-generation prompts but exclude them
from the persisted user-visible message copy. Add coverage for the CAD
context visibility and mapper behavior.

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

server/internal/application/design_service.go

@@ -669,6 +669,10 @@ func (s *DesignService) AgentChat(ctx context.Context, projectID string, req des
 	if prompt == "" {
 		return design.AgentThread{}, fmt.Errorf("%w: prompt is required", design.ErrInvalidInput)
 	}
+	visiblePrompt := design.NormalizePrompt(visiblePromptFromAgentMessages(req.Messages))
+	if visiblePrompt == "" {
+		visiblePrompt = prompt
+	}
 
 	mode := strings.TrimSpace(req.Mode)
 	if mode == "" {
@@ -703,7 +707,7 @@ func (s *DesignService) AgentChat(ctx context.Context, projectID string, req des
 				Role:      "user",
 				Type:      "user",
 				Title:     "新的设计需求",
-				Content:   prompt,
+				Content:   visiblePrompt,
 				ThreadID:  threadID,
 				ActionID:  actionID,
 				StepID:    newID(),
@@ -5153,6 +5157,14 @@ func isGeneratedImageContent(value string) bool {
 }
 
 func promptFromAgentMessages(messages []design.AgentChatMessage) string {
+	return promptFromAgentMessagesWithVisibility(messages, false)
+}
+
+func visiblePromptFromAgentMessages(messages []design.AgentChatMessage) string {
+	return promptFromAgentMessagesWithVisibility(messages, true)
+}
+
+func promptFromAgentMessagesWithVisibility(messages []design.AgentChatMessage, visibleOnly bool) string {
 	var builder strings.Builder
 	for _, message := range messages {
 		if strings.TrimSpace(message.Role) != "" && strings.ToLower(strings.TrimSpace(message.Role)) != "user" {
@@ -5161,7 +5173,8 @@ func promptFromAgentMessages(messages []design.AgentChatMessage) string {
 		for _, content := range message.Contents {
 			switch strings.ToLower(strings.TrimSpace(content.Type)) {
 			case "text":
-				if strings.EqualFold(strings.TrimSpace(content.TextSource), "settings") {
+				textSource := strings.TrimSpace(content.TextSource)
+				if strings.EqualFold(textSource, "settings") || (visibleOnly && strings.EqualFold(textSource, "cad-context")) {
 					continue
 				}
 				if text := strings.TrimSpace(content.Text); text != "" {
@@ -5207,7 +5220,8 @@ func hasUserPromptTextInAgentMessages(messages []design.AgentChatMessage) bool {
 			if strings.ToLower(strings.TrimSpace(content.Type)) != "text" {
 				continue
 			}
-			if strings.EqualFold(strings.TrimSpace(content.TextSource), "settings") {
+			textSource := strings.TrimSpace(content.TextSource)
+			if strings.EqualFold(textSource, "settings") || strings.EqualFold(textSource, "cad-context") {
 				continue
 			}
 			text := stripPromptReferenceDirectives(stripImageGeneratorDirectiveLines(content.Text))