feat(canvas): 云端 Agent 画布 - 支持分镜连接、脚本节点与资产关系持久化

backend/internal/canvas/capability/builtin.go

@@ -93,8 +93,12 @@ func BuiltinRegistry() *Registry {
 			GoodFor:       []string{"多镜头规划", "镜头连续性", "逐镜审查和微调", "逐镜生成图片或视频", "需要他人接手维护的内容"},
 			NotIdealFor:   []string{"只有一个画面的快速试验", "一次性临时提示词", "仅需要阅读排版的普通文档"},
 			Tradeoffs:     []string{"前期录入成本高于文本节点", "但能保留镜头级结构、资产关系和后续维护能力"},
-			Actions:       []string{"read_rows", "append_row", "update_row", "remove_row", "generate_storyboard"},
+			Actions:       []string{"read_rows", "append_row", "update_row", "remove_row", "generate_storyboard", "connect_assets", "update_node"},
+			InputKind:     "text",
+			Connection:    ConnectionPolicy{CanSource: true, CanTarget: true, AcceptedInputKinds: []string{"audio", "character", "image", "text", "video"}},
+			CanUpdate:     true,
 			SummaryFields: []string{"storyboard"}, DetailFields: []string{"storyboard"}, ProjectionKind: "storyboard", ProjectionField: "storyboard",
+			PatchFields: titleAndPositionPatchFields(),
 			CreateMetadata: func(string) map[string]any {
 				return map[string]any{"status": "idle", "workflowKind": "script", "storyboard": map[string]any{"rows": []any{}, "visibleColumns": []any{"shotNumber", "durationSeconds", "videoMotionPrompt", "dialogue", "assets"}, "referenceNodeIds": []any{}}}
 			},
@@ -178,14 +182,11 @@ func generatedMediaSemantics(nodeType string) generatedMediaCapabilitySemantics
 	}
 }
 
-func editableNodeFields(contentPath, contentLabel, contentDescription string) map[string]PatchField {
+func titleAndPositionPatchFields() map[string]PatchField {
 	fields := map[string]PatchField{
 		"title": {
 			Path: "title", Kind: patchKindString, Label: "节点名称", Order: 10, Description: "节点标题", MaxRunes: maxAgentNodeTitleRunes,
 		},
-		"content": {
-			Path: contentPath, Kind: patchKindString, Label: contentLabel, Order: 20, Description: contentDescription, MaxRunes: maxAgentNodeContentRunes,
-		},
 	}
 	for key, field := range positionPatchFields() {
 		fields[key] = field
@@ -193,6 +194,14 @@ func editableNodeFields(contentPath, contentLabel, contentDescription string) ma
 	return fields
 }
 
+func editableNodeFields(contentPath, contentLabel, contentDescription string) map[string]PatchField {
+	fields := titleAndPositionPatchFields()
+	fields["content"] = PatchField{
+		Path: contentPath, Kind: patchKindString, Label: contentLabel, Order: 20, Description: contentDescription, MaxRunes: maxAgentNodeContentRunes,
+	}
+	return fields
+}
+
 // positionPatchFields 是坐标字段：模型可以直接指定节点位置（微调），批量整理走 canvas_arrange_nodes。
 // 坐标上限与整理侧的收敛范围一致，避免写进离谱的几何值。
 func positionPatchFields() map[string]PatchField {