feat: FormatAdapter 接入 splitsprite+gifmaker 管线

- FormatAdapter: 精灵表模式(单图)自动调用 splitsprite.Process 拆分帧
- 拆分后每帧编码为独立 PNG Asset，Metadata 包含 GIFPreview 字节
- 多图/非精灵表模式保持原样透传
- AssetParams 新增 GridRows/GridCols 覆盖投影检测
- AssetMetadata 新增 GIFPreview 字段

backend/internal/service/nodes.go

@@ -1,10 +1,16 @@
 package service
 
 import (
+	"bytes"
 	"context"
 	"fmt"
+	"image/png"
 	"strings"
 
+	"gen2d/internal/logger"
+	"gen2d/pkg/gifmaker"
+	"gen2d/pkg/splitsprite"
+
 	"github.com/cloudwego/eino/compose"
 )
 
@@ -127,7 +133,7 @@ var qualitySupervisorNode = compose.InvokableLambda(func(ctx context.Context, im
 	return input, nil
 })
 
-// formatAdapterNode 节点：从 state 读取图片，格式转换，组装输出。
+// formatAdapterNode 节点：精灵表格式时调用 splitsprite 拆分 + gifmaker 生成 GIF 预览。
 var formatAdapterNode = compose.InvokableLambda(func(ctx context.Context, input PipelineInput) (PipelineOutput, error) {
 	var images []GeneratedImage
 	_ = compose.ProcessState[*PipelineState](ctx, func(_ context.Context, state *PipelineState) error {
@@ -135,6 +141,18 @@ var formatAdapterNode = compose.InvokableLambda(func(ctx context.Context, input
 		return nil
 	})
 
+	params := input.Params
+	resolution := params.Resolution
+	if resolution <= 0 {
+		resolution = 64
+	}
+
+	// 精灵表模式：单张图时拆分 + GIF 预览；多图时已是独立帧，透传
+	if params.Format == "spritesheet" && len(images) == 1 {
+		return processSpriteSheet(ctx, images[0], params, resolution)
+	}
+
+	// 普通模式：原样透传
 	assets := make([]Asset, len(images))
 	for i, img := range images {
 		assets[i] = Asset{
@@ -144,23 +162,79 @@ var formatAdapterNode = compose.InvokableLambda(func(ctx context.Context, input
 		}
 	}
 
-	resolution := input.Params.Resolution
-	if resolution <= 0 {
-		resolution = 64
+	return PipelineOutput{
+		Assets: assets,
+		Metadata: AssetMetadata{
+			FrameWidth:  resolution,
+			FrameHeight: resolution,
+			FrameCount:  len(images),
+			Directions:  params.Frames.Directions,
+		},
+	}, nil
+})
+
+// processSpriteSheet 将单张精灵表拆分为独立帧并生成 GIF 预览。
+func processSpriteSheet(ctx context.Context, img GeneratedImage, params AssetParams, resolution int) (PipelineOutput, error) {
+	l := logger.FromCtx(ctx)
+	src, err := png.Decode(bytes.NewReader(img.Data))
+	if err != nil {
+		l.Error("format_adapter decode sprite sheet failed", "error", err)
+		return PipelineOutput{}, fmt.Errorf("decode sprite sheet: %w", err)
 	}
 
-	metadata := AssetMetadata{
-		FrameWidth:  resolution,
-		FrameHeight: resolution,
-		FrameCount:  len(images),
-		Directions:  input.Params.Frames.Directions,
+	opts := splitsprite.DefaultOptions()
+	if params.GridRows > 0 && params.GridCols > 0 {
+		opts.GridRows = params.GridRows
+		opts.GridCols = params.GridCols
+	}
+
+	frames, err := splitsprite.Process(src, opts)
+	if err != nil {
+		l.Error("format_adapter split sprite sheet failed", "error", err)
+		return PipelineOutput{}, fmt.Errorf("split sprite sheet: %w", err)
+	}
+	l.Info("format_adapter split sprite sheet", "frame_count", len(frames))
+
+	// 帧 → Asset
+	assets := make([]Asset, 0, len(frames))
+	for i, f := range frames {
+		var buf bytes.Buffer
+		if err := png.Encode(&buf, f); err != nil {
+			l.Error("format_adapter encode frame failed", "error", err)
+			return PipelineOutput{}, fmt.Errorf("encode frame %d: %w", i, err)
+		}
+		assets = append(assets, Asset{
+			Data:   buf.Bytes(),
+			Format: "png",
+			URL:    fmt.Sprintf("output/frame_%03d.png", i),
+		})
+	}
+
+	// GIF 预览
+	var gifBuf bytes.Buffer
+	if err := gifmaker.Encode(&gifBuf, frames, nil); err != nil {
+		l.Warn("format_adapter generate GIF preview failed", "error", err)
+	} else {
+		l.Info("format_adapter generated GIF preview", "size_bytes", gifBuf.Len())
+	}
+
+	fw, fh := 0, 0
+	if len(frames) > 0 {
+		b := frames[0].Bounds()
+		fw, fh = b.Dx(), b.Dy()
 	}
 
 	return PipelineOutput{
-		Assets:   assets,
-		Metadata: metadata,
+		Assets: assets,
+		Metadata: AssetMetadata{
+			FrameWidth:  fw,
+			FrameHeight: fh,
+			FrameCount:  len(frames),
+			Directions:  params.Frames.Directions,
+			GIFPreview:  gifBuf.Bytes(),
+		},
 	}, nil
-})
+}
 
 // buildStyleDescription 将风格键值对转为自然语言描述，供 PromptAgent 注入。
 func buildStyleDescription(projectStyle, taskStyle map[string]string) string {

backend/internal/service/types.go

@@ -36,11 +36,14 @@ type AssetParams struct {
 	Resolution int
 	Frames     FrameParams
 	Format     string // "spritesheet" / "individual"
+	// GridRows / GridCols override projection-based split for sprite sheets.
+	GridRows int
+	GridCols int
 }
 
 // FrameParams 帧参数
 type FrameParams struct {
-	Directions        int
+	Directions         int
 	FramesPerDirection int
 }
 
@@ -65,4 +68,5 @@ type AssetMetadata struct {
 	FrameHeight int
 	FrameCount  int
 	Directions  int
+	GIFPreview  []byte `json:"-"` // animated GIF preview (not serialized)
 }