Version: 0.9.65.dev.260503

后端：
1. 阶段 1.5/1.6
收口 llm-service / rag-service，统一模型出口与检索基础设施入口，清退 backend/infra/llm 与 backend/infra/rag 旧实现；
2. 同步更新相关调用链与微服务迁移计划文档

backend/services/rag/chunk/text_chunker.go

@@ -0,0 +1,85 @@
+package chunk
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/LoveLosita/smartflow/backend/services/rag/core"
+)
+
+// TextChunker 是默认文本切块器。
+type TextChunker struct{}
+
+func NewTextChunker() *TextChunker {
+	return &TextChunker{}
+}
+
+// Chunk 对文本执行固定窗口切块。
+//
+// 步骤化说明：
+// 1. 先做空白归一，避免无效块进入向量库；
+// 2. 再按 chunk_size/overlap 滑窗切割；
+// 3. 每块继承原文 metadata，并补充 chunk 序号。
+func (c *TextChunker) Chunk(_ context.Context, doc core.SourceDocument, opt core.ChunkOption) ([]core.Chunk, error) {
+	if strings.TrimSpace(doc.ID) == "" {
+		return nil, fmt.Errorf("empty document id")
+	}
+	text := strings.TrimSpace(doc.Text)
+	if text == "" {
+		return nil, nil
+	}
+	if opt.ChunkSize <= 0 {
+		opt.ChunkSize = 400
+	}
+	if opt.ChunkOverlap < 0 {
+		opt.ChunkOverlap = 0
+	}
+	if opt.ChunkOverlap >= opt.ChunkSize {
+		opt.ChunkOverlap = opt.ChunkSize / 5
+	}
+
+	runes := []rune(text)
+	step := opt.ChunkSize - opt.ChunkOverlap
+	if step <= 0 {
+		step = opt.ChunkSize
+	}
+
+	result := make([]core.Chunk, 0, len(runes)/step+1)
+	order := 0
+	for start := 0; start < len(runes); start += step {
+		end := start + opt.ChunkSize
+		if end > len(runes) {
+			end = len(runes)
+		}
+		chunkText := strings.TrimSpace(string(runes[start:end]))
+		if chunkText == "" {
+			continue
+		}
+		metadata := cloneMap(doc.Metadata)
+		metadata["chunk_order"] = order
+		result = append(result, core.Chunk{
+			ID:         fmt.Sprintf("%s#%d", doc.ID, order),
+			DocumentID: doc.ID,
+			Text:       chunkText,
+			Order:      order,
+			Metadata:   metadata,
+		})
+		order++
+		if end == len(runes) {
+			break
+		}
+	}
+	return result, nil
+}
+
+func cloneMap(src map[string]any) map[string]any {
+	if len(src) == 0 {
+		return map[string]any{}
+	}
+	dst := make(map[string]any, len(src))
+	for k, v := range src {
+		dst[k] = v
+	}
+	return dst
+}