uploads,tools,config,main: 将 upload_file 返回路径改为服务器端绝对路径并透传给 spark_submit

之前 upload_file 把文件写到 DataDir/uploads/<filename>，返回相对路径
uploads/hello.txt。MCP 服务器与 agent 不在同一台机器，agent 无法构造服务
器本地路径，因此 spark_submit 无法定位脚本。

改为由新的 internal/uploads 包 mint 一个 32 字符十六进制 file_id，文件落盘为
DataDir/uploads/<file_id>，元数据写入 <file_id>.meta.json（原始文件名只存在
sidecar 里）。upload_file 返回 {file_id, path, name, size, sha256}，其中 path
是绝对路径。spark_submit 的 description 明确要求 LLM 直接把 upload_file 返回
的 path 放进 args，不要自己构造路径。

为什么只在描述里约束而不在代码里拒绝非 mint 的绝对路径：集群本地已有路径
（如 /opt/spark/examples/pi.py）是合法的 spark-submit 参数，代码不能替
LLM 拒绝。

测试锁定：
- internal/uploads: Save 往返、AbsPath/Validate 非法路径、Sweep 过期/未过期/
  孤立 sidecar
- internal/mcp/tools: upload_file 新响应字段、spark_submit 透传 mint 路径与
  集群本地路径

刻意未做：S3/HDFS 上传、给 spark_submit 新增 file_id 参数、在代码层面拒绝
集群本地绝对路径。

破坏性变更：upload_file 响应从相对 path 改为绝对 path，并新增 file_id/name/
sha256 字段。该工具尚无外部调用者。

Co-Authored-By: Claude <noreply@anthropic.com>

internal/mcp/tools/upload_file.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"encoding/base64"
 	"fmt"
-	"os"
 	"path/filepath"
 	"regexp"
 
@@ -19,7 +18,7 @@ var filenameRegex = regexp.MustCompile(`^[a-zA-Z0-9._-]+$`)
 // NewUploadFileTool returns the schema for the upload_file MCP Tool.
 func NewUploadFileTool() mcp.Tool {
 	return mcp.NewTool(UploadFileName,
-		mcp.WithDescription("Upload a script or config file to ./data/uploads/ so it can be referenced by spark_submit later."),
+		mcp.WithDescription("Upload a script or config file to the server's data/uploads/ directory. Returns {file_id, path, name, size, sha256}. To submit it, pass the returned `path` as one of the args in spark_submit (e.g. args=[<path>, '--class', 'Main']). The path is server-side; the agent does not need to construct one."),
 		mcp.WithString("filename",
 			mcp.Required(),
 			mcp.Description("Plain file name without path separators (1-128 chars, [a-zA-Z0-9._-])"),
@@ -60,6 +59,10 @@ func (d *Deps) UploadFileHandler(ctx context.Context, req mcp.CallToolRequest) (
 		return errResult("upload_file: " + err.Error()), nil
 	}
 
+	if d.UploadStore == nil {
+		return errResult("upload_file: upload store not configured"), nil
+	}
+
 	var data []byte
 	switch encoding {
 	case "base64":
@@ -72,17 +75,17 @@ func (d *Deps) UploadFileHandler(ctx context.Context, req mcp.CallToolRequest) (
 		data = []byte(content)
 	}
 
-	final := filepath.Join(d.DataDir, "uploads", filename)
-	if err := os.MkdirAll(filepath.Dir(final), 0o750); err != nil {
-		return errResult("upload_file: create uploads dir: " + err.Error()), nil
-	}
-	if err := os.WriteFile(final, data, 0o640); err != nil {
-		return errResult("upload_file: write file: " + err.Error()), nil
+	fileID, _, size, sha256Hex, absPath, err := d.UploadStore.Save(data, filename)
+	if err != nil {
+		return errResult("upload_file: save upload: " + err.Error()), nil
 	}
 
 	result := map[string]any{
-		"path": fmt.Sprintf("uploads/%s", filename),
-		"size": len(data),
+		"file_id": fileID,
+		"path":    absPath,
+		"name":    filename,
+		"size":    size,
+		"sha256":  sha256Hex,
 	}
 	return textResult(encodeJSON(result)), nil
 }