feat(go-api): migrate agent file download handler to Go with strict P… (#15769)

## What does this PR do?

This PR migrates the Agent Temporary File Download endpoint (`GET
/api/v1/agents/download`) from the Python backend to the Go backend,
optimizing the data retrieval flow and maintaining strict functional
parity. It also fixes a persistent parsing error in the Sandbox code
execution node.

## Checklist
- [x] Code logic matches Python implementation
- [x] All local unit tests passed
- [x] No breaking changes to existing router interfaces

Co-authored-by: Yingfeng <yingfeng.zhang@gmail.com>

internal/handler/agent.go

@@ -22,6 +22,8 @@ import (
 	"io"
 	"mime/multipart"
 	"net/http"
+	"net/url"
+	"ragflow/internal/utility"
 	"strconv"
 	"strings"
 
@@ -36,19 +38,24 @@ import (
 
 // AgentHandler agent handler
 // fileUploader is the subset of FileService used by agent handlers.
-type fileUploader interface {
+type agentFileService interface {
 	UploadFile(tenantID, parentID string, files []*multipart.FileHeader) ([]map[string]interface{}, error)
+	DownloadAgentFile(tenantID, location string) ([]byte, error)
 }
 
 // AgentHandler agent handler
 type AgentHandler struct {
 	agentService *service.AgentService
-	fileService  fileUploader
+	fileService  agentFileService
 }
 
 // NewAgentHandler create agent handler
+
 func NewAgentHandler(agentService *service.AgentService, fileService *service.FileService) *AgentHandler {
-	return &AgentHandler{agentService: agentService, fileService: fileService}
+	return &AgentHandler{
+		agentService: agentService,
+		fileService:  fileService,
+	}
 }
 
 // ListAgents lists agent canvases for the current user.
@@ -655,14 +662,42 @@ func (h *AgentHandler) UpdateAgentTags(c *gin.Context) {
 	})
 }
 
-// GetPrompts returns the default prompts used by the agent.
-// @Summary Get Agent Prompts
-// @Description Returns the default prompts used by the agent, such as task analysis, plan generation, reflection, and citation guidelines.
-// @Tags agents
-// @Produce json
-// @Security ApiKeyAuth
-// @Success 200 {object} map[string]interface{}
-// @Router /api/v1/agents/prompts [get]
+func (h *AgentHandler) DownloadAgentFile(c *gin.Context) {
+	user, errorCode, errorMessage := GetUser(c)
+	if errorCode != common.CodeSuccess {
+		jsonError(c, errorCode, errorMessage)
+		return
+	}
+
+	fileID := c.Query("id")
+	if fileID == "" {
+		jsonError(c, common.CodeArgumentError, "id parameter is required")
+		return
+	}
+
+	blob, err := h.fileService.DownloadAgentFile(user.ID, fileID)
+	if err != nil {
+		jsonError(c, common.CodeServerError, err.Error())
+		return
+	}
+
+	ext := utility.GetFileExtension(fileID)
+	contentType := utility.GetContentType(ext, "")
+	if contentType != "" {
+		c.Header("Content-Type", contentType)
+	} else {
+		c.Header("Content-Type", "application/octet-stream")
+	}
+
+	if utility.ShouldForceAttachment(ext, contentType) {
+		c.Header("X-Content-Type-Options", "nosniff")
+		encodedName := url.QueryEscape(fileID)
+		c.Header("Content-Disposition", "attachment; filename*=UTF-8''"+encodedName)
+	}
+
+	c.Data(http.StatusOK, contentType, blob)
+}
+
 func (h *AgentHandler) GetPrompts(c *gin.Context) {
 	if _, errorCode, errorMessage := GetUser(c); errorCode != common.CodeSuccess {
 		jsonError(c, errorCode, errorMessage)

internal/handler/agent_test.go

@@ -18,6 +18,7 @@ package handler
 
 import (
 	"encoding/json"
+	"mime/multipart"
 	"net/http"
 	"net/http/httptest"
 	"strings"
@@ -979,9 +980,71 @@ func TestListAgentTemplates_RequiresAuth(t *testing.T) {
 	}
 }
 
+type fakeAgentFileService struct {
+	blob []byte
+	err  error
+}
+
+func (f *fakeAgentFileService) UploadFile(tenantID, parentID string, files []*multipart.FileHeader) ([]map[string]interface{}, error) {
+	return nil, nil
+}
+
+func (f *fakeAgentFileService) DownloadAgentFile(tenantID, location string) ([]byte, error) {
+	return f.blob, f.err
+}
+
+func TestDownloadAgentFile_Success(t *testing.T) {
+	c, w, _ := setupGinContextWithUserAndDB(t, http.MethodGet, "/api/v1/agents/download?id=test-file.pdf")
+
+	fakeFileSvc := &fakeAgentFileService{
+		blob: []byte("test content"),
+		err:  nil,
+	}
+
+	h := &AgentHandler{
+		agentService: service.NewAgentService(),
+		fileService:  fakeFileSvc,
+	}
+
+	h.DownloadAgentFile(c)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+
+	if w.Header().Get("Content-Type") != "application/pdf" {
+		t.Errorf("expected Content-Type application/pdf, got %s", w.Header().Get("Content-Type"))
+	}
+
+	if w.Body.String() != "test content" {
+		t.Errorf("expected 'test content', got %s", w.Body.String())
+	}
+}
+
+func TestDownloadAgentFile_MissingID(t *testing.T) {
+	c, w, _ := setupGinContextWithUserAndDB(t, http.MethodGet, "/api/v1/agents/download")
+
+	h := &AgentHandler{
+		agentService: service.NewAgentService(),
+		fileService:  &fakeAgentFileService{},
+	}
+
+	h.DownloadAgentFile(c)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200 (json error return), got %d", w.Code)
+	}
+
+	var resp map[string]interface{}
+	json.Unmarshal(w.Body.Bytes(), &resp)
+	if code, _ := resp["code"].(float64); code != float64(common.CodeArgumentError) {
+		t.Errorf("expected code 102, got %v", code)
+	}
+}
+
 func TestGetPrompts_Success(t *testing.T) {
 	c, w, _ := setupGinContextWithUserAndDB(t, http.MethodGet, "/api/v1/agents/prompts")
-	
+
 	// Create handler with fake or real service.
 	h := NewAgentHandler(service.NewAgentService(), nil)
 	h.GetPrompts(c)

internal/handler/agent_upload_test.go

@@ -235,4 +235,7 @@ func TestUploadAgentFileHandler_TeamMemberTenant(t *testing.T) {
 }
 
 // sp returns a pointer to the given string.
-func sp(s string) *string { return &s }
+func sp(s string) *string { return &s }
+func (f *fakeUploadFileService) DownloadAgentFile(tenantID, location string) ([]byte, error) {
+	panic("DownloadAgentFile should not be called during upload tests")
+}