✨ Feat: Add presigned URL support for external MCP tool file access and improve agent execution flow by xuyaqist · Pull Request #2839 · ModelEngine-Group/nexent

xuyaqist · 2026-04-22T09:36:53Z

Feat: Add presigned URL support for external MCP tool file access and improve agent execution flow

Add presigned URL generation during file uploads with 24-hour validity
- Extended upload_file() and upload_fileobj() to generate presigned URLs
- Changed default URL expiration from 1 hour to 24 hours
- Added generate_presigned_url and presigned_url_expires parameters

Update agent prompts to prevent fabricated observation results（避免在思考阶段，模型没有执行代码，但模拟输出了结果造成模型幻觉的问题）
- Removed manual "Observe Results:" output from execution flow
- System now provides "Observation:" marker with real execution results
- Added MCP tool markers ([MCP]) in tool listings
- Added file URL usage guide for MCP vs internal tools
Include historical file attachments in agent context
- Pass minio_files from conversation history to agent
- Enables agent to reference files from previous conversation turns

Update frontend to handle presigned URLs
- Store and transmit presigned_url for each attachment
- Updated TypeScript types to include presigned_url field

Made-with: Cursor

… improve agent execution flow

Copilot

Pull request overview

This PR adds presigned download URL support (default 24h) for externally hosted tools (e.g., MCP) to access uploaded files, updates agent prompts/execution guidance to avoid fabricated “observation” content, and extends agent context so historical attachments from conversation history are available during runs.

Changes:

Backend: generate/propagate presigned URLs on upload, and extend default URL expiry from 1h → 24h across storage URL helpers/endpoints.
Agent/runtime: include historical minio_files in the agent’s prompt context and update prompts to rely on system-provided Observation: outputs.
Frontend: persist/transmit presigned_url on attachments and pass historical attachment metadata in history.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
test/backend/database/test_attachment_db.py	Updates upload tests to cover presigned URL behavior and new flags.
frontend/types/chat.ts	Extends attachment types to include `presigned_url`.
frontend/lib/chatMessageExtractor.ts	Preserves `presigned_url` when hydrating messages from API responses.
frontend/lib/chat/chatAttachmentUtils.ts	Captures presigned URLs from upload results and attaches them to outgoing message metadata.
frontend/app/[locale]/chat/internal/chatInterface.tsx	Sends presigned URLs + historical attachments in the agent run payload.
backend/prompts/utils/prompt_generate_zh.yaml	Removes manual “Observe Results” pattern; relies on system `Observation:` marker.
backend/prompts/utils/prompt_generate_en.yaml	Same as above for English.
backend/prompts/manager_system_prompt_template_zh.yaml	Adds `[MCP]` markers and file URL usage guidance in manager prompt.
backend/prompts/manager_system_prompt_template_en.yaml	Same as above for English.
backend/prompts/managed_system_prompt_template_zh.yaml	Adds `[MCP]` markers and file URL usage guidance in managed prompt.
backend/prompts/managed_system_prompt_template_en.yaml	Same as above for English.
backend/database/client.py	Changes default presigned URL expiry to 24h.
backend/database/attachment_db.py	Adds presigned URL generation to uploads; updates URL expiry defaults and list behavior.
backend/apps/file_management_app.py	Updates API defaults/docs for URL expiry to 24h.
backend/agents/create_agent_info.py	Appends both S3 and presigned URLs to query context and includes historical files.

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

Copilot · 2026-04-22T09:45:37Z

    @patch('backend.database.attachment_db.os.path.exists')
    @patch('backend.database.attachment_db.os.path.getsize')
    @patch('backend.database.attachment_db.os.path.basename')
-    def test_upload_file_nonexistent_file(self, mock_basename, mock_getsize, mock_exists):
-        """Test upload_file with nonexistent file"""
+    @patch('backend.database.attachment_db.get_file_url')
+    def test_upload_file_without_presigned_url(self, mock_get_file_url, mock_basename, mock_getsize, mock_exists):
+        """Test upload_file when generate_presigned_url is False"""
        mock_basename.return_value = 'test.txt'
-        mock_exists.return_value = False
-        mock_getsize.return_value = 0
+        mock_exists.return_value = True
+        mock_getsize.return_value = 1024
+        minio_client_mock.upload_file.return_value = (True, '/bucket/attachments/test.txt')
+
+        result = upload_file('/path/to/test.txt', 'attachments/test.txt', 'bucket', generate_presigned_url=False)
+
+        assert result['success'] is True
+        assert 'url' in result
+        assert 'presigned_url' not in result
+        mock_get_file_url.assert_not_called()
+


The previous test that covered the “nonexistent file” path for upload_file() appears to have been replaced. That branch (file_size falling back to 0 when os.path.exists is false) is still present in upload_file(), so it would be good to keep a dedicated test for the nonexistent-file scenario in addition to the new presigned-URL tests.

Copilot · 2026-04-22T09:45:38Z

    @patch('backend.database.attachment_db.generate_object_name')
-    def test_upload_fileobj_preserves_file_position(self, mock_generate):
+    @patch('backend.database.attachment_db.get_file_url')
+    def test_upload_fileobj_preserves_file_position(self, mock_get_file_url, mock_generate):
        """Test upload_fileobj preserves original file position"""
        mock_generate.return_value = 'attachments/test.txt'
        minio_client_mock.upload_fileobj.return_value = (True, '/bucket/attachments/test.txt')
+        mock_get_file_url.return_value = {'success': True, 'url': 'http://minio:9000/presigned-url'}

        file_obj = BytesIO(b'test data')
        original_pos = 4
        file_obj.seek(original_pos)

        result = upload_fileobj(file_obj, 'test.txt', 'bucket')

-        # File position should be restored
        assert file_obj.tell() == original_pos


test_upload_fileobj_preserves_file_position verifies the stream position is restored, but it doesn’t assert that the upload reads from the beginning of the file (it uses a stubbed upload_fileobj that never reads). Since upload_fileobj() currently passes the stream through as-is, a non-zero starting position could lead to truncated uploads without this test catching it. Consider strengthening this test by using an upload_fileobj mock that reads file_obj and asserting the full content was uploaded while still restoring the original position.

Copilot · 2026-04-22T09:45:39Z

+          .map((msg) => {
+            const historyItem: any = {
+              role: msg.role,
+              content:
+                msg.role === ROLE_ASSISTANT
+                  ? msg.finalAnswer?.trim() || msg.content || ""
+                  : msg.content || "",
+            };


The new history mapping uses any for historyItem, which drops type safety for the request payload (and makes it easy to accidentally send malformed history). Consider introducing an explicit type for the history items (including optional minio_files) instead of any.

Copilot · 2026-04-22T09:45:39Z

+            if (msg.attachments && msg.attachments.length > 0) {
+              historyItem.minio_files = msg.attachments.map((attachment) => ({
+                object_name: attachment.object_name || "",
+                name: attachment.name,
+                type: attachment.type,
+                size: attachment.size,
+                url: attachment.url || "",
+                presigned_url: attachment.presigned_url || "",
+                description: attachment.description || "",
+              }));


When constructing historyItem.minio_files, optional fields are forced to empty strings (""). This increases payload size and makes it harder for the backend to distinguish “missing” vs “present but empty”. Prefer leaving fields as undefined (so they’re omitted from JSON) or conditionally adding keys only when values exist.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

codecov · 2026-04-23T03:28:40Z

Codecov Report

❌ Patch coverage is 90.00000% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
backend/agents/create_agent_info.py	89.74%	1 Missing and 3 partials ⚠️
backend/database/attachment_db.py	86.66%	0 Missing and 2 partials ⚠️

📢 Thoughts on this report? Let us know!

xuyaqist added 6 commits April 21, 2026 10:04

修复调用多模态工具导致502Bad Gateway问题

05a2143

Bugfix: Add tooltip to tab labels in ToolManagement and SkillManagement

86b9bc1

Made-with: Cursor

Merge branch 'xyq/bugfix' into xyq/feat_file_url

38366db

Merge branch 'develop' into xyq/feat_file_url

4c376cb

Merge branch 'develop' into xyq/feat_file_url

5c60b5c

Feat: Add presigned URL support for external MCP tool file access and…

a57f158

… improve agent execution flow

Copilot AI review requested due to automatic review settings April 22, 2026 09:36

xuyaqist requested review from Dallas98 and WMC001 as code owners April 22, 2026 09:36

xuyaqist changed the base branch from main to develop April 22, 2026 09:37

Copilot started reviewing on behalf of xuyaqist April 22, 2026 09:37 View session

xuyaqist changed the title ~~Feat: Add presigned URL support for external MCP tool file access and improve agent execution flow~~ ✨ Feat: Add presigned URL support for external MCP tool file access and improve agent execution flow Apr 22, 2026

Copilot AI reviewed Apr 22, 2026

View reviewed changes

xuyaqist and others added 5 commits April 23, 2026 10:27

使用已有的types，而非重复定义

596391e

针对用户上传的文件进行去重处理，限制文件最大个数

96f9237

Update frontend/types/chat.ts

5ec52a4

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update frontend/types/chat.ts

d34c72a

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

新增测试用例

92f8bbb

xuyaqist added 2 commits April 23, 2026 14:15

Merge branch 'develop' into xyq/feat_file_url

429fc94

修复单元测试

cacee65

Dallas98 approved these changes Apr 23, 2026

View reviewed changes

Dallas98 merged commit 98a9509 into develop Apr 23, 2026
15 of 16 checks passed

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

✨ Feat: Add presigned URL support for external MCP tool file access and improve agent execution flow#2839

✨ Feat: Add presigned URL support for external MCP tool file access and improve agent execution flow#2839
Dallas98 merged 13 commits intodevelopfrom
xyq/feat_file_url

xuyaqist commented Apr 22, 2026 •

edited

Loading

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI Apr 22, 2026

Uh oh!

Copilot AI Apr 22, 2026

Uh oh!

Uh oh!

Uh oh!

Copilot AI Apr 22, 2026

Uh oh!

Copilot AI Apr 22, 2026

Uh oh!

Uh oh!

Uh oh!

codecov Bot commented Apr 23, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Conversation

xuyaqist commented Apr 22, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Copilot AI Apr 22, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Apr 22, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Copilot AI Apr 22, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Apr 22, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

codecov Bot commented Apr 23, 2026

Codecov Report

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

xuyaqist commented Apr 22, 2026 •

edited

Loading