{"code":"not_found","message":"File not found or signature is invalid","status":404}

### Self Checks

- [x] I have read the [Contributing Guide](https://github.com/langgenius/dify/blob/main/CONTRIBUTING.md) and [Language Policy](https://github.com/langgenius/dify/issues/1542).
- [x] This is only for bug report, if you would like to ask a question, please head to [Discussions](https://github.com/langgenius/dify/discussions/categories/general).
- [x] I have searched for existing issues [search for existing issues](https://github.com/langgenius/dify/issues), including closed ones.
- [x] I confirm that I am using English to submit this report, otherwise it will be closed.
- [x] 【中文用户 & Non English User】请使用英语提交，否则会被关闭 ：）
- [x] Please do not modify this template :) and fill in all the required fields.

### Dify version

1.16.1

### Cloud or Self Hosted

Self Hosted (Docker)

### Steps to reproduce

access url like : mydomain/files/f288ddba-591f-49cc-b365-a3fec7d2884e/file-preview?timestamp=1786324954&nonce=e708a9548e65d9e8c4ebd3db9fa0623&sign=F1ghUfcx3Pfw2vex1aLS6sQtSIPqqCPhQ4CwsSHK_ks=

show error:{"code":"not_found","message":"File not found or signature is invalid","status":404}

### ✔️ Expected Behavior

show picture normal .

### ❌ Actual Behavior

show error:{"code":"not_found","message":"File not found or signature is invalid","status":404}

Start by reproducing the self-hosted Docker issue at the /files/{id}/file-preview endpoint using the signed URL shown in the report. Trace how the timestamp, nonce, and sign parameters are handled, then verify that a valid image URL displays normally instead of returning the 404 response.

Written by the indexing model from the issue text.