After using qwen long to upload and parse Excel files in the agent, the file disappeared and was not passed to the interface. The files parameter was empty

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### Dify version

1.15.0

### Cloud or Self Hosted

Cloud

### Steps to reproduce

```

where my excel file?

### ✔️ Expected Behavior

I will upload the Excel file and send it to the model for analysis, and then the results will be displayed

### ❌ Actual Behavior

_No response_

Start by reproducing the upload and parsing flow in Dify 1.15.0 with qwen long and an Excel file, then trace where the file is lost before the files parameter reaches the interface. Done means the uploaded file is passed to the model and the analysis results are displayed; no source file or test is named in the report.

Written by the indexing model from the issue text.