If the first round of conversation includes attachments, and the second round also includes attachments, an error will occur. The large model I used is Qwen 3.8-27B-FP8.

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### Dify version

1.16.1

### Cloud or Self Hosted

Self Hosted (Docker)

### Steps to reproduce

If the first round of conversation includes attachments, and the second round also includes attachments, an error will occur. The large model I used is Qwen 3.8-27B-FP8.

### ✔️ Expected Behavior

Normally, remember the attachments of the first round while analyzing the files of the second round.

### ❌ Actual Behavior

report an error：{
"text": "处理失败！",
"error_message": "req_id: 28798a2a82 PluginInvokeError: {\"args\":{\"description\":\"[models] Error: API request failed with status code 400: {\\\"error\\\":{\\\"message\\\":\\\"Unsupported chat content part type: 'file'. Supported types: audio_embeds, audio_url, image_embeds, image_pil, image_url, input_audio, input_image, input_text, output_text, prompt_embeds, refusal, text, thinking, tool_reference, video_url. (parameter=type, value=file)\\\",\\\"type\\\":\\\"BadRequestError\\\",\\\"param\\\":\\\"type\\\",\\\"code\\\":400}}\"},\"error_type\":\"InvokeError\",\"message\":\"[models] Error: API request failed with status code 400: {\\\"error\\\":{\\\"message\\\":\\\"Unsupported chat content part type: 'file'. Supported types: audio_embeds, audio_url, image_embeds, image_pil, image_url, input_audio, input_image, input_text, output_text, prompt_embeds, refusal, text, thinking, tool_reference, video_url. (parameter=type, value=file)\\\",\\\"type\\\":\\\"BadRequestError\\\",\\\"param\\\":\\\"type\\\",\\\"code\\\":400}}\"}",
"error_type": "PluginInvokeError"
}

No file or test is named. First reproduce the failure on Dify 1.16.1 with a self-hosted Docker setup, Qwen 3.8-27B-FP8, and attachments in two consecutive conversation rounds; then trace the attachment handling and model request path shown by the PluginInvokeError. Done means the second round succeeds while retaining and analyzing the first round’s attachments.

Written by the indexing model from the issue text.