LLM simplifies citations for filenames with special characters, breaking document links

Description

When uploading documents via the user upload feature (with USE_USER_UPLOAD=true and AZURE_ENFORCE_ACCESS_CONTROL=true), the sourcefile field in the Azure AI Search index gets a "- " prefix that shouldn't be there.

Steps to Reproduce

1. Enable user upload and access control:
   复制

   azd env set USE_USER_UPLOAD true
   azd env set AZURE_ENFORCE_ACCESS_CONTROL true
   azd provision && azd deploy

2. Log in and upload a document (e.g., PyCon US 2025.pdf)
3. Query the search index to inspect the indexed document

Expected Behavior

The sourcefile field should match the original filename:

sourcefile: "PyCon US 2025.pdf"

Actual Behavior

The sourcefile field has a "- " prefix:

sourcefile: "- PyCon US 2025.pdf"

Impact

This causes the /content/<path> route to return 403 Forbidden when trying to view the document, because check_path_auth() filters by sourcefile eq 'PyCon US 2025.pdf' but the indexed value is '- PyCon US 2025.pdf'.

Environment

• User upload enabled with ADLS Gen2
• Access control enforcement enabled
• Local development (may also affect deployed environments)