Fix WeasyPrint PDF Failure

My Lambda function—paired with a shared layer—builds a Jinja2-based HTML, converts it to PDF with WeasyPrint, then streams the result straight into the DocuSign API. Right now the whole flow halts because WeasyPrint never returns a file; the Lambda logs end with a silent failure and no PDF reaches DocuSign, so the envelope stays empty.

I need you to dive into the code, replicate the failure, and get clean, correctly rendered PDFs moving through to DocuSign again. You should already be comfortable with:

• WeasyPrint quirks inside the AWS Lambda environment (fonts, Pango/Cairo, headless dependencies)
• Jinja2 template debugging
• Python 3.12 packaging for Lambda layers
• DocuSign eSignature API envelope creation

Once you trace the root cause, update the Lambda (and layer if necessary), redeploy, and show that:

1. HTML renders without errors.
2. WeasyPrint returns a valid PDF buffer every invocation.
3. The DocuSign envelope is created with the PDF attached and visible to recipients.

Please tell me about similar troubleshooting you have done with WeasyPrint, Lambda layers, or DocuSign; just a brief outline of your experience is enough—no need for lengthy proposals.