Prepare a form from documents: a proposal of every answer with its source, what is missing, and where documents disagree, before writing, plus attachments for a package. Same inputs as fill_form_from_context (form_id for a form already in the library, or pdf_url/pdf_base64 for a new one, plus context_text and/or context_urls), but nothing is written into the PDF: read the proposal, answer what is missing, then commit. policy is safe (write high and medium confidence) or strict (high only). Returns a job_id and a proposal_id; poll get_job about every 20 seconds. Billed as one context fill; the first 5 each month are free. Optional retention: ephemeral or account_default (default: the account's own setting); it applies only when this call creates the form (pdf_url, pdf_base64 or library), since an existing form keeps the setting it was created with. Ephemeral processing: source and output documents are deleted 60 to 70 minutes after the last activity on a form.