pdfcraft-print

Layer L4: printing (execution plan M10.5).

let pages = select_pages(count, Some("1-3, ii, 9-"), &labels, Subset::All, false)?;
let settings = Settings { pages, paper: PAPERS[0].1, layout: Layout::multiple(4), ..Default::default() };
let sheets = layout(&display_sizes, &settings)?;   // geometry only (previews)
let pdf = impose(&doc, &settings)?;                // the print-ready PDF
spool::submit(&pdf, &spool::Job { printer: None, copies: 2, ..Default::default() })?;

Size: fit (to the sheet minus an 18 pt margin), actual size, shrink oversized, custom %; centred; auto orientation turns the sheet for landscape pages.
Multiple: 2/4/6/9/16 (or any n) pages per sheet, horizontal/vertical (reversed) order, page borders, auto-rotation of pages that don't match the cell.
Cut and stack (Multiple's page order): consecutive pages in each cell's pile, with aligned cut marks in the gutters. For example, 10 pages at 4 per sheet give [1, 4, 7, 10], [2, 5, 8, blank], [3, 6, 9, blank]. Print single-sided, keep sheets in output order, cut at the marks, then stack the cell piles from left to right, top to bottom. Blank cells can be discarded. Page ranges and Reverse pages are applied before imposition. Duplex imposition is not supported. Headless: doc_print with layout: "multiple", order: "cut-stack" and per_sheet: 4 (or any supported grid size), plus path or printer.
Booklet: saddle-stitch imposition padded to a multiple of 4; both sides, front or back only; left or right binding.
Poster: tile scale, overlap shared by neighbouring tiles, cut marks.
Comments & forms: document, + markups, + stamps, or form fields only; annotations print only with their Print flag, drawn from their appearance streams (Algorithm 8.1).

Each source page becomes a Form XObject (its content wrapped in q/Q, plus the printable annotations); sheets place them with a clip. The result is a fresh, unencrypted, garbage-collected file (callers check the print permission).

spool talks to CUPS: printers come from lpstat -p -d (the queues) and lpstat -e (driverless destinations no queue exists for; CUPS builds a temporary one when the job arrives), jobs go to lp with copies, collation, duplex and monochrome options. The job is piped to lp on stdin and never written to a temp file, where another local user could read or swap it. Other platforms report that printing to a printer isn't available yet; the print-ready PDF can always be saved.

Not yet: Windows and web spoolers, print as image, poster labels, PostScript output, colour conversion for grayscale.