Reject unsupported handout perPage values in file.export

Found while testing crates/engine/src/cmd/file.rs:362 (pdf_options) with crates/pdf/src/lib.rs:364-371 (handout_boxes)

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/file.rs

@@ -359,7 +359,13 @@ pub fn pdf_options(p: &Value, count: usize) -> Result<deckcraft_pdf::PdfOptions>
     let mut o = deckcraft_pdf::PdfOptions { layout: deckcraft_pdf::PageLayout::Slides, ..Default::default() };
     o.layout = match str_param(p, "layout").unwrap_or("slides") {
         "notes" => deckcraft_pdf::PageLayout::Notes,
-        "handouts" => deckcraft_pdf::PageLayout::Handouts { per_page: usize_param(p, "perPage").unwrap_or(6).clamp(1, 9) as u8 },
+        "handouts" => {
+            let per_page = usize_param(p, "perPage").unwrap_or(6);
+            if ![1, 2, 3, 4, 6, 9].contains(&per_page) {
+                return Err(bad("file.export", format!("perPage {per_page} isn't one of 1, 2, 3, 4, 6, 9")));
+            }
+            deckcraft_pdf::PageLayout::Handouts { per_page: per_page as u8 }
+        }
         _ => deckcraft_pdf::PageLayout::Slides,
     };
     o.dpi = f64_or(p, "dpi", o.dpi).clamp(36.0, 600.0);

crates/engine/src/tests.rs

@@ -2410,6 +2410,19 @@ fn pdf_options_take_paper_and_orientation() {
     assert!(cmd::file::pdf_options(&json!({"orientation": "sideways"}), 1).is_err());
 }
 
+/// Handout `perPage` accepts only 1, 2, 3, 4, 6 and 9; anything else is an error, not a 9-up page.
+#[test]
+fn pdf_options_reject_unsupported_per_page() {
+    for n in [1, 2, 3, 4, 6, 9] {
+        let o = cmd::file::pdf_options(&json!({"layout": "handouts", "perPage": n}), 1).unwrap();
+        assert!(matches!(o.layout, deckcraft_pdf::PageLayout::Handouts { per_page } if per_page as usize == n));
+    }
+    for n in [0, 5, 7, 8, 10] {
+        let e = cmd::file::pdf_options(&json!({"layout": "handouts", "perPage": n}), 1).unwrap_err();
+        assert!(e.to_string().contains("1, 2, 3, 4, 6, 9"), "perPage {n}: {e}");
+    }
+}
+
 #[test]
 fn shape_line_sets_compound_and_arrow_sizes() {
     // The Format Shape pane's Line page: compound type, arrowheads and their sizes.