M2: a page without its own /MediaBox inherits its parent's before the US Letter fallback, tested (view.render-pages)

Tests only: the page model and the renderer size a page whose /Pages parent carries the
/MediaBox (ISO 32000-2 §7.7.3.4) at that box, 300 x 400, not US Letter.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pq7HyCHD1R3rywQBPCHXZA

crates/model/src/lib.rs

@@ -272,6 +272,20 @@ mod tests {
         assert_eq!(p.display_size(&d), (612.0, 792.0));
     }
 
+    /// A page without a `/MediaBox` of its own inherits its `/Pages` parent's (ISO 32000-2
+    /// §7.7.3.4): only a box neither has falls back to US Letter.
+    #[test]
+    fn a_page_inherits_its_parents_media_box_before_falling_back_to_letter() {
+        let d = doc_from(&[
+            "<< /Type /Catalog /Pages 2 0 R >>".to_string(),
+            "<< /Type /Pages /Kids [3 0 R] /Count 1 /MediaBox [0 0 300 400] >>".to_string(),
+            "<< /Type /Page /Parent 2 0 R >>".to_string(),
+        ]);
+        let p = &pages(&d)[0];
+        assert_eq!(p.crop(&d), [0.0, 0.0, 300.0, 400.0]);
+        assert_eq!(p.display_size(&d), (300.0, 400.0));
+    }
+
     /// A `/MediaBox` without area (`[0 0 0 0]`) is US Letter too, as the renderer draws it.
     #[test]
     fn a_page_whose_media_box_has_no_area_is_letter() {

crates/render/src/raster/tests.rs

@@ -5538,6 +5538,27 @@ trailer << /Root 1 0 R >>
     }
 }
 
+/// A page without a `/MediaBox` of its own inherits its `/Pages` parent's (ISO 32000-2 §7.7.3.4)
+/// before any fallback: rendered and inspected at 300 × 400, not US Letter.
+#[test]
+fn a_page_inherits_its_parents_media_box_before_falling_back_to_letter() {
+    let pdf = b"%PDF-1.4
+1 0 obj << /Type /Catalog /Pages 2 0 R >> endobj
+2 0 obj << /Type /Pages /Kids [3 0 R] /Count 1 /MediaBox [0 0 300 400] >> endobj
+3 0 obj << /Type /Page /Parent 2 0 R /Contents 4 0 R >> endobj
+4 0 obj << /Length 25 >> stream
+0 0 1 rg 10 10 50 50 re f
+endstream endobj
+trailer << /Root 1 0 R >>
+%%EOF"
+        .to_vec();
+    let page = render_first_page(pdf.clone());
+    assert_eq!((page.width, page.height), (300, 400), "rendered size");
+    assert_eq!(rgb_at(&page.rgba, page.width as usize, 30, 400 - 30), [0, 0, 255]);
+    let info = crate::inspect(Arc::new(pdf), None).expect("inspect");
+    assert_eq!((info.pages[0].width, info.pages[0].height), (300.0, 400.0), "inspected size");
+}
+
 /// A page whose content expands far beyond its compressed stream stops at the expansion budget,
 /// which is 64 times the compressed size and at least `MAX_DECODED_STREAM`, and the page says so.
 #[test]