Reject signs and exponents in ExportSize::parse

Found while testing crates/doc/src/props.rs:1394 (ExportSize::parse, `num.parse::<f64>()`)

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

crates/doc/src/props.rs

@@ -1399,6 +1399,10 @@ impl ExportSize {
             Some((i, c)) if c.is_ascii_alphabetic() => (s.get(..i)?.trim(), Some(c)),
             _ => (s.as_str(), None),
         };
+        // Plain decimal only: no sign, exponent, "inf" or "nan".
+        if !num.bytes().all(|b| b.is_ascii_digit() || b == b'.') {
+            return None;
+        }
         let value: f64 = num.parse().ok()?;
         match unit {
             None | Some('x') => ExportSize::Scale { value },

crates/engine/src/import_export_tests.rs

@@ -283,7 +283,7 @@ fn export_sizes_parse_and_label() {
         assert_eq!(ExportSize::parse(text), Some(want), "{text}");
         assert_eq!(ExportSize::parse(&want.label()), Some(want));
     }
-    for bad in ["", "x", "0x", "-1x", "NaNx", "infx", "65x", "20000w", "2q", "2xx"] {
+    for bad in ["", "x", "0x", "-1x", "NaNx", "infx", "65x", "20000w", "2q", "2xx", "+2x", "+512w", "2e0x", "2E0x", "+0.5x"] {
         assert_eq!(ExportSize::parse(bad), None, "{bad}");
     }
     let e = |size, suffix: &str, format| ExportSetting { size, suffix: suffix.into(), format, ..Default::default() };