Never crash: Fix export size panic for very long strips

Apply the 1 px and 65535 px bounds in turn instead of clamping between bounds that can cross.

crates/engine/src/export.rs

@@ -131,8 +131,9 @@ impl Resize {
             ResizeMode::Percent => v / 100.0,
         };
         let k = if self.dont_enlarge { k.min(1.0) } else { k };
-        // at least one pixel, at most the encoders' 65535 limit
-        k.clamp(1.0 / short, 65_535.0 / long)
+        // at least one pixel, at most the encoders' 65535 limit; the limit wins for a photo more
+        // than 65535 times as long as it is short (where `clamp` would panic: min above max)
+        k.max(1.0 / short).min(65_535.0 / long)
     }
 
     /// Output size for a `w × h` (cropped, full-resolution) photo.
@@ -2783,6 +2784,33 @@ mod tests {
         }
     }
 
+    /// A photo more than 65535 times as long as it is short (a 70000 × 1 strip) made `scale`
+    /// clamp with its lower bound above its upper one, which panics, in the export and in the
+    /// Export dialog's preview on the UI thread. The encoders' limit wins, the short edge keeps a
+    /// pixel.
+    #[test]
+    fn resize_survives_photos_too_long_for_the_encoders() {
+        let modes = [
+            json!({"longEdge": 2000}),
+            json!({"shortEdge": 1}),
+            json!({"width": 500, "height": 500}),
+            json!({"megapixels": 1}),
+            json!({"percent": 50}),
+            json!({"percent": 1000, "dontEnlarge": false}),
+        ];
+        for p in modes {
+            for (w, h) in [(70_000.0, 1.0), (1.0, 70_000.0), (1e9, 3.0), (65_536.0, 1.0)] {
+                let r = ExportOptions::from_json(&p).resize.unwrap();
+                let (ow, oh) = r.apply(w, h);
+                assert!((1..=65_535).contains(&ow) && (1..=65_535).contains(&oh), "{p} on {w}×{h}: {ow}×{oh}");
+                assert!(r.scale(w, h).is_finite());
+            }
+        }
+        // (a short edge under a pixel would be scaled up to one, which the limit then caps)
+        assert_eq!(Resize::long_edge(2000).apply(70_000.0, 1.0), (65_535, 1));
+        assert_eq!(Resize::long_edge(2000).apply(1.0, 70_000.0), (1, 65_535));
+    }
+
     /// A flat field of a saturated green inside Display P3 but outside sRGB, rendered into `space`.
     fn p3_green(space: OutputSpace) -> Rgba8 {
         use lightcraft_color::{DISPLAY_P3, REC2020};

docs/whats-new.md

@@ -2,6 +2,10 @@
 
 ## 2026-10-13
 
+### Reliability
+- Exporting a photo more than 65,535 times as long as it is wide (a one-pixel strip), or opening the Export dialog's
+  watermark preview for it, no longer crashes LightCraft; the export is capped at the encoders' 65,535 pixels.
+
 ### Slider drags on large raws
 - Dragging a slider no longer re-renders the edited photo's filmstrip thumbnail on every frame; it follows once you
   let go. On a 64 MP raw the first of those renders decoded the whole file again, which held up the loupe's