Never crash: algo pyramids and ui-egui parity without expect (#40)

Three remaining expect() sites in files no open PR touches:
algo::inpaint::complete and algo::pyramid::gaussian loop with while-let
instead of levels.last().expect(), and ui-egui parity::compute indexes
the menu it just pushed instead of last_mut().expect().

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/algo/src/inpaint.rs

@@ -358,8 +358,7 @@ pub fn complete(w: usize, h: usize, ch: usize, img: &[f32], hole: &[bool], p: &C
     let mut levels = vec![Level { w, h, img: img.to_vec(), hole: hole.to_vec() }];
     let mut ext = (bx1 - bx0).max(by1 - by0);
     let mut exts = vec![ext];
-    loop {
-        let l = levels.last().expect("non-empty");
+    while let Some(l) = levels.last() {
         if ext <= 2 * psz || l.w / 2 < 3 * psz || l.h / 2 < 3 * psz {
             break;
         }

crates/algo/src/pyramid.rs

@@ -90,7 +90,7 @@ pub fn expand(l: &Level, ch: usize, w: usize, h: usize) -> Vec<f32> {
 pub fn gaussian(w: usize, h: usize, ch: usize, px: &[f32], levels: usize) -> Vec<Level> {
     let mut out = vec![Level { w, h, px: px.to_vec() }];
     while out.len() < levels.max(1) {
-        let last = out.last().expect("non-empty");
+        let Some(last) = out.last() else { break };
         if last.w <= 1 && last.h <= 1 {
             break;
         }

crates/ui-egui/src/parity.rs

@@ -62,13 +62,14 @@ pub fn compute() -> Parity {
             continue;
         }
         let top = path.first().copied().unwrap_or("?");
-        let m = match menus.iter().position(|m| m.menu == top) {
-            Some(i) => &mut menus[i],
+        let i = match menus.iter().position(|m| m.menu == top) {
+            Some(i) => i,
             None => {
                 menus.push(MenuParity { menu: top.to_string(), live: 0, total: 0, missing: Vec::new() });
-                menus.last_mut().expect("just pushed")
+                menus.len() - 1
             }
         };
+        let Some(m) = menus.get_mut(i) else { continue };
         m.total += 1;
         if is_live(id) {
             m.live += 1;