Fix viewport jitter when annotating with search active (#1254) (#1283)

When an annotation was added or edited, page_changed cleared search matches for the page and reset f.current to None. When the background text reload finished, refresh_find_page saw f.current.is_none() and invoked flash_match(), setting view.goto and causing the canvas viewport to jump after every drawn element.

- Preserve search state in page_changed instead of prematurely clearing matches and current match index.
- In refresh_find_page, gate flash_match() so it only jumps when no match was previously selected (e.g. initial search query), avoiding viewport jumps during background text reloads.
- Add regression test marking_while_searching_does_not_jitter_or_reset_search_state.

Fixes #1254

crates/ui-egui/src/canvas.rs

@@ -840,10 +840,6 @@ impl DocView {
         if self.selection.is_some_and(|s| s.page == page) {
             self.selection = None;
         }
-        if let Some(f) = self.find.as_mut() {
-            f.matches.retain(|(p, _)| *p != page);
-            f.current = None;
-        }
     }
 
     /// Pages drawn last frame and their screen rectangles.
@@ -916,17 +912,16 @@ impl DocView {
         f.matches.retain(|(p, _)| *p != page);
         f.matches.extend(text.find_opts(&f.case_query, f.case_sensitive, f.whole_words).into_iter().map(|r| (page, r)));
         f.matches.sort_by_key(|(p, r)| (*p, r.start));
-        f.current = match current_key {
-            Some(k) => f.matches.iter().position(|m| *m == k),
-            None => None,
-        };
+        f.current = current_key.as_ref().and_then(|k| f.matches.iter().position(|m| m == k));
         if f.current.is_none() && !f.matches.is_empty() {
             // First match at or after the page being viewed.
             let cur = self.current;
             let i = f.matches.iter().position(|(p, _)| *p >= cur).unwrap_or(0);
             f.current = Some(i);
             let (p, _) = f.matches[i];
-            self.flash_match(p);
+            if current_key.is_none() {
+                self.flash_match(p);
+            }
         }
     }
 
@@ -1548,6 +1543,11 @@ impl DocView {
                 None => {
                     log::warn!("page {} text: {}", r.request.page + 1, r.error.unwrap_or_default());
                     self.text_failed.insert(r.request.page);
+                    if let Some(f) = self.find.as_mut() {
+                        let current_key = f.current.and_then(|c| f.matches.get(c).cloned());
+                        f.matches.retain(|(p, _)| *p != r.request.page);
+                        f.current = current_key.and_then(|k| f.matches.iter().position(|m| *m == k));
+                    }
                 }
             }
             return 0;

crates/ui-egui/tests/viewer.rs

@@ -169,6 +169,63 @@ fn find_shortcuts_advance_and_retreat_matches() {
     assert_eq!(h.state().views[0].find.as_ref().unwrap().current, Some((start + n - 1) % n));
 }
 
+#[test]
+fn marking_while_searching_does_not_jitter_or_reset_search_state() {
+    let mut h = harness();
+    h.state_mut().active = Some(0);
+    h.run_steps(2);
+    h.state_mut().views[0].open_find();
+    h.state_mut().views[0].find.as_mut().unwrap().query = "page".into();
+    h.state_mut().views[0].rerun_find();
+    let deadline = std::time::Instant::now() + std::time::Duration::from_secs(20);
+    while std::time::Instant::now() < deadline {
+        h.run_steps(2);
+        std::thread::sleep(std::time::Duration::from_millis(5));
+        if h.state().views[0].find.as_ref().unwrap().matches.len() >= 15 {
+            break;
+        }
+    }
+    assert_eq!(h.state().views[0].find.as_ref().unwrap().matches.len(), 15);
+    let current_before = h.state().views[0].find.as_ref().unwrap().current;
+    assert!(current_before.is_some());
+    // Clear any pending goto from initial find
+    h.run_steps(2);
+    assert!(h.state().views[0].goto.is_none());
+
+    // User draws or marks an annotation on page 0
+    let shape = pdfcraft_engine::Shape::Ink {
+        strokes: vec![vec![[10.0, 10.0], [20.0, 20.0]]],
+    };
+    let stroke = pdfcraft_engine::Edit::AddAnnotation(pdfcraft_engine::NewAnnotation {
+        page: 0,
+        style: pdfcraft_engine::Style::default_for(&shape),
+        shape,
+        contents: String::new(),
+        author: "tester".into(),
+    });
+    h.state_mut().apply_edit(stroke);
+
+    // Right after applying the edit, search matches and current match must still be valid
+    assert_eq!(
+        h.state().views[0].find.as_ref().unwrap().current,
+        current_before,
+        "applying an annotation must not wipe current search match"
+    );
+
+    // Let the canvas process the reload
+    let reload_deadline = std::time::Instant::now() + std::time::Duration::from_secs(5);
+    while std::time::Instant::now() < reload_deadline {
+        h.run_steps(2);
+        std::thread::sleep(std::time::Duration::from_millis(5));
+        assert!(h.state().views[0].goto.is_none(), "page reload after annotation must not set goto / trigger display jitter");
+        if h.state().views[0].glyph_screen_pos(0, 0).is_some() {
+            break;
+        }
+    }
+    assert_eq!(h.state().views[0].find.as_ref().unwrap().current, current_before);
+    assert_eq!(h.state().views[0].find.as_ref().unwrap().matches.len(), 15);
+}
+
 #[test]
 fn layouts_fit_height_labels_and_system_theme() {
     use pdfcraft_ui_egui::canvas::{Fit, PageLayout};