Keep paragraph styles aligned in Find and Replace with line breaks

Found while testing crates/engine/src/cmd/typemenu.rs:668 (find_replace / edit_runs)

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

crates/engine/src/cmd/typemenu.rs

@@ -665,16 +665,39 @@ fn find_replace(s: &mut Session, p: &Value) -> Result<Value> {
     if total == 0 {
         return Ok(json!({ "count": 0 }));
     }
-    edit_runs::<()>(s, "Replace", &ids, |text, _| {
-        let mut out = String::with_capacity(text.len());
-        let mut last = 0;
-        for (a, b) in find_all(text, &find, mc, ww) {
-            out.push_str(&text[last..a]);
-            out.push_str(&rep);
-            last = b;
+    super::overprint::edit_counted(s, "Replace", |d| {
+        let mut changed = 0;
+        for id in &ids {
+            let Some(NodeKind::Text(t)) = d.node_mut(*id).map(|n| &mut n.kind) else { continue };
+            // Matches as (run, start, end) with offsets inside the run. Inline graphics are art, not
+            // characters to rewrite.
+            let mut hits = vec![];
+            let mut base = 0;
+            for (ri, r) in t.runs.iter().enumerate() {
+                if r.inline.is_none() {
+                    for (a, b) in find_all(&r.text, &find, mc, ww) {
+                        if r.text.get(a..b) != Some(rep.as_str()) {
+                            hits.push((ri, base + a, base + b, a, b));
+                        }
+                    }
+                }
+                base += r.text.len();
+            }
+            if hits.is_empty() {
+                continue;
+            }
+            // Last match first, so the offsets of earlier ones stay valid. The paragraph styles follow
+            // each edit, as `text.editRange` does.
+            for (ri, ta, tb, a, b) in hits.into_iter().rev() {
+                t.splice_paras(ta, tb, &rep);
+                if let Some(r) = t.runs.get_mut(ri) {
+                    r.text.replace_range(a..b, &rep);
+                }
+            }
+            changed += 1;
+            refresh_bounds(t);
         }
-        out.push_str(&text[last..]);
-        out
+        Ok(changed)
     })?;
     Ok(json!({ "count": total }))
 }

crates/engine/tests/find_replace_paras.rs

@@ -0,0 +1,44 @@
+//! `edit.findReplace` keeps per-paragraph styles lined up with the text when a find or replace
+//! string holds a line break, as `text.editRange` does.
+// Integration tests: unwrapping and panicking on failure is fine here, unlike in shipped code (AGENTS.md › Robustness).
+#![allow(clippy::unwrap_used, clippy::expect_used, clippy::panic)]
+
+use serde_json::json;
+use vectorcraft_doc::{Justify, NodeId, NodeKind};
+use vectorcraft_testkit::fixtures::{self, exec, id_of};
+
+/// "A\nB\nC" with B centred and C right-aligned.
+fn setup() -> (vectorcraft_engine::Session, NodeId) {
+    let mut s = fixtures::session_with(400.0, 300.0);
+    let id = id_of(&exec(&mut s, "text.create", json!({"x": 20, "y": 100, "text": "A\nB\nC", "size": 20})));
+    exec(&mut s, "text.setStyle", json!({"id": id.0, "start": 2, "end": 3, "justify": "center"}));
+    exec(&mut s, "text.setStyle", json!({"id": id.0, "start": 4, "end": 5, "justify": "right"}));
+    exec(&mut s, "select.none", json!({}));
+    (s, id)
+}
+
+fn state(s: &vectorcraft_engine::Session, id: NodeId) -> (String, Vec<Justify>) {
+    match &s.doc().unwrap().doc.node(id).unwrap().kind {
+        NodeKind::Text(t) => (t.plain_text(), t.paragraph_styles().iter().map(|p| p.justify).collect()),
+        _ => panic!("not text"),
+    }
+}
+
+#[test]
+fn replacement_adding_a_line_break_keeps_later_paragraph_styles() {
+    let (mut s, id) = setup();
+    assert_eq!(state(&s, id).1, [Justify::Auto, Justify::Center, Justify::Right]);
+    exec(&mut s, "edit.findReplace", json!({"find": "A", "replace": "A\nA2", "ids": [id.0]}));
+    let (text, styles) = state(&s, id);
+    assert_eq!(text, "A\nA2\nB\nC");
+    assert_eq!(styles, [Justify::Auto, Justify::Auto, Justify::Center, Justify::Right]);
+}
+
+#[test]
+fn find_text_with_a_line_break_merges_paragraphs_like_edit_range() {
+    let (mut s, id) = setup();
+    exec(&mut s, "edit.findReplace", json!({"find": "A\nB", "replace": "AB", "ids": [id.0]}));
+    let (text, styles) = state(&s, id);
+    assert_eq!(text, "AB\nC");
+    assert_eq!(styles, [Justify::Auto, Justify::Right]);
+}