Avoid slicing text inside multi-byte characters

Right-to-left line reordering walked each atom's byte range and sliced the
line at every byte, panicking when a neutral multi-byte character such as a
guillemet preceded the first strong character. Walk characters instead.

FIND/FINDALL located the REPLACE keyword in a Unicode-uppercased copy and
sliced the original with that offset; uppercasing can change byte length
(dotless i, ligatures). Uppercase ASCII only, which keeps offsets aligned.
FILLET and CHAMFER inline R/D shorthands now test the original text before
slicing past the first character.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/app/commands/inquiry.rs

@@ -1302,8 +1302,9 @@ impl OpenCADStudio {
                 let all_mode = cmd.starts_with("FINDALL");
                 let rest = cmd.split_once(' ').map(|(_, r)| r.trim()).unwrap_or("");
 
-                // Split at " REPLACE " keyword (case-insensitive)
-                let (search, replacement) = if let Some(pos) = rest.to_uppercase().find(" REPLACE ")
+                // Split at " REPLACE " keyword (case-insensitive). ASCII case
+                // mapping keeps byte offsets valid for slicing `rest`.
+                let (search, replacement) = if let Some(pos) = rest.to_ascii_uppercase().find(" REPLACE ")
                 {
                     (&rest[..pos], Some(rest[pos + 9..].trim()))
                 } else {
@@ -2386,3 +2387,20 @@ mod align_selected_bounds_tests {
         assert_eq!(line_start_x(&app, b), 2.0, "b must keep its offset from a, not collapse onto it");
     }
 }
+
+#[cfg(test)]
+mod find_replace_command_tests {
+    use super::*;
+
+    /// Unicode case mapping can change a string's byte length (`ı` uppercases
+    /// to `I`), so the REPLACE keyword split must not slice with offsets
+    /// taken from a case-mapped copy.
+    #[test]
+    fn find_replace_accepts_search_text_whose_case_mapping_changes_length() {
+        for cmd in ["FIND ı REPLACE x", "FINDALL fi REPLACE fi", "FIND ʼn replace n"] {
+            let mut app = OpenCADStudio::new_for_test();
+            let i = app.active_tab;
+            let _ = app.dispatch_inquiry(cmd, i);
+        }
+    }
+}