Keep combining marks inside spell-check words

Found while testing crates/engine/src/spell.rs:693 (paragraph_words, the `inside` closure)

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

crates/engine/src/spell.rs

@@ -709,7 +709,8 @@ pub fn paragraph_words(p: &deckcraft_model::Paragraph, default: &str) -> Vec<Wor
         chars.extend(r.content().chars().map(|c| (c, ri)));
     }
     let lang_of = |ri: usize| p.runs.get(ri).and_then(|r| r.props.lang.clone()).filter(|l| !l.is_empty()).unwrap_or_else(|| default.to_string());
-    let inside = |c: char| c.is_alphanumeric() || c == '\'' || c == '’' || c == '-';
+    // Combining marks (decomposed accents) belong to the letter before them.
+    let inside = |c: char| c.is_alphanumeric() || deckcraft_model::words::is_combining_mark(c) || c == '\'' || c == '’' || c == '-';
     let mut out = vec![];
     let mut i = 0;
     while i < chars.len() {
@@ -725,7 +726,7 @@ pub fn paragraph_words(p: &deckcraft_model::Paragraph, default: &str) -> Vec<Wor
         while a < b && !chars[a].0.is_alphanumeric() {
             a += 1;
         }
-        while b > a && !chars[b - 1].0.is_alphanumeric() {
+        while b > a && !chars[b - 1].0.is_alphanumeric() && !deckcraft_model::words::is_combining_mark(chars[b - 1].0) {
             b -= 1;
         }
         let text: String = chars[a..b].iter().map(|c| c.0).collect();
@@ -819,6 +820,13 @@ SFX D Y 1\nSFX D 0 ed/S .\n";
         Dictionary::parse(AFF.as_bytes(), DIC.as_bytes())
     }
 
+    #[test]
+    fn nfd_word_not_split() {
+        let p = deckcraft_model::Paragraph::new("Das na\u{ef}ve Caf\u{e9} und cafe\u{301} na\u{308}ive");
+        let w: Vec<String> = paragraph_words(&p, "en-US").into_iter().map(|w| w.text).collect();
+        assert_eq!(w, ["Das", "na\u{ef}ve", "Caf\u{e9}", "und", "cafe\u{301}", "na\u{308}ive"]);
+    }
+
     #[test]
     fn curly_apostrophe_matches_ascii_entry() {
         let d = Dictionary::parse(AFF.as_bytes(), "2\ndon't\nwork\n".as_bytes());

crates/model/src/words.rs

@@ -90,11 +90,16 @@ fn base_class(c: char) -> Class {
         c if c.is_alphanumeric() => Class::Word,
         c if is_symbol(c) => Class::Symbol,
         // A combining mark with no base (or any other mark) stays with letters.
-        '\u{300}'..='\u{36f}' | '\u{1ab0}'..='\u{1aff}' | '\u{1dc0}'..='\u{1dff}' | '\u{20d0}'..='\u{20ff}' | '\u{fe20}'..='\u{fe2f}' => Class::Word,
+        c if is_combining_mark(c) => Class::Word,
         _ => Class::Punct,
     }
 }
 
+/// Whether `c` is a combining mark (a decomposed accent), which belongs to the letter before it.
+pub fn is_combining_mark(c: char) -> bool {
+    matches!(c, '\u{300}'..='\u{36f}' | '\u{1ab0}'..='\u{1aff}' | '\u{1dc0}'..='\u{1dff}' | '\u{20d0}'..='\u{20ff}' | '\u{fe20}'..='\u{fe2f}')
+}
+
 fn clusters(text: &str) -> Vec<Cluster> {
     let mut out: Vec<Cluster> = Vec::new();
     let mut firsts: Vec<char> = Vec::new();