Tagged Text: decode only the escapes we write; other backslashes stay literal

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

crates/textimport/src/tagged.rs

@@ -37,14 +37,20 @@ fn escape_value(v: &str) -> String {
     out
 }
 
-/// A tag value with backslash escapes removed.
+/// A tag value with the escapes `escape_value` writes (`\\`, `\<`, `\>`) decoded. Any other
+/// backslash, including a trailing one, stays literal, as older files and InDesign's `\:` expect.
 fn unescape_value(v: &str) -> String {
     let mut out = String::with_capacity(v.len());
-    let mut it = v.chars();
+    let mut it = v.chars().peekable();
     while let Some(c) = it.next() {
-        match c {
-            '\\' => out.extend(it.next()),
-            c => out.push(c),
+        if c == '\\'
+            && let Some(&n) = it.peek()
+            && matches!(n, '\\' | '<' | '>')
+        {
+            out.push(n);
+            it.next();
+        } else {
+            out.push(c);
         }
     }
     out
@@ -312,6 +318,15 @@ mod tests {
         }
     }
 
+    /// A backslash that isn't one of our escapes (older files, InDesign's `\:`) stays literal.
+    #[test]
+    fn unknown_backslashes_in_style_names_stay_literal() {
+        assert_eq!(unescape_value(r"x\y"), r"x\y");
+        assert_eq!(unescape_value(r"a\:b"), r"a\:b");
+        assert_eq!(unescape_value("end\\"), "end\\");
+        assert_eq!(unescape_value(r"\<a\>\\"), r"<a>\");
+    }
+
     #[test]
     fn tagged_text_round_trips() {
         let src = "<ASCII-WIN>\r\n<Version:7>\r\n<ParaStyle:Head>Caf<0x00E9> \\<1\\>\r\n<ParaStyle:Body>A <CharStyle:Em>word<CharStyle:> and <cSize:18.000000>big<cSize:> text";