M6: test that a radio group with /PCOn items saves the clicked button's item and reopens on it

Round trip through the session for the static radio fixture with /PCOn
items 1 2 next to /Opt [(1) (2)] and position states /0 /1: a click on
either button saves that button's own item to the datasets, reopening
turns the same button on with nothing rewritten, and taking the XFA out
notes no lost data. With radio_dataset_value as before dbea0793e the
second button saves "1" (left: Some("1"), right: Some("2")).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pq7HyCfwzyRXj4VfQAVVdv

crates/engine/src/tests.rs

@@ -6170,6 +6170,35 @@ fn stripping_xfa_takes_a_radio_items_pcon_as_the_fields_value() {
     assert_eq!(lost(&s, id), Vec::<String>::new());
 }
 
+/// A radio group whose buttons carry `/PCOn` items `1` `2` next to `/Opt [(1) (2)]` and on
+/// states named by position (`/0`, `/1`): a click on either button saves that button's own item
+/// to the datasets, reopening turns the same button on with nothing rewritten, and taking the XFA
+/// out notes no lost data. The state `/1` used to match the first button's item `1`, so the
+/// second button saved `1` and came back as the first.
+#[test]
+fn a_radio_group_with_pcon_items_saves_and_reopens_the_clicked_button() {
+    let lang = "form1[0].page1[0].lang[0]";
+    let data_of = |bytes: Arc<Vec<u8>>| {
+        let cos = pdfcraft_cos::Document::open(bytes).unwrap();
+        let data = pdfcraft_xfa::parse_datasets(&pdfcraft_xfa::read_packets(&cos).unwrap().unwrap().xdp).unwrap();
+        data.text_at(&pdfcraft_xfa::som_to_path(lang)).map(str::to_owned)
+    };
+    let value = |s: &Session, id: DocId| s.get(id).unwrap().form.iter().find(|f| f.name == lang).unwrap().value.clone();
+    let form = Arc::new(pdfcraft_xfa::fixtures::static_radio_shell_with_pcon("<form1><page1><lang/></page1></form1>", ["1", "2"]));
+    let mut s = Session::new().with_clock(|| 1_700_000_000);
+    for (state, item) in [("0", "1"), ("1", "2")] {
+        let id = s.open("blank.pdf", None, form.clone(), None).unwrap();
+        s.apply(id, Edit::SetFieldValue { name: lang.into(), value: FieldValue::Radio(Some(state.into())) }).unwrap();
+        let saved = s.save_bytes(id).unwrap();
+        assert_eq!(data_of(saved.clone()).as_deref(), Some(item), "clicked {state}");
+        let again = s.open("again.pdf", None, saved, None).unwrap();
+        assert_eq!(value(&s, again), [state], "clicked {state}");
+        assert!(!s.get(again).unwrap().info.warnings.iter().any(|w| w.contains("taken from this form's XFA data")), "clicked {state}");
+        s.apply(again, Edit::XfaToStatic).unwrap();
+        assert!(!s.get(again).unwrap().info.warnings.iter().any(|w| w.contains("held a value other than the form's XFA data")), "clicked {state}");
+    }
+}
+
 /// A static XFA form whose values are only in its datasets takes every one on opening, as
 /// filling the fields one at a time would leave it: values, appearances and the note; a
 /// read-only field keeps its own value.