[PP1] show.setup showMediaControls survives a pptx save and reopen

PowerPoint stores Show media controls as the p14:showMediaCtrls extension inside
p:showPr (uri {2FDB2607-...}); absent means shown. Write it when hidden, read it back.

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

crates/pptx/src/read.rs

@@ -1283,6 +1283,7 @@ fn read_show(sp: &El, shows: &HashMap<String, String>) -> ShowSettings {
         without_narration: sp.bool("showNarration") == Some(false),
         without_animation: sp.bool("showAnimation") == Some(false),
         use_timings: sp.bool("useTimings").unwrap_or(true),
+        show_media_controls: sp.find("showMediaCtrls").and_then(|e| e.bool("val")).unwrap_or(true),
         ..Default::default()
     };
     if sp.child("browse").is_some() {

crates/pptx/src/write.rs

@@ -1181,6 +1181,14 @@ fn pres_props_xml(p: &Presentation) -> Vec<u8> {
     w.open0("p:penClr");
     w.val("a:srgbClr", s.pen_color.hex());
     w.close("p:penClr");
+    if !s.show_media_controls {
+        // "Show media controls" is PowerPoint's p14 extension; absent means shown.
+        w.open0("p:extLst");
+        w.open("p:ext", A::new().a("uri", "{2FDB2607-1784-4EEB-B798-7EB5836EED8A}"));
+        w.empty("p14:showMediaCtrls", A::new().a("xmlns:p14", NS_P14).a("val", 0));
+        w.close("p:ext");
+        w.close("p:extLst");
+    }
     w.close("p:showPr");
     w.close("p:presentationPr");
     w.finish()

crates/pptx/tests/it/roundtrip.rs

@@ -1969,3 +1969,12 @@ fn default_durations_match_powerpoint() {
         assert_eq!(a.4, ms, "{effect}");
     }
 }
+
+/// Show media controls is PowerPoint's `p14:showMediaCtrls` extension inside `p:showPr`.
+#[test]
+fn hidden_media_controls_survive_save_and_reopen() {
+    let mut p = Presentation::default();
+    p.show.show_media_controls = false;
+    assert!(!round(&p).show.show_media_controls);
+    assert!(round(&Presentation::default()).show.show_media_controls);
+}