tests: pin the Class II MKB gate and the primary Dolby Vision dvcC

The Class II fixture was a bare type record, which derives nothing with or without the gate;
the planted derivable MKB now derives under a pre-recorded type and not under Class II. The
primary DV track's dvcC bytes (base layer present, compatibility id 0) are asserted beside
the enhancement-layer track's.

src/aacs/derive.rs

@@ -1244,6 +1244,24 @@ mod position_recovery_tests {
         }
     }
 
+    // The Class II gate is what refuses the derivation: the planted MKB derives its media key
+    // as a pre-recorded block, and the same records under the Class II type derive nothing.
+    #[test]
+    fn a_class_ii_type_refuses_an_otherwise_derivable_mkb() {
+        let p = plant_mkb();
+        let pk = aesg3(&p.dkey, 1);
+        assert_eq!(
+            derive_media_key_from_pk(&p.mkb, &[pk]),
+            Some(p.mk),
+            "control"
+        );
+        let mut class2 = p.mkb.clone();
+        class2[4..8].copy_from_slice(&MKB_TYPE_10_CLASS_II.to_be_bytes());
+        assert_eq!(mkb_type(&class2), Some(MkbType::ClassII));
+        assert!(MkbTables::parse(&class2).is_none());
+        assert_eq!(derive_media_key_from_pk(&class2, &[pk]), None);
+    }
+
     /// Sanity-check the fixture itself before anything is asserted about the
     /// functions under test: an MKB the parser cannot read would make every
     /// "returns None" body look correct.

src/mux/mkv.rs

@@ -7782,6 +7782,16 @@ mod tests {
         assert_eq!(MkvTrack::video(&v).dv_config, Some(want));
     }
 
+    // A primary DV track carries its own base layer: rpu=1 el=1 bl=1, compatibility id 0.
+    #[test]
+    fn dolby_vision_primary_track_dvcc_bytes() {
+        let mut v = uhd_video(HdrFormat::DolbyVision, ColorSpace::Bt2020);
+        v.frame_rate = crate::disc::FrameRate::F23_976;
+        let mut want = vec![0u8; 24];
+        want[..5].copy_from_slice(&[0x01, 0x00, 0x0E, 0x37, 0x00]);
+        assert_eq!(MkvTrack::video(&v).dv_config, Some(want));
+    }
+
     // dvcC level follows the 2160p frame rate; unknown rate keeps the 2160p24 level.
     #[test]
     fn dv_level_follows_the_frame_rate() {