test(jitter): seq_before wraparound + buffer overflow/resync

Add unit tests for the jitter buffer's untested pure logic: seq_before's
wrapping u32 comparison — basic ordering, the u32::MAX→0 forward wrap, and
the exact < (1<<31) half-range tipping point (0x7FFF_FFFF before, 0x8000_0000
not) — and insert's MAX_BUFFERED_FRAMES overflow path (caps depth, drops the
oldest frame, resyncs the playout head next_seq to the new front). Tests-only;
no production change.

Implemented by Gemini (junior implementer), reviewed and verified by senior
(cargo build + clippy --all-targets + cargo test all green).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/core/jitter.rs

@@ -189,4 +189,38 @@ mod tests {
         jb.insert(5, frame(&mut enc, 600));
         assert_eq!(jb.packets.len(), 1); // only seq 7 remains buffered
     }
+
+    #[test]
+    fn test_seq_before_ordering() {
+        // Basic ordering
+        assert!(seq_before(0, 1));
+        assert!(!seq_before(1, 0));
+        assert!(!seq_before(5, 5));
+        assert!(seq_before(100, 101));
+        assert!(!seq_before(101, 100));
+
+        // Wraparound
+        assert!(seq_before(u32::MAX, 0));
+        assert!(!seq_before(0, u32::MAX));
+
+        // Half-range boundary
+        assert!(seq_before(0, 0x7FFF_FFFF));
+        assert!(!seq_before(0, 0x8000_0000));
+    }
+
+    #[test]
+    fn test_jitter_buffer_overflow_resync() {
+        let mut jb = JitterBuffer::new().unwrap();
+        assert!(jb.next_seq.is_none());
+
+        let count = MAX_BUFFERED_FRAMES + 1;
+        for seq in 0..count {
+            jb.insert(seq as u32, vec![0u8]);
+        }
+
+        assert_eq!(jb.packets.len(), MAX_BUFFERED_FRAMES);
+        assert!(!jb.packets.contains_key(&0));
+        assert_eq!(jb.next_seq, Some(1));
+    }
 }
+