Reject regressed stream PTS before submitting it to the decoder

tools/chatgui-android/app/src/test/java/com/utun/chat/data/StreamDecodePumpTest.kt

@@ -106,4 +106,11 @@ class StreamDecodePumpTest {
         assertTrue(pump.ended); assertEquals(0, pump.inflight); assertEquals(-1L, pump.oldestSubmittedPts)
         assertEquals(1, released); pump.checkProgress(30_000_000, true)
     }
+
+    @Test fun regressedInputPtsIsRejectedBeforeTheCodecReceivesIt() {
+        val codec = Codec(1); codec.pump.offer(Frame(100), 0); codec.pump.step(100, 0)
+        codec.pump.offer(Frame(100), 1)
+        assertThrows(IllegalStateException::class.java) { codec.pump.step(100, 1) }
+        assertTrue(codec.queued.isEmpty()); assertEquals(1L, codec.pump.inputCount)
+    }
 }