docs: record frag_send and the current testing state

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

echolot-app/core-engine/src/test/kotlin/app/echo_lot/engine/LiveDownstreamTest.kt

@@ -44,7 +44,9 @@ class LiveDownstreamTest {
         for (t in tests) println("${t.type}  status=${t.status}  metrics=${t.metrics}")
         for (f in findings) println("finding ${f.code} [${f.severity}] ${f.title}")
 
-        assertEquals(3, tests.size, "expected pmtud_down, frag_delivery and a downstream train")
+        // Assert on what is present, not on how many: adding a measurement should not be a
+        // test edit. (It was, once — hence the note.)
+        assertTrue(tests.size >= 3, "expected at least the three downstream tests, got ${tests.size}")
         val byType = tests.associateBy { it.type }
 
         val pmtud = assertNotNull(byType[TestType.MTU_PMTUD_DOWN], "no mtu.pmtud_down test")
@@ -58,6 +60,17 @@ class LiveDownstreamTest {
         val frag = assertNotNull(byType[TestType.MTU_FRAG_DELIVERY], "no mtu.frag_delivery test")
         assertNotNull(frag.metrics?.get("largest_delivered_bytes"))
 
+        // Fragment ordering runs only when fragments arrive at all, and only against a server
+        // that can craft them — so it is checked when present rather than required.
+        byType[TestType.MTU_FRAG_ORDERING]?.let { fo ->
+            val m = fo.metrics?.toString() ?: ""
+            println("fragment ordering: ${fo.status} $m")
+            if (fo.status != TestStatus.UNSUPPORTED) {
+                assertTrue(m.contains("in_order"), "no per-ordering result: $m")
+                assertTrue(m.contains("reversed"), "reversed ordering was never attempted: $m")
+            }
+        }
+
         val train = assertNotNull(byType[TestType.TRAIN_UDP_DOWNSTREAM], "no downstream train")
         assertNotNull(train.evidence, "a train without columnar evidence is not recomputable")
         val received = train.metrics?.get("received")?.toString()?.toIntOrNull() ?: 0