test(#1199): schema degradation log must be per-PacketStore (RED)

Item 5/6. Two PacketStore instances + same warning message → only one
log emission today because schemaDegradationLogged is a package-level
sync.Map. Tests asserting the warning are order-dependent. RED.

cmd/server/schema_degradation_per_store_test.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"bytes"
+	"log"
+	"strings"
+	"testing"
+)
+
+// TestSchemaDegradationLogIsPerStore asserts that two independent
+// PacketStore instances both emit a schema-degradation warning for the
+// same message. With the (pre-#1199) package-level sync.Map, the second
+// instance silently swallows the warning — that is order-dependent test
+// pollution and is exactly what item 5/6 of #1199 calls out.
+//
+// RED: today, only the first store logs; the second is suppressed by the
+// package-level sentinel. GREEN follow-up moves the sentinel to a
+// PacketStore field so each instance has a fresh dedupe set.
+func TestSchemaDegradationLogIsPerStore(t *testing.T) {
+	var buf bytes.Buffer
+	prev := log.Writer()
+	prevFlags := log.Flags()
+	log.SetOutput(&buf)
+	log.SetFlags(0)
+	t.Cleanup(func() {
+		log.SetOutput(prev)
+		log.SetFlags(prevFlags)
+	})
+
+	const msg = "test-schema-degradation-marker-1199"
+
+	s1 := &PacketStore{}
+	s2 := &PacketStore{}
+	s1.logSchemaDegradationOnce(msg)
+	s2.logSchemaDegradationOnce(msg)
+
+	hits := strings.Count(buf.String(), msg)
+	if hits != 2 {
+		t.Fatalf("expected 2 log emissions (one per PacketStore), got %d. "+
+			"package-level sentinel pollutes across instances — move to a "+
+			"struct field. log buffer:\n%s", hits, buf.String())
+	}
+}