feat(loadtest): sync add real 500-session capacity harness

internal/store/redisstore/ratelimit_test.go

@@ -0,0 +1,32 @@
+package redisstore
+
+import "testing"
+
+func TestDecodeRateLimitIncrementResultAcceptsPTTLBoundary(t *testing.T) {
+	count, ttlMillis, err := decodeRateLimitIncrementResult([]interface{}{int64(7), int64(0)})
+	if err != nil {
+		t.Fatalf("decode zero PTTL: %v", err)
+	}
+	if count != 7 || ttlMillis != 0 {
+		t.Fatalf("decoded count=%d ttl=%d, want 7/0", count, ttlMillis)
+	}
+}
+
+func TestDecodeRateLimitIncrementResultRejectsInvalidShape(t *testing.T) {
+	tests := []struct {
+		name  string
+		value any
+	}{
+		{name: "wrong type", value: "7,1"},
+		{name: "wrong length", value: []interface{}{int64(7)}},
+		{name: "zero count", value: []interface{}{int64(0), int64(1)}},
+		{name: "negative ttl", value: []interface{}{int64(7), int64(-1)}},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if _, _, err := decodeRateLimitIncrementResult(test.value); err == nil {
+				t.Fatal("expected decode error")
+			}
+		})
+	}
+}