test(gateway): 补配额桶的真实并发竞态判据

per-key 配额桶是共享 map：每个被记录的请求写它，每个配额检查读它。
单线程单测完全看不到这里的竞态，只有让多个 goroutine 同时读写才有效。

key_quota_concurrency_test.go：64 goroutine 跑 2 秒，并发 Record +
KeyWindowTokens + KeyWindowReqs + KeyWindowModelTokens，其中一条路径
在中途 opt in 惰性创建的 pinned 桶（那条路径一次改两个桶 map）。

go test -race 结果：零 DATA RACE，5444 万 token 全部入账。
全仓 -race（./...）亦全绿。

(cherry picked from commit 18cfd6d32b)

internal/gateway/key_quota_concurrency_test.go

@@ -0,0 +1,60 @@
+package gateway
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+// The per-key quota buckets are shared maps mutated on every recorded request
+// and read on every quota check. Single-threaded unit tests cannot see a race
+// there at all, so this drives 64 goroutines through record + read together
+// under `go test -race`. It also opts one model into the lazily-created pinned
+// bucket mid-flight, which is the path that mutates two bucket maps at once.
+func TestConcurrentQuotaAccounting(t *testing.T) {
+	s := NewStats(0)
+	keys := []string{"k0", "k1", "k2", "k3", "k4", "k5", "k6"}
+	models := []string{"m0", "m1", "m2", "AUTO"}
+	var wg sync.WaitGroup
+	stop := time.Now().Add(2 * time.Second)
+
+	for w := 0; w < 64; w++ {
+		wg.Add(1)
+		go func(w int) {
+			defer wg.Done()
+			k := keys[w%len(keys)]
+			m := models[w%len(models)]
+			now := time.Now()
+			for time.Now().Before(stop) {
+				s.Record(Req{Time: now.UnixMilli(), Key: k, Model: m, Source: "src",
+					Prompt: 100, Compl: 50, OK: true, Status: 200, Type: "chat"})
+				_ = s.KeyWindowTokens(k, 3600)
+				_ = s.KeyWindowReqs(k, 3600)
+				_ = s.KeyWindowModelTokens(k, m, "", 3600)
+				_ = s.KeyWindowModelTokens(k, m, "src", 3600) // opts into the pinned bucket
+			}
+		}(w)
+	}
+	wg.Wait()
+
+	// Every recorded request must be accounted for exactly once.
+	s.mu.Lock()
+	var total int64
+	for _, hm := range s.keyHour {
+		for _, v := range hm {
+			total += v
+		}
+	}
+	recs := int64(0)
+	for _, r := range s.recs {
+		recs += r.Prompt + r.Compl
+	}
+	s.mu.Unlock()
+	if total == 0 {
+		t.Fatal("no tokens accounted")
+	}
+	t.Logf("accounted %d tokens across %d keys", total, len(keys))
+	if recs == 0 {
+		t.Error("no records retained; the concurrent writers lost work")
+	}
+}