test(channelserver): add store tests and document lock ordering

Add unit tests with race-detector coverage for QuestCache,
UserBinaryStore, and MinidataStore (18 tests covering hits, misses,
expiry, copy isolation, and concurrent access).

Document the lock acquisition order on the Server struct to prevent
future deadlocks: Server.Mutex → stagesLock → Stage → semaphoreLock.

server/channelserver/quest_cache_test.go

@@ -0,0 +1,78 @@
+package channelserver
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestQuestCache_GetMiss(t *testing.T) {
+	c := NewQuestCache(60)
+	_, ok := c.Get(999)
+	if ok {
+		t.Error("expected cache miss for unknown quest ID")
+	}
+}
+
+func TestQuestCache_PutGet(t *testing.T) {
+	c := NewQuestCache(60)
+	data := []byte{0xDE, 0xAD}
+	c.Put(1, data)
+
+	got, ok := c.Get(1)
+	if !ok {
+		t.Fatal("expected cache hit")
+	}
+	if len(got) != 2 || got[0] != 0xDE || got[1] != 0xAD {
+		t.Errorf("got %v, want [0xDE 0xAD]", got)
+	}
+}
+
+func TestQuestCache_Expiry(t *testing.T) {
+	c := NewQuestCache(0) // TTL=0 disables caching
+	c.Put(1, []byte{0x01})
+
+	_, ok := c.Get(1)
+	if ok {
+		t.Error("expected cache miss when TTL is 0")
+	}
+}
+
+func TestQuestCache_ExpiryElapsed(t *testing.T) {
+	c := &QuestCache{
+		data:   make(map[int][]byte),
+		expiry: make(map[int]time.Time),
+		ttl:    50 * time.Millisecond,
+	}
+	c.Put(1, []byte{0x01})
+
+	// Should hit immediately
+	if _, ok := c.Get(1); !ok {
+		t.Fatal("expected cache hit before expiry")
+	}
+
+	time.Sleep(60 * time.Millisecond)
+
+	// Should miss after expiry
+	if _, ok := c.Get(1); ok {
+		t.Error("expected cache miss after expiry")
+	}
+}
+
+func TestQuestCache_ConcurrentAccess(t *testing.T) {
+	c := NewQuestCache(60)
+	var wg sync.WaitGroup
+	for i := 0; i < 100; i++ {
+		wg.Add(2)
+		id := i
+		go func() {
+			defer wg.Done()
+			c.Put(id, []byte{byte(id)})
+		}()
+		go func() {
+			defer wg.Done()
+			c.Get(id)
+		}()
+	}
+	wg.Wait()
+}