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/minidata_store_test.go

@@ -0,0 +1,57 @@
+package channelserver
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestMinidataStore_GetMiss(t *testing.T) {
+	s := NewMinidataStore()
+	_, ok := s.Get(1)
+	if ok {
+		t.Error("expected miss for unknown charID")
+	}
+}
+
+func TestMinidataStore_SetGet(t *testing.T) {
+	s := NewMinidataStore()
+	data := []byte{0xAA, 0xBB}
+	s.Set(42, data)
+
+	got, ok := s.Get(42)
+	if !ok {
+		t.Fatal("expected hit")
+	}
+	if len(got) != 2 || got[0] != 0xAA {
+		t.Errorf("got %v, want [0xAA 0xBB]", got)
+	}
+}
+
+func TestMinidataStore_Overwrite(t *testing.T) {
+	s := NewMinidataStore()
+	s.Set(1, []byte{0x01})
+	s.Set(1, []byte{0x02})
+
+	got, _ := s.Get(1)
+	if got[0] != 0x02 {
+		t.Error("overwrite should replace previous value")
+	}
+}
+
+func TestMinidataStore_ConcurrentAccess(t *testing.T) {
+	s := NewMinidataStore()
+	var wg sync.WaitGroup
+	for i := uint32(0); i < 100; i++ {
+		wg.Add(2)
+		charID := i
+		go func() {
+			defer wg.Done()
+			s.Set(charID, []byte{byte(charID)})
+		}()
+		go func() {
+			defer wg.Done()
+			s.Get(charID)
+		}()
+	}
+	wg.Wait()
+}