test(wecom): align dedupe rotation behavior and add helper tests

Match rotation semantics to prior behavior by fully resetting the dedupe map
once the size limit is exceeded, and add focused tests for duplicate detection
and boundary rotation behavior.

pkg/channels/wecom/dedupe.go

@@ -19,9 +19,9 @@ func markMessageProcessed(msgMu *sync.RWMutex, processedMsgs *map[string]bool, m
 	}
 	(*processedMsgs)[msgID] = true
 
-	// Keep the newest message marker when rotating to bound memory growth.
+	// Keep existing behavior: when over limit, reset dedupe map entirely.
 	if len(*processedMsgs) > maxEntries {
-		*processedMsgs = map[string]bool{msgID: true}
+		*processedMsgs = make(map[string]bool)
 	}
 
 	return true

pkg/channels/wecom_dedupe_test.go

@@ -0,0 +1,42 @@
+package channels
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestMarkMessageProcessed_DuplicateDetection(t *testing.T) {
+	var mu sync.RWMutex
+	processed := make(map[string]bool)
+
+	if ok := markMessageProcessed(&mu, &processed, "msg-1", 1000); !ok {
+		t.Fatalf("first message should be accepted")
+	}
+
+	if ok := markMessageProcessed(&mu, &processed, "msg-1", 1000); ok {
+		t.Fatalf("duplicate message should be rejected")
+	}
+}
+
+func TestMarkMessageProcessed_RotationClearsMapAtBoundary(t *testing.T) {
+	var mu sync.RWMutex
+	processed := make(map[string]bool)
+
+	if ok := markMessageProcessed(&mu, &processed, "msg-1", 1); !ok {
+		t.Fatalf("first message should be accepted")
+	}
+	if len(processed) != 1 {
+		t.Fatalf("expected map size 1 after first insert, got %d", len(processed))
+	}
+
+	// Inserting second unique message exceeds maxEntries and should reset map.
+	if ok := markMessageProcessed(&mu, &processed, "msg-2", 1); !ok {
+		t.Fatalf("second unique message should be accepted")
+	}
+	if len(processed) != 0 {
+		t.Fatalf("expected map to be reset after rotation, got size %d", len(processed))
+	}
+	if processed["msg-2"] {
+		t.Fatalf("expected current message marker to be cleared after rotation")
+	}
+}