Fix empty Feishu image messages

server/internal/integrations/lark/feishu_channel_test.go

@@ -189,6 +189,23 @@ func TestChannelMessageFromLark_NormalizesAndStashesRaw(t *testing.T) {
 	}
 }
 
+func TestChannelMessageFromLark_ImageKeepsPlaceholder(t *testing.T) {
+	cm := channelMessageFromLark(InboundMessage{
+		MessageID:   "om_image",
+		ChatID:      "oc",
+		ChatType:    ChatTypeP2P,
+		Body:        "[Image]",
+		MessageType: "image",
+	})
+
+	if cm.Type != channel.MsgTypeImage {
+		t.Fatalf("image must normalize to image, got %q", cm.Type)
+	}
+	if cm.Text != "[Image]" {
+		t.Fatalf("image placeholder lost during normalization: %q", cm.Text)
+	}
+}
+
 func TestChannelMsgType(t *testing.T) {
 	cases := map[string]channel.MsgType{
 		"":              channel.MsgTypeText,

server/internal/integrations/lark/ws_frame_decoder.go

@@ -91,16 +91,20 @@ func (d *LarkJSONFrameDecoder) Decode(payload []byte, inst Installation) (Inboun
 		botUnionID = inst.BotUnionID.String
 	}
 
-	// text + post are flattened synchronously here (no external calls —
-	// the decoder must stay fast and dependency-free). merge_forward
-	// leaves Body empty: it needs an HTTP round-trip to expand and is
-	// handled downstream by the enricher, which keys off MessageType.
-	// Other types (image, file, …) also leave Body empty in this MVP;
-	// attachment ingestion is a separate issue.
+	// All directly renderable types are flattened synchronously here (no
+	// external calls — the decoder must stay fast and dependency-free).
+	// Media messages become stable placeholders such as [Image], so an
+	// image-only event never lands in chat history as an empty message.
+	// merge_forward alone leaves Body empty: it needs an HTTP round-trip to
+	// expand and is handled downstream by the enricher.
 	switch evt.Message.MessageType {
 	case "text", "post":
 		msg.Body = resolveMentions(flattenContent(evt.Message.MessageType, evt.Message.Content),
 			evt.Message.Mentions, inst.BotOpenID, botUnionID)
+	case "merge_forward":
+		// Expanded by InboundEnricher.
+	default:
+		msg.Body = flattenContent(evt.Message.MessageType, evt.Message.Content)
 	}
 
 	// Snapshot the user's own text as the command source BEFORE any

server/internal/integrations/lark/ws_frame_decoder_test.go

@@ -429,7 +429,7 @@ func TestLarkJSONFrameDecoderMessageContentEmptyOnInvalidContentJSON(t *testing.
 	}
 }
 
-func TestLarkJSONFrameDecoderNonTextMessageHasEmptyBody(t *testing.T) {
+func TestLarkJSONFrameDecoderImageMessageHasPlaceholderBody(t *testing.T) {
 	t.Parallel()
 	raw := []byte(`{
 		"type":"event_callback",
@@ -443,8 +443,8 @@ func TestLarkJSONFrameDecoderNonTextMessageHasEmptyBody(t *testing.T) {
 	if err != nil || !ok {
 		t.Fatalf("ok=%v err=%v", ok, err)
 	}
-	if msg.Body != "" {
-		t.Errorf("Body = %q; non-text messages should have empty body in MVP", msg.Body)
+	if msg.Body != "[Image]" {
+		t.Errorf("Body = %q; want [Image]", msg.Body)
 	}
 	if msg.MessageID == "" {
 		t.Error("MessageID should still be populated for non-text events")