diff --git a/AGENTS.md b/AGENTS.md
index 4b7903b2..7e478246 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -28,11 +28,31 @@ deploy/       # Deployment artifacts
   quickstart/ # One-shot local/UAT Compose stack (PG+pgvector+Redis+Meilisearch+Mailhog)
   fluentd/    # Log shipping config
 docs/         # Project documentation (architecture, requirements, plans, reports)
+  chatwoot/   # Upstream Chatwoot source snapshot; primary behavioral reference
 ```
 
 The **Go module root is `backend/`** — run all `go` commands from there.
 Build context for Docker is the **repository root** (`.`), not `backend/`.
 
+## Upstream Chatwoot Reference (Required)
+
+GoChat is a Go-language translation and port of Chatwoot. When a behavior,
+API contract, data model, event payload, frontend interaction, or edge case is
+unclear or appears incorrect, **inspect the upstream implementation under
+`docs/chatwoot/` before designing or changing the GoChat solution**.
+
+- Trace the complete upstream path first: controller/handler → service/builder
+  → model callback → serializer → frontend consumer.
+- Preserve Chatwoot's externally visible behavior and payload contracts when
+  translating Rails/Ruby implementation details into GoChat's layered Go
+  architecture.
+- Reuse the upstream fix pattern and regression cases where practical instead
+  of inventing a parallel behavior from the current Go code alone.
+- Treat `docs/chatwoot/` as read-only reference code. Production changes belong
+  in `backend/`, `frontend/`, or other GoChat-owned directories.
+- If GoChat intentionally diverges from Chatwoot, document the reason, affected
+  contract, and verification coverage in the change.
+
 ## Build & Test Commands
 
 All Go commands run from `backend/`:
diff --git a/backend/internal/handler/webhook/incoming_persister.go b/backend/internal/handler/webhook/incoming_persister.go
index fb2c82e6..04419fdf 100644
--- a/backend/internal/handler/webhook/incoming_persister.go
+++ b/backend/internal/handler/webhook/incoming_persister.go
@@ -3,7 +3,9 @@ package webhook
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
+	"strings"
 	"time"
 
 	"github.com/google/uuid"
@@ -538,8 +540,27 @@ func (p *IncomingPersister) createMessage(ctx context.Context, tx *gorm.DB, inbo
 	if len(msg.Attachments) > 0 {
 		contentAttrs["attachments"] = msg.Attachments
 	}
-	if msg.ReplyToID != "" {
-		contentAttrs["in_reply_to"] = msg.ReplyToID
+	if replyToExternalID := strings.TrimSpace(msg.ReplyToID); replyToExternalID != "" {
+		// Chatwoot stores provider reply references as in_reply_to_external_id,
+		// then resolves the same-conversation message by source_id before save.
+		// Keep in_reply_to strictly as the internal numeric message ID expected by
+		// the dashboard and its cursor-based message API.
+		var replyMessage model.Message
+		err := tx.WithContext(ctx).
+			Where("conversation_id = ? AND source_id = ?", conversation.ID, replyToExternalID).
+			First(&replyMessage).Error
+		if err == nil {
+			contentAttrs["in_reply_to"] = replyMessage.ID
+			contentAttrs["in_reply_to_external_id"] = replyMessage.SourceID
+		} else if errors.Is(err, gorm.ErrRecordNotFound) {
+			// Match Chatwoot's InReplyToMessageBuilder: unresolved references
+			// are normalized to null instead of being persisted as an invalid
+			// internal message ID.
+			contentAttrs["in_reply_to"] = nil
+			contentAttrs["in_reply_to_external_id"] = nil
+		} else {
+			return nil, err
+		}
 	}
 	message := model.Message{
 		ConversationID:       conversation.ID,
diff --git a/backend/internal/handler/webhook/webhook_lookup_test.go b/backend/internal/handler/webhook/webhook_lookup_test.go
index e5087265..c17ebc13 100644
--- a/backend/internal/handler/webhook/webhook_lookup_test.go
+++ b/backend/internal/handler/webhook/webhook_lookup_test.go
@@ -575,6 +575,81 @@ func TestIncomingPersisterCreatesConversationMessageAndDedupes(t *testing.T) {
 	}
 }
 
+func TestIncomingPersisterNormalizesExternalReplyReference(t *testing.T) {
+	db := newWebhookLookupTestDB(t)
+	inbox := seedWebhookInbox(t, db, "telegram")
+	persister := NewIncomingPersister(db)
+
+	original, err := persister.PersistIncoming(t.Context(), &inbox, &channel.IncomingMessage{
+		ChannelType: channel.ChannelTelegram,
+		SourceID:    "tg-reply-source-1",
+		SenderID:    "tg-reply-user-1",
+		SenderName:  "Reply User",
+		SenderType:  channel.SenderContact,
+		Content:     "original",
+		ContentType: channel.ContentText,
+		InboxID:     inbox.ID,
+		AccountID:   inbox.AccountID,
+	})
+	if err != nil {
+		t.Fatalf("persist original message: %v", err)
+	}
+
+	reply, err := persister.PersistIncoming(t.Context(), &inbox, &channel.IncomingMessage{
+		ChannelType: channel.ChannelTelegram,
+		SourceID:    "tg-reply-source-2",
+		SenderID:    "tg-reply-user-1",
+		SenderName:  "Reply User",
+		SenderType:  channel.SenderContact,
+		Content:     "reply",
+		ContentType: channel.ContentText,
+		ReplyToID:   "tg-reply-source-1",
+		InboxID:     inbox.ID,
+		AccountID:   inbox.AccountID,
+	})
+	if err != nil {
+		t.Fatalf("persist reply message: %v", err)
+	}
+
+	attrs := map[string]interface{}{}
+	if err := json.Unmarshal(reply.Message.ContentAttributes, &attrs); err != nil {
+		t.Fatalf("decode reply content attributes: %v", err)
+	}
+	if got := uint(attrs["in_reply_to"].(float64)); got != original.Message.ID {
+		t.Fatalf("expected internal in_reply_to %d, got %#v", original.Message.ID, attrs["in_reply_to"])
+	}
+	if got := attrs["in_reply_to_external_id"]; got != original.Message.SourceID {
+		t.Fatalf("expected external reply id %q, got %#v", original.Message.SourceID, got)
+	}
+
+	unresolved, err := persister.PersistIncoming(t.Context(), &inbox, &channel.IncomingMessage{
+		ChannelType: channel.ChannelTelegram,
+		SourceID:    "tg-reply-source-3",
+		SenderID:    "tg-reply-user-1",
+		SenderName:  "Reply User",
+		SenderType:  channel.SenderContact,
+		Content:     "unresolved reply",
+		ContentType: channel.ContentText,
+		ReplyToID:   "tg-missing-source",
+		InboxID:     inbox.ID,
+		AccountID:   inbox.AccountID,
+	})
+	if err != nil {
+		t.Fatalf("persist unresolved reply message: %v", err)
+	}
+
+	unresolvedAttrs := map[string]interface{}{}
+	if err := json.Unmarshal(unresolved.Message.ContentAttributes, &unresolvedAttrs); err != nil {
+		t.Fatalf("decode unresolved reply content attributes: %v", err)
+	}
+	if got, ok := unresolvedAttrs["in_reply_to"]; !ok || got != nil {
+		t.Fatalf("expected unresolved internal reply id to be null, got %#v", unresolvedAttrs)
+	}
+	if got, ok := unresolvedAttrs["in_reply_to_external_id"]; !ok || got != nil {
+		t.Fatalf("expected unresolved external reply id to be null, got %#v", unresolvedAttrs)
+	}
+}
+
 func TestIncomingPersisterQueuesIncomingMessageWithWorker(t *testing.T) {
 	db := newWebhookLookupTestDB(t)
 	inbox := seedWebhookInbox(t, db, "telegram")
diff --git a/frontend/app/javascript/dashboard/components-next/message/MessageList.vue b/frontend/app/javascript/dashboard/components-next/message/MessageList.vue
index df689a71..4212dc33 100644
--- a/frontend/app/javascript/dashboard/components-next/message/MessageList.vue
+++ b/frontend/app/javascript/dashboard/components-next/message/MessageList.vue
@@ -52,6 +52,16 @@ const currentChat = useMapGetter('getSelectedChat');
 
 // Cache for fetched reply messages to avoid duplicate API calls
 const fetchedReplyMessages = reactive(new Map());
+const pendingReplyMessageFetches = new Map();
+
+const replyMessageMatches = (message, referenceId) => {
+  const normalizedReferenceId = String(referenceId);
+  return (
+    String(message.id) === normalizedReferenceId ||
+    message.source_id === normalizedReferenceId ||
+    message.sourceId === normalizedReferenceId
+  );
+};
 
 /**
  * Fetches a specific message from the API by trying to get messages around it
@@ -60,33 +70,58 @@ const fetchedReplyMessages = reactive(new Map());
  * @returns {Promise<Object|null>} - The fetched message or null if not found/error
  */
 const fetchReplyMessage = async (messageId, conversationId) => {
+  const cacheKey = String(messageId);
+
   // Return cached result if already fetched
-  if (fetchedReplyMessages.has(messageId)) {
-    return fetchedReplyMessages.get(messageId);
+  if (fetchedReplyMessages.has(cacheKey)) {
+    return fetchedReplyMessages.get(cacheKey);
   }
 
-  try {
-    const response = await MessageApi.getPreviousMessages({
-      conversationId,
-      before: messageId + 100,
-      after: messageId - 100,
-    });
+  const numericMessageId = Number(messageId);
+  if (!Number.isSafeInteger(numericMessageId) || numericMessageId <= 0) {
+    // Legacy provider payloads may contain an external source ID here. Never
+    // pass those strings to the numeric before/after cursor endpoint.
+    fetchedReplyMessages.set(cacheKey, null);
+    return null;
+  }
 
-    const messages = response.data?.payload || [];
-    const targetMessage = messages.find(msg => msg.id === messageId);
+  if (pendingReplyMessageFetches.has(cacheKey)) {
+    return pendingReplyMessageFetches.get(cacheKey);
+  }
 
-    if (targetMessage) {
-      const camelCaseMessage = useCamelCase(targetMessage);
-      fetchedReplyMessages.set(messageId, camelCaseMessage);
-      return camelCaseMessage;
+  const request = (async () => {
+    try {
+      const response = await MessageApi.getPreviousMessages({
+        conversationId,
+        before: numericMessageId + 100,
+        after: numericMessageId - 100,
+      });
+
+      const messages = response.data?.payload || [];
+      const targetMessage = messages.find(
+        message => Number(message.id) === numericMessageId
+      );
+
+      if (targetMessage) {
+        const camelCaseMessage = useCamelCase(targetMessage);
+        fetchedReplyMessages.set(cacheKey, camelCaseMessage);
+        return camelCaseMessage;
+      }
+
+      // Cache null result to avoid repeated API calls
+      fetchedReplyMessages.set(cacheKey, null);
+      return null;
+    } catch (error) {
+      fetchedReplyMessages.set(cacheKey, null);
+      return null;
     }
+  })();
 
-    // Cache null result to avoid repeated API calls
-    fetchedReplyMessages.set(messageId, null);
-    return null;
-  } catch (error) {
-    fetchedReplyMessages.set(messageId, null);
-    return null;
+  pendingReplyMessageFetches.set(cacheKey, request);
+  try {
+    return await request;
+  } finally {
+    pendingReplyMessageFetches.delete(cacheKey);
   }
 };
 
@@ -137,19 +172,23 @@ const getInReplyToMessage = parentMessage => {
 
   if (!inReplyToMessageId) return null;
 
+  const cacheKey = String(inReplyToMessageId);
+
   // Try to find in current messages first
-  let replyMessage = props.messages?.find(msg => msg.id === inReplyToMessageId);
+  let replyMessage = props.messages?.find(message =>
+    replyMessageMatches(message, inReplyToMessageId)
+  );
 
   // Then try store messages
   if (!replyMessage && currentChat.value?.messages) {
-    replyMessage = currentChat.value.messages.find(
-      msg => msg.id === inReplyToMessageId
+    replyMessage = currentChat.value.messages.find(message =>
+      replyMessageMatches(message, inReplyToMessageId)
     );
   }
 
   // Then check fetch cache
-  if (!replyMessage && fetchedReplyMessages.has(inReplyToMessageId)) {
-    replyMessage = fetchedReplyMessages.get(inReplyToMessageId);
+  if (!replyMessage && fetchedReplyMessages.has(cacheKey)) {
+    replyMessage = fetchedReplyMessages.get(cacheKey);
   }
 
   // If still not found and we have conversation context, fetch it