diff --git a/coderd/x/chatd/chatd.go b/coderd/x/chatd/chatd.go
index ee9b6f08c6..32837ba6f1 100644
--- a/coderd/x/chatd/chatd.go
+++ b/coderd/x/chatd/chatd.go
@@ -2350,6 +2350,13 @@ func (p *Server) PromoteQueued(
 	p.publishMessage(opts.ChatID, promoted)
 	p.publishStatus(opts.ChatID, updatedChat.Status, updatedChat.WorkerID)
 	p.publishChatPubsubEvent(updatedChat, codersdk.ChatWatchEventKindStatusChange, nil)
+	// Marker for ENG-2645: confirms post-TX publishes ran.
+	p.logger.Debug(ctx, "promote queued completed",
+		slog.F("chat_id", opts.ChatID),
+		slog.F("promoted_id", promoted.ID),
+		slog.F("synthetic_count", len(syntheticResults)),
+		slog.F("status", updatedChat.Status),
+	)
 	p.signalWake()
 
 	return result, nil
@@ -4777,12 +4784,25 @@ func (p *Server) SubscribeAuthorized(
 				}
 				return
 			case notify := <-notifications:
+				// Marker for ENG-2645: subscriber received pubsub notify.
+				p.logger.Debug(mergedCtx, "stream subscriber received notify",
+					slog.F("chat_id", chatID),
+					slog.F("after_message_id", notify.AfterMessageID),
+					slog.F("status", notify.Status),
+					slog.F("queue_update", notify.QueueUpdate),
+					slog.F("last_message_id", lastMessageID),
+				)
 				if notify.AfterMessageID > 0 || notify.FullRefresh {
 					if notify.FullRefresh {
 						lastMessageID = 0
 					}
+					var (
+						deliveredCount int
+						source         string
+					)
 					cached := p.getCachedDurableMessages(chatID, lastMessageID)
 					if !notify.FullRefresh && len(cached) > 0 {
+						source = "cache"
 						for _, event := range cached {
 							select {
 							case <-mergedCtx.Done():
@@ -4791,6 +4811,7 @@ func (p *Server) SubscribeAuthorized(
 							}
 							lastMessageID = event.Message.ID
 						}
+						deliveredCount = len(cached)
 					} else if newMessages, msgErr := p.db.GetChatMessagesByChatID(mergedCtx, database.GetChatMessagesByChatIDParams{
 						ChatID:  chatID,
 						AfterID: lastMessageID,
@@ -4800,6 +4821,7 @@ func (p *Server) SubscribeAuthorized(
 							slog.Error(msgErr),
 						)
 					} else {
+						source = "db"
 						for _, msg := range newMessages {
 							if msg.ID <= lastMessageID {
 								continue
@@ -4815,8 +4837,17 @@ func (p *Server) SubscribeAuthorized(
 							}:
 							}
 							lastMessageID = msg.ID
+							deliveredCount++
 						}
 					}
+					// Marker for ENG-2645: subscriber delivered durable messages.
+					p.logger.Debug(mergedCtx, "stream subscriber delivered messages",
+						slog.F("chat_id", chatID),
+						slog.F("after_message_id", notify.AfterMessageID),
+						slog.F("source", source),
+						slog.F("delivered_count", deliveredCount),
+						slog.F("last_message_id", lastMessageID),
+					)
 				}
 				if notify.Status != "" {
 					status := database.ChatStatus(notify.Status)
diff --git a/coderd/x/chatd/chatd_test.go b/coderd/x/chatd/chatd_test.go
index a66c4d2c6a..2cd3c9cc74 100644
--- a/coderd/x/chatd/chatd_test.go
+++ b/coderd/x/chatd/chatd_test.go
@@ -9130,8 +9130,10 @@ func TestPromoteQueuedWhileRequiresActionMixedTools(t *testing.T) {
 		select {
 		case ev := <-events:
 			if ev.Type != codersdk.ChatStreamEventTypeMessage || ev.Message == nil {
+				t.Logf("subscriber consumed non-message event type=%s", ev.Type)
 				return false
 			}
+			t.Logf("subscriber consumed message id=%d role=%s match_promoted=%t", ev.Message.ID, ev.Message.Role, ev.Message.ID == promoteResult.PromotedMessage.ID)
 			switch ev.Message.Role {
 			case codersdk.ChatMessageRoleTool:
 				syntheticPublishCount++