fix(mailserver): reduce memory usage by skipping aggregation when not needed

- Applied a minimal, low-risk optimization to reduce backend memory usage during background historic sync.
- Kept existing public behavior unchanged for normal/API-triggered sync calls.
- Added an internal path that skips building and merging MessengerResponse payloads when results are not needed.
- Wired the async background trigger to use that non-aggregating path.

Author: jrainville

protocol/messenger_mailserver.go

@@ -263,8 +263,13 @@ func (m *Messenger) resetFiltersPriority(filters types2.ChatFilters) error {
 	return nil
 }
 
-// RequestAllHistoricMessages requests all the historic messages for any topic
+// RequestAllHistoricMessages requests all the historic messages for any topic.
+// It keeps aggregating all responses for callers that need the merged payload.
 func (m *Messenger) RequestAllHistoricMessages(withRetries bool) (*MessengerResponse, error) {
+	return m.requestAllHistoricMessages(withRetries, true)
+}
+
+func (m *Messenger) requestAllHistoricMessages(withRetries bool, aggregateResponses bool) (*MessengerResponse, error) {
 	shouldSync, err := m.shouldSync()
 	if err != nil {
 		return nil, err
@@ -307,7 +312,10 @@ func (m *Messenger) RequestAllHistoricMessages(withRetries bool) (*MessengerResp
 		m.historicSyncMu.Unlock()
 	}()
 
-	allResponses := &MessengerResponse{}
+	var allResponses *MessengerResponse
+	if aggregateResponses {
+		allResponses = &MessengerResponse{}
+	}
 
 	filters := m.messaging.ChatFilters()
 	err = m.updateFiltersPriority(filters)
@@ -330,7 +338,7 @@ func (m *Messenger) RequestAllHistoricMessages(withRetries bool) (*MessengerResp
 		if err != nil {
 			return nil, err
 		}
-		if response != nil {
+		if aggregateResponses && response != nil {
 			allResponses.AddChats(response.Chats())
 			allResponses.AddMessages(response.Messages())
 		}
@@ -341,7 +349,7 @@ func (m *Messenger) RequestAllHistoricMessages(withRetries bool) (*MessengerResp
 	if err != nil {
 		return nil, err
 	}
-	if response != nil {
+	if aggregateResponses && response != nil {
 		allResponses.AddChats(response.Chats())
 		allResponses.AddMessages(response.Messages())
 	}

protocol/messenger_mailserver_cycle.go

@@ -51,7 +51,7 @@ func (m *Messenger) asyncRequestAllHistoricMessages() {
 
 	go func() {
 		defer gocommon.LogOnPanic()
-		_, err := m.RequestAllHistoricMessages(true)
+		_, err := m.requestAllHistoricMessages(true, false)
 		if err != nil {
 			m.logger.Error("failed to request historic messages", zap.Error(err))
 		}