Export: fix from-date boundary and respect range in topic media loader

Address edge cases on top of the offset_date jump:

* SingleMessageAfter: switch the comparison to >= so a split whose newest
  message has date == singlePeerFrom is not pre-skipped by the count
  probe. SkipMessageByDate keeps messages with singlePeerFrom <= date, so
  the pre-iteration filter must match that inclusive lower bound.

* requestChatMessages (onlyMyMessages branch): messages.search uses
  strict > for min_date and strict < for max_date, while the exporter's
  canonical range is [singlePeerFrom, singlePeerTill). Pass
  min_date = singlePeerFrom - 1 to keep messages dated exactly
  singlePeerFrom; max_date stays singlePeerTill.

* loadNextTopicMessageFile: skip media download for messages outside the
  date range, mirroring loadNextMessageFile for the chat path. Without
  this, topic exports with a date filter still trigger downloads for
  out-of-range messages.

* changelog.txt: add a user-facing entry.

Author: Lertov2424232

Telegram/SourceFiles/export/data/export_data_types.cpp

@@ -2607,7 +2607,10 @@ bool SingleMessageAfter(
 		const MTPmessages_Messages &data,
 		TimeId date) {
 	const auto single = SingleMessageDate(data);
-	return (single > 0 && single > date);
+	// Inclusive lower bound: SkipMessageByDate keeps messages with
+	// `singlePeerFrom <= date`, so a split whose newest message has the
+	// exact `singlePeerFrom` date must not be pre-skipped here.
+	return (single > 0 && single >= date);
 }
 
 bool SkipMessageByDate(const Message &message, const Settings &settings) {

Telegram/SourceFiles/export/export_api_wrap.cpp

@@ -1941,8 +1941,13 @@ void ApiWrap::requestChatMessages(
 		: (splitsCount + splitIndex);
 	// Narrow server-side scan when the user requested a date range, so we
 	// don't pull every message in the chat just to skip them client-side.
+	// messages.search uses strict comparison for both bounds (date >
+	// min_date and date < max_date), while the exporter's canonical range
+	// is `[singlePeerFrom, singlePeerTill)` (see SkipMessageByDate). To
+	// match it exactly we shift min_date down by 1 and pass singlePeerTill
+	// through unchanged.
 	const auto minDate = (_settings->singlePeerFrom > 0)
-		? _settings->singlePeerFrom
+		? (_settings->singlePeerFrom - 1)
 		: 0;
 	const auto maxDate = (_settings->singlePeerTill > 0)
 		? _settings->singlePeerTill
@@ -2603,6 +2608,9 @@ void ApiWrap::loadNextTopicMessageFile() {
 		; _topicProcess->fileIndex < list.size()
 		; ++_topicProcess->fileIndex) {
 		auto &message = list[_topicProcess->fileIndex];
+		if (Data::SkipMessageByDate(message, *_settings)) {
+			continue;
+		}
 		if (!messageCustomEmojiReady(message)) {
 			return;
 		}

changelog.txt

@@ -1,5 +1,6 @@
 6.8.3 beta (19.05.26)
 
+- Export now jumps to the picked "from date" instead of walking the whole chat.
 - In-app markdown file viewer.
 - Native Instant View support.
 - Native external webapp viewer on Linux.