fix(relations): Fix duplicate messages in thread pagination

The /relations endpoint was incorrectly modifying the pagination starting
point with from.saturating_inc(dir), causing duplicate events to appear
when scrolling up in message threads. This was particularly noticeable
when viewing replies in Element.

The fix removes the incorrect increment/decrement logic and adds proper
filtering to exclude the starting event itself from results. The endpoint
now uses ShortEventId directly as the pagination token, avoiding issues
with PduCount in federated environments where events can arrive out of
order.

Fixes: #814

src/api/client/relations.rs

@@ -109,13 +109,13 @@ async fn paginate_relations_with_filter(
 	recurse: bool,
 	dir: Direction,
 ) -> Result<get_relating_events::v1::Response> {
-	let start: PduCount = from
+	let start: PduCount = from.and_then(|s| s.parse::<u64>().ok()).map_or_else(
-		.map(str::parse)
+		|| match dir {
-		.transpose()?
-		.unwrap_or_else(|| match dir {
 			| Direction::Forward => PduCount::min(),
 			| Direction::Backward => PduCount::max(),
-		});
+		},
+		PduCount::Normal,
+	);
 
 	let to: Option<PduCount> = to.map(str::parse).flat_ok();
 
@@ -156,9 +156,7 @@ async fn paginate_relations_with_filter(
 		| Direction::Forward => events.last(),
 		| Direction::Backward => events.first(),
 	}
-	.map(at!(0))
+	.map(|(count, _)| count.into_unsigned().to_string());
-	.as_ref()
-	.map(ToString::to_string);
 
 	Ok(get_relating_events::v1::Response {
 		next_batch,

src/service/rooms/pdu_metadata/data.rs

@@ -61,9 +61,10 @@ impl Data {
 		from: PduCount,
 		dir: Direction,
 	) -> impl Stream<Item = (PduCount, impl Event)> + Send + '_ {
+		let from_unsigned = from.into_unsigned();
 		let mut current = ArrayVec::<u8, 16>::new();
 		current.extend(target.to_be_bytes());
-		current.extend(from.saturating_inc(dir).into_unsigned().to_be_bytes());
+		current.extend(from_unsigned.to_be_bytes());
 		let current = current.as_slice();
 		match dir {
 			| Direction::Forward => self.tofrom_relation.raw_keys_from(current).boxed(),
@@ -73,6 +74,17 @@ impl Data {
 		.ready_take_while(move |key| key.starts_with(&target.to_be_bytes()))
 		.map(|to_from| u64_from_u8(&to_from[8..16]))
 		.map(PduCount::from_unsigned)
+		.ready_filter(move |count| {
+			if from == PduCount::min() || from == PduCount::max() {
+				true
+			} else {
+				let count_unsigned = count.into_unsigned();
+				match dir {
+					| Direction::Forward => count_unsigned > from_unsigned,
+					| Direction::Backward => count_unsigned < from_unsigned,
+				}
+			}
+		})
 		.wide_filter_map(move |shorteventid| async move {
 			let pdu_id: RawPduId = PduId { shortroomid, shorteventid }.into();