fix(spaces): allow PL omission when users_default matches, handle semaphore errors

- PL omission check now allows omitting a space-managed user if the
  proposed users_default equals their space-granted PL
- Semaphore acquire errors cause early return instead of silent proceed

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/service/rooms/roles/mod.rs

@@ -719,7 +719,9 @@ impl Service {
 				pending.insert(space_id.clone())
 			};
 
-			let _permit = this.enforcement_semaphore.acquire().await;
+			let Ok(_permit) = this.enforcement_semaphore.acquire().await else {
+				return;
+			};
 
 			// Always repopulate cache first
 			this.populate_space(&space_id).await;
@@ -829,7 +831,9 @@ impl Service {
 
 		let this = Arc::clone(self);
 		self.server.runtime().spawn(async move {
-			let _permit = this.enforcement_semaphore.acquire().await;
+			let Ok(_permit) = this.enforcement_semaphore.acquire().await else {
+				return;
+			};
 
 			// Read the actual m.space.child state event to check via
 			let child_event_type = StateEventType::SpaceChild;
@@ -984,7 +988,9 @@ impl Service {
 
 		let this = Arc::clone(self);
 		self.server.runtime().spawn(async move {
-			let _permit = this.enforcement_semaphore.acquire().await;
+			let Ok(_permit) = this.enforcement_semaphore.acquire().await else {
+				return;
+			};
 
 			if let Err(e) = this.auto_join_qualifying_rooms(&space_id, &user_id).await {
 				debug_warn!(user_id = %user_id, error = ?e, "Auto-join on Space join failed");

src/service/rooms/timeline/build.rs

@@ -166,7 +166,7 @@ pub async fn build_and_append_pdu(
 						.max();
 					if let Some(space_pl) = space_pl {
 						match proposed.users.get(user_id) {
-							| None => {
+							| None if i64::from(proposed.users_default) != space_pl => {
 								debug_warn!(
 									user_id = %user_id,
 									room_id = %room_id,