Selecting a container space recurses into sub-spaces like desktop

mautrix-discord nests server/DM spaces inside a top-level Discord space;
filtering on the container's direct children matched no rooms, so the rail
tap looked dead. The selection filter now walks child spaces recursively
(cycle-guarded), matching element-web's SpaceStore behavior.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

features/home/impl/src/main/kotlin/io/element/android/features/home/impl/roomlist/RoomListPresenter.kt

@@ -156,7 +156,6 @@ class RoomListPresenter(
                 }
             }
         }
-        val blapSpaceChildIds = blapSpaceChildren[selectedSpaceId].orEmpty()
         // Blap: union of everything owned by any space (real children + SDK descendants),
         // persisted so Home is clean right away on cold start. Grows immediately as spaces
         // report in; replaced exactly once every space has reported (so rooms removed from
@@ -333,12 +332,29 @@ class RoomListPresenter(
             }
         }
 
-        LaunchedEffect(filtersState.filterSelectionStates, spaceFiltersState.selectedFilter(), blapSpaceChildIds) {
+        LaunchedEffect(filtersState.filterSelectionStates, spaceFiltersState.selectedFilter(), blapSpaceChildren, spaceFilters) {
             val selectedFilters = filtersState.selectedFilters().map { filter -> filter.into() }
             // Blap: union the space's real child list into the SDK's descendants — bridge
             // spaces whose children are DM portals (mautrix-telegram) otherwise come up empty.
+            // Expansion is RECURSIVE like desktop's SpaceStore: container spaces (mautrix-discord
+            // nests server/DM spaces inside a top space) contribute their sub-spaces' rooms too,
+            // otherwise selecting the container matches no rooms at all.
             val selectedSpaceFilter = spaceFiltersState.selectedFilter()?.let { filter ->
-                RoomListFilter.Identifiers((filter.descendants.toSet() + blapSpaceChildIds).toList())
+                val descendantsBySpace = spaceFilters.associate { it.spaceRoom.roomId to it.descendants }
+                val ids = mutableSetOf<RoomId>()
+                val visited = mutableSetOf<RoomId>()
+                val queue = ArrayDeque(listOf(filter.spaceRoom.roomId))
+                while (queue.isNotEmpty()) {
+                    val spaceId = queue.removeFirst()
+                    if (!visited.add(spaceId)) continue
+                    val direct = blapSpaceChildren[spaceId].orEmpty() + descendantsBySpace[spaceId].orEmpty()
+                    for (id in direct) {
+                        ids += id
+                        // Known space → recurse into its children as well.
+                        if (id in blapSpaceChildren || id in descendantsBySpace) queue += id
+                    }
+                }
+                RoomListFilter.Identifiers(ids.toList())
             }
             val allFilters = RoomListFilter.All(selectedFilters + listOfNotNull(selectedSpaceFilter))
             roomListDataSource.updateFilter(allFilters)