fix: settle merged pagination and drop duplicate rows (#47)

PaginationState computed hasMore as `fetched.count >= pageSize`, but merged
views return the combined, de-duplicated result of N instances, so the merged
count cleared the single-source threshold and kept hasMore true past the real
end (extra empty fetches). loadMore also appended without de-duping against
already-loaded items, so overlapping involvement queries and shifting pages
could produce duplicate TaggedItem.id entries in the ForEach.

Add an optional dedupeKey to PaginationState that de-duplicates across pages via
a running seen-set, and base hasMore on whether a page contributed new items
when dedupeKey is set. Single-source pagination keeps the page-size heuristic
unchanged. Merged Issues/PRs, Repositories, and Notifications views opt in with
dedupeKey = { $0.id }.

Forji/Forji/Helpers/PaginationState.swift

@@ -15,6 +15,13 @@ final class PaginationState<Item> {
     let pageSize: Int
     var cacheName: String?
 
+    /// Optional key extractor enabling cross-page de-duplication. Merged views set
+    /// this because they combine paginated results from several instances, where
+    /// the same item can resurface on a later page (overlapping involvement
+    /// queries) and the merged page size no longer matches `pageSize`.
+    @ObservationIgnored var dedupeKey: ((Item) -> AnyHashable)?
+    @ObservationIgnored private var seenKeys = Set<AnyHashable>()
+
     init(pageSize: Int = 20) {
         self.pageSize = pageSize
     }
@@ -42,8 +49,10 @@ final class PaginationState<Item> {
             do {
                 let fetched = try await fetch(1, pageSize)
                 guard !Task.isCancelled else { return }
-                items = fetched
-                hasMore = fetched.count >= pageSize
+                if dedupeKey != nil { seenKeys.removeAll() }
+                let newItems = deduped(fetched)
+                items = newItems
+                hasMore = computeHasMore(fetched: fetched, newItems: newItems)
                 currentPage = 2
                 hasLoaded = true
             } catch is CancellationError {
@@ -72,8 +81,9 @@ final class PaginationState<Item> {
             do {
                 let fetched = try await fetch(currentPage, pageSize)
                 guard !Task.isCancelled else { return }
-                items.append(contentsOf: fetched)
-                hasMore = fetched.count >= pageSize
+                let newItems = deduped(fetched)
+                items.append(contentsOf: newItems)
+                hasMore = computeHasMore(fetched: fetched, newItems: newItems)
                 self.currentPage = currentPage + 1
             } catch is CancellationError {
                 // Ignore cancellation
@@ -95,6 +105,24 @@ final class PaginationState<Item> {
     func invalidate() {
         hasLoaded = false
     }
+
+    /// Filters out items already seen on a previous page when `dedupeKey` is set,
+    /// recording the new keys. Without a `dedupeKey` the page passes through
+    /// unchanged so single-source pagination keeps its existing behavior.
+    private func deduped(_ fetched: [Item]) -> [Item] {
+        guard let dedupeKey else { return fetched }
+        return fetched.filter { seenKeys.insert(dedupeKey($0)).inserted }
+    }
+
+    /// For merged sources the de-duplicated, multi-instance page size no longer
+    /// matches `pageSize`, so "more pages exist" means "this page contributed new
+    /// items." Single sources keep the page-size heuristic.
+    private func computeHasMore(fetched: [Item], newItems: [Item]) -> Bool {
+        if dedupeKey != nil {
+            return !newItems.isEmpty
+        }
+        return fetched.count >= pageSize
+    }
 }
 
 // MARK: - Disk cache

Forji/Forji/Views/MergedNotificationsOverviewView.swift

@@ -11,6 +11,7 @@ struct MergedNotificationsOverviewView: View {
         self.manager = manager
         let state = PaginationState<TaggedItem<NotificationThread>>()
         state.cacheName = "merged_notifications"
+        state.dedupeKey = { $0.id }
         state.loadFromCache()
         state.rehydrate(from: manager)
         _pagination = State(initialValue: state)

Forji/Forji/Views/MergedRepositoryListView.swift

@@ -14,6 +14,7 @@ struct MergedRepositoryListView: View {
         self.manager = manager
         let state = PaginationState<TaggedItem<Repository>>()
         state.cacheName = "merged_repos"
+        state.dedupeKey = { $0.id }
         state.loadFromCache()
         state.rehydrate(from: manager)
         _pagination = State(initialValue: state)

Forji/Forji/Views/MergedSearchableOverviewView.swift

@@ -68,6 +68,7 @@ struct MergedSearchableOverviewView<Row: View, Detail: View, CreateView: View>:
 
         let state = PaginationState<TaggedItem<Issue>>()
         state.cacheName = "merged_\(config.issueType)"
+        state.dedupeKey = { $0.id }
         state.loadFromCache()
         state.rehydrate(from: manager)
         _pagination = State(initialValue: state)