straw: infinite-scroll pagination for channel + search

Wire the new strawcore continuation fetchers through UniFFI and add
load-more-on-scroll to the Channel and Search screens — previously both
loaded only page 1 and stopped.

FFI (rust/strawcore): search() now returns Page{items, continuation};
channelInfo carries videos_continuation; new searchContinuation() and
channelVideosContinuation() suspend funs map the core ContinuationPage.

Channel + Search ViewModels: loadMore() fetches the next page, dedups by
url, advances the token, and stops when the token runs out or a page
yields zero net-new items (guards a looping continuation). Result-set
swaps (channel switch / new submit / cache preview) cancel the in-flight
page, and a token fence inside the state update prevents a stale page
being spliced into a replaced list. Screens add a near-end LazyColumn
trigger (rememberLazyListState + derivedStateOf) and a footer spinner.

strawApp/src/main/kotlin/com/sulkta/straw/feature/channel/ChannelScreen.kt

@@ -23,6 +23,7 @@ import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material3.Button
@@ -35,6 +36,7 @@ import androidx.compose.material3.OutlinedButton
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
@@ -106,7 +108,26 @@ fun ChannelScreen(
         val filteredVideos = remember(state.videos, hideShorts) {
             com.sulkta.straw.util.applyContentFilters(state.videos, hideShorts = hideShorts)
         }
+        val listState = rememberLazyListState()
+        // Infinite scroll: when the user nears the end of the loaded rows
+        // and the channel still has a continuation token, pull the next
+        // page. derivedStateOf so this only recomputes on scroll, not on
+        // every recomposition.
+        val shouldLoadMore by remember {
+            derivedStateOf {
+                val layout = listState.layoutInfo
+                val total = layout.totalItemsCount
+                val lastVisible = layout.visibleItemsInfo.lastOrNull()?.index ?: 0
+                total > 0 && lastVisible >= total - 3
+            }
+        }
+        LaunchedEffect(shouldLoadMore, state.videosContinuation, state.loadingMore) {
+            if (shouldLoadMore && state.videosContinuation != null && !state.loadingMore) {
+                vm.loadMore()
+            }
+        }
         LazyColumn(
+            state = listState,
             modifier = Modifier.fillMaxSize().statusBarsPadding(),
             contentPadding = rememberBottomContentPadding(),
         ) {
@@ -178,6 +199,14 @@ fun ChannelScreen(
                 )
                 HorizontalDivider()
             }
+            if (state.loadingMore) {
+                item {
+                    Box(
+                        modifier = Modifier.fillMaxWidth().padding(16.dp),
+                        contentAlignment = Alignment.Center,
+                    ) { CircularProgressIndicator() }
+                }
+            }
         }
         }
     }

strawApp/src/main/kotlin/com/sulkta/straw/feature/channel/ChannelViewModel.kt

@@ -39,6 +39,15 @@ data class ChannelUiState(
      * data while believing it's B.
      */
     val loadedUrl: String? = null,
+    /**
+     * Token for the next page of the Videos tab. Non-null means more
+     * videos can be loaded via [ChannelViewModel.loadMore]; null means
+     * the channel is exhausted (or YT stopped handing out
+     * continuations) and the list is complete.
+     */
+    val videosContinuation: String? = null,
+    /** True while a [ChannelViewModel.loadMore] fetch is in flight. */
+    val loadingMore: Boolean = false,
 )
 
 class ChannelViewModel : ViewModel() {
@@ -51,6 +60,12 @@ class ChannelViewModel : ViewModel() {
     // / MED-1.
     private var inFlight: Job? = null
 
+    // Tracked separately from inFlight so (a) a channel switch cancels an
+    // in-flight pagination fetch, and (b) loadMore never races the
+    // initial load's job bookkeeping. Cancelled whenever we reset for a
+    // new/rejected channel.
+    private var loadMoreJob: Job? = null
+
     fun load(channelUrl: String) {
         // Snapshot _ui once so the two reads agree.
         val snap = _ui.value
@@ -64,6 +79,8 @@ class ChannelViewModel : ViewModel() {
         if (!isAllowedYtUrl(channelUrl)) {
             inFlight?.cancel()
             inFlight = null
+            loadMoreJob?.cancel()
+            loadMoreJob = null
             _ui.update {
                 ChannelUiState(
                     loading = false,
@@ -74,6 +91,8 @@ class ChannelViewModel : ViewModel() {
             return
         }
         inFlight?.cancel()
+        loadMoreJob?.cancel()
+        loadMoreJob = null
         _ui.update { ChannelUiState(loading = true, loadedUrl = channelUrl) }
         inFlight = viewModelScope.launch {
             try {
@@ -100,6 +119,7 @@ class ChannelViewModel : ViewModel() {
                         avatar = ch.avatar,
                         videos = videos,
                         loadedUrl = channelUrl,
+                        videosContinuation = ch.videosContinuation,
                     )
                 }
             } catch (t: Throwable) {
@@ -120,4 +140,63 @@ class ChannelViewModel : ViewModel() {
             }
         }
     }
+
+    /**
+     * Append the next page of the channel's Videos tab. No-op when there
+     * is no continuation token (list complete), the initial load is
+     * still running, or a page fetch is already in flight. Soft-fails: a
+     * failed page clears the spinner and drops the token so we don't spin
+     * on a broken continuation — the already-loaded videos stay put, no
+     * error banner over a working list.
+     */
+    fun loadMore() {
+        val snap = _ui.value
+        val token = snap.videosContinuation ?: return
+        if (snap.loading || snap.loadingMore) return
+        val url = snap.loadedUrl ?: return
+        _ui.update { it.copy(loadingMore = true) }
+        loadMoreJob = viewModelScope.launch {
+            try {
+                val page = uniffi.strawcore.channelVideosContinuation(token)
+                // Channel switched out from under us mid-fetch.
+                if (_ui.value.loadedUrl != url) return@launch
+                val newItems = page.items.map { v ->
+                    StreamItem(
+                        url = v.url,
+                        title = v.title.ifBlank { "(no title)" },
+                        uploader = v.uploader,
+                        uploaderUrl = v.uploaderUrl,
+                        thumbnail = v.thumbnail,
+                        durationSeconds = v.durationSeconds,
+                        viewCount = v.viewCount,
+                        uploadDateRelative = v.uploadDateRelative,
+                    )
+                }
+                _ui.update { st ->
+                    // Fence: channel must be unchanged AND this must still
+                    // be the live token (a switch/reload must not get a
+                    // stale page spliced in).
+                    if (st.loadedUrl != url || st.videosContinuation != token) {
+                        return@update st
+                    }
+                    // De-dup by url — a continuation occasionally repeats a
+                    // tail item; appending blind would double-render it.
+                    val seen = st.videos.mapTo(HashSet()) { it.url }
+                    val fresh = newItems.filter { seen.add(it.url) }
+                    st.copy(
+                        videos = st.videos + fresh,
+                        // Zero net-new (all dups / a looping continuation)
+                        // → stop, or the near-end trigger busy-loops on a
+                        // dead-end token.
+                        videosContinuation = if (fresh.isEmpty()) null else page.continuation,
+                        loadingMore = false,
+                    )
+                }
+            } catch (t: Throwable) {
+                if (t is CancellationException) throw t
+                if (_ui.value.loadedUrl != url) return@launch
+                _ui.update { it.copy(loadingMore = false, videosContinuation = null) }
+            }
+        }
+    }
 }

strawApp/src/main/kotlin/com/sulkta/straw/feature/search/SearchScreen.kt

@@ -22,6 +22,7 @@ import androidx.compose.foundation.layout.statusBarsPadding
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.foundation.text.KeyboardActions
 import androidx.compose.foundation.text.KeyboardOptions
@@ -31,6 +32,8 @@ import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
@@ -166,7 +169,25 @@ fun SearchScreen(
                 val filteredResults = remember(state.results, hideShorts) {
                     com.sulkta.straw.util.applyContentFilters(state.results, hideShorts = hideShorts)
                 }
+                val listState = rememberLazyListState()
+                // Infinite scroll: near the end of a live result set with a
+                // continuation token, pull the next page. Cache previews
+                // have a null continuation, so this stays quiet for them.
+                val shouldLoadMore by remember {
+                    derivedStateOf {
+                        val layout = listState.layoutInfo
+                        val total = layout.totalItemsCount
+                        val lastVisible = layout.visibleItemsInfo.lastOrNull()?.index ?: 0
+                        total > 0 && lastVisible >= total - 3
+                    }
+                }
+                LaunchedEffect(shouldLoadMore, state.continuation, state.loadingMore) {
+                    if (shouldLoadMore && state.continuation != null && !state.loadingMore) {
+                        vm.loadMore()
+                    }
+                }
                 LazyColumn(
+                    state = listState,
                     modifier = Modifier.fillMaxSize(),
                     contentPadding = rememberBottomContentPadding(),
                 ) {
@@ -186,6 +207,14 @@ fun SearchScreen(
                         )
                         HorizontalDivider()
                     }
+                    if (state.loadingMore) {
+                        item {
+                            Box(
+                                modifier = Modifier.fillMaxWidth().padding(16.dp),
+                                contentAlignment = Alignment.Center,
+                            ) { CircularProgressIndicator() }
+                        }
+                    }
                 }
             }
         }

strawApp/src/main/kotlin/com/sulkta/straw/feature/search/SearchViewModel.kt

@@ -33,6 +33,14 @@ data class SearchUiState(
      * show a faint "from cache" hint without blocking the list.
      */
     val fromCache: Boolean = false,
+    /**
+     * Token for the next page of network results. Non-null only for a
+     * live (non-cache) result set with more pages; null for cache
+     * previews and once the last page is reached.
+     */
+    val continuation: String? = null,
+    /** True while a [SearchViewModel.loadMore] fetch is in flight. */
+    val loadingMore: Boolean = false,
 )
 
 @kotlinx.serialization.Serializable
@@ -106,6 +114,11 @@ class SearchViewModel : ViewModel() {
     // submit" intent — only a fresh submit cancels me.
     private var inFlight: Job? = null
 
+    // Pagination fetch for the current live result set. Cancelled
+    // whenever that set is replaced (new submit, or a cache preview
+    // swaps in) so a late page can't append to stale results.
+    private var loadMoreJob: Job? = null
+
     fun onQueryChange(q: String) {
         // Clear any prior error state when the user resumes typing —
         // a failed submit's banner used to persist into the next
@@ -115,18 +128,29 @@ class SearchViewModel : ViewModel() {
         if (Settings.get().cacheEnabled.value && q.trim().length >= 2) {
             val matches = reactiveFilter(q.trim())
             if (matches.isNotEmpty()) {
+                // Cache preview replaces the live set → kill its pagination
+                // and drop the token (cache views don't paginate).
+                loadMoreJob?.cancel()
                 _ui.update {
                     it.copy(
                         results = matches,
                         fromCache = true,
                         loading = false,
+                        continuation = null,
+                        loadingMore = false,
                     )
                 }
             } else if (_ui.value.fromCache) {
-                _ui.update { it.copy(results = emptyList(), fromCache = false) }
+                loadMoreJob?.cancel()
+                _ui.update {
+                    it.copy(results = emptyList(), fromCache = false, continuation = null)
+                }
             }
         } else if (q.isBlank()) {
-            _ui.update { it.copy(results = emptyList(), fromCache = false) }
+            loadMoreJob?.cancel()
+            _ui.update {
+                it.copy(results = emptyList(), fromCache = false, continuation = null)
+            }
         }
     }
 
@@ -151,6 +175,9 @@ class SearchViewModel : ViewModel() {
         // prior coroutine had already advanced past its `ensureActive`
         // gate by the time the new submit got around to cancelling.
         inFlight?.cancel()
+        // A fresh submit invalidates any in-flight pagination of the
+        // previous result set; drop its token until page 1 lands.
+        loadMoreJob?.cancel()
 
         if (cached != null && cached.isNotEmpty()) {
             _ui.update {
@@ -159,6 +186,8 @@ class SearchViewModel : ViewModel() {
                     error = null,
                     results = cached,
                     fromCache = true,
+                    continuation = null,
+                    loadingMore = false,
                 )
             }
         } else {
@@ -168,6 +197,8 @@ class SearchViewModel : ViewModel() {
                     error = null,
                     results = emptyList(),
                     fromCache = false,
+                    continuation = null,
+                    loadingMore = false,
                 )
             }
         }
@@ -176,8 +207,9 @@ class SearchViewModel : ViewModel() {
             try {
                 // strawcore.search() is suspend on the tokio runtime baked
                 // into libstrawcore.so — no Dispatchers.IO wrap needed.
-                val rustItems = uniffi.strawcore.search(q)
-                val items = rustItems.map { r ->
+                // Returns a Page now: items + the first continuation token.
+                val page = uniffi.strawcore.search(q)
+                val items = page.items.map { r ->
                     StreamItem(
                         url = r.url,
                         title = r.title.ifBlank { "(no title)" },
@@ -200,6 +232,7 @@ class SearchViewModel : ViewModel() {
                         loading = false,
                         results = items,
                         fromCache = false,
+                        continuation = page.continuation,
                     )
                 }
                 // Record AFTER the search succeeds so mistyped queries
@@ -233,6 +266,69 @@ class SearchViewModel : ViewModel() {
         }
     }
 
+    /**
+     * Append the next page of network search results. No-op for cache
+     * previews (which don't paginate), when there's no continuation
+     * token, or while a page fetch / fresh submit is already running.
+     * Cancellation is the fence: a fresh submit or a cache-preview swap
+     * cancels [loadMoreJob], so a late page can never append to a
+     * replaced result set. Soft-fails: a broken page clears the spinner
+     * and drops the token rather than showing an error over a usable
+     * list.
+     */
+    fun loadMore() {
+        val snap = _ui.value
+        if (snap.fromCache) return
+        val token = snap.continuation ?: return
+        if (snap.loading || snap.loadingMore) return
+        _ui.update { it.copy(loadingMore = true) }
+        loadMoreJob = viewModelScope.launch {
+            try {
+                val page = uniffi.strawcore.searchContinuation(token)
+                // Cancelled mid-fetch (new submit / cache swap) → the
+                // suspend call above already threw; this is the belt for
+                // the gap before the update lands.
+                ensureActive()
+                val newItems = page.items.map { r ->
+                    StreamItem(
+                        url = r.url,
+                        title = r.title.ifBlank { "(no title)" },
+                        uploader = r.uploader,
+                        uploaderUrl = r.uploaderUrl,
+                        thumbnail = r.thumbnail,
+                        durationSeconds = r.durationSeconds,
+                        viewCount = r.viewCount,
+                        uploadDateRelative = r.uploadDateRelative,
+                    )
+                }
+                _ui.update { st ->
+                    // Fence: only append if THIS token is still the live
+                    // one and we haven't flipped to a cache preview. A
+                    // result-set swap (new submit / cache preview) must
+                    // never get a stale page spliced in. (Cancellation
+                    // already guards this; this is belt + braces and makes
+                    // the invariant explicit.)
+                    if (st.fromCache || st.continuation != token) return@update st
+                    // De-dup by url — continuation pages occasionally
+                    // repeat a boundary item.
+                    val seen = st.results.mapTo(HashSet()) { it.url }
+                    val fresh = newItems.filter { seen.add(it.url) }
+                    st.copy(
+                        results = st.results + fresh,
+                        // Zero net-new items (all dups / a looping
+                        // continuation) → stop, or the near-end trigger
+                        // would busy-loop against a dead-end token.
+                        continuation = if (fresh.isEmpty()) null else page.continuation,
+                        loadingMore = false,
+                    )
+                }
+            } catch (t: Throwable) {
+                if (t is CancellationException) throw t
+                _ui.update { it.copy(loadingMore = false, continuation = null) }
+            }
+        }
+    }
+
     /**
      * Walk the in-memory `pool` and return items whose title or uploader
      * contains the query. Case-insensitive, capped at 60 results.