android: pull the board down to sync (M12 step 6)

Every sync so far has been a button press on a screen you have to navigate to.
On a phone the gesture for "check if there's anything new" is a pull, and not
having it is the kind of absence people read as the app not syncing at all.

**The gesture is INERT when this device has no server.** `Modifier.pullToRefresh`
takes an `enabled`, which is why the modifier and the indicator are wired by hand
instead of using `PullToRefreshBox` — that wrapper is less code and offers no way
to turn the gesture off. An unlinked device has nowhere to pull from, and a
gesture that always comes back empty is how people learn a control is broken.
Same reasoning as the drawer badge staying silent when unlinked: local-only is
this app's resting state, not a fault.

**A failed refresh reaches the board.** Otherwise the spinner retracts and
nothing happens, which is indistinguishable from "you were already up to date" —
the one outcome it must not be confused with. It renders as a second banner
rather than replacing the store-error one: those are different facts about
different halves of the app, and hiding either behind the other reports the
wrong problem. Dismissing is honest — the note is still pending, `hasPending`
still says so, and the next cycle reports the same fault if it persists.

**The empty board is now a `LazyColumn` holding one centred item.** Pull-to-
refresh works through nested scroll, and a layout that never scrolls never
dispatches any, so on the old plain `Column` the gesture would have been dead on
exactly the screen where it matters most: linked, board empty, notes still on the
server. Looks identical.

The five sync facts the board needs arrive as one `BoardSync` rather than five
parameters, for the reason `EditorAction` exists: `summary` and `error` are both
`String?` and both about sync, so positionally they could be swapped with nothing
to catch it.

Still no automatic sync — no background cycle, no sync-on-resume. This is a
faster way to ask, not a decision to stop asking. TalkBack users cannot perform
a pull; the drawer's Sync → Sync now remains the accessible path, unchanged.

Verified against the real artifact rather than from memory, since `material3`
resolves through the BOM: 1.4.0's sources confirm `pullToRefresh` has `enabled`,
and that none of `pullToRefresh`, `rememberPullToRefreshState`, `Indicator` or
`PullToRefreshBox` is `@ExperimentalMaterial3Api` there — only two deprecated
members are. So no `@OptIn`, which is what keeps the build at zero warnings.

android/app/src/main/java/com/fabledsword/thoughtsync/MainActivity.kt

@@ -14,6 +14,7 @@ import androidx.compose.ui.res.stringResource
 import androidx.lifecycle.viewmodel.compose.viewModel
 import com.fabledsword.thoughtsync.core.ThoughtSync
 import com.fabledsword.thoughtsync.ui.BoardScreen
+import com.fabledsword.thoughtsync.ui.BoardSync
 import com.fabledsword.thoughtsync.ui.BoardViewModel
 import com.fabledsword.thoughtsync.ui.ComposeSheet
 import com.fabledsword.thoughtsync.ui.NoteEditorScreen
@@ -111,7 +112,17 @@ private fun App(core: ThoughtSync) {
                 state = board.state,
                 onOpen = board::open,
                 onOpenNote = board::openNote,
-                syncSummary = syncSummary(sync),
+                sync =
+                    BoardSync(
+                        summary = syncSummary(sync),
+                        error = sync.state.syncError,
+                        refreshing = sync.state.syncing,
+                        // Only a linked device has anywhere to pull FROM. The
+                        // board never learns this itself — one owner for the fact.
+                        canRefresh = sync.state.linked,
+                        onRefresh = sync::syncNow,
+                        onDismissError = sync::dismissSyncError,
+                    ),
                 onOpenSync = { showingSync = true },
                 onSearch = board::search,
                 onCompose = { composing = true },

android/app/src/main/java/com/fabledsword/thoughtsync/ui/BoardScreen.kt

@@ -1,6 +1,7 @@
 package com.fabledsword.thoughtsync.ui
 
 import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.PaddingValues
 import androidx.compose.foundation.layout.Row
@@ -11,6 +12,7 @@ import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.layout.statusBarsPadding
+import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.staggeredgrid.LazyVerticalStaggeredGrid
 import androidx.compose.foundation.lazy.staggeredgrid.StaggeredGridCells
 import androidx.compose.foundation.lazy.staggeredgrid.items
@@ -38,6 +40,9 @@ import androidx.compose.material3.NavigationDrawerItem
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
+import androidx.compose.material3.pulltorefresh.PullToRefreshDefaults
+import androidx.compose.material3.pulltorefresh.pullToRefresh
+import androidx.compose.material3.pulltorefresh.rememberPullToRefreshState
 import androidx.compose.material3.rememberDrawerState
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.rememberCoroutineScope
@@ -56,13 +61,7 @@ fun BoardScreen(
     state: BoardState,
     onOpen: (Destination) -> Unit,
     onOpenNote: (Note) -> Unit,
-    /**
-     * One line of sync state for the drawer, or null when there is nothing worth
-     * saying. Passed in rather than read from [BoardState]: sync has its own view
-     * model, and giving the board a copy of it would be two sources of truth for
-     * whether this device is linked.
-     */
-    syncSummary: String?,
+    sync: BoardSync,
     onOpenSync: () -> Unit,
     onSearch: (String) -> Unit,
     onCompose: () -> Unit,
@@ -77,7 +76,7 @@ fun BoardScreen(
             NavigationDrawer(
                 current = state.destination,
                 labels = state.labels,
-                syncSummary = syncSummary,
+                syncSummary = sync.summary,
                 onOpen = {
                     onOpen(it)
                     scope.launch { drawerState.close() }
@@ -112,17 +111,73 @@ fun BoardScreen(
                 state.error?.let { message ->
                     ErrorBanner(message = message, onDismiss = onDismissError)
                 }
+                // Stacked rather than one-or-the-other. A store failure and a sync
+                // failure are different facts about different halves of the app;
+                // hiding either behind the other would report the wrong problem.
+                sync.error?.let { message ->
+                    ErrorBanner(message = message, onDismiss = sync.onDismissError)
+                }
 
-                when {
-                    state.loading -> LoadingBoard()
-                    state.notes.isEmpty() -> EmptyBoard(state)
-                    else -> NoteBoard(notes = state.notes, onOpenNote = onOpenNote)
+                val pull = rememberPullToRefreshState()
+                Box(
+                    modifier =
+                        Modifier
+                            .fillMaxSize()
+                            .pullToRefresh(
+                                isRefreshing = sync.refreshing,
+                                state = pull,
+                                // INERT on a device with no server, rather than
+                                // spinning and finding nothing: there is no remote
+                                // to fetch from, and a gesture that always comes
+                                // back empty teaches people it is broken.
+                                enabled = sync.canRefresh && !state.loading,
+                                onRefresh = sync.onRefresh,
+                            ),
+                ) {
+                    when {
+                        state.loading -> LoadingBoard()
+                        state.notes.isEmpty() -> EmptyBoard(state)
+                        else -> NoteBoard(notes = state.notes, onOpenNote = onOpenNote)
+                    }
+                    // `PullToRefreshBox` would be less code, but it takes no
+                    // `enabled`, so the modifier and the indicator are wired by
+                    // hand to keep the gate above.
+                    PullToRefreshDefaults.Indicator(
+                        state = pull,
+                        isRefreshing = sync.refreshing,
+                        modifier = Modifier.align(Alignment.TopCenter),
+                    )
                 }
             }
         }
     }
 }
 
+/**
+ * Everything the board knows about sync, which is deliberately not much.
+ *
+ * A holder rather than six loose parameters, for the reason `EditorAction`
+ * exists: [summary] and [error] are both `String?` and both about sync, so as
+ * positional arguments they could be swapped with nothing to catch it. Named
+ * fields make that unsayable.
+ *
+ * Passed in rather than read from [BoardState]. Sync has its own view model, and
+ * giving the board a second copy of "is this device linked" would be two sources
+ * of truth for one fact.
+ */
+data class BoardSync(
+    /** One line for the drawer badge, or null when there is nothing worth saying. */
+    val summary: String?,
+    /** The last sync failure, still unacknowledged. */
+    val error: String?,
+    /** A sync is in flight — drives the indicator, whoever started it. */
+    val refreshing: Boolean,
+    /** Whether there is a server to refresh FROM. False means the gesture is off. */
+    val canRefresh: Boolean,
+    val onRefresh: () -> Unit,
+    val onDismissError: () -> Unit,
+)
+
 /**
  * A search field IS the top bar, following the phone convention rather than the
  * desktop's title-plus-sidebar.
@@ -303,18 +358,27 @@ private fun EmptyBoard(state: BoardState) {
                 stringResource(R.string.board_empty_title) to stringResource(R.string.board_empty_body)
         }
 
-    Column(
-        modifier = Modifier.fillMaxSize().padding(32.dp),
+    // A LazyColumn holding one centred item, NOT a plain Column. Pull-to-refresh
+    // works through nested scroll, and a layout that never scrolls never dispatches
+    // any — so on a Column the gesture would be dead on exactly the screen where it
+    // matters most: linked, board empty, notes still on the server.
+    LazyColumn(
+        modifier = Modifier.fillMaxSize(),
+        contentPadding = PaddingValues(32.dp),
         horizontalAlignment = Alignment.CenterHorizontally,
         verticalArrangement = Arrangement.Center,
     ) {
-        Text(text = title, style = MaterialTheme.typography.titleMedium)
-        Spacer(Modifier.height(8.dp))
-        Text(
-            text = body,
-            style = MaterialTheme.typography.bodyMedium,
-            color = MaterialTheme.colorScheme.onSurfaceVariant,
-        )
+        item {
+            Column(horizontalAlignment = Alignment.CenterHorizontally) {
+                Text(text = title, style = MaterialTheme.typography.titleMedium)
+                Spacer(Modifier.height(8.dp))
+                Text(
+                    text = body,
+                    style = MaterialTheme.typography.bodyMedium,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                )
+            }
+        }
     }
 }
 

android/app/src/main/java/com/fabledsword/thoughtsync/ui/SyncViewModel.kt

@@ -278,6 +278,18 @@ class SyncViewModel(
         state = state.copy(lastRevoke = null)
     }
 
+    /**
+     * Acknowledge a sync failure.
+     *
+     * Exists because the BOARD reports these too, and a banner the person cannot
+     * get rid of is worse than the failure it describes. Clearing is honest here:
+     * an unsynced note is still pending, `hasPending` still says so, and the next
+     * cycle will report the same fault if it is still there.
+     */
+    fun dismissSyncError() {
+        state = state.copy(syncError = null)
+    }
+
     companion object {
         fun factory(
             core: ThoughtSync,