Add split pane UI for new conversation screen.

app/build.gradle.kts

@@ -508,7 +508,6 @@ dependencies {
   implementation(project(":core-ui"))
 
   implementation(libs.androidx.fragment.ktx)
-  implementation(libs.androidx.fragment.compose)
   implementation(libs.androidx.appcompat) {
     version {
       strictly("1.6.1")

app/src/main/AndroidManifest.xml

@@ -697,6 +697,11 @@
               android:configChanges="touchscreen|keyboard|keyboardHidden|orientation|screenLayout|screenSize"
               android:exported="false"/>
 
+    <activity
+              android:name=".conversation.NewConversationActivityV2"
+              android:exported="false"
+              android:theme="@style/Signal.DayNight.NoActionBar" />
+
     <activity android:name=".recipients.ui.findby.FindByActivity"
               android:theme="@style/Theme.Signal.DayNight.NoActionBar"
               android:windowSoftInputMode="adjustResize"

app/src/main/java/org/thoughtcrime/securesms/ContactSelectionListFragment.java

@@ -138,16 +138,16 @@ public final class ContactSelectionListFragment extends LoggingFragment {
   private TextView                        headerActionView;
   private ContactSearchMediator           contactSearchMediator;
 
-  @Nullable private NewConversationCallback              newConversationCallback;
-  @Nullable private FindByCallback                       findByCallback;
-  @Nullable private NewCallCallback                      newCallCallback;
-  @Nullable private ScrollCallback                       scrollCallback;
-  @Nullable private OnItemLongClickListener              onItemLongClickListener;
-  private           SelectionLimits                      selectionLimit    = SelectionLimits.NO_LIMITS;
-  private           Set<RecipientId>                     currentSelection;
-  private           boolean                              isMulti;
-  private           boolean                              canSelectSelf;
-  private           boolean                              resetPositionOnCommit = false;
+  @Nullable private NewConversationCallback newConversationCallback;
+  @Nullable private FindByCallback          findByCallback;
+  @Nullable private NewCallCallback         newCallCallback;
+  @Nullable private ScrollCallback          scrollCallback;
+  @Nullable private OnItemLongClickListener onItemLongClickListener;
+  private           SelectionLimits         selectionLimit        = SelectionLimits.NO_LIMITS;
+  private           Set<RecipientId>        currentSelection;
+  private           boolean                 isMulti;
+  private           boolean                 canSelectSelf;
+  private           boolean                 resetPositionOnCommit = false;
 
   private           ListClickListener                    listClickListener = new ListClickListener();
   @Nullable private SwipeRefreshLayout.OnRefreshListener onRefreshListener;
@@ -161,7 +161,7 @@ public final class ContactSelectionListFragment extends LoggingFragment {
     }
 
     if (context instanceof FindByCallback) {
-      findByCallback = (FindByCallback) context;
+      showFindByUsernameAndPhoneOptions((FindByCallback) context);
     }
 
     if (context instanceof NewCallCallback) {
@@ -177,11 +177,11 @@ public final class ContactSelectionListFragment extends LoggingFragment {
     }
 
     if (getParentFragment() instanceof OnContactSelectedListener) {
-      onContactSelectedListener = (OnContactSelectedListener) getParentFragment();
+      setOnContactSelectedListener((OnContactSelectedListener) getParentFragment());
     }
 
     if (context instanceof OnContactSelectedListener) {
-      onContactSelectedListener = (OnContactSelectedListener) context;
+      setOnContactSelectedListener((OnContactSelectedListener) context);
     }
 
     if (context instanceof OnSelectionLimitReachedListener) {
@@ -209,6 +209,14 @@ public final class ContactSelectionListFragment extends LoggingFragment {
     }
   }
 
+  public void showFindByUsernameAndPhoneOptions(@Nullable FindByCallback callback) {
+    this.findByCallback = callback;
+  }
+
+  public void setOnContactSelectedListener(@Nullable OnContactSelectedListener listener) {
+    this.onContactSelectedListener = listener;
+  }
+
   @Override
   public void onActivityCreated(Bundle icicle) {
     super.onActivityCreated(icicle);
@@ -221,7 +229,7 @@ public final class ContactSelectionListFragment extends LoggingFragment {
     super.onStart();
 
     if (hasContactsPermissions(requireContext()) && !TextSecurePreferences.hasSuccessfullyRetrievedDirectory(getActivity())) {
-        handleContactPermissionGranted();
+      handleContactPermissionGranted();
     } else {
       requireActivity().getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_HIDDEN);
       contactSearchMediator.refresh();
@@ -232,13 +240,13 @@ public final class ContactSelectionListFragment extends LoggingFragment {
   public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
     View view = inflater.inflate(R.layout.contact_selection_list_fragment, container, false);
 
-    emptyText                = view.findViewById(android.R.id.empty);
-    recyclerView             = view.findViewById(R.id.recycler_view);
-    swipeRefresh             = view.findViewById(R.id.swipe_refresh);
-    fastScroller             = view.findViewById(R.id.fast_scroller);
-    chipRecycler             = view.findViewById(R.id.chipRecycler);
-    constraintLayout         = view.findViewById(R.id.container);
-    headerActionView         = view.findViewById(R.id.header_action);
+    emptyText        = view.findViewById(android.R.id.empty);
+    recyclerView     = view.findViewById(R.id.recycler_view);
+    swipeRefresh     = view.findViewById(R.id.swipe_refresh);
+    fastScroller     = view.findViewById(R.id.fast_scroller);
+    chipRecycler     = view.findViewById(R.id.chipRecycler);
+    constraintLayout = view.findViewById(R.id.container);
+    headerActionView = view.findViewById(R.id.header_action);
 
     final LinearLayoutManager layoutManager = new LinearLayoutManager(requireContext());
 
@@ -441,7 +449,7 @@ public final class ContactSelectionListFragment extends LoggingFragment {
   @Override
   public void onDestroyView() {
     super.onDestroyView();
-    constraintLayout = null;
+    constraintLayout  = null;
     onRefreshListener = null;
   }
 
@@ -723,7 +731,7 @@ public final class ContactSelectionListFragment extends LoggingFragment {
 
           SimpleTask.run(getViewLifecycleOwner().getLifecycle(), () -> {
             return UsernameRepository.fetchAciForUsername(UsernameUtil.sanitizeUsernameFromSearch(username));
-          }, result  -> {
+          }, result -> {
             loadingDialog.dismiss();
 
             // TODO Could be more specific with errors
@@ -756,10 +764,10 @@ public final class ContactSelectionListFragment extends LoggingFragment {
                 selectedContact.getNumber(),
                 Optional.empty(),
                 allowed -> {
-              if (allowed) {
-                markContactSelected(selectedContact);
-              }
-            });
+                  if (allowed) {
+                    markContactSelected(selectedContact);
+                  }
+                });
           } else {
             markContactSelected(selectedContact);
           }
@@ -913,9 +921,10 @@ public final class ContactSelectionListFragment extends LoggingFragment {
       builder.setQuery(contactSearchState.getQuery());
 
       if ((newConversationCallback != null || findByCallback != null) &&
-          !hasContactsPermissions(requireContext())                     &&
+          !hasContactsPermissions(requireContext()) &&
           !SignalStore.uiHints().getDismissedContactsPermissionBanner() &&
-          !hasQuery) {
+          !hasQuery)
+      {
         builder.arbitrary(ContactSelectionListAdapter.ArbitraryRepository.ArbitraryRow.FIND_CONTACTS_BANNER.getCode());
       }
 

app/src/main/java/org/thoughtcrime/securesms/components/ContactFilterView.java

@@ -25,8 +25,13 @@ import org.thoughtcrime.securesms.util.ServiceUtil;
 import org.thoughtcrime.securesms.util.TextSecurePreferences;
 import org.thoughtcrime.securesms.util.ViewUtil;
 
+/**
+ * A search input field for finding recipients.
+ * <p>
+ * In compose, use RecipientSearchField instead.
+ */
 public final class ContactFilterView extends FrameLayout {
-  private   OnFilterChangedListener listener;
+  private OnFilterChangedListener listener;
 
   private final EditText        searchText;
   private final AnimatingToggle toggle;

app/src/main/java/org/thoughtcrime/securesms/components/compose/ScreenTitlePane.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2025 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.components.compose
+
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+import org.thoughtcrime.securesms.window.WindowSizeClass
+
+/**
+ * Displays the screen title for split-pane UIs on tablets and foldable devices.
+ */
+@Composable
+fun ScreenTitlePane(
+  title: String,
+  modifier: Modifier = Modifier
+) {
+  val windowSizeClass = WindowSizeClass.rememberWindowSizeClass()
+
+  Text(
+    text = title,
+    style = MaterialTheme.typography.headlineLarge,
+    color = MaterialTheme.colorScheme.onSurface,
+    modifier = modifier
+      .padding(
+        start = if (windowSizeClass.isExtended()) 80.dp else 20.dp,
+        end = 20.dp,
+        top = 12.dp,
+        bottom = 12.dp
+      )
+  )
+}

app/src/main/java/org/thoughtcrime/securesms/conversation/NewConversationActivityV2.kt

@@ -0,0 +1,152 @@
+/*
+ * Copyright 2025 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.conversation
+
+import android.content.Context
+import android.content.Intent
+import android.os.Bundle
+import androidx.activity.compose.setContent
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.widthIn
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.material3.adaptive.ExperimentalMaterial3AdaptiveApi
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.vector.ImageVector
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.res.vectorResource
+import androidx.compose.ui.unit.dp
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import org.signal.core.ui.compose.AllDevicePreviews
+import org.signal.core.ui.compose.Previews
+import org.signal.core.ui.compose.Scaffolds
+import org.signal.core.ui.compose.theme.SignalTheme
+import org.thoughtcrime.securesms.PassphraseRequiredActivity
+import org.thoughtcrime.securesms.R
+import org.thoughtcrime.securesms.components.compose.ScreenTitlePane
+import org.thoughtcrime.securesms.util.viewModel
+import org.thoughtcrime.securesms.window.AppScaffoldWithTopBar
+import org.thoughtcrime.securesms.window.WindowSizeClass
+import org.thoughtcrime.securesms.window.rememberAppScaffoldNavigator
+
+/**
+ * Allows the user to start a new conversation by selecting a recipient.
+ *
+ * A modernized compose-based replacement for [org.thoughtcrime.securesms.NewConversationActivity].
+ */
+class NewConversationActivityV2 : PassphraseRequiredActivity() {
+  companion object {
+    @JvmStatic
+    fun createIntent(context: Context): Intent = Intent(context, NewConversationActivityV2::class.java)
+  }
+
+  private val viewModel by viewModel { NewConversationViewModel() }
+
+  override fun onCreate(savedInstanceState: Bundle?, ready: Boolean) {
+    super.onCreate(savedInstanceState, ready)
+
+    setContent {
+      val uiState by viewModel.uiState.collectAsStateWithLifecycle()
+
+      SignalTheme {
+        NewConversationScreen(
+          uiState = uiState,
+          callbacks = object : Callbacks {
+            override fun onBackPressed() = onBackPressedDispatcher.onBackPressed()
+          }
+        )
+      }
+    }
+  }
+}
+
+@OptIn(ExperimentalMaterial3Api::class, ExperimentalMaterial3AdaptiveApi::class)
+@Composable
+private fun NewConversationScreen(
+  uiState: NewConversationUiState,
+  callbacks: Callbacks
+) {
+  val windowSizeClass = WindowSizeClass.rememberWindowSizeClass()
+  val isSplitPane = windowSizeClass.isSplitPane(forceSplitPaneOnCompactLandscape = uiState.forceSplitPaneOnCompactLandscape)
+
+  AppScaffoldWithTopBar(
+    topBarContent = {
+      Scaffolds.DefaultTopAppBar(
+        title = if (!isSplitPane) stringResource(R.string.NewConversationActivity__new_message) else "",
+        titleContent = { _, title -> Text(text = title, style = MaterialTheme.typography.titleLarge) },
+        navigationIcon = ImageVector.vectorResource(R.drawable.symbol_arrow_start_24),
+        navigationContentDescription = stringResource(R.string.DefaultTopAppBar__navigate_up_content_description),
+        onNavigationClick = callbacks::onBackPressed
+      )
+    },
+    listContent = {
+      if (isSplitPane) {
+        ScreenTitlePane(
+          title = stringResource(R.string.NewConversationActivity__new_message),
+          modifier = Modifier.fillMaxSize()
+        )
+      } else {
+        DetailPaneContent()
+      }
+    },
+
+    detailContent = {
+      Box(
+        contentAlignment = Alignment.Center,
+        modifier = Modifier.fillMaxSize()
+      ) {
+        DetailPaneContent(
+          modifier = Modifier
+            .widthIn(max = windowSizeClass.detailPaneMaxContentWidth)
+        )
+      }
+    },
+
+    navigator = rememberAppScaffoldNavigator(
+      isSplitPane = isSplitPane
+    )
+  )
+}
+
+private interface Callbacks {
+  fun onBackPressed()
+
+  object Empty : Callbacks {
+    override fun onBackPressed() = Unit
+  }
+}
+
+@Composable
+private fun DetailPaneContent(
+  modifier: Modifier = Modifier
+) {
+  RecipientPicker(
+    showFindByUsernameAndPhoneOptions = true,
+    callbacks = RecipientPickerCallbacks.Empty, // TODO(jeffrey) implement callbacks
+    modifier = modifier
+      .fillMaxSize()
+      .padding(vertical = 12.dp)
+  )
+}
+
+@AllDevicePreviews
+@Composable
+private fun NewConversationScreenPreview() {
+  Previews.Preview {
+    NewConversationScreen(
+      uiState = NewConversationUiState(
+        forceSplitPaneOnCompactLandscape = false
+      ),
+      callbacks = Callbacks.Empty
+    )
+  }
+}

app/src/main/java/org/thoughtcrime/securesms/conversation/NewConversationViewModel.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2025 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.conversation
+
+import androidx.lifecycle.ViewModel
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import org.thoughtcrime.securesms.keyvalue.SignalStore
+
+class NewConversationViewModel : ViewModel() {
+  private val _uiState = MutableStateFlow(NewConversationUiState())
+  val uiState: StateFlow<NewConversationUiState> = _uiState.asStateFlow()
+}
+
+data class NewConversationUiState(
+  val forceSplitPaneOnCompactLandscape: Boolean = SignalStore.internal.forceSplitPaneOnCompactLandscape
+)

app/src/main/java/org/thoughtcrime/securesms/conversation/RecipientPicker.kt

@@ -0,0 +1,155 @@
+/*
+ * Copyright 2025 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.conversation
+
+import androidx.annotation.StringRes
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.DisposableEffect
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.saveable.rememberSaveable
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.viewinterop.AndroidView
+import androidx.fragment.compose.rememberFragmentState
+import org.signal.core.ui.compose.DayNightPreviews
+import org.signal.core.ui.compose.Fragments
+import org.thoughtcrime.securesms.ContactSelectionListFragment
+import org.thoughtcrime.securesms.components.ContactFilterView
+import org.thoughtcrime.securesms.recipients.RecipientId
+
+/**
+ * Provides a recipient search and selection UI.
+ */
+@Composable
+fun RecipientPicker(
+  showFindByUsernameAndPhoneOptions: Boolean,
+  callbacks: RecipientPickerCallbacks,
+  modifier: Modifier = Modifier
+) {
+  var searchQuery by rememberSaveable { mutableStateOf("") }
+
+  Column(
+    modifier = modifier
+  ) {
+    RecipientSearchField(
+      onFilterChanged = { filter ->
+        searchQuery = filter
+      },
+      modifier = Modifier
+        .fillMaxWidth()
+        .padding(horizontal = 16.dp)
+    )
+
+    RecipientSearchResultsList(
+      searchQuery = searchQuery,
+      showFindByUsernameAndPhoneOptions = showFindByUsernameAndPhoneOptions,
+      callbacks = callbacks,
+      modifier = Modifier
+        .fillMaxSize()
+        .padding(top = 8.dp)
+    )
+  }
+}
+
+/**
+ * A search input field for finding recipients.
+ *
+ * Intended to be a compose-based replacement for [ContactFilterView].
+ */
+@Composable
+private fun RecipientSearchField(
+  onFilterChanged: (String) -> Unit,
+  @StringRes hintText: Int? = null,
+  modifier: Modifier = Modifier
+) {
+  val context = LocalContext.current
+  val wrappedView = remember {
+    ContactFilterView(context, null, 0).apply {
+      hintText?.let { setHint(it) }
+    }
+  }
+
+  DisposableEffect(onFilterChanged) {
+    wrappedView.setOnFilterChangedListener { filter -> onFilterChanged(filter) }
+    onDispose {
+      wrappedView.setOnFilterChangedListener(null)
+    }
+  }
+
+  AndroidView(
+    factory = { wrappedView },
+    modifier = modifier
+  )
+}
+
+@Composable
+private fun RecipientSearchResultsList(
+  searchQuery: String,
+  showFindByUsernameAndPhoneOptions: Boolean,
+  callbacks: RecipientPickerCallbacks,
+  modifier: Modifier = Modifier
+) {
+  val fragmentState = rememberFragmentState()
+  var currentFragment by remember { mutableStateOf<ContactSelectionListFragment?>(null) }
+
+  Fragments.Fragment<ContactSelectionListFragment>(
+    fragmentState = fragmentState,
+    onUpdate = { fragment ->
+      currentFragment = fragment
+      currentFragment?.view?.setPadding(0, 0, 0, 0)
+
+      if (showFindByUsernameAndPhoneOptions) {
+        fragment.showFindByUsernameAndPhoneOptions(object : ContactSelectionListFragment.FindByCallback {
+          override fun onFindByUsername() = callbacks.onFindByUsernameClicked()
+          override fun onFindByPhoneNumber() = callbacks.onFindByPhoneNumberClicked()
+        })
+      }
+    },
+    modifier = modifier
+  )
+
+  var previousQueryText by rememberSaveable { mutableStateOf("") }
+  LaunchedEffect(searchQuery) {
+    if (previousQueryText != searchQuery) {
+      if (searchQuery.isNotBlank()) {
+        currentFragment?.setQueryFilter(searchQuery)
+      } else {
+        currentFragment?.resetQueryFilter()
+      }
+      previousQueryText = searchQuery
+    }
+  }
+}
+
+@DayNightPreviews
+@Composable
+private fun RecipientPickerPreview() {
+  RecipientPicker(
+    showFindByUsernameAndPhoneOptions = true,
+    callbacks = RecipientPickerCallbacks.Empty
+  )
+}
+
+interface RecipientPickerCallbacks {
+  fun onFindByUsernameClicked()
+  fun onFindByPhoneNumberClicked()
+  fun onRecipientClicked(id: RecipientId)
+
+  object Empty : RecipientPickerCallbacks {
+    override fun onFindByUsernameClicked() = Unit
+    override fun onFindByPhoneNumberClicked() = Unit
+    override fun onRecipientClicked(id: RecipientId) = Unit
+  }
+}

app/src/main/java/org/thoughtcrime/securesms/window/AppScaffold.kt

@@ -38,6 +38,7 @@ import androidx.compose.ui.layout.layout
 import androidx.compose.ui.platform.LocalConfiguration
 import androidx.compose.ui.platform.LocalInspectionMode
 import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.zIndex
 import androidx.window.core.ExperimentalWindowCoreApi
@@ -86,6 +87,12 @@ enum class WindowSizeClass(
   EXTENDED_PORTRAIT(Navigation.RAIL),
   EXTENDED_LANDSCAPE(Navigation.RAIL);
 
+  val listPaneDefaultPreferredWidth: Dp
+    get() = if (isExtended()) 416.dp else 316.dp
+
+  val detailPaneMaxContentWidth: Dp = 624.dp
+  val horizontalPartitionDefaultSpacerSize: Dp = 12.dp
+
   fun isCompact(): Boolean = this == COMPACT_PORTRAIT || this == COMPACT_LANDSCAPE
   fun isMedium(): Boolean = this == MEDIUM_PORTRAIT || this == MEDIUM_LANDSCAPE
   fun isExtended(): Boolean = this == EXTENDED_PORTRAIT || this == EXTENDED_LANDSCAPE
@@ -93,8 +100,11 @@ enum class WindowSizeClass(
   fun isLandscape(): Boolean = this == COMPACT_LANDSCAPE || this == MEDIUM_LANDSCAPE || this == EXTENDED_LANDSCAPE
   fun isPortrait(): Boolean = !isLandscape()
 
-  fun isSplitPane(): Boolean {
-    return if (isLargeScreenSupportEnabled() && SignalStore.internal.forceSplitPaneOnCompactLandscape) {
+  @JvmOverloads
+  fun isSplitPane(
+    forceSplitPaneOnCompactLandscape: Boolean = SignalStore.internal.forceSplitPaneOnCompactLandscape
+  ): Boolean {
+    return if (isLargeScreenSupportEnabled() && forceSplitPaneOnCompactLandscape) {
       this != COMPACT_PORTRAIT
     } else {
       this.navigation != Navigation.BAR

app/src/main/java/org/thoughtcrime/securesms/window/AppScaffoldNavigator.kt

@@ -19,7 +19,9 @@ import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
+import androidx.compose.ui.platform.LocalInspectionMode
 import androidx.compose.ui.unit.Dp
+import org.thoughtcrime.securesms.keyvalue.SignalStore
 
 /**
  * AppScaffoldNavigator wraps a delegate navigator (such as the value returned by [rememberThreePaneScaffoldNavigatorDelegate]
@@ -85,9 +87,12 @@ open class AppScaffoldNavigator<T> @RememberInComposition constructor(private va
 @OptIn(ExperimentalMaterial3AdaptiveApi::class)
 @Composable
 fun rememberAppScaffoldNavigator(
-  isSplitPane: Boolean,
-  horizontalPartitionSpacerSize: Dp,
-  defaultPanePreferredWidth: Dp
+  windowSizeClass: WindowSizeClass = WindowSizeClass.rememberWindowSizeClass(),
+  isSplitPane: Boolean = windowSizeClass.isSplitPane(
+    forceSplitPaneOnCompactLandscape = if (LocalInspectionMode.current) false else SignalStore.internal.forceSplitPaneOnCompactLandscape
+  ),
+  horizontalPartitionSpacerSize: Dp = windowSizeClass.horizontalPartitionDefaultSpacerSize,
+  defaultPanePreferredWidth: Dp = windowSizeClass.listPaneDefaultPreferredWidth
 ): AppScaffoldNavigator<Any> {
   val delegate = rememberThreePaneScaffoldNavigatorDelegate(
     isSplitPane,

app/src/main/java/org/thoughtcrime/securesms/window/AppScaffoldWithTopBar.kt

@@ -0,0 +1,142 @@
+/*
+ * Copyright 2025 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.window
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.material3.adaptive.ExperimentalMaterial3AdaptiveApi
+import androidx.compose.material3.adaptive.layout.PaneExpansionState
+import androidx.compose.material3.adaptive.layout.ThreePaneScaffoldScope
+import androidx.compose.material3.adaptive.layout.rememberPaneExpansionState
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.vector.ImageVector
+import androidx.compose.ui.platform.LocalInspectionMode
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.res.vectorResource
+import androidx.compose.ui.text.style.TextAlign
+import org.signal.core.ui.compose.AllDevicePreviews
+import org.signal.core.ui.compose.Previews
+import org.signal.core.ui.compose.Scaffolds
+import org.thoughtcrime.securesms.R
+import org.thoughtcrime.securesms.keyvalue.SignalStore
+
+/**
+ * Wraps [AppScaffold], adding a top app bar that spans across both the list and detail panes.
+ */
+@OptIn(ExperimentalMaterial3AdaptiveApi::class)
+@Composable
+fun AppScaffoldWithTopBar(
+  navigator: AppScaffoldNavigator<Any> = rememberAppScaffoldNavigator(),
+  topBarContent: @Composable () -> Unit = {},
+  detailContent: @Composable () -> Unit = {},
+  navRailContent: @Composable () -> Unit = {},
+  bottomNavContent: @Composable () -> Unit = {},
+  paneExpansionState: PaneExpansionState = rememberPaneExpansionState(),
+  paneExpansionDragHandle: (@Composable ThreePaneScaffoldScope.(PaneExpansionState) -> Unit)? = null,
+  animatorFactory: AppScaffoldAnimationStateFactory = AppScaffoldAnimationStateFactory.Default,
+  listContent: @Composable () -> Unit
+) {
+  val windowSizeClass = WindowSizeClass.rememberWindowSizeClass()
+  val isSplitPane = windowSizeClass.isSplitPane(
+    forceSplitPaneOnCompactLandscape = if (LocalInspectionMode.current) false else SignalStore.internal.forceSplitPaneOnCompactLandscape
+  )
+
+  if (isSplitPane) {
+    Column {
+      topBarContent()
+
+      AppScaffold(
+        navigator = navigator,
+        detailContent = detailContent,
+        navRailContent = navRailContent,
+        bottomNavContent = bottomNavContent,
+        paneExpansionState = paneExpansionState,
+        paneExpansionDragHandle = paneExpansionDragHandle,
+        animatorFactory = animatorFactory,
+        listContent = listContent
+      )
+    }
+  } else {
+    AppScaffold(
+      navigator = navigator,
+      detailContent = detailContent,
+      navRailContent = navRailContent,
+      bottomNavContent = bottomNavContent,
+      paneExpansionState = paneExpansionState,
+      paneExpansionDragHandle = paneExpansionDragHandle,
+      animatorFactory = animatorFactory,
+      listContent = {
+        Scaffold(topBar = topBarContent) { paddingValues ->
+          Box(modifier = Modifier.padding(paddingValues)) {
+            listContent()
+          }
+        }
+      }
+    )
+  }
+}
+
+@OptIn(ExperimentalMaterial3Api::class, ExperimentalMaterial3AdaptiveApi::class)
+@AllDevicePreviews
+@Composable
+private fun AppScaffoldWithTopBarPreview() {
+  Previews.Preview {
+    val windowSizeClass = WindowSizeClass.rememberWindowSizeClass()
+    val isSplitPane = windowSizeClass.isSplitPane(forceSplitPaneOnCompactLandscape = false)
+
+    AppScaffoldWithTopBar(
+      navigator = rememberAppScaffoldNavigator(),
+
+      topBarContent = {
+        Scaffolds.DefaultTopAppBar(
+          title = if (!isSplitPane) stringResource(R.string.NewConversationActivity__new_message) else "",
+          titleContent = { _, title -> Text(text = title, style = MaterialTheme.typography.titleLarge) },
+          navigationIcon = ImageVector.vectorResource(R.drawable.symbol_arrow_start_24),
+          navigationContentDescription = "",
+          onNavigationClick = { }
+        )
+      },
+
+      listContent = {
+        Box(
+          contentAlignment = Alignment.Center,
+          modifier = Modifier
+            .fillMaxSize()
+            .background(color = Color.Red)
+        ) {
+          Text(
+            text = "ListContent\n$windowSizeClass",
+            textAlign = TextAlign.Center
+          )
+        }
+      },
+
+      detailContent = {
+        Box(
+          contentAlignment = Alignment.Center,
+          modifier = Modifier
+            .fillMaxSize()
+            .background(color = Color.Blue)
+        ) {
+          Text(
+            text = "DetailContent",
+            textAlign = TextAlign.Center
+          )
+        }
+      }
+    )
+  }
+}

app/src/main/res/values/strings.xml

@@ -5926,8 +5926,8 @@
         <item quantity="other">%1$s are not Signal users</item>
     </plurals>
 
-    <!-- ContactFilterView -->
-    <string name="ContactFilterView__search_name_or_number">Search name or number</string>
+    <!-- Hint text that shows in the recipient search box when no text is entered yet. -->
+    <string name="ContactFilterView__search_name_or_number">Name, username or number</string>
 
     <!-- VoiceNotePlayerView -->
     <string name="VoiceNotePlayerView__dot_s">· %1$s</string>

core-ui/build.gradle.kts

@@ -29,4 +29,5 @@ dependencies {
   api(libs.androidx.compose.material3.adaptive.navigation)
   api(libs.androidx.compose.ui.tooling.preview)
   debugApi(libs.androidx.compose.ui.tooling.core)
+  api(libs.androidx.fragment.compose)
 }

core-ui/src/main/java/org/signal/core/ui/compose/Fragments.kt

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2025 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.signal.core.ui.compose
+
+import android.os.Bundle
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.wrapContentSize
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalInspectionMode
+import androidx.fragment.app.Fragment
+import androidx.fragment.compose.AndroidFragment
+import androidx.fragment.compose.FragmentState
+import androidx.fragment.compose.rememberFragmentState
+import org.signal.core.ui.compose.Fragments.Fragment
+
+object Fragments {
+  /**
+   * Wraps an [Fragment], displaying the fragment at runtime or a placeholder in compose previews to avoid rendering errors that occur when
+   * using [Fragment] in @Preview composables.
+   */
+  @Composable
+  inline fun <reified T : Fragment> Fragment(
+    modifier: Modifier = Modifier,
+    fragmentState: FragmentState = rememberFragmentState(),
+    arguments: Bundle = Bundle.EMPTY,
+    noinline onUpdate: (T) -> Unit = { }
+  ) {
+    if (!LocalInspectionMode.current) {
+      AndroidFragment(clazz = T::class.java, modifier, fragmentState, arguments, onUpdate)
+    } else {
+      Text(
+        text = "[${T::class.simpleName}]",
+        style = MaterialTheme.typography.bodyLarge,
+        modifier = modifier
+          .fillMaxSize()
+          .background(Color.Gray)
+          .wrapContentSize(Alignment.Center)
+      )
+    }
+  }
+
+  /**
+   * Wraps an [Fragment], displaying the fragment at runtime or a placeholder in compose previews to avoid rendering errors that occur when
+   * using [Fragment] in @Preview composables.
+   */
+  @Composable
+  fun <T : Fragment> Fragment(
+    clazz: Class<T>,
+    modifier: Modifier = Modifier,
+    fragmentState: FragmentState = rememberFragmentState(),
+    arguments: Bundle = Bundle.EMPTY,
+    onUpdate: (T) -> Unit = { }
+  ) {
+    if (!LocalInspectionMode.current) {
+      AndroidFragment(clazz = clazz, modifier, fragmentState, arguments, onUpdate)
+    } else {
+      Text(
+        text = "[${clazz.simpleName}]",
+        style = MaterialTheme.typography.bodyLarge,
+        modifier = modifier
+          .fillMaxSize()
+          .background(Color.Gray)
+          .wrapContentSize(Alignment.Center)
+      )
+    }
+  }
+}