Keep FAB position stable when AppBottomBar is hidden

AppBottomBar returns nothing on canPop entries (drawer pushes, in-app
navigations), so the floating action button drops by the bar's height
when navigating into a screen and rises again on a tab root. Reserve the
50dp gap at the FAB site via a fabBottomBarPadding(nav) modifier so the
button stays at a consistent vertical position regardless of the bar's
visibility on EmojiPacks, BookmarkGroups, and InterestSets.

https://claude.ai/code/session_01QSk7CnjNtbcgS3XBD5WEZy

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/bottombars/AppBottomBar.kt

@@ -54,6 +54,11 @@ import com.vitorpamplona.amethyst.ui.theme.Size10Modifier
 import com.vitorpamplona.amethyst.ui.theme.Size24dp
 import com.vitorpamplona.amethyst.ui.theme.Size27dp
 
+/** Content height of the [AppBottomBar] (the 50.dp Column inside [RenderBottomMenu]),
+ * exclusive of the system navigation-bar inset. Used by FAB callers that want to
+ * reserve the same vertical space when the bar hides itself on canPop entries. */
+val AppBottomBarHeight = 50.dp
+
 @Composable
 fun AppBottomBar(
     selectedRoute: Route?,
@@ -99,7 +104,7 @@ private fun RenderBottomMenu(
                 .background(MaterialTheme.colorScheme.background)
                 .windowInsetsPadding(windowInsets)
                 .consumeWindowInsets(windowInsets)
-                .height(50.dp),
+                .height(AppBottomBarHeight),
     ) {
         HorizontalDivider(
             thickness = DividerThickness,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/bottombars/FabBottomBarPadding.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.ui.navigation.bottombars
+
+import androidx.compose.foundation.layout.padding
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import com.vitorpamplona.amethyst.ui.navigation.navs.INav
+
+/**
+ * Reserves the visual space the [AppBottomBar] occupies on root tab entries so a
+ * FloatingActionButton stays at the same vertical position whether or not the bar is
+ * rendered. [AppBottomBar] hides itself on canPop entries (drawer pushes, in-app
+ * navigations) — without this padding the FAB drops by [AppBottomBarHeight] there.
+ *
+ * The system-navigation-bar inset is already handled by the surrounding Scaffold, so
+ * only the bar's content height needs to be reserved.
+ */
+@Composable
+fun Modifier.fabBottomBarPadding(nav: INav): Modifier = if (nav.canPop()) padding(bottom = AppBottomBarHeight) else this

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/bookmarkgroups/list/ListOfBookmarkGroupsScreen.kt

@@ -40,6 +40,7 @@ import com.vitorpamplona.amethyst.model.nip51Lists.OldBookmarkListState
 import com.vitorpamplona.amethyst.model.nip51Lists.PinListState
 import com.vitorpamplona.amethyst.model.nip51Lists.labeledBookmarkLists.LabeledBookmarkList
 import com.vitorpamplona.amethyst.ui.navigation.bottombars.AppBottomBar
+import com.vitorpamplona.amethyst.ui.navigation.bottombars.fabBottomBarPadding
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.navigation.routes.Route
 import com.vitorpamplona.amethyst.ui.navigation.topbars.TopBarWithBackButton
@@ -130,7 +131,10 @@ fun ListOfBookmarkGroupsFeed(
             }
         },
         floatingActionButton = {
-            BookmarkGroupFab(onAddGroup = addBookmarkGroup)
+            BookmarkGroupFab(
+                onAddGroup = addBookmarkGroup,
+                modifier = Modifier.fabBottomBarPadding(nav),
+            )
         },
     ) { paddingValues ->
         Column(
@@ -160,7 +164,10 @@ fun ListOfBookmarkGroupsFeed(
 }
 
 @Composable
-fun BookmarkGroupFab(onAddGroup: () -> Unit) {
+fun BookmarkGroupFab(
+    onAddGroup: () -> Unit,
+    modifier: Modifier = Modifier,
+) {
     ExtendedFloatingActionButton(
         text = {
             Text(text = stringRes(R.string.follow_set_create_btn_label))
@@ -174,5 +181,6 @@ fun BookmarkGroupFab(onAddGroup: () -> Unit) {
         onClick = onAddGroup,
         shape = CircleShape,
         containerColor = MaterialTheme.colorScheme.primary,
+        modifier = modifier,
     )
 }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/emojipacks/list/ListOfEmojiPacksScreen.kt

@@ -62,6 +62,7 @@ import com.vitorpamplona.amethyst.ui.components.M3ActionDialog
 import com.vitorpamplona.amethyst.ui.components.M3ActionRow
 import com.vitorpamplona.amethyst.ui.components.M3ActionSection
 import com.vitorpamplona.amethyst.ui.navigation.bottombars.AppBottomBar
+import com.vitorpamplona.amethyst.ui.navigation.bottombars.fabBottomBarPadding
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.navigation.routes.Route
 import com.vitorpamplona.amethyst.ui.navigation.topbars.TopBarWithBackButton
@@ -126,7 +127,10 @@ fun ListOfEmojiPacksFeed(
             }
         },
         floatingActionButton = {
-            EmojiPackFab(onAddPack = addEmojiPack)
+            EmojiPackFab(
+                onAddPack = addEmojiPack,
+                modifier = Modifier.fabBottomBarPadding(nav),
+            )
         },
     ) { paddingValues ->
         Column(
@@ -308,7 +312,10 @@ private fun MyEmojiListRow(
 }
 
 @Composable
-fun EmojiPackFab(onAddPack: () -> Unit) {
+fun EmojiPackFab(
+    onAddPack: () -> Unit,
+    modifier: Modifier = Modifier,
+) {
     ExtendedFloatingActionButton(
         text = {
             Text(text = stringRes(R.string.new_emoji_pack))
@@ -322,5 +329,6 @@ fun EmojiPackFab(onAddPack: () -> Unit) {
         onClick = onAddPack,
         shape = CircleShape,
         containerColor = MaterialTheme.colorScheme.primary,
+        modifier = modifier,
     )
 }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/interestSets/list/ListOfInterestSetsScreen.kt

@@ -48,6 +48,7 @@ import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.commons.icons.symbols.Icon
 import com.vitorpamplona.amethyst.commons.icons.symbols.MaterialSymbols
 import com.vitorpamplona.amethyst.ui.navigation.bottombars.AppBottomBar
+import com.vitorpamplona.amethyst.ui.navigation.bottombars.fabBottomBarPadding
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.navigation.routes.Route
 import com.vitorpamplona.amethyst.ui.navigation.topbars.TopBarWithBackButton
@@ -82,7 +83,10 @@ fun ListOfInterestSetsScreen(
             }
         },
         floatingActionButton = {
-            InterestSetFab(onAdd = { nav.nav(Route.InterestSetMetadataEdit()) })
+            InterestSetFab(
+                onAdd = { nav.nav(Route.InterestSetMetadataEdit()) },
+                modifier = Modifier.fabBottomBarPadding(nav),
+            )
         },
     ) { paddingValues ->
         Column(
@@ -155,7 +159,10 @@ private fun EmptyInterestSets() {
 }
 
 @Composable
-fun InterestSetFab(onAdd: () -> Unit) {
+fun InterestSetFab(
+    onAdd: () -> Unit,
+    modifier: Modifier = Modifier,
+) {
     ExtendedFloatingActionButton(
         text = {
             Text(text = stringRes(R.string.interest_set_create_btn_label))
@@ -169,5 +176,6 @@ fun InterestSetFab(onAdd: () -> Unit) {
         onClick = onAdd,
         shape = CircleShape,
         containerColor = MaterialTheme.colorScheme.primary,
+        modifier = modifier,
     )
 }