fix(nav): make canPop reactive so back-swipe transitions don't leave stale arrows

The previous fix added a start-destination short-circuit, but it only
helped if controller.currentBackStackEntry happened to be Home at the
moment canPop was called. During a back-swipe, the popping entry can
still be the current entry while Home is being revealed, so the
short-circuit didn't fire — and once the gesture finished, nothing
re-evaluated canPop, so the stale 'true' stuck.

Make canPop @Composable and read currentBackStackEntryAsState so call
sites recompose when the back stack settles after any navigation or
back-swipe transition. All existing callers (top bars, app bottom bar,
profile header, screen-level scaffolds) are already in @Composable
contexts, so no signature changes ripple out.

https://claude.ai/code/session_01PrirRcL7g8iX7vTqqLTkBS

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/navs/EmptyNav.kt

@@ -22,6 +22,7 @@ package com.vitorpamplona.amethyst.ui.navigation.navs
 
 import androidx.compose.material3.DrawerState
 import androidx.compose.material3.DrawerValue
+import androidx.compose.runtime.Composable
 import androidx.compose.runtime.Stable
 import com.vitorpamplona.amethyst.ui.navigation.routes.Route
 import kotlinx.coroutines.CoroutineScope
@@ -46,6 +47,7 @@ class EmptyNav : INav {
 
     override fun navBottomBar(route: Route) {}
 
+    @Composable
     override fun canPop(): Boolean = false
 
     override fun popBack() {}

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/navs/INav.kt

@@ -21,6 +21,7 @@
 package com.vitorpamplona.amethyst.ui.navigation.navs
 
 import androidx.compose.material3.DrawerState
+import androidx.compose.runtime.Composable
 import androidx.compose.runtime.Stable
 import com.vitorpamplona.amethyst.ui.navigation.routes.Route
 import kotlinx.coroutines.CoroutineScope
@@ -43,6 +44,7 @@ interface INav {
 
     fun navBottomBar(route: Route)
 
+    @Composable
     fun canPop(): Boolean
 
     fun popBack()

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/navs/Nav.kt

@@ -23,8 +23,12 @@ package com.vitorpamplona.amethyst.ui.navigation.navs
 import android.annotation.SuppressLint
 import androidx.compose.material3.DrawerState
 import androidx.compose.material3.DrawerValue
+import androidx.compose.runtime.Composable
 import androidx.compose.runtime.Stable
+import androidx.compose.runtime.getValue
+import androidx.navigation.NavGraph.Companion.findStartDestination
 import androidx.navigation.NavHostController
+import androidx.navigation.compose.currentBackStackEntryAsState
 import com.vitorpamplona.amethyst.ui.navigation.BOTTOM_NAV_ROOT_KEY
 import com.vitorpamplona.amethyst.ui.navigation.isBottomNavRoot
 import com.vitorpamplona.amethyst.ui.navigation.routes.Route
@@ -93,9 +97,20 @@ class Nav(
         }
     }
 
+    @Composable
     override fun canPop(): Boolean {
-        val current = controller.currentBackStackEntry ?: return false
-        if (current.isBottomNavRoot()) return false
+        // Observe the current entry as State so consumers recompose when the
+        // back stack settles after a navigation or back-swipe transition.
+        // A non-reactive read would leave a stale value behind: e.g. on
+        // back-swipe to Home, previousBackStackEntry is still the popping
+        // entry until the gesture finishes, and nothing would re-evaluate
+        // canPop afterwards.
+        val current by controller.currentBackStackEntryAsState()
+        val entry = current ?: return false
+        if (entry.isBottomNavRoot()) return false
+        // Home is the graph's start destination and nothing can sit below
+        // it, so a back arrow there is never meaningful.
+        if (entry.destination.id == controller.graph.findStartDestination().id) return false
         return controller.previousBackStackEntry != null
     }