fix(navigation): prevent duplicate Sheet key crash

Broaden sheet dedup in CodeNavigator.navigate() to match on toString()
(which mirrors SaveableStateProvider contentKey) instead of structural
equality. This prevents the race where pendingSheetDismiss callbacks
push a duplicate Sheet entry onto the NavBackStack.

Also wrap the pendingSheetDismiss callback in a single
Snapshot.withMutableSnapshot for atomicity.

Signed-off-by: Brandon McAnsh <git@bmcreations.dev>

Author: bmc08gt

apps/flipcash/core/src/main/kotlin/com/flipcash/app/core/extensions/CodeNavigator.kt

@@ -1,5 +1,6 @@
 package com.flipcash.app.core.extensions
 
+import androidx.compose.runtime.snapshots.Snapshot
 import androidx.navigation3.runtime.NavKey
 import com.flipcash.app.core.AppRoute
 import com.getcode.navigation.core.CodeNavigator
@@ -39,10 +40,12 @@ fun CodeNavigator.navigateTo(routes: List<NavKey>, options: NavOptions = NavOpti
         // The callback is invoked by ModalBottomSheetScene after the dismiss
         // animation completes and the old entry is removed from the backstack.
         pendingSheetDismiss = {
-            sheetGeneration++
-            resolved.forEachIndexed { index, route ->
-                val navOptions = if (index == 0) options else NavOptions()
-                navigate(route, navOptions)
+            Snapshot.withMutableSnapshot {
+                sheetGeneration++
+                resolved.forEachIndexed { index, route ->
+                    val navOptions = if (index == 0) options else NavOptions()
+                    navigate(route, navOptions)
+                }
             }
         }
     } else {

apps/flipcash/shared/router/src/test/kotlin/com/flipcash/app/router/internal/NavigateToTest.kt

@@ -226,5 +226,55 @@ class NavigateToTest {
         }
     }
 
+    @Test
+    fun `navigate deduplicates identical sheet that was not removed by onBack`() {
+        // Reproduces the production crash: a stale Sheet(Wallet,[]) remains on the
+        // backstack after onBack removed the wrong entry during a dismiss animation.
+        // A subsequent navigate for the same Sheet must not produce a duplicate.
+        val navigator = createNavigator(
+            AppRoute.Main.Scanner,
+            AppRoute.Main.Sheet(AppRoute.Sheets.Wallet),
+        )
+
+        // Simulate: something pushed on top during dismiss, onBack removed that
+        // instead of the sheet, so the old sheet is still here.
+        // Now navigate to the same sheet again.
+        navigator.navigate(
+            AppRoute.Main.Sheet(AppRoute.Sheets.Wallet),
+            NavOptions(debugRouting = false),
+        )
+
+        val sheets = navigator.backStack.filterIsInstance<AppRoute.Main.Sheet>()
+        assertEquals(1, sheets.size, "Expected exactly one Sheet on the backstack")
+    }
+
+    @Test
+    fun `double navigateTo with pending dismiss does not produce duplicate sheets`() {
+        val navigator = createNavigator(
+            AppRoute.Main.Scanner,
+            AppRoute.Main.Sheet(AppRoute.Sheets.Wallet),
+        )
+
+        // First navigate sets pendingSheetDismiss
+        navigator.navigateTo(listOf(AppRoute.Sheets.Menu), options = quietOptions)
+        assertNotNull(navigator.pendingSheetDismiss)
+
+        // Second navigate overwrites pendingSheetDismiss
+        navigator.navigateTo(listOf(AppRoute.Sheets.Menu), options = quietOptions)
+
+        // Simulate: onBack removes old sheet, then callback fires
+        navigator.backStack.removeAt(navigator.backStack.lastIndex)
+        navigator.pendingSheetDismiss!!.invoke()
+
+        // Simulate a stale callback also firing navigate for the same sheet
+        navigator.navigate(
+            AppRoute.Main.Sheet(AppRoute.Sheets.Menu),
+            NavOptions(debugRouting = false),
+        )
+
+        val sheets = navigator.backStack.filterIsInstance<AppRoute.Main.Sheet>()
+        assertEquals(1, sheets.size, "Expected exactly one Sheet on the backstack")
+    }
+
     // endregion
 }

ui/navigation/src/main/kotlin/com/getcode/navigation/core/CodeNavigator.kt

@@ -115,7 +115,7 @@ data class CodeNavigator(
                             if (backStack.isNotEmpty()) backStack.removeAt(backStack.lastIndex)
                         }
                         if (route is Sheet) {
-                            backStack.removeAll { it == route }
+                            backStack.removeAll { it is Sheet && it.toString() == route.toString() }
                         }
                         backStack.add(route)
                     }
@@ -126,10 +126,10 @@ data class CodeNavigator(
                     if (route is Sheet || currentRouteKey != route) {
                         // Sheet routes must be unique on the backstack —
                         // SaveableStateProvider uses contentKey (toString()) and
-                        // crashes on duplicates. Remove any existing instance
-                        // before pushing the new one.
+                        // crashes on duplicates. Remove any entry whose contentKey
+                        // (toString()) matches before pushing the new one.
                         if (route is Sheet) {
-                            backStack.removeAll { it == route }
+                            backStack.removeAll { it is Sheet && it.toString() == route.toString() }
                         }
                         backStack.add(route)
                     }
@@ -139,7 +139,7 @@ data class CodeNavigator(
                 Snapshot.withMutableSnapshot {
                     if (route is Sheet || currentRouteKey != route) {
                         if (route is Sheet) {
-                            backStack.removeAll { it == route }
+                            backStack.removeAll { it is Sheet && it.toString() == route.toString() }
                         }
                         backStack.add(route)
                         val lastIndex = backStack.lastIndex - 1