fix(navigation): back-fill newly-added nav bar buttons into persisted order

apps/flipcash/core/src/main/kotlin/com/flipcash/app/core/navigation/NavBarConfig.kt

@@ -13,11 +13,29 @@ data class NavBarConfig(
         fun deserialize(value: String): NavBarConfig {
             if (value.isBlank()) return Default
             val parts = value.split("|")
-            val order = parts.getOrNull(0)
+            val stored = parts.getOrNull(0)
                 ?.split(",")
                 ?.mapNotNull { runCatching { NavBarButton.valueOf(it) }.getOrNull() }
                 ?.ifEmpty { NavBarButton.defaultOrder }
                 ?: NavBarButton.defaultOrder
+            // Back-fill any buttons added after this order was persisted (e.g. Tips),
+            // inserting each at its position in defaultOrder so it lands where intended
+            // rather than getting appended. Without this, a persisted order that predates
+            // a new button would never surface it, even when its feature flag is enabled.
+            val order = if (stored.containsAll(NavBarButton.defaultOrder)) {
+                stored
+            } else {
+                NavBarButton.defaultOrder.fold(stored) { acc, button ->
+                    if (button in acc) {
+                        acc
+                    } else {
+                        val insertAt = NavBarButton.defaultOrder
+                            .subList(0, NavBarButton.defaultOrder.indexOf(button))
+                            .let { preceding -> acc.indexOfLast { it in preceding } + 1 }
+                        acc.toMutableList().apply { add(insertAt, button) }
+                    }
+                }
+            }
             val label = parts.getOrNull(1)
                 ?.let { runCatching { GiveButtonLabel.valueOf(it) }.getOrNull() }
                 ?: GiveButtonLabel.Give

apps/flipcash/core/src/test/kotlin/com/flipcash/app/core/navigation/NavBarConfigTest.kt

@@ -0,0 +1,65 @@
+package com.flipcash.app.core.navigation
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class NavBarConfigTest {
+
+    @Test
+    fun `blank string yields the default config`() {
+        assertEquals(NavBarConfig.Default, NavBarConfig.deserialize(""))
+    }
+
+    @Test
+    fun `round-trips a full, current order`() {
+        val config = NavBarConfig(
+            order = listOf(NavBarButton.Wallet, NavBarButton.Give, NavBarButton.Discover, NavBarButton.Send, NavBarButton.Tips),
+            giveButtonLabel = GiveButtonLabel.Cash,
+        )
+        assertEquals(config, NavBarConfig.deserialize(config.serialize()))
+    }
+
+    @Test
+    fun `back-fills a button added after the order was persisted, at its default position`() {
+        // A nav bar order persisted before Tips was added to the enum/defaultOrder.
+        val legacy = "Discover,Give,Send,Wallet|Cash"
+
+        val order = NavBarConfig.deserialize(legacy).order
+
+        assertTrue(NavBarButton.Tips in order, "Tips should be back-filled into a legacy order")
+        // Inserted at its defaultOrder position (between Send and Wallet), not appended.
+        assertEquals(
+            listOf(NavBarButton.Discover, NavBarButton.Give, NavBarButton.Send, NavBarButton.Tips, NavBarButton.Wallet),
+            order,
+        )
+    }
+
+    @Test
+    fun `back-fill preserves a user's custom ordering of existing buttons`() {
+        val legacy = "Wallet,Send,Give,Discover|Cash"
+
+        val order = NavBarConfig.deserialize(legacy).order
+
+        assertTrue(NavBarButton.Tips in order)
+        // Existing buttons keep the user's reversed order; only the missing one is added.
+        assertEquals(
+            listOf(NavBarButton.Wallet, NavBarButton.Send, NavBarButton.Give, NavBarButton.Discover),
+            order.filterNot { it == NavBarButton.Tips },
+        )
+    }
+
+    @Test
+    fun `unknown button names are dropped and missing known ones back-filled`() {
+        val order = NavBarConfig.deserialize("Discover,Bogus,Give,Send,Wallet|Cash").order
+
+        assertEquals(NavBarButton.defaultOrder, order)
+    }
+
+    @Test
+    fun `empty order falls back to the default order`() {
+        val order = NavBarConfig.deserialize("|Cash").order
+
+        assertEquals(NavBarButton.defaultOrder, order)
+    }
+}