fix(xqt): tolerate unknown timeline instructions

social/xqt/src/commonMain/kotlin/dev/dimension/flare/data/network/xqt/XQTJson.kt

@@ -0,0 +1,25 @@
+package dev.dimension.flare.data.network.xqt
+
+import dev.dimension.flare.common.JSON_WITH_ENCODE_DEFAULT
+import dev.dimension.flare.data.network.xqt.model.InstructionUnion
+import dev.dimension.flare.data.network.xqt.model.UnknownInstruction
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.modules.SerializersModule
+import kotlinx.serialization.modules.polymorphic
+
+internal val XQT_JSON =
+    Json(JSON_WITH_ENCODE_DEFAULT) {
+        serializersModule =
+            SerializersModule {
+                include(JSON_WITH_ENCODE_DEFAULT.serializersModule)
+                polymorphic(InstructionUnion::class) {
+                    defaultDeserializer { type ->
+                        if (type == null) {
+                            null
+                        } else {
+                            UnknownInstruction.serializer()
+                        }
+                    }
+                }
+            }
+    }

social/xqt/src/commonMain/kotlin/dev/dimension/flare/data/network/xqt/XQTService.kt

@@ -1,6 +1,5 @@
 package dev.dimension.flare.data.network.xqt
 
-import dev.dimension.flare.common.JSON_WITH_ENCODE_DEFAULT
 import dev.dimension.flare.common.Locale
 import dev.dimension.flare.data.network.ktorClient
 import dev.dimension.flare.data.network.ktorfit
@@ -71,7 +70,7 @@ private fun config(
     url: String = baseUrl,
     accountKey: MicroBlogKey? = null,
     chocolateFlow: Flow<String>? = null,
-) = ktorfit(url, json = JSON_WITH_ENCODE_DEFAULT) {
+) = ktorfit(url, json = XQT_JSON) {
     expectSuccess = false
     install(XQTHeaderPlugin) {
         this.chocolateFlow = chocolateFlow

social/xqt/src/commonMain/kotlin/dev/dimension/flare/data/network/xqt/model/UnknownInstruction.kt

@@ -0,0 +1,7 @@
+package dev.dimension.flare.data.network.xqt.model
+
+import kotlinx.serialization.Serializable
+
+// Unrecognized server instructions must not prevent known timeline entries from loading.
+@Serializable
+internal data object UnknownInstruction : InstructionUnion

social/xqt/src/commonTest/kotlin/dev/dimension/flare/data/network/xqt/XQTJsonTest.kt

@@ -0,0 +1,126 @@
+package dev.dimension.flare.data.network.xqt
+
+import dev.dimension.flare.data.network.xqt.model.CursorType
+import dev.dimension.flare.data.network.xqt.model.NotificationsTimelineResponse
+import dev.dimension.flare.data.network.xqt.model.TimelineAddEntries
+import dev.dimension.flare.data.network.xqt.model.TimelineNotification
+import dev.dimension.flare.data.network.xqt.model.TimelineTerminateTimeline
+import dev.dimension.flare.data.network.xqt.model.TimelineTimelineCursor
+import dev.dimension.flare.data.network.xqt.model.TimelineTimelineItem
+import kotlinx.serialization.SerializationException
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertIs
+import kotlin.test.assertNotNull
+
+class XQTJsonTest {
+    @Test
+    fun unknownInstructionsPreserveNotificationsAndCursors() {
+        val response =
+            decodeNotifications(
+                """{"type":"TimelineFutureInstruction","payload":{"items":[1,{"nested":true}]}}""",
+                ADDED_NOTIFICATION_AND_CURSOR,
+                """{"entry_ids":["notification-removed"],"type":"TimelineRemoveEntries"}""",
+                """{"type":"TimelineTerminateTimeline","direction":"Bottom"}""",
+                """{"type":"AnotherFutureInstruction","payload":null}""",
+            )
+        val instructions = assertNotNull(response.data.viewerV2.userResults.result.notificationTimeline.timeline).instructions
+        val entries = instructions.filterIsInstance<TimelineAddEntries>().single().propertyEntries
+
+        assertEquals(listOf("notification-kept", "cursor-bottom"), entries.map { it.entryId })
+        val item = assertIs<TimelineTimelineItem>(entries[0].content)
+        val notification = assertIs<TimelineNotification>(item.itemContent)
+        assertEquals("notification-kept", notification.id)
+        assertEquals("Someone liked your post", notification.richMessage.text)
+        val cursor = assertIs<TimelineTimelineCursor>(entries[1].content)
+        assertEquals(CursorType.bottom, cursor.cursorType)
+        assertEquals("next-page", cursor.value)
+        assertEquals(
+            TimelineTerminateTimeline.Direction.bottom,
+            instructions.filterIsInstance<TimelineTerminateTimeline>().single().direction,
+        )
+    }
+
+    @Test
+    fun responseContainingOnlyUnknownInstructionsStillDecodes() {
+        val response =
+            decodeNotifications(
+                """{"type":"TimelineRemoveEntries","entry_ids":["notification-removed"]}""",
+                """{"type":"TimelineFutureInstruction","unrecognized_field":{}}""",
+            )
+        val instructions = assertNotNull(response.data.viewerV2.userResults.result.notificationTimeline.timeline).instructions
+
+        assertEquals(emptyList(), instructions.filterIsInstance<TimelineAddEntries>())
+    }
+
+    @Test
+    fun malformedKnownInstructionsStillFail() {
+        assertFailsWith<SerializationException> {
+            decodeNotifications("""{"type":"TimelineAddEntries"}""")
+        }
+    }
+
+    @Test
+    fun instructionsWithoutATypeStillFail() {
+        assertFailsWith<SerializationException> {
+            decodeNotifications("""{"entries":[]}""")
+        }
+    }
+
+    private fun decodeNotifications(vararg instructions: String): NotificationsTimelineResponse =
+        XQT_JSON.decodeFromString(
+            """
+            {
+              "data": {
+                "viewer_v2": {
+                  "user_results": {
+                    "result": {
+                      "__typename": "User",
+                      "rest_id": "me",
+                      "notification_timeline": {
+                        "timeline": {"instructions": [${instructions.joinToString()}]}
+                      }
+                    }
+                  }
+                }
+              }
+            }
+            """.trimIndent(),
+        )
+}
+
+private val ADDED_NOTIFICATION_AND_CURSOR =
+    """
+    {
+      "type": "TimelineAddEntries",
+      "entries": [
+        {
+          "entryId": "notification-kept",
+          "sortIndex": "2",
+          "content": {
+            "entryType": "TimelineTimelineItem",
+            "itemContent": {
+              "__typename": "TimelineNotification",
+              "id": "notification-kept",
+              "itemType": "TimelineNotification",
+              "notification_icon": "heart_icon",
+              "notification_url": {"url": "/notifications"},
+              "rich_message": {"text": "Someone liked your post"},
+              "template": {},
+              "timestamp_ms": "1788156000000"
+            }
+          }
+        },
+        {
+          "entryId": "cursor-bottom",
+          "sortIndex": "1",
+          "content": {
+            "entryType": "TimelineTimelineCursor",
+            "cursorType": "Bottom",
+            "value": "next-page"
+          }
+        }
+      ]
+    }
+    """.trimIndent()