fix(chat): keep messages chronological across ID rollover

packages/ui/src/sync/message-ordering.ts

@@ -0,0 +1,57 @@
+import type { Message } from "@opencode-ai/sdk/v2/client"
+
+const getCreatedAt = (message: Message): number => {
+  const value = (message as { time?: { created?: unknown } }).time?.created
+  return typeof value === "number" && Number.isFinite(value) ? value : 0
+}
+
+/**
+ * Message IDs identify records; they are not chronology. OpenCode's sortable
+ * ID timestamp rolls over, so a newly created `msg_000...` can follow a legacy
+ * `msg_fff...`. Creation time is the authoritative transcript order, with ID
+ * used only to make equal timestamps deterministic.
+ */
+export const compareMessagesChronologically = (left: Message, right: Message): number => {
+  const createdAtDifference = getCreatedAt(left) - getCreatedAt(right)
+  if (createdAtDifference !== 0) return createdAtDifference
+  if (left.id < right.id) return -1
+  if (left.id > right.id) return 1
+  return 0
+}
+
+export const sortMessagesChronologically = <T extends Message>(messages: readonly T[]): T[] => (
+  [...messages].sort(compareMessagesChronologically)
+)
+
+export const findMessageIndex = (messages: readonly Message[], messageID: string): number => (
+  messages.findIndex((message) => message.id === messageID)
+)
+
+export const insertMessageChronologically = <T extends Message>(messages: T[], message: T): number => {
+  let low = 0
+  let high = messages.length
+  while (low < high) {
+    const middle = (low + high) >>> 1
+    if (compareMessagesChronologically(messages[middle], message) < 0) {
+      low = middle + 1
+    } else {
+      high = middle
+    }
+  }
+  messages.splice(low, 0, message)
+  return low
+}
+
+/** Return the messages before the marker's current array position. */
+export const messagesBefore = <T extends Message>(messages: readonly T[], messageID?: string): T[] => {
+  if (!messageID) return messages as T[]
+  const index = findMessageIndex(messages, messageID)
+  return index < 0 ? messages as T[] : messages.slice(0, index)
+}
+
+/** Return the marker and all messages after its current array position. */
+export const messagesFrom = <T extends Message>(messages: readonly T[], messageID?: string): T[] => {
+  if (!messageID) return []
+  const index = findMessageIndex(messages, messageID)
+  return index < 0 ? [] : messages.slice(index)
+}