ENH - prioritize recent SMS contacts

frontend/src/utils/messages.test.ts

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+import { describe, expect, it } from 'vitest'
+
+import type { SmsConversation } from '@/types/messages'
+import {
+  sortContactsByMessageRecency,
+  sortConversationsByRecency,
+} from '@/utils/messages'
+
+function conversation(
+  phoneNumber: string,
+  lastMessageAt: string,
+): SmsConversation {
+  return {
+    lastMessage: phoneNumber,
+    lastMessageAt,
+    lastMessageType: 'text',
+    phoneNumber,
+    unread: 0,
+  }
+}
+
+const conversations = [
+  conversation('5550000001', '2026-08-12 10:00:00'),
+  conversation('5550000002', '2026-08-12 12:00:00'),
+]
+
+describe('SMS recency ordering', () => {
+  it('places the conversation with the newest message first', () => {
+    expect(
+      sortConversationsByRecency(conversations).map(
+        (item) => item.phoneNumber,
+      ),
+    ).toEqual(['5550000002', '5550000001'])
+  })
+
+  it('places recently messaged contacts before unused contacts', () => {
+    const contacts = [
+      { name: 'Unused', phone_number: '5550000003' },
+      { name: 'Older', phone_number: '5550000001' },
+      { name: 'Newest', phone_number: '5550000002' },
+    ]
+
+    expect(
+      sortContactsByMessageRecency(contacts, conversations).map(
+        (item) => item.name,
+      ),
+    ).toEqual(['Newest', 'Older', 'Unused'])
+  })
+})

frontend/src/utils/messages.ts

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+import type { SmsConversation } from '@/types/messages'
+import { parseDatabaseDate } from '@/utils/date'
+
+function conversationTime(conversation: SmsConversation): number {
+  const timestamp = parseDatabaseDate(conversation.lastMessageAt).getTime()
+  return Number.isNaN(timestamp) ? 0 : timestamp
+}
+
+export function sortConversationsByRecency(
+  conversations: SmsConversation[],
+): SmsConversation[] {
+  return conversations
+    .map((conversation, index) => ({ conversation, index }))
+    .sort(
+      (left, right) =>
+        conversationTime(right.conversation) -
+          conversationTime(left.conversation) || left.index - right.index,
+    )
+    .map(({ conversation }) => conversation)
+}
+
+export function sortContactsByMessageRecency<
+  T extends { phone_number: string },
+>(contacts: T[], conversations: SmsConversation[]): T[] {
+  const activity = new Map(
+    conversations.map((conversation) => [
+      conversation.phoneNumber,
+      conversationTime(conversation),
+    ]),
+  )
+  return contacts
+    .map((contact, index) => ({ contact, index }))
+    .sort((left, right) => {
+      const leftActivity = activity.get(left.contact.phone_number)
+      const rightActivity = activity.get(right.contact.phone_number)
+      if (leftActivity === undefined && rightActivity === undefined)
+        return left.index - right.index
+      if (leftActivity === undefined) return 1
+      if (rightActivity === undefined) return -1
+      return rightActivity - leftActivity || left.index - right.index
+    })
+    .map(({ contact }) => contact)
+}