diff --git a/core/network/src/main/java/ru/forbion/f7cloud/core/network/CardDavClient.kt b/core/network/src/main/java/ru/forbion/f7cloud/core/network/CardDavClient.kt
index 2a95432..80bb238 100644
--- a/core/network/src/main/java/ru/forbion/f7cloud/core/network/CardDavClient.kt
+++ b/core/network/src/main/java/ru/forbion/f7cloud/core/network/CardDavClient.kt
@@ -69,6 +69,53 @@ object CardDavClient {
         return out.distinctBy { "${it.uid}|${it.email}" }
     }
 
+    /**
+     * Дешёвая «подпись» состояния адресных книг — CTag коллекций (расширение
+     * CalendarServer, поддерживается Nextcloud), с фолбэком на sync-token.
+     * Один PROPFIND depth:1 без address-data. Если подпись не изменилась с прошлой
+     * синхронизации — контакты качать не нужно. null при ошибке/неподдержке → полный sync.
+     */
+    fun collectionSignature(
+        client: OkHttpClient,
+        serverUrl: String,
+        userId: String,
+    ): String? = runCatching {
+        val base = davAddressBooksBaseUrl(serverUrl, userId)
+        val body = """
+            <?xml version="1.0" encoding="utf-8"?>
+            <d:propfind xmlns:d="DAV:" xmlns:cs="http://calendarserver.org/ns/">
+              <d:prop><cs:getctag/><d:sync-token/></d:prop>
+            </d:propfind>
+        """.trimIndent()
+        val xml = propfind(client, base, depth = 1, body)
+        parseCollectionSignature(xml).ifBlank { null }
+    }.getOrNull()
+
+    /**
+     * Парсит PROPFIND-ответ в стабильную подпись «href=ctag» (по книгам, отсортировано).
+     * Regex-парсинг (как ICS в проекте) — чистая функция, тестируется без Android XmlPull.
+     */
+    internal fun parseCollectionSignature(xml: String): String {
+        val entries = sortedSetOf<String>()
+        for (m in responseBlockPattern.findAll(xml)) {
+            val block = m.value
+            val href = hrefTagPattern.find(block)?.groupValues?.get(1)?.trim().orEmpty()
+            val tag = (
+                getctagPattern.find(block)?.groupValues?.get(1)
+                    ?: syncTokenPattern.find(block)?.groupValues?.get(1)
+                )?.trim().orEmpty()
+            if (href.isNotBlank() && tag.isNotBlank()) {
+                entries += "$href=$tag"
+            }
+        }
+        return entries.joinToString("\n")
+    }
+
+    private val responseBlockPattern = Regex("(?is)<(?:\\w+:)?response\\b.*?</(?:\\w+:)?response>")
+    private val hrefTagPattern = Regex("(?is)<(?:\\w+:)?href>(.*?)</(?:\\w+:)?href>")
+    private val getctagPattern = Regex("(?is)<(?:\\w+:)?getctag>(.*?)</(?:\\w+:)?getctag>")
+    private val syncTokenPattern = Regex("(?is)<(?:\\w+:)?sync-token>(.*?)</(?:\\w+:)?sync-token>")
+
     fun createContact(
         client: OkHttpClient,
         serverUrl: String,
diff --git a/core/network/src/test/java/ru/forbion/f7cloud/core/network/CardDavSignatureTest.kt b/core/network/src/test/java/ru/forbion/f7cloud/core/network/CardDavSignatureTest.kt
new file mode 100644
index 0000000..5603c77
--- /dev/null
+++ b/core/network/src/test/java/ru/forbion/f7cloud/core/network/CardDavSignatureTest.kt
@@ -0,0 +1,56 @@
+package ru.forbion.f7cloud.core.network
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNotEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * Тесты подписи коллекций CardDAV (CTag/sync-token) — основа инкрементальной
+ * синхронизации: если подпись не изменилась, контакты не перекачиваются.
+ */
+class CardDavSignatureTest {
+
+    private val ns = """xmlns:d="DAV:" xmlns:cs="http://calendarserver.org/ns/""""
+
+    private fun body(vararg responses: String) =
+        """<?xml version="1.0"?><d:multistatus $ns>${responses.joinToString("")}</d:multistatus>"""
+
+    private fun resp(href: String, ctag: String? = null, token: String? = null) = """
+        <d:response>
+          <d:href>$href</d:href>
+          <d:propstat><d:prop>
+            ${ctag?.let { "<cs:getctag>$it</cs:getctag>" } ?: ""}
+            ${token?.let { "<d:sync-token>$it</d:sync-token>" } ?: ""}
+          </d:prop></d:propstat>
+        </d:response>
+    """.trimIndent()
+
+    @Test fun ctag_signature_is_stable_and_sorted() {
+        val a = CardDavClient.parseCollectionSignature(
+            body(resp("/dav/addressbooks/u/b1/", ctag = "111"), resp("/dav/addressbooks/u/b2/", ctag = "222")),
+        )
+        // порядок ответов не влияет на подпись
+        val b = CardDavClient.parseCollectionSignature(
+            body(resp("/dav/addressbooks/u/b2/", ctag = "222"), resp("/dav/addressbooks/u/b1/", ctag = "111")),
+        )
+        assertEquals(a, b)
+        assertTrue(a.contains("/dav/addressbooks/u/b1/=111"))
+        assertTrue(a.contains("/dav/addressbooks/u/b2/=222"))
+    }
+
+    @Test fun ctag_change_changes_signature() {
+        val before = CardDavClient.parseCollectionSignature(body(resp("/b1/", ctag = "111")))
+        val after = CardDavClient.parseCollectionSignature(body(resp("/b1/", ctag = "999")))
+        assertNotEquals(before, after)
+    }
+
+    @Test fun sync_token_fallback_when_no_ctag() {
+        val sig = CardDavClient.parseCollectionSignature(body(resp("/b1/", token = "http://sabre/sync/42")))
+        assertEquals("/b1/=http://sabre/sync/42", sig)
+    }
+
+    @Test fun empty_when_no_tags() {
+        assertEquals("", CardDavClient.parseCollectionSignature(body(resp("/b1/"))))
+    }
+}
diff --git a/feature/contacts/src/main/java/ru/forbion/f7cloud/feature/contacts/ContactsRepository.kt b/feature/contacts/src/main/java/ru/forbion/f7cloud/feature/contacts/ContactsRepository.kt
index 93e5f92..ba82d89 100644
--- a/feature/contacts/src/main/java/ru/forbion/f7cloud/feature/contacts/ContactsRepository.kt
+++ b/feature/contacts/src/main/java/ru/forbion/f7cloud/feature/contacts/ContactsRepository.kt
@@ -74,6 +74,18 @@ class ContactsRepository(context: Context) {
         ) {
             return dao.getAll(key).map { it.toItem() }
         }
+        // Дешёвая проверка CTag: если адресные книги не менялись (и бэкфиллы сделаны) —
+        // полный PROPFIND всех vCard не нужен, отдаём кэш. Это ускоряет pull-to-refresh.
+        val needsBackfill = needsPhotoBackfill || needsDetailsBackfill
+        val client = authedClient(session)
+        val userId = session.davUserId ?: OcsUserResolver.resolveDavUserId(session)
+        val currentSig = CardDavClient.collectionSignature(client, session.serverUrl, userId)
+        if (!needsBackfill && currentSig != null &&
+            currentSig == prefs.getString(ctagKey(key), null)
+        ) {
+            prefs.edit().putLong(lastSyncKey(key), System.currentTimeMillis()).apply()
+            return dao.getAll(key).map { it.toItem() }
+        }
         val remote = fetchRemoteContacts(session)
         val entities = remote.map { contact ->
             ContactEntity(
@@ -95,11 +107,12 @@ class ContactsRepository(context: Context) {
             )
         }
         dao.replaceAll(key, entities)
-        prefs.edit()
+        val editor = prefs.edit()
             .putLong(lastSyncKey(key), System.currentTimeMillis())
             .putBoolean(photoSyncDoneKey(key), true)
             .putBoolean(detailsSyncDoneKey(key), true)
-            .apply()
+        if (currentSig != null) editor.putString(ctagKey(key), currentSig) else editor.remove(ctagKey(key))
+        editor.apply()
         return entities.map { it.toItem() }
     }
 
@@ -190,6 +203,8 @@ class ContactsRepository(context: Context) {
 
     private fun lastSyncKey(accountKey: String) = "last_sync_$accountKey"
 
+    private fun ctagKey(accountKey: String) = "ctag_$accountKey"
+
     private fun photoSyncDoneKey(accountKey: String) = "photo_sync_done_$accountKey"
 
     private fun detailsSyncDoneKey(accountKey: String) = "details_sync_done_$accountKey"