[All Platforms] 2.1.0 - Sync Optimizations

2025-10-15 18:17:19 -06:00
32 changed files with 1538 additions and 409 deletions
--- a/android/app/build.gradle.kts
+++ b/android/app/build.gradle.kts
@@ -16,8 +16,8 @@ android {
        applicationId = "com.atridad.ascently"
        minSdk = 31
        targetSdk = 36
-        versionCode = 41
-        versionName = "2.0.1"
+        versionCode = 42
+        versionName = "2.1.0"

        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
    }
--- a/android/app/src/main/java/com/atridad/ascently/data/format/BackupFormat.kt
+++ b/android/app/src/main/java/com/atridad/ascently/data/format/BackupFormat.kt
@@ -32,13 +32,12 @@ data class BackupGym(
        val supportedClimbTypes: List<ClimbType>,
        val difficultySystems: List<DifficultySystem>,
        @kotlinx.serialization.SerialName("customDifficultyGrades")
-        val customDifficultyGrades: List<String> = emptyList(),
+        val customDifficultyGrades: List<String>? = null,
        val notes: String? = null,
        val createdAt: String,
        val updatedAt: String
 ) {
    companion object {
-        /** Create BackupGym from native Android Gym model */
        fun fromGym(gym: Gym): BackupGym {
            return BackupGym(
                    id = gym.id,
@@ -46,7 +45,7 @@ data class BackupGym(
                    location = gym.location,
                    supportedClimbTypes = gym.supportedClimbTypes,
                    difficultySystems = gym.difficultySystems,
-                    customDifficultyGrades = gym.customDifficultyGrades,
+                    customDifficultyGrades = gym.customDifficultyGrades.ifEmpty { null },
                    notes = gym.notes,
                    createdAt = gym.createdAt,
                    updatedAt = gym.updatedAt
@@ -54,7 +53,6 @@ data class BackupGym(
        }
    }

-    /** Convert to native Android Gym model */
    fun toGym(): Gym {
        return Gym(
                id = id,
@@ -62,7 +60,7 @@ data class BackupGym(
                location = location,
                supportedClimbTypes = supportedClimbTypes,
                difficultySystems = difficultySystems,
-                customDifficultyGrades = customDifficultyGrades,
+                customDifficultyGrades = customDifficultyGrades ?: emptyList(),
                notes = notes,
                createdAt = createdAt,
                updatedAt = updatedAt
@@ -79,7 +77,7 @@ data class BackupProblem(
        val description: String? = null,
        val climbType: ClimbType,
        val difficulty: DifficultyGrade,
-        val tags: List<String> = emptyList(),
+        val tags: List<String>? = null,
        val location: String? = null,
        val imagePaths: List<String>? = null,
        val isActive: Boolean = true,
@@ -89,7 +87,6 @@ data class BackupProblem(
        val updatedAt: String
 ) {
    companion object {
-        /** Create BackupProblem from native Android Problem model */
        fun fromProblem(problem: Problem): BackupProblem {
            return BackupProblem(
                    id = problem.id,
@@ -112,7 +109,6 @@ data class BackupProblem(
        }
    }

-    /** Convert to native Android Problem model */
    fun toProblem(): Problem {
        return Problem(
                id = id,
@@ -121,7 +117,7 @@ data class BackupProblem(
                description = description,
                climbType = climbType,
                difficulty = difficulty,
-                tags = tags,
+                tags = tags ?: emptyList(),
                location = location,
                imagePaths = imagePaths ?: emptyList(),
                isActive = isActive,
@@ -132,7 +128,6 @@ data class BackupProblem(
        )
    }

-    /** Create a copy with updated image paths for import processing */
    fun withUpdatedImagePaths(newImagePaths: List<String>): BackupProblem {
        return copy(imagePaths = newImagePaths.ifEmpty { null })
    }
@@ -153,7 +148,6 @@ data class BackupClimbSession(
        val updatedAt: String
 ) {
    companion object {
-        /** Create BackupClimbSession from native Android ClimbSession model */
        fun fromClimbSession(session: ClimbSession): BackupClimbSession {
            return BackupClimbSession(
                    id = session.id,
@@ -170,7 +164,6 @@ data class BackupClimbSession(
        }
    }

-    /** Convert to native Android ClimbSession model */
    fun toClimbSession(): ClimbSession {
        return ClimbSession(
                id = id,
@@ -203,7 +196,6 @@ data class BackupAttempt(
        val updatedAt: String? = null
 ) {
    companion object {
-        /** Create BackupAttempt from native Android Attempt model */
        fun fromAttempt(attempt: Attempt): BackupAttempt {
            return BackupAttempt(
                    id = attempt.id,
@@ -221,7 +213,6 @@ data class BackupAttempt(
        }
    }

-    /** Convert to native Android Attempt model */
    fun toAttempt(): Attempt {
        return Attempt(
                id = id,
--- a/android/app/src/main/java/com/atridad/ascently/data/health/HealthConnectStub.kt
+++ b/android/app/src/main/java/com/atridad/ascently/data/health/HealthConnectStub.kt
@@ -66,7 +66,6 @@ class HealthConnectManager(private val context: Context) {
        }
    }

-    /** Check if Health Connect is available on this device */
    fun isHealthConnectAvailable(): Flow<Boolean> = flow {
        try {
            if (!_isCompatible.value) {
@@ -82,10 +81,6 @@ class HealthConnectManager(private val context: Context) {
        }
    }

-    /**
-     * Enable or disable Health Connect integration and automatically request permissions if
-     * enabling
-     */
    suspend fun setEnabled(enabled: Boolean) {
        preferences.edit().putBoolean("enabled", enabled).apply()
        _isEnabled.value = enabled
@@ -105,13 +100,11 @@ class HealthConnectManager(private val context: Context) {
        }
    }

-    /** Update the permissions granted state */
    fun setPermissionsGranted(granted: Boolean) {
        preferences.edit().putBoolean("permissions", granted).apply()
        _hasPermissions.value = granted
    }

-    /** Check if all required permissions are granted */
    suspend fun hasAllPermissions(): Boolean {
        return try {
            if (!_isCompatible.value || healthConnectClient == null) {
@@ -132,7 +125,6 @@ class HealthConnectManager(private val context: Context) {
        }
    }

-    /** Check if Health Connect is ready for use */
    suspend fun isReady(): Boolean {
        return try {
            if (!_isEnabled.value || !_isCompatible.value || healthConnectClient == null)
@@ -148,12 +140,10 @@ class HealthConnectManager(private val context: Context) {
        }
    }

-    /** Get permission request contract */
    fun getPermissionRequestContract(): ActivityResultContract<Set<String>, Set<String>> {
        return PermissionController.createRequestPermissionResultContract()
    }

-    /** Get required permissions as strings */
    fun getRequiredPermissions(): Set<String> {
        return try {
            REQUIRED_PERMISSIONS.map { it }.toSet()
@@ -163,7 +153,6 @@ class HealthConnectManager(private val context: Context) {
        }
    }

-    /** Sync a completed climbing session to Health Connect (only when auto-sync is enabled) */
    @SuppressLint("RestrictedApi")
    suspend fun syncCompletedSession(
            session: ClimbSession,
@@ -271,7 +260,6 @@ class HealthConnectManager(private val context: Context) {
        }
    }

-    /** Auto-sync a completed session if enabled - this is the only way to sync sessions */
    suspend fun autoSyncCompletedSession(
            session: ClimbSession,
            gymName: String,
@@ -293,7 +281,6 @@ class HealthConnectManager(private val context: Context) {
        }
    }

-    /** Estimate calories burned during climbing */
    private fun estimateCaloriesForClimbing(durationMinutes: Long, attemptCount: Int): Double {
        val baseCaloriesPerMinute = 8.0
        val intensityMultiplier =
@@ -305,7 +292,6 @@ class HealthConnectManager(private val context: Context) {
        return durationMinutes * baseCaloriesPerMinute * intensityMultiplier
    }

-    /** Create heart rate data */
    @SuppressLint("RestrictedApi")
    private fun createHeartRateRecord(
            startTime: Instant,
@@ -347,9 +333,7 @@ class HealthConnectManager(private val context: Context) {
        }
    }

-    /** Check if ready for use */
    fun isReadySync(): Boolean {
        return _isEnabled.value && _hasPermissions.value
    }
-
 }
--- a/android/app/src/main/java/com/atridad/ascently/data/repository/ClimbRepository.kt
+++ b/android/app/src/main/java/com/atridad/ascently/data/repository/ClimbRepository.kt
@@ -251,23 +251,15 @@ class ClimbRepository(database: AscentlyDatabase, private val context: Context)
        }
    }

-    /**
-     * Sets the callback for auto-sync functionality. This should be called by the SyncService to
-     * register itself for auto-sync triggers.
-     */
    fun setAutoSyncCallback(callback: (() -> Unit)?) {
        autoSyncCallback = callback
    }

-    /**
-     * Triggers auto-sync if enabled. This is called after any data modification to keep data
-     * synchronized across devices automatically.
-     */
    private fun triggerAutoSync() {
        autoSyncCallback?.invoke()
    }

-    private fun trackDeletion(itemId: String, itemType: String) {
+    fun trackDeletion(itemId: String, itemType: String) {
        val currentDeletions = getDeletedItems().toMutableList()
        val newDeletion =
                DeletedItem(id = itemId, type = itemType, deletedAt = DateFormatUtils.nowISO8601())
--- a/android/app/src/main/java/com/atridad/ascently/data/sync/DeltaSyncModels.kt
+++ b/android/app/src/main/java/com/atridad/ascently/data/sync/DeltaSyncModels.kt
@@ -0,0 +1,30 @@
+package com.atridad.ascently.data.sync
+
+import com.atridad.ascently.data.format.BackupAttempt
+import com.atridad.ascently.data.format.BackupClimbSession
+import com.atridad.ascently.data.format.BackupGym
+import com.atridad.ascently.data.format.BackupProblem
+import com.atridad.ascently.data.format.DeletedItem
+import kotlinx.serialization.Serializable
+
+/** Request structure for delta sync - sends only changes since last sync */
+@Serializable
+data class DeltaSyncRequest(
+        val lastSyncTime: String,
+        val gyms: List<BackupGym>,
+        val problems: List<BackupProblem>,
+        val sessions: List<BackupClimbSession>,
+        val attempts: List<BackupAttempt>,
+        val deletedItems: List<DeletedItem>
+)
+
+/** Response structure for delta sync - receives only changes from server */
+@Serializable
+data class DeltaSyncResponse(
+        val serverTime: String,
+        val gyms: List<BackupGym>,
+        val problems: List<BackupProblem>,
+        val sessions: List<BackupClimbSession>,
+        val attempts: List<BackupAttempt>,
+        val deletedItems: List<DeletedItem>
+)
--- a/android/app/src/main/java/com/atridad/ascently/data/sync/SyncService.kt
+++ b/android/app/src/main/java/com/atridad/ascently/data/sync/SyncService.kt
@@ -19,6 +19,9 @@ import com.atridad.ascently.utils.ImageNamingUtils
 import com.atridad.ascently.utils.ImageUtils
 import java.io.IOException
 import java.io.Serializable
+import java.text.SimpleDateFormat
+import java.util.Date
+import java.util.Locale
 import java.util.concurrent.TimeUnit
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
@@ -63,6 +66,7 @@ class SyncService(private val context: Context, private val repository: ClimbRep
        prettyPrint = true
        ignoreUnknownKeys = true
        explicitNulls = false
+        coerceInputValues = true
    }

    // State
@@ -195,26 +199,33 @@ class SyncService(private val context: Context, private val repository: ClimbRep
                                serverBackup.sessions.isNotEmpty() ||
                                serverBackup.attempts.isNotEmpty()

-                when {
-                    !hasLocalData && hasServerData -> {
-                        Log.d(TAG, "No local data found, performing full restore from server")
-                        val imagePathMapping = syncImagesFromServer(serverBackup)
-                        importBackupToRepository(serverBackup, imagePathMapping)
-                        Log.d(TAG, "Full restore completed")
-                    }
-                    hasLocalData && !hasServerData -> {
-                        Log.d(TAG, "No server data found, uploading local data to server")
-                        uploadData(localBackup)
-                        syncImagesForBackup(localBackup)
-                        Log.d(TAG, "Initial upload completed")
-                    }
-                    hasLocalData && hasServerData -> {
-                        Log.d(TAG, "Both local and server data exist, merging (server wins)")
-                        mergeDataSafely(serverBackup)
-                        Log.d(TAG, "Merge completed")
-                    }
-                    else -> {
-                        Log.d(TAG, "No data to sync")
+                // If both client and server have been synced before, use delta sync
+                val lastSyncTimeStr = sharedPreferences.getString(Keys.LAST_SYNC_TIME, null)
+                if (hasLocalData && hasServerData && lastSyncTimeStr != null) {
+                    Log.d(TAG, "Using delta sync for incremental updates")
+                    performDeltaSync(lastSyncTimeStr)
+                } else {
+                    when {
+                        !hasLocalData && hasServerData -> {
+                            Log.d(TAG, "No local data found, performing full restore from server")
+                            val imagePathMapping = syncImagesFromServer(serverBackup)
+                            importBackupToRepository(serverBackup, imagePathMapping)
+                            Log.d(TAG, "Full restore completed")
+                        }
+                        hasLocalData && !hasServerData -> {
+                            Log.d(TAG, "No server data found, uploading local data to server")
+                            uploadData(localBackup)
+                            syncImagesForBackup(localBackup)
+                            Log.d(TAG, "Initial upload completed")
+                        }
+                        hasLocalData && hasServerData -> {
+                            Log.d(TAG, "Both local and server data exist, merging (server wins)")
+                            mergeDataSafely(serverBackup)
+                            Log.d(TAG, "Merge completed")
+                        }
+                        else -> {
+                            Log.d(TAG, "No data to sync")
+                        }
                    }
                }

@@ -230,6 +241,265 @@ class SyncService(private val context: Context, private val repository: ClimbRep
        }
    }

+    private suspend fun performDeltaSync(lastSyncTimeStr: String) {
+        Log.d(TAG, "Starting delta sync with lastSyncTime=$lastSyncTimeStr")
+
+        // Parse last sync time to filter modified items
+        val lastSyncDate = parseISO8601(lastSyncTimeStr) ?: Date(0)
+
+        // Collect items modified since last sync
+        val allGyms = repository.getAllGyms().first()
+        val modifiedGyms =
+                allGyms
+                        .filter { gym -> parseISO8601(gym.updatedAt)?.after(lastSyncDate) == true }
+                        .map { BackupGym.fromGym(it) }
+
+        val allProblems = repository.getAllProblems().first()
+        val modifiedProblems =
+                allProblems
+                        .filter { problem ->
+                            parseISO8601(problem.updatedAt)?.after(lastSyncDate) == true
+                        }
+                        .map { problem ->
+                            val backupProblem = BackupProblem.fromProblem(problem)
+                            val normalizedImagePaths =
+                                    problem.imagePaths.mapIndexed { index, _ ->
+                                        ImageNamingUtils.generateImageFilename(problem.id, index)
+                                    }
+                            if (normalizedImagePaths.isNotEmpty()) {
+                                backupProblem.copy(imagePaths = normalizedImagePaths)
+                            } else {
+                                backupProblem
+                            }
+                        }
+
+        val allSessions = repository.getAllSessions().first()
+        val modifiedSessions =
+                allSessions
+                        .filter { session ->
+                            parseISO8601(session.updatedAt)?.after(lastSyncDate) == true
+                        }
+                        .map { BackupClimbSession.fromClimbSession(it) }
+
+        val allAttempts = repository.getAllAttempts().first()
+        val modifiedAttempts =
+                allAttempts
+                        .filter { attempt ->
+                            parseISO8601(attempt.createdAt)?.after(lastSyncDate) == true
+                        }
+                        .map { BackupAttempt.fromAttempt(it) }
+
+        val allDeletions = repository.getDeletedItems()
+        val modifiedDeletions =
+                allDeletions.filter { item ->
+                    parseISO8601(item.deletedAt)?.after(lastSyncDate) == true
+                }
+
+        Log.d(
+                TAG,
+                "Delta sync sending: gyms=${modifiedGyms.size}, problems=${modifiedProblems.size}, sessions=${modifiedSessions.size}, attempts=${modifiedAttempts.size}, deletions=${modifiedDeletions.size}"
+        )
+
+        // Create delta request
+        val deltaRequest =
+                DeltaSyncRequest(
+                        lastSyncTime = lastSyncTimeStr,
+                        gyms = modifiedGyms,
+                        problems = modifiedProblems,
+                        sessions = modifiedSessions,
+                        attempts = modifiedAttempts,
+                        deletedItems = modifiedDeletions
+                )
+
+        val requestBody =
+                json.encodeToString(DeltaSyncRequest.serializer(), deltaRequest)
+                        .toRequestBody("application/json".toMediaType())
+
+        val request =
+                Request.Builder()
+                        .url("$serverUrl/sync/delta")
+                        .header("Authorization", "Bearer $authToken")
+                        .post(requestBody)
+                        .build()
+
+        val deltaResponse =
+                withContext(Dispatchers.IO) {
+                    try {
+                        httpClient.newCall(request).execute().use { response ->
+                            if (response.isSuccessful) {
+                                val body = response.body?.string()
+                                if (!body.isNullOrEmpty()) {
+                                    json.decodeFromString(DeltaSyncResponse.serializer(), body)
+                                } else {
+                                    throw SyncException.InvalidResponse("Empty response body")
+                                }
+                            } else {
+                                handleHttpError(response.code)
+                            }
+                        }
+                    } catch (e: IOException) {
+                        throw SyncException.NetworkError(e.message ?: "Network error")
+                    }
+                }
+
+        Log.d(
+                TAG,
+                "Delta sync received: gyms=${deltaResponse.gyms.size}, problems=${deltaResponse.problems.size}, sessions=${deltaResponse.sessions.size}, attempts=${deltaResponse.attempts.size}, deletions=${deltaResponse.deletedItems.size}"
+        )
+
+        // Apply server changes to local data
+        applyDeltaResponse(deltaResponse)
+
+        // Sync only modified problem images
+        syncModifiedImages(modifiedProblems)
+    }
+
+    private fun parseISO8601(dateString: String): Date? {
+        return try {
+            val format = SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss", Locale.US)
+            format.parse(dateString)
+        } catch (e: Exception) {
+            null
+        }
+    }
+
+    private suspend fun applyDeltaResponse(response: DeltaSyncResponse) {
+        // Temporarily disable auto-sync to prevent recursive sync triggers
+        repository.setAutoSyncCallback(null)
+
+        try {
+            // Download images for new/modified problems from server
+            val imagePathMapping = mutableMapOf<String, String>()
+            for (problem in response.problems) {
+                problem.imagePaths?.forEach { imagePath ->
+                    val serverFilename = imagePath.substringAfterLast('/')
+                    try {
+                        val localImagePath = downloadImage(serverFilename)
+                        if (localImagePath != null) {
+                            imagePathMapping[imagePath] = localImagePath
+                        }
+                    } catch (e: Exception) {
+                        Log.w(TAG, "Failed to download image $imagePath: ${e.message}")
+                    }
+                }
+            }
+
+            // Merge gyms - check if exists and compare timestamps
+            val existingGyms = repository.getAllGyms().first()
+            for (backupGym in response.gyms) {
+                val existing = existingGyms.find { it.id == backupGym.id }
+                if (existing == null || backupGym.updatedAt >= existing.updatedAt) {
+                    val gym = backupGym.toGym()
+                    if (existing != null) {
+                        repository.updateGym(gym)
+                    } else {
+                        repository.insertGym(gym)
+                    }
+                }
+            }
+
+            // Merge problems
+            val existingProblems = repository.getAllProblems().first()
+            for (backupProblem in response.problems) {
+                val updatedImagePaths =
+                        backupProblem.imagePaths?.map { oldPath ->
+                            imagePathMapping[oldPath] ?: oldPath
+                        }
+                val problemToMerge = backupProblem.copy(imagePaths = updatedImagePaths)
+                val problem = problemToMerge.toProblem()
+
+                val existing = existingProblems.find { it.id == backupProblem.id }
+                if (existing == null || backupProblem.updatedAt >= existing.updatedAt) {
+                    if (existing != null) {
+                        repository.updateProblem(problem)
+                    } else {
+                        repository.insertProblem(problem)
+                    }
+                }
+            }
+
+            // Merge sessions
+            val existingSessions = repository.getAllSessions().first()
+            for (backupSession in response.sessions) {
+                val session = backupSession.toClimbSession()
+                val existing = existingSessions.find { it.id == backupSession.id }
+                if (existing == null || backupSession.updatedAt >= existing.updatedAt) {
+                    if (existing != null) {
+                        repository.updateSession(session)
+                    } else {
+                        repository.insertSession(session)
+                    }
+                }
+            }
+
+            // Merge attempts
+            val existingAttempts = repository.getAllAttempts().first()
+            for (backupAttempt in response.attempts) {
+                val attempt = backupAttempt.toAttempt()
+                val existing = existingAttempts.find { it.id == backupAttempt.id }
+                if (existing == null || backupAttempt.createdAt >= existing.createdAt) {
+                    if (existing != null) {
+                        repository.updateAttempt(attempt)
+                    } else {
+                        repository.insertAttempt(attempt)
+                    }
+                }
+            }
+
+            // Apply deletions
+            applyDeletions(response.deletedItems)
+
+            // Update deletion records
+            val allDeletions = repository.getDeletedItems() + response.deletedItems
+            repository.clearDeletedItems()
+            allDeletions.distinctBy { "${it.type}:${it.id}" }.forEach {
+                repository.trackDeletion(it.id, it.type)
+            }
+        } finally {
+            // Re-enable auto-sync
+            repository.setAutoSyncCallback { serviceScope.launch { triggerAutoSync() } }
+        }
+    }
+
+    private suspend fun applyDeletions(
+            deletions: List<com.atridad.ascently.data.format.DeletedItem>
+    ) {
+        val existingGyms = repository.getAllGyms().first()
+        val existingProblems = repository.getAllProblems().first()
+        val existingSessions = repository.getAllSessions().first()
+        val existingAttempts = repository.getAllAttempts().first()
+
+        for (item in deletions) {
+            when (item.type) {
+                "gym" -> {
+                    existingGyms.find { it.id == item.id }?.let { repository.deleteGym(it) }
+                }
+                "problem" -> {
+                    existingProblems.find { it.id == item.id }?.let { repository.deleteProblem(it) }
+                }
+                "session" -> {
+                    existingSessions.find { it.id == item.id }?.let { repository.deleteSession(it) }
+                }
+                "attempt" -> {
+                    existingAttempts.find { it.id == item.id }?.let { repository.deleteAttempt(it) }
+                }
+            }
+        }
+    }
+
+    private suspend fun syncModifiedImages(modifiedProblems: List<BackupProblem>) {
+        if (modifiedProblems.isEmpty()) return
+
+        Log.d(TAG, "Syncing images for ${modifiedProblems.size} modified problems")
+
+        for (backupProblem in modifiedProblems) {
+            backupProblem.imagePaths?.forEach { imagePath ->
+                val filename = imagePath.substringAfterLast('/')
+                uploadImage(imagePath, filename)
+            }
+        }
+    }
+
    private suspend fun downloadData(): ClimbDataBackup {
        val request =
                Request.Builder()
--- a/android/app/src/main/java/com/atridad/ascently/utils/MigrationManager.kt
+++ b/android/app/src/main/java/com/atridad/ascently/utils/MigrationManager.kt
@@ -5,10 +5,6 @@ import android.content.SharedPreferences
 import android.util.Log
 import androidx.core.content.edit

-/**
- * Handles migration of data from OpenClimb to Ascently This includes SharedPreferences, database
- * names, and other local storage
- */
 class MigrationManager(private val context: Context) {

    companion object {
--- a/android/app/src/test/java/com/atridad/openclimb/SyncMergeLogicTest.kt
+++ b/android/app/src/test/java/com/atridad/openclimb/SyncMergeLogicTest.kt
@@ -457,10 +457,6 @@ class SyncMergeLogicTest {

    @Test
    fun `test active sessions excluded from sync`() {
-        // Test scenario: Active sessions should not be included in sync data
-        // This tests the new behavior where active sessions are excluded from sync
-        // until they are completed
-
        val allLocalSessions =
                listOf(
                        BackupClimbSession(
--- a/docs/astro.config.mjs
+++ b/docs/astro.config.mjs
@@ -40,6 +40,7 @@ export default defineConfig({
          items: [
            { label: "Overview", slug: "sync/overview" },
            { label: "Quick Start", slug: "sync/quick-start" },
+            { label: "API Reference", slug: "sync/api-reference" },
          ],
        },
        {
--- a/docs/package.json
+++ b/docs/package.json
@@ -26,7 +26,7 @@
  },
  "dependencies": {
    "@astrojs/node": "^9.5.0",
-    "@astrojs/starlight": "^0.36.0",
+    "@astrojs/starlight": "^0.36.1",
    "astro": "^5.14.5",
    "sharp": "^0.34.4"
  }
--- a/docs/pnpm-lock.yaml
+++ b/docs/pnpm-lock.yaml
@@ -12,8 +12,8 @@ importers:
        specifier: ^9.5.0
        version: 9.5.0(astro@5.14.5(@types/node@24.7.2)(rollup@4.52.4)(typescript@5.9.3))
      '@astrojs/starlight':
-        specifier: ^0.36.0
-        version: 0.36.0(astro@5.14.5(@types/node@24.7.2)(rollup@4.52.4)(typescript@5.9.3))
+        specifier: ^0.36.1
+        version: 0.36.1(astro@5.14.5(@types/node@24.7.2)(rollup@4.52.4)(typescript@5.9.3))
      astro:
        specifier: ^5.14.5
        version: 5.14.5(@types/node@24.7.2)(rollup@4.52.4)(typescript@5.9.3)
@@ -50,8 +50,8 @@ packages:
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    resolution: {integrity: sha512-4aHkvcOZBWJigRmMIAJwRQXBS+ayoP5z40OklTXYXhUDhwusz+DyDl+nSshY6y9DvkVEavwNcFO8FD81iGhXjg==}

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+  '@astrojs/starlight@0.36.1':
+    resolution: {integrity: sha512-Fmt8mIsAIZN18Y4YQDI6p521GsYGe4hYxh9jWmz0pHBXnS5J7Na3TSXNya4eyIymCcKkuiKFbs7b/knsdGVYPg==}
    peerDependencies:
      astro: ^5.5.0

@@ -91,158 +91,158 @@ packages:
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+  '@esbuild/aix-ppc64@0.25.11':
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    engines: {node: '>=18'}
    cpu: [ppc64]
    os: [aix]

-  '@esbuild/android-arm64@0.25.10':
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+  '@esbuild/android-arm64@0.25.11':
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    engines: {node: '>=18'}
    cpu: [arm64]
    os: [android]

-  '@esbuild/android-arm@0.25.10':
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+  '@esbuild/android-arm@0.25.11':
+    resolution: {integrity: sha512-uoa7dU+Dt3HYsethkJ1k6Z9YdcHjTrSb5NUy66ZfZaSV8hEYGD5ZHbEMXnqLFlbBflLsl89Zke7CAdDJ4JI+Gg==}
    engines: {node: '>=18'}
    cpu: [arm]
    os: [android]

-  '@esbuild/android-x64@0.25.10':
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+  '@esbuild/android-x64@0.25.11':
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    engines: {node: '>=18'}
    cpu: [x64]
    os: [android]

-  '@esbuild/darwin-arm64@0.25.10':
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+  '@esbuild/darwin-arm64@0.25.11':
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    engines: {node: '>=18'}
    cpu: [arm64]
    os: [darwin]

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+  '@esbuild/darwin-x64@0.25.11':
+    resolution: {integrity: sha512-+hfp3yfBalNEpTGp9loYgbknjR695HkqtY3d3/JjSRUyPg/xd6q+mQqIb5qdywnDxRZykIHs3axEqU6l1+oWEQ==}
    engines: {node: '>=18'}
    cpu: [x64]
    os: [darwin]

-  '@esbuild/freebsd-arm64@0.25.10':
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+  '@esbuild/freebsd-arm64@0.25.11':
+    resolution: {integrity: sha512-CmKjrnayyTJF2eVuO//uSjl/K3KsMIeYeyN7FyDBjsR3lnSJHaXlVoAK8DZa7lXWChbuOk7NjAc7ygAwrnPBhA==}
    engines: {node: '>=18'}
    cpu: [arm64]
    os: [freebsd]

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+  '@esbuild/freebsd-x64@0.25.11':
+    resolution: {integrity: sha512-Dyq+5oscTJvMaYPvW3x3FLpi2+gSZTCE/1ffdwuM6G1ARang/mb3jvjxs0mw6n3Lsw84ocfo9CrNMqc5lTfGOw==}
    engines: {node: '>=18'}
    cpu: [x64]
    os: [freebsd]

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+  '@esbuild/linux-arm64@0.25.11':
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    cpu: [arm64]
    os: [linux]

-  '@esbuild/linux-arm@0.25.10':
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+  '@esbuild/linux-arm@0.25.11':
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    cpu: [arm]
    os: [linux]

-  '@esbuild/linux-ia32@0.25.10':
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+  '@esbuild/linux-ia32@0.25.11':
+    resolution: {integrity: sha512-TmnJg8BMGPehs5JKrCLqyWTVAvielc615jbkOirATQvWWB1NMXY77oLMzsUjRLa0+ngecEmDGqt5jiDC6bfvOw==}
    engines: {node: '>=18'}
    cpu: [ia32]
    os: [linux]

-  '@esbuild/linux-loong64@0.25.10':
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+  '@esbuild/linux-loong64@0.25.11':
+    resolution: {integrity: sha512-DIGXL2+gvDaXlaq8xruNXUJdT5tF+SBbJQKbWy/0J7OhU8gOHOzKmGIlfTTl6nHaCOoipxQbuJi7O++ldrxgMw==}
    engines: {node: '>=18'}
    cpu: [loong64]
    os: [linux]

-  '@esbuild/linux-mips64el@0.25.10':
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+  '@esbuild/linux-mips64el@0.25.11':
+    resolution: {integrity: sha512-Osx1nALUJu4pU43o9OyjSCXokFkFbyzjXb6VhGIJZQ5JZi8ylCQ9/LFagolPsHtgw6himDSyb5ETSfmp4rpiKQ==}
    engines: {node: '>=18'}
    cpu: [mips64el]
    os: [linux]

-  '@esbuild/linux-ppc64@0.25.10':
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+  '@esbuild/linux-ppc64@0.25.11':
+    resolution: {integrity: sha512-nbLFgsQQEsBa8XSgSTSlrnBSrpoWh7ioFDUmwo158gIm5NNP+17IYmNWzaIzWmgCxq56vfr34xGkOcZ7jX6CPw==}
    engines: {node: '>=18'}
    cpu: [ppc64]
    os: [linux]

-  '@esbuild/linux-riscv64@0.25.10':
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+  '@esbuild/linux-riscv64@0.25.11':
+    resolution: {integrity: sha512-HfyAmqZi9uBAbgKYP1yGuI7tSREXwIb438q0nqvlpxAOs3XnZ8RsisRfmVsgV486NdjD7Mw2UrFSw51lzUk1ww==}
    engines: {node: '>=18'}
    cpu: [riscv64]
    os: [linux]

-  '@esbuild/linux-s390x@0.25.10':
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+  '@esbuild/linux-s390x@0.25.11':
+    resolution: {integrity: sha512-HjLqVgSSYnVXRisyfmzsH6mXqyvj0SA7pG5g+9W7ESgwA70AXYNpfKBqh1KbTxmQVaYxpzA/SvlB9oclGPbApw==}
    engines: {node: '>=18'}
    cpu: [s390x]
    os: [linux]

-  '@esbuild/linux-x64@0.25.10':
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+  '@esbuild/linux-x64@0.25.11':
+    resolution: {integrity: sha512-HSFAT4+WYjIhrHxKBwGmOOSpphjYkcswF449j6EjsjbinTZbp8PJtjsVK1XFJStdzXdy/jaddAep2FGY+wyFAQ==}
    engines: {node: '>=18'}
    cpu: [x64]
    os: [linux]

-  '@esbuild/netbsd-arm64@0.25.10':
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+  '@esbuild/netbsd-arm64@0.25.11':
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    engines: {node: '>=18'}
    cpu: [arm64]
    os: [netbsd]

-  '@esbuild/netbsd-x64@0.25.10':
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+  '@esbuild/netbsd-x64@0.25.11':
+    resolution: {integrity: sha512-u7tKA+qbzBydyj0vgpu+5h5AeudxOAGncb8N6C9Kh1N4n7wU1Xw1JDApsRjpShRpXRQlJLb9wY28ELpwdPcZ7A==}
    engines: {node: '>=18'}
    cpu: [x64]
    os: [netbsd]

-  '@esbuild/openbsd-arm64@0.25.10':
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+  '@esbuild/openbsd-arm64@0.25.11':
+    resolution: {integrity: sha512-Qq6YHhayieor3DxFOoYM1q0q1uMFYb7cSpLD2qzDSvK1NAvqFi8Xgivv0cFC6J+hWVw2teCYltyy9/m/14ryHg==}
    engines: {node: '>=18'}
    cpu: [arm64]
    os: [openbsd]

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    cpu: [x64]
    os: [openbsd]

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+  '@esbuild/openharmony-arm64@0.25.11':
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    engines: {node: '>=18'}
    cpu: [arm64]
    os: [openharmony]

-  '@esbuild/sunos-x64@0.25.10':
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+  '@esbuild/sunos-x64@0.25.11':
+    resolution: {integrity: sha512-nq2xdYaWxyg9DcIyXkZhcYulC6pQ2FuCgem3LI92IwMgIZ69KHeY8T4Y88pcwoLIjbed8n36CyKoYRDygNSGhA==}
    engines: {node: '>=18'}
    cpu: [x64]
    os: [sunos]

-  '@esbuild/win32-arm64@0.25.10':
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+  '@esbuild/win32-arm64@0.25.11':
+    resolution: {integrity: sha512-3XxECOWJq1qMZ3MN8srCJ/QfoLpL+VaxD/WfNRm1O3B4+AZ/BnLVgFbUV3eiRYDMXetciH16dwPbbHqwe1uU0Q==}
    engines: {node: '>=18'}
    cpu: [arm64]
    os: [win32]

-  '@esbuild/win32-ia32@0.25.10':
-    resolution: {integrity: sha512-QHPDbKkrGO8/cz9LKVnJU22HOi4pxZnZhhA2HYHez5Pz4JeffhDjf85E57Oyco163GnzNCVkZK0b/n4Y0UHcSw==}
+  '@esbuild/win32-ia32@0.25.11':
+    resolution: {integrity: sha512-3ukss6gb9XZ8TlRyJlgLn17ecsK4NSQTmdIXRASVsiS2sQ6zPPZklNJT5GR5tE/MUarymmy8kCEf5xPCNCqVOA==}
    engines: {node: '>=18'}
    cpu: [ia32]
    os: [win32]

-  '@esbuild/win32-x64@0.25.10':
-    resolution: {integrity: sha512-9KpxSVFCu0iK1owoez6aC/s/EdUQLDN3adTxGCqxMVhrPDj6bt5dbrHDXUuq+Bs2vATFBBrQS5vdQ/Ed2P+nbw==}
+  '@esbuild/win32-x64@0.25.11':
+    resolution: {integrity: sha512-D7Hpz6A2L4hzsRpPaCYkQnGOotdUpDzSGRIv9I+1ITdHROSFUWW95ZPZWQmGka1Fg7W3zFJowyn9WGwMJ0+KPA==}
    engines: {node: '>=18'}
    cpu: [x64]
    os: [win32]
@@ -811,8 +811,8 @@ packages:
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    engines: {node: '>=18'}

-  devalue@5.3.2:
-    resolution: {integrity: sha512-UDsjUbpQn9kvm68slnrs+mfxwFkIflOhkanmyabZ8zOYk8SMEIbJ3TK+88g70hSIeytu4y18f0z/hYHMTrXIWw==}
+  devalue@5.4.1:
+    resolution: {integrity: sha512-YtoaOfsqjbZQKGIMRYDWKjUmSB4VJ/RElB+bXZawQAQYAo4xu08GKTMVlsZDTF6R2MbAgjcAQRPI5eIyRAT2OQ==}

  devlop@1.1.0:
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@@ -861,8 +861,8 @@ packages:
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    resolution: {integrity: sha512-8Ja+rNJ0Lt56Pcf3TAmpBZjmx8ZcK5Ts4cAzIOjsjevg9oSXJnl6SUQ2EevU8tv3h6ZLWmoKL5H4fgWvdvfETw==}

-  esbuild@0.25.10:
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+  esbuild@0.25.11:
+    resolution: {integrity: sha512-KohQwyzrKTQmhXDW1PjCv3Tyspn9n5GcY2RTDqeORIdIJY8yKIF7sTSopFmn/wpMPW4rdPXI0UE5LJLuq3bx0Q==}
    engines: {node: '>=18'}
    hasBin: true

@@ -1344,8 +1344,8 @@ packages:
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    engines: {node: '>=14.16'}

-  package-manager-detector@1.4.0:
-    resolution: {integrity: sha512-rRZ+pR1Usc+ND9M2NkmCvE/LYJS+8ORVV9X0KuNSY/gFsp7RBHJM/ADh9LYq4Vvfq6QkKrW6/weuh8SMEtN5gw==}
+  package-manager-detector@1.4.1:
+    resolution: {integrity: sha512-dSMiVLBEA4XaNJ0PRb4N5cV/SEP4BWrWZKBmfF+OUm2pQTiZ6DDkKeWaltwu3JRhLoy59ayIkJ00cx9K9CaYTg==}

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@@ -1753,8 +1753,8 @@ packages:
  vfile@6.0.3:
    resolution: {integrity: sha512-KzIbH/9tXat2u30jf+smMwFCsno4wHVdNmzFyL+T/L3UGqqk6JKfVqOFOZEpZSHADH1k40ab6NUIXZq422ov3Q==}

-  vite@6.3.7:
-    resolution: {integrity: sha512-mQYaKepA0NGMBsz8Xktt3tJUG5ELE2iT7IJ+ssXI6nxVdE2sFc/d/6w/JByqMLvWg8hNKHpPgzjgOkrhpKFnrA==}
+  vite@6.4.0:
+    resolution: {integrity: sha512-oLnWs9Hak/LOlKjeSpOwD6JMks8BeICEdYMJBf6P4Lac/pO9tKiv/XhXnAM7nNfSkZahjlCZu9sS50zL8fSnsw==}
    engines: {node: ^18.0.0 || ^20.0.0 || >=22.0.0}
    hasBin: true
    peerDependencies:
@@ -1922,7 +1922,7 @@ snapshots:
      stream-replace-string: 2.0.0
      zod: 3.25.76

-  '@astrojs/starlight@0.36.0(astro@5.14.5(@types/node@24.7.2)(rollup@4.52.4)(typescript@5.9.3))':
+  '@astrojs/starlight@0.36.1(astro@5.14.5(@types/node@24.7.2)(rollup@4.52.4)(typescript@5.9.3))':
    dependencies:
      '@astrojs/markdown-remark': 6.3.8
      '@astrojs/mdx': 4.3.7(astro@5.14.5(@types/node@24.7.2)(rollup@4.52.4)(typescript@5.9.3))
@@ -1993,82 +1993,82 @@ snapshots:
      tslib: 2.8.1
    optional: true

-  '@esbuild/aix-ppc64@0.25.10':
+  '@esbuild/aix-ppc64@0.25.11':
    optional: true

-  '@esbuild/android-arm64@0.25.10':
+  '@esbuild/android-arm64@0.25.11':
    optional: true

-  '@esbuild/android-arm@0.25.10':
+  '@esbuild/android-arm@0.25.11':
    optional: true

-  '@esbuild/android-x64@0.25.10':
+  '@esbuild/android-x64@0.25.11':
    optional: true

-  '@esbuild/darwin-arm64@0.25.10':
+  '@esbuild/darwin-arm64@0.25.11':
    optional: true

-  '@esbuild/darwin-x64@0.25.10':
+  '@esbuild/darwin-x64@0.25.11':
    optional: true

-  '@esbuild/freebsd-arm64@0.25.10':
+  '@esbuild/freebsd-arm64@0.25.11':
    optional: true

-  '@esbuild/freebsd-x64@0.25.10':
+  '@esbuild/freebsd-x64@0.25.11':
    optional: true

-  '@esbuild/linux-arm64@0.25.10':
+  '@esbuild/linux-arm64@0.25.11':
    optional: true

-  '@esbuild/linux-arm@0.25.10':
+  '@esbuild/linux-arm@0.25.11':
    optional: true

-  '@esbuild/linux-ia32@0.25.10':
+  '@esbuild/linux-ia32@0.25.11':
    optional: true

-  '@esbuild/linux-loong64@0.25.10':
+  '@esbuild/linux-loong64@0.25.11':
    optional: true

-  '@esbuild/linux-mips64el@0.25.10':
+  '@esbuild/linux-mips64el@0.25.11':
    optional: true

-  '@esbuild/linux-ppc64@0.25.10':
+  '@esbuild/linux-ppc64@0.25.11':
    optional: true

-  '@esbuild/linux-riscv64@0.25.10':
+  '@esbuild/linux-riscv64@0.25.11':
    optional: true

-  '@esbuild/linux-s390x@0.25.10':
+  '@esbuild/linux-s390x@0.25.11':
    optional: true

-  '@esbuild/linux-x64@0.25.10':
+  '@esbuild/linux-x64@0.25.11':
    optional: true

-  '@esbuild/netbsd-arm64@0.25.10':
+  '@esbuild/netbsd-arm64@0.25.11':
    optional: true

-  '@esbuild/netbsd-x64@0.25.10':
+  '@esbuild/netbsd-x64@0.25.11':
    optional: true

-  '@esbuild/openbsd-arm64@0.25.10':
+  '@esbuild/openbsd-arm64@0.25.11':
    optional: true

-  '@esbuild/openbsd-x64@0.25.10':
+  '@esbuild/openbsd-x64@0.25.11':
    optional: true

-  '@esbuild/openharmony-arm64@0.25.10':
+  '@esbuild/openharmony-arm64@0.25.11':
    optional: true

-  '@esbuild/sunos-x64@0.25.10':
+  '@esbuild/sunos-x64@0.25.11':
    optional: true

-  '@esbuild/win32-arm64@0.25.10':
+  '@esbuild/win32-arm64@0.25.11':
    optional: true

-  '@esbuild/win32-ia32@0.25.10':
+  '@esbuild/win32-ia32@0.25.11':
    optional: true

-  '@esbuild/win32-x64@0.25.10':
+  '@esbuild/win32-x64@0.25.11':
    optional: true

  '@expressive-code/core@0.41.3':
@@ -2453,12 +2453,12 @@ snapshots:
      cssesc: 3.0.0
      debug: 4.4.3
      deterministic-object-hash: 2.0.2
-      devalue: 5.3.2
+      devalue: 5.4.1
      diff: 5.2.0
      dlv: 1.1.3
      dset: 3.1.4
      es-module-lexer: 1.7.0
-      esbuild: 0.25.10
+      esbuild: 0.25.11
      estree-walker: 3.0.3
      flattie: 1.1.1
      fontace: 0.3.1
@@ -2474,7 +2474,7 @@ snapshots:
      neotraverse: 0.6.18
      p-limit: 6.2.0
      p-queue: 8.1.1
-      package-manager-detector: 1.4.0
+      package-manager-detector: 1.4.1
      picomatch: 4.0.3
      prompts: 2.4.2
      rehype: 13.0.2
@@ -2489,8 +2489,8 @@ snapshots:
      unist-util-visit: 5.0.0
      unstorage: 1.17.1
      vfile: 6.0.3
-      vite: 6.3.7(@types/node@24.7.2)
-      vitefu: 1.1.1(vite@6.3.7(@types/node@24.7.2))
+      vite: 6.4.0(@types/node@24.7.2)
+      vitefu: 1.1.1(vite@6.4.0(@types/node@24.7.2))
      xxhash-wasm: 1.1.0
      yargs-parser: 21.1.1
      yocto-spinner: 0.2.3
@@ -2638,7 +2638,7 @@ snapshots:
    dependencies:
      base-64: 1.0.0

-  devalue@5.3.2: {}
+  devalue@5.4.1: {}

  devlop@1.1.0:
    dependencies:
@@ -2680,34 +2680,34 @@ snapshots:
      esast-util-from-estree: 2.0.0
      vfile-message: 4.0.3

-  esbuild@0.25.10:
+  esbuild@0.25.11:
    optionalDependencies:
-      '@esbuild/aix-ppc64': 0.25.10
-      '@esbuild/android-arm': 0.25.10
-      '@esbuild/android-arm64': 0.25.10
-      '@esbuild/android-x64': 0.25.10
-      '@esbuild/darwin-arm64': 0.25.10
-      '@esbuild/darwin-x64': 0.25.10
-      '@esbuild/freebsd-arm64': 0.25.10
-      '@esbuild/freebsd-x64': 0.25.10
-      '@esbuild/linux-arm': 0.25.10
-      '@esbuild/linux-arm64': 0.25.10
-      '@esbuild/linux-ia32': 0.25.10
-      '@esbuild/linux-loong64': 0.25.10
-      '@esbuild/linux-mips64el': 0.25.10
-      '@esbuild/linux-ppc64': 0.25.10
-      '@esbuild/linux-riscv64': 0.25.10
-      '@esbuild/linux-s390x': 0.25.10
-      '@esbuild/linux-x64': 0.25.10
-      '@esbuild/netbsd-arm64': 0.25.10
-      '@esbuild/netbsd-x64': 0.25.10
-      '@esbuild/openbsd-arm64': 0.25.10
-      '@esbuild/openbsd-x64': 0.25.10
-      '@esbuild/openharmony-arm64': 0.25.10
-      '@esbuild/sunos-x64': 0.25.10
-      '@esbuild/win32-arm64': 0.25.10
-      '@esbuild/win32-ia32': 0.25.10
-      '@esbuild/win32-x64': 0.25.10
+      '@esbuild/aix-ppc64': 0.25.11
+      '@esbuild/android-arm': 0.25.11
+      '@esbuild/android-arm64': 0.25.11
+      '@esbuild/android-x64': 0.25.11
+      '@esbuild/darwin-arm64': 0.25.11
+      '@esbuild/darwin-x64': 0.25.11
+      '@esbuild/freebsd-arm64': 0.25.11
+      '@esbuild/freebsd-x64': 0.25.11
+      '@esbuild/linux-arm': 0.25.11
+      '@esbuild/linux-arm64': 0.25.11
+      '@esbuild/linux-ia32': 0.25.11
+      '@esbuild/linux-loong64': 0.25.11
+      '@esbuild/linux-mips64el': 0.25.11
+      '@esbuild/linux-ppc64': 0.25.11
+      '@esbuild/linux-riscv64': 0.25.11
+      '@esbuild/linux-s390x': 0.25.11
+      '@esbuild/linux-x64': 0.25.11
+      '@esbuild/netbsd-arm64': 0.25.11
+      '@esbuild/netbsd-x64': 0.25.11
+      '@esbuild/openbsd-arm64': 0.25.11
+      '@esbuild/openbsd-x64': 0.25.11
+      '@esbuild/openharmony-arm64': 0.25.11
+      '@esbuild/sunos-x64': 0.25.11
+      '@esbuild/win32-arm64': 0.25.11
+      '@esbuild/win32-ia32': 0.25.11
+      '@esbuild/win32-x64': 0.25.11

  escape-html@1.0.3: {}

@@ -3595,7 +3595,7 @@ snapshots:

  p-timeout@6.1.4: {}

-  package-manager-detector@1.4.0: {}
+  package-manager-detector@1.4.1: {}

  pagefind@1.4.0:
    optionalDependencies:
@@ -4116,9 +4116,9 @@ snapshots:
      '@types/unist': 3.0.3
      vfile-message: 4.0.3

-  vite@6.3.7(@types/node@24.7.2):
+  vite@6.4.0(@types/node@24.7.2):
    dependencies:
-      esbuild: 0.25.10
+      esbuild: 0.25.11
      fdir: 6.5.0(picomatch@4.0.3)
      picomatch: 4.0.3
      postcss: 8.5.6
@@ -4128,9 +4128,9 @@ snapshots:
      '@types/node': 24.7.2
      fsevents: 2.3.3

-  vitefu@1.1.1(vite@6.3.7(@types/node@24.7.2)):
+  vitefu@1.1.1(vite@6.4.0(@types/node@24.7.2)):
    optionalDependencies:
-      vite: 6.3.7(@types/node@24.7.2)
+      vite: 6.4.0(@types/node@24.7.2)

  web-namespaces@2.0.1: {}

--- a/docs/pnpm-workspace.yaml
+++ b/docs/pnpm-workspace.yaml
@@ -1,3 +0,0 @@
-onlyBuiltDependencies:
-  - esbuild
-  - sharp
--- a/docs/src/content/docs/reference/example.md
+++ b/docs/src/content/docs/reference/example.md
@@ -1,51 +0,0 @@
---
-title: Sync Server API
-description: API endpoints for the Ascently sync server
---
-
-The sync server provides a minimal REST API for data synchronization.
-
-## Authentication
-
-All endpoints require an `Authorization: Bearer <your-auth-token>` header.
-
-## Endpoints
-
-### Data Sync
-
-**GET /sync**
- Download `ascently.json` file
- Returns: JSON data file or 404 if no data exists
-
-**POST /sync**
- Upload `ascently.json` file
- Body: JSON data
- Returns: Success confirmation
-
-### Images
-
-**GET /images/{imageName}**
- Download an image file
- Returns: Image file or 404 if not found
-
-**POST /images/{imageName}**
- Upload an image file
- Body: Image data
- Returns: Success confirmation
-
-## Example Usage
-
-```bash
-# Download data
-curl -H "Authorization: Bearer your-token" \
-     http://localhost:8080/sync
-
-# Upload data
-curl -X POST \
-     -H "Authorization: Bearer your-token" \
-     -H "Content-Type: application/json" \
-     -d @ascently.json \
-     http://localhost:8080/sync
-```
-
-See `main.go` in the sync directory for implementation details.
--- a/docs/src/content/docs/sync/api-reference.md
+++ b/docs/src/content/docs/sync/api-reference.md
@@ -0,0 +1,152 @@
+---
+title: API Reference
+description: Complete API documentation for the Ascently sync server
+---
+
+Complete reference for all sync server endpoints.
+
+## Authentication
+
+All endpoints require a bearer token in the `Authorization` header:
+
+```
+Authorization: Bearer your-auth-token
+```
+
+Unauthorized requests return `401 Unauthorized`.
+
+## Endpoints
+
+### Health Check
+
+**`GET /health`**
+
+Check if the server is running.
+
+**Response:**
+```json
+{
+  "status": "ok",
+  "version": "2.0.0"
+}
+```
+
+### Full Sync - Download
+
+**`GET /sync`**
+
+Download the entire dataset from the server.
+
+**Response:**
+```json
+{
+  "exportedAt": "2024-01-15T10:30:00.000Z",
+  "version": "2.0",
+  "formatVersion": "2.0",
+  "gyms": [...],
+  "problems": [...],
+  "sessions": [...],
+  "attempts": [...],
+  "deletedItems": [...]
+}
+```
+
+Returns `200 OK` with the backup data, or `404 Not Found` if no data exists.
+
+### Full Sync - Upload
+
+**`POST /sync`**
+
+Upload your entire dataset to the server. This overwrites all server data.
+
+**Request Body:**
+```json
+{
+  "exportedAt": "2024-01-15T10:30:00.000Z",
+  "version": "2.0",
+  "formatVersion": "2.0",
+  "gyms": [...],
+  "problems": [...],
+  "sessions": [...],
+  "attempts": [...],
+  "deletedItems": [...]
+}
+```
+
+**Response:**
+```
+200 OK
+```
+
+### Delta Sync
+
+**`POST /sync/delta`**
+
+Sync only changed data since your last sync. Much faster than full sync.
+
+**Request Body:**
+```json
+{
+  "lastSyncTime": "2024-01-15T10:00:00.000Z",
+  "gyms": [...],
+  "problems": [...],
+  "sessions": [...],
+  "attempts": [...],
+  "deletedItems": [...]
+}
+```
+
+Include only items modified after `lastSyncTime`. The server merges your changes with its data using last-write-wins based on `updatedAt` timestamps.
+
+**Response:**
+```json
+{
+  "serverTime": "2024-01-15T10:30:00.000Z",
+  "gyms": [...],
+  "problems": [...],
+  "sessions": [...],
+  "attempts": [...],
+  "deletedItems": [...]
+}
+```
+
+Returns only server items modified after your `lastSyncTime`. Save `serverTime` as your new `lastSyncTime` for the next delta sync.
+
+### Image Upload
+
+**`POST /images/upload?filename={name}`**
+
+Upload an image file.
+
+**Query Parameters:**
+- `filename`: Image filename (e.g., `problem_abc123_0.jpg`)
+
+**Request Body:**
+Binary image data (JPEG, PNG, GIF, or WebP)
+
+**Response:**
+```
+200 OK
+```
+
+### Image Download
+
+**`GET /images/download?filename={name}`**
+
+Download an image file.
+
+**Query Parameters:**
+- `filename`: Image filename
+
+**Response:**
+Binary image data with appropriate `Content-Type` header.
+
+Returns `404 Not Found` if the image doesn't exist.
+
+## Notes
+
+- All timestamps are ISO 8601 format with milliseconds
+- Active sessions (status `active`) are excluded from sync
+- Images are stored separately and referenced by filename
+- The server stores everything in a single `ascently.json` file
+- No versioning or history - last write wins
--- a/docs/src/content/docs/sync/overview.md
+++ b/docs/src/content/docs/sync/overview.md
@@ -3,28 +3,49 @@ title: Self-Hosted Sync Overview
 description: Learn about Ascently's optional sync server for cross-device data synchronization
 ---

-You can run your own sync server to keep your data in sync across devices. The server is lightweight and easy to set up using Docker.
+Run your own sync server to keep your data in sync across devices. The server is lightweight and easy to set up with Docker.

 ## How It Works

-This server uses a single `ascently.json` file for your data and a directory for images. The last client to upload wins, overwriting the old data. Authentication is just a static bearer token.
+The server stores your data in a single `ascently.json` file and images in a directory. It's simple: last write wins. Authentication is a static bearer token you set.

-## API
+## Features

-All endpoints require an `Authorization: Bearer <your-auth-token>` header.
+- **Delta sync**: Only syncs changed data
+- **Image sync**: Automatically syncs problem images
+- **Conflict resolution**: Last-write-wins based on timestamps
+- **Cross-platform**: Works with iOS and Android clients
+- **Privacy**: Your data, your server, no analytics

- `GET /sync`: Download `ascently.json`
- `POST /sync`: Upload `ascently.json`
- `GET /images/{imageName}`: Download an image
- `POST /images/{imageName}`: Upload an image
+## API Endpoints
+
+- `GET /health` - Health check
+- `GET /sync` - Download full dataset
+- `POST /sync` - Upload full dataset
+- `POST /sync/delta` - Sync only changes (recommended)
+- `POST /images/upload?filename={name}` - Upload image
+- `GET /images/download?filename={name}` - Download image
+
+All endpoints require `Authorization: Bearer <your-token>` header.
+
+See the [API Reference](/sync/api-reference/) for complete documentation.

 ## Getting Started

-The easiest way to get started is with the [Quick Start guide](/sync/quick-start/) using Docker Compose.
+Check out the [Quick Start guide](/sync/quick-start/) to get your server running with Docker Compose.

 You'll need:
 - Docker and Docker Compose
 - A secure authentication token
 - A place to store your data

-The server will be available at `http://localhost:8080` by default. Configure your clients with your server URL and auth token to start syncing.
+The server will be available at `http://localhost:8080` by default. Configure your Ascently apps with your server URL and auth token to start syncing.
+
+## How Sync Works
+
+1. **First sync**: Client uploads or downloads full dataset
+2. **Subsequent syncs**: Client uses delta sync to only transfer changed data
+3. **Conflicts**: Resolved automatically using timestamps (newer wins)
+4. **Images**: Synced automatically with problem data
+
+Active sessions are excluded from sync until completed.
--- a/docs/src/content/docs/sync/quick-start.md
+++ b/docs/src/content/docs/sync/quick-start.md
@@ -3,7 +3,7 @@ title: Quick Start
 description: Get your Ascently sync server running with Docker Compose
 ---

-Get your Ascently sync server up and running using Docker Compose.
+Get your sync server running in minutes with Docker Compose.

 ## Prerequisites

@@ -12,50 +12,158 @@ Get your Ascently sync server up and running using Docker Compose.

 ## Setup

-1. Create a `.env` file with your configuration:
+1. Create a `docker-compose.yml` file:

-```env
-IMAGE=git.atri.dad/atridad/ascently-sync:latest
-APP_PORT=8080
-AUTH_TOKEN=your-super-secret-token
-DATA_FILE=/data/ascently.json
-IMAGES_DIR=/data/images
-ROOT_DIR=./ascently-data
+```yaml
+version: '3.8'
+
+services:
+  ascently-sync:
+    image: git.atri.dad/atridad/ascently-sync:latest
+    ports:
+      - "8080:8080"
+    environment:
+      - AUTH_TOKEN=${AUTH_TOKEN}
+      - DATA_FILE=/data/ascently.json
+      - IMAGES_DIR=/data/images
+    volumes:
+      - ./ascently-data:/data
+    restart: unless-stopped
 ```

-Set `AUTH_TOKEN` to a long, random string. `ROOT_DIR` is where the server will store its data on your machine.
+2. Create a `.env` file in the same directory:

-2. Use the provided `docker-compose.yml` in the `sync/` directory:
+```env
+AUTH_TOKEN=your-super-secret-token-here
+```
+
+Replace `your-super-secret-token-here` with a secure random token (see below).
+
+3. Start the server:

 ```bash
-cd sync/
 docker-compose up -d
 ```

 The server will be available at `http://localhost:8080`.

-## Configure Your Clients
+## Generate a Secure Token

-Configure your Ascently apps with:
- **Server URL**: `http://your-server-ip:8080` (or your domain)
- **Auth Token**: The token from your `.env` file
-
-Enable sync and perform your first sync to start synchronizing data across devices.
-
-## Generating a Secure Token
-
-Generate a secure authentication token:
+Use this command to generate a secure authentication token:

 ```bash
-# On Linux/macOS
 openssl rand -base64 32
 ```

-Keep this token secure and don't share it publicly.
+Copy the output and paste it into your `.env` file as the `AUTH_TOKEN`.

-## Accessing Remotely
+Keep this token secret and don't commit it to version control.

-For remote access, you'll need to:
- Set up port forwarding on your router (port 8080)
- Use your public IP address or set up a domain name
- Consider using HTTPS with a reverse proxy for security
+## Configure Your Apps
+
+Open Ascently on your iOS or Android device:
+
+1. Go to **Settings**
+2. Scroll to **Sync Configuration**
+3. Enter your **Server URL**: `http://your-server-ip:8080`
+4. Enter your **Auth Token**: (the token from your `.env` file)
+5. Tap **Test Connection** to verify it works
+6. Enable **Auto Sync**
+7. Tap **Sync Now** to perform your first sync
+
+Repeat this on all your devices to keep them in sync.
+
+## Verify It's Working
+
+Check the server logs:
+
+```bash
+docker-compose logs -f ascently-sync
+```
+
+You should see logs like:
+
+```
+Delta sync from 192.168.1.100: lastSyncTime=2024-01-15T10:00:00.000Z, gyms=1, problems=5, sessions=2, attempts=10, deletedItems=0
+```
+
+## Remote Access
+
+To access your server remotely:
+
+### Option 1: Port Forwarding
+
+1. Forward port 8080 on your router to your server
+2. Find your public IP address
+3. Use `http://your-public-ip:8080` as the server URL
+
+### Option 2: Domain Name (Recommended)
+
+1. Get a domain name and point it to your server
+2. Set up a reverse proxy (nginx, Caddy, Traefik)
+3. Enable HTTPS with Let's Encrypt
+4. Use `https://sync.yourdomain.com` as the server URL
+
+Example nginx config with HTTPS:
+
+```nginx
+server {
+    listen 443 ssl http2;
+    server_name sync.yourdomain.com;
+
+    ssl_certificate /etc/letsencrypt/live/sync.yourdomain.com/fullchain.pem;
+    ssl_certificate_key /etc/letsencrypt/live/sync.yourdomain.com/privkey.pem;
+
+    location / {
+        proxy_pass http://localhost:8080;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+    }
+}
+```
+
+## Updating
+
+Pull the latest image and restart:
+
+```bash
+docker-compose pull
+docker-compose up -d
+```
+
+Your data is stored in `./ascently-data` and persists across updates.
+
+## Troubleshooting
+
+### Connection Failed
+
+- Check the server is running: `docker-compose ps`
+- Verify the auth token matches on server and client
+- Check firewall settings and port forwarding
+- Test locally first with `http://localhost:8080`
+
+### Sync Errors
+
+- Check server logs: `docker-compose logs ascently-sync`
+- Verify your device has internet connection
+- Try disabling and re-enabling sync
+- Perform a manual sync from Settings
+
+### Data Location
+
+All data is stored in `./ascently-data/`:
+
+```
+ascently-data/
+├── ascently.json    # Your climb data
+└── images/          # Problem images
+```
+
+You can back this up or move it to another server.
+
+## Next Steps
+
+- Read the [API Reference](/sync/api-reference/) for advanced usage
+- Set up automated backups of your `ascently-data` directory
+- Configure HTTPS for secure remote access
+- Monitor server logs for sync activity
--- a/ios/Ascently.xcodeproj/project.pbxproj
+++ b/ios/Ascently.xcodeproj/project.pbxproj
@@ -465,7 +465,7 @@
 				CODE_SIGN_ENTITLEMENTS = Ascently/Ascently.entitlements;
 				CODE_SIGN_IDENTITY = "Apple Development";
 				CODE_SIGN_STYLE = Automatic;
-				CURRENT_PROJECT_VERSION = 26;
+				CURRENT_PROJECT_VERSION = 27;
 				DEVELOPMENT_TEAM = 4BC9Y2LL4B;
 				DRIVERKIT_DEPLOYMENT_TARGET = 24.6;
 				ENABLE_PREVIEWS = YES;
@@ -487,7 +487,7 @@
 					"@executable_path/Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 15.6;
-				MARKETING_VERSION = 2.0.0;
+				MARKETING_VERSION = 2.1.0;
 				PRODUCT_BUNDLE_IDENTIFIER = com.atridad.Ascently;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
@@ -513,7 +513,7 @@
 				CODE_SIGN_ENTITLEMENTS = Ascently/Ascently.entitlements;
 				CODE_SIGN_IDENTITY = "Apple Development";
 				CODE_SIGN_STYLE = Automatic;
-				CURRENT_PROJECT_VERSION = 26;
+				CURRENT_PROJECT_VERSION = 27;
 				DEVELOPMENT_TEAM = 4BC9Y2LL4B;
 				DRIVERKIT_DEPLOYMENT_TARGET = 24.6;
 				ENABLE_PREVIEWS = YES;
@@ -535,7 +535,7 @@
 					"@executable_path/Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 15.6;
-				MARKETING_VERSION = 2.0.0;
+				MARKETING_VERSION = 2.1.0;
 				PRODUCT_BUNDLE_IDENTIFIER = com.atridad.Ascently;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
@@ -602,7 +602,7 @@
 				ASSETCATALOG_COMPILER_WIDGET_BACKGROUND_COLOR_NAME = WidgetBackground;
 				CODE_SIGN_ENTITLEMENTS = SessionStatusLiveExtension.entitlements;
 				CODE_SIGN_STYLE = Automatic;
-				CURRENT_PROJECT_VERSION = 26;
+				CURRENT_PROJECT_VERSION = 27;
 				DEVELOPMENT_TEAM = 4BC9Y2LL4B;
 				GENERATE_INFOPLIST_FILE = YES;
 				INFOPLIST_FILE = SessionStatusLive/Info.plist;
@@ -613,7 +613,7 @@
 					"@executable_path/Frameworks",
 					"@executable_path/../../Frameworks",
 				);
-				MARKETING_VERSION = 2.0.0;
+				MARKETING_VERSION = 2.1.0;
 				PRODUCT_BUNDLE_IDENTIFIER = com.atridad.Ascently.SessionStatusLive;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SKIP_INSTALL = YES;
@@ -632,7 +632,7 @@
 				ASSETCATALOG_COMPILER_WIDGET_BACKGROUND_COLOR_NAME = WidgetBackground;
 				CODE_SIGN_ENTITLEMENTS = SessionStatusLiveExtension.entitlements;
 				CODE_SIGN_STYLE = Automatic;
-				CURRENT_PROJECT_VERSION = 26;
+				CURRENT_PROJECT_VERSION = 27;
 				DEVELOPMENT_TEAM = 4BC9Y2LL4B;
 				GENERATE_INFOPLIST_FILE = YES;
 				INFOPLIST_FILE = SessionStatusLive/Info.plist;
@@ -643,7 +643,7 @@
 					"@executable_path/Frameworks",
 					"@executable_path/../../Frameworks",
 				);
-				MARKETING_VERSION = 2.0.0;
+				MARKETING_VERSION = 2.1.0;
 				PRODUCT_BUNDLE_IDENTIFIER = com.atridad.Ascently.SessionStatusLive;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SKIP_INSTALL = YES;
--- a/ios/Ascently.xcodeproj/project.xcworkspace/xcuserdata/atridad.xcuserdatad/UserInterfaceState.xcuserstate
+++ b/ios/Ascently.xcodeproj/project.xcworkspace/xcuserdata/atridad.xcuserdatad/UserInterfaceState.xcuserstate
--- a/ios/Ascently/ContentView.swift
+++ b/ios/Ascently/ContentView.swift
@@ -111,7 +111,6 @@ struct ContentView: View {
            Task {
                try? await Task.sleep(nanoseconds: 300_000_000)  // 0.3 seconds
                await dataManager.onAppBecomeActive()
-                // Ensure health integration is verified
                await dataManager.healthKitService.verifyAndRestoreIntegration()
            }
        }
--- a/ios/Ascently/Models/BackupFormat.swift
+++ b/ios/Ascently/Models/BackupFormat.swift
@@ -55,7 +55,6 @@ struct BackupGym: Codable {
    let createdAt: String
    let updatedAt: String

-    /// Initialize from native iOS Gym model
    init(from gym: Gym) {
        self.id = gym.id.uuidString
        self.name = gym.name
@@ -71,7 +70,6 @@ struct BackupGym: Codable {
        self.updatedAt = formatter.string(from: gym.updatedAt)
    }

-    /// Initialize with explicit parameters for import
    init(
        id: String,
        name: String,
@@ -94,7 +92,6 @@ struct BackupGym: Codable {
        self.updatedAt = updatedAt
    }

-    /// Convert to native iOS Gym model
    func toGym() throws -> Gym {
        let formatter = ISO8601DateFormatter()
        formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
@@ -137,7 +134,6 @@ struct BackupProblem: Codable {
    let createdAt: String
    let updatedAt: String

-    /// Initialize from native iOS Problem model
    init(from problem: Problem) {
        self.id = problem.id.uuidString
        self.gymId = problem.gymId.uuidString
@@ -158,7 +154,6 @@ struct BackupProblem: Codable {
        self.updatedAt = formatter.string(from: problem.updatedAt)
    }

-    /// Initialize with explicit parameters for import
    init(
        id: String,
        gymId: String,
@@ -191,7 +186,6 @@ struct BackupProblem: Codable {
        self.updatedAt = updatedAt
    }

-    /// Convert to native iOS Problem model
    func toProblem() throws -> Problem {
        let formatter = ISO8601DateFormatter()
        formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
@@ -224,7 +218,6 @@ struct BackupProblem: Codable {
        )
    }

-    /// Create a copy with updated image paths for import processing
    func withUpdatedImagePaths(_ newImagePaths: [String]) -> BackupProblem {
        return BackupProblem(
            id: self.id,
@@ -258,7 +251,6 @@ struct BackupClimbSession: Codable {
    let createdAt: String
    let updatedAt: String

-    /// Initialize from native iOS ClimbSession model
    init(from session: ClimbSession) {
        self.id = session.id.uuidString
        self.gymId = session.gymId.uuidString
@@ -275,7 +267,6 @@ struct BackupClimbSession: Codable {
        self.updatedAt = formatter.string(from: session.updatedAt)
    }

-    /// Initialize with explicit parameters for import
    init(
        id: String,
        gymId: String,
@@ -300,7 +291,6 @@ struct BackupClimbSession: Codable {
        self.updatedAt = updatedAt
    }

-    /// Convert to native iOS ClimbSession model
    func toClimbSession() throws -> ClimbSession {
        let formatter = ISO8601DateFormatter()
        formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
@@ -347,7 +337,6 @@ struct BackupAttempt: Codable {
    let createdAt: String
    let updatedAt: String?

-    /// Initialize from native iOS Attempt model
    init(from attempt: Attempt) {
        self.id = attempt.id.uuidString
        self.sessionId = attempt.sessionId.uuidString
@@ -365,7 +354,6 @@ struct BackupAttempt: Codable {
        self.updatedAt = formatter.string(from: attempt.updatedAt)
    }

-    /// Initialize with explicit parameters for import
    init(
        id: String,
        sessionId: String,
@@ -392,7 +380,6 @@ struct BackupAttempt: Codable {
        self.updatedAt = updatedAt
    }

-    /// Convert to native iOS Attempt model
    func toAttempt() throws -> Attempt {
        let formatter = ISO8601DateFormatter()
        formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
--- a/ios/Ascently/Models/DeltaSyncFormat.swift
+++ b/ios/Ascently/Models/DeltaSyncFormat.swift
@@ -0,0 +1,26 @@
+//
+//  DeltaSyncFormat.swift
+//  Ascently
+//
+//  Delta sync structures for incremental data synchronization
+//
+
+import Foundation
+
+struct DeltaSyncRequest: Codable {
+    let lastSyncTime: String
+    let gyms: [BackupGym]
+    let problems: [BackupProblem]
+    let sessions: [BackupClimbSession]
+    let attempts: [BackupAttempt]
+    let deletedItems: [DeletedItem]
+}
+
+struct DeltaSyncResponse: Codable {
+    let serverTime: String
+    let gyms: [BackupGym]
+    let problems: [BackupProblem]
+    let sessions: [BackupClimbSession]
+    let attempts: [BackupAttempt]
+    let deletedItems: [DeletedItem]
+}
--- a/ios/Ascently/Services/HealthKitService.swift
+++ b/ios/Ascently/Services/HealthKitService.swift
@@ -31,7 +31,6 @@ class HealthKitService: ObservableObject {
        }
    }

-    /// Restore active workout state
    private func restoreActiveWorkout() {
        if let startDate = userDefaults.object(forKey: workoutStartDateKey) as? Date,
            let sessionIdString = userDefaults.string(forKey: workoutSessionIdKey),
@@ -43,7 +42,6 @@ class HealthKitService: ObservableObject {
        }
    }

-    /// Persist active workout state
    private func persistActiveWorkout() {
        if let startDate = currentWorkoutStartDate, let sessionId = currentWorkoutSessionId {
            userDefaults.set(startDate, forKey: workoutStartDateKey)
@@ -54,7 +52,6 @@ class HealthKitService: ObservableObject {
        }
    }

-    /// Verify and restore health integration
    func verifyAndRestoreIntegration() async {
        guard isEnabled else { return }

--- a/ios/Ascently/Services/SyncService.swift
+++ b/ios/Ascently/Services/SyncService.swift
@@ -136,6 +136,314 @@ class SyncService: ObservableObject {
        }
    }

+    func performDeltaSync(dataManager: ClimbingDataManager) async throws {
+        guard isConfigured else {
+            throw SyncError.notConfigured
+        }
+
+        guard let url = URL(string: "\(serverURL)/sync/delta") else {
+            throw SyncError.invalidURL
+        }
+
+        // Get last sync time, or use epoch if never synced
+        let lastSync = lastSyncTime ?? Date(timeIntervalSince1970: 0)
+        let formatter = ISO8601DateFormatter()
+        let lastSyncString = formatter.string(from: lastSync)
+
+        // Collect items modified since last sync
+        let modifiedGyms = dataManager.gyms.filter { gym in
+            gym.updatedAt > lastSync
+        }.map { BackupGym(from: $0) }
+
+        let modifiedProblems = dataManager.problems.filter { problem in
+            problem.updatedAt > lastSync
+        }.map { problem -> BackupProblem in
+            var backupProblem = BackupProblem(from: problem)
+            if !problem.imagePaths.isEmpty {
+                let normalizedPaths = problem.imagePaths.enumerated().map { index, _ in
+                    ImageNamingUtils.generateImageFilename(
+                        problemId: problem.id.uuidString, imageIndex: index)
+                }
+                return BackupProblem(
+                    id: backupProblem.id,
+                    gymId: backupProblem.gymId,
+                    name: backupProblem.name,
+                    description: backupProblem.description,
+                    climbType: backupProblem.climbType,
+                    difficulty: backupProblem.difficulty,
+                    tags: backupProblem.tags,
+                    location: backupProblem.location,
+                    imagePaths: normalizedPaths,
+                    isActive: backupProblem.isActive,
+                    dateSet: backupProblem.dateSet,
+                    notes: backupProblem.notes,
+                    createdAt: backupProblem.createdAt,
+                    updatedAt: backupProblem.updatedAt
+                )
+            }
+            return backupProblem
+        }
+
+        let modifiedSessions = dataManager.sessions.filter { session in
+            session.status != .active && session.updatedAt > lastSync
+        }.map { BackupClimbSession(from: $0) }
+
+        let activeSessionIds = Set(
+            dataManager.sessions.filter { $0.status == .active }.map { $0.id })
+        let modifiedAttempts = dataManager.attempts.filter { attempt in
+            !activeSessionIds.contains(attempt.sessionId) && attempt.createdAt > lastSync
+        }.map { BackupAttempt(from: $0) }
+
+        let modifiedDeletions = dataManager.getDeletedItems().filter { item in
+            if let deletedDate = formatter.date(from: item.deletedAt) {
+                return deletedDate > lastSync
+            }
+            return false
+        }
+
+        print(
+            "iOS DELTA SYNC: Sending gyms=\(modifiedGyms.count), problems=\(modifiedProblems.count), sessions=\(modifiedSessions.count), attempts=\(modifiedAttempts.count), deletions=\(modifiedDeletions.count)"
+        )
+
+        // Create delta request
+        let deltaRequest = DeltaSyncRequest(
+            lastSyncTime: lastSyncString,
+            gyms: modifiedGyms,
+            problems: modifiedProblems,
+            sessions: modifiedSessions,
+            attempts: modifiedAttempts,
+            deletedItems: modifiedDeletions
+        )
+
+        let encoder = JSONEncoder()
+        encoder.dateEncodingStrategy = .iso8601
+        let jsonData = try encoder.encode(deltaRequest)
+
+        var request = URLRequest(url: url)
+        request.httpMethod = "POST"
+        request.setValue("Bearer \(authToken)", forHTTPHeaderField: "Authorization")
+        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
+        request.setValue("application/json", forHTTPHeaderField: "Accept")
+        request.httpBody = jsonData
+
+        let (data, response) = try await URLSession.shared.data(for: request)
+
+        guard let httpResponse = response as? HTTPURLResponse else {
+            throw SyncError.invalidResponse
+        }
+
+        switch httpResponse.statusCode {
+        case 200:
+            break
+        case 401:
+            throw SyncError.unauthorized
+        default:
+            throw SyncError.serverError(httpResponse.statusCode)
+        }
+
+        let decoder = JSONDecoder()
+        let deltaResponse = try decoder.decode(DeltaSyncResponse.self, from: data)
+
+        print(
+            "iOS DELTA SYNC: Received gyms=\(deltaResponse.gyms.count), problems=\(deltaResponse.problems.count), sessions=\(deltaResponse.sessions.count), attempts=\(deltaResponse.attempts.count), deletions=\(deltaResponse.deletedItems.count)"
+        )
+
+        // Apply server changes to local data
+        try await applyDeltaResponse(deltaResponse, dataManager: dataManager)
+
+        // Sync only modified problem images
+        try await syncModifiedImages(modifiedProblems: modifiedProblems, dataManager: dataManager)
+
+        // Update last sync time to server time
+        if let serverTime = formatter.date(from: deltaResponse.serverTime) {
+            lastSyncTime = serverTime
+            userDefaults.set(lastSyncTime, forKey: Keys.lastSyncTime)
+        }
+    }
+
+    private func applyDeltaResponse(_ response: DeltaSyncResponse, dataManager: ClimbingDataManager)
+        async throws
+    {
+        let formatter = ISO8601DateFormatter()
+
+        // Download images for new/modified problems from server
+        var imagePathMapping: [String: String] = [:]
+        for problem in response.problems {
+            guard let imagePaths = problem.imagePaths, !imagePaths.isEmpty else { continue }
+
+            for (index, imagePath) in imagePaths.enumerated() {
+                let serverFilename = URL(fileURLWithPath: imagePath).lastPathComponent
+
+                do {
+                    let imageData = try await downloadImage(filename: serverFilename)
+                    let consistentFilename = ImageNamingUtils.generateImageFilename(
+                        problemId: problem.id, imageIndex: index)
+                    let imageManager = ImageManager.shared
+                    _ = try imageManager.saveImportedImage(imageData, filename: consistentFilename)
+                    imagePathMapping[serverFilename] = consistentFilename
+                } catch SyncError.imageNotFound {
+                    print("Image not found on server: \(serverFilename)")
+                    continue
+                } catch {
+                    print("Failed to download image \(serverFilename): \(error)")
+                    continue
+                }
+            }
+        }
+
+        // Merge gyms
+        for backupGym in response.gyms {
+            if let index = dataManager.gyms.firstIndex(where: { $0.id.uuidString == backupGym.id })
+            {
+                let existing = dataManager.gyms[index]
+                if backupGym.updatedAt >= formatter.string(from: existing.updatedAt) {
+                    dataManager.gyms[index] = try backupGym.toGym()
+                }
+            } else {
+                dataManager.gyms.append(try backupGym.toGym())
+            }
+        }
+
+        // Merge problems
+        for backupProblem in response.problems {
+            var problemToMerge = backupProblem
+            if !imagePathMapping.isEmpty, let imagePaths = backupProblem.imagePaths {
+                let updatedPaths = imagePaths.compactMap { imagePathMapping[$0] ?? $0 }
+                problemToMerge = BackupProblem(
+                    id: backupProblem.id,
+                    gymId: backupProblem.gymId,
+                    name: backupProblem.name,
+                    description: backupProblem.description,
+                    climbType: backupProblem.climbType,
+                    difficulty: backupProblem.difficulty,
+                    tags: backupProblem.tags,
+                    location: backupProblem.location,
+                    imagePaths: updatedPaths,
+                    isActive: backupProblem.isActive,
+                    dateSet: backupProblem.dateSet,
+                    notes: backupProblem.notes,
+                    createdAt: backupProblem.createdAt,
+                    updatedAt: backupProblem.updatedAt
+                )
+            }
+
+            if let index = dataManager.problems.firstIndex(where: {
+                $0.id.uuidString == problemToMerge.id
+            }) {
+                let existing = dataManager.problems[index]
+                if problemToMerge.updatedAt >= formatter.string(from: existing.updatedAt) {
+                    dataManager.problems[index] = try problemToMerge.toProblem()
+                }
+            } else {
+                dataManager.problems.append(try problemToMerge.toProblem())
+            }
+        }
+
+        // Merge sessions
+        for backupSession in response.sessions {
+            if let index = dataManager.sessions.firstIndex(where: {
+                $0.id.uuidString == backupSession.id
+            }) {
+                let existing = dataManager.sessions[index]
+                if backupSession.updatedAt >= formatter.string(from: existing.updatedAt) {
+                    dataManager.sessions[index] = try backupSession.toClimbSession()
+                }
+            } else {
+                dataManager.sessions.append(try backupSession.toClimbSession())
+            }
+        }
+
+        // Merge attempts
+        for backupAttempt in response.attempts {
+            if let index = dataManager.attempts.firstIndex(where: {
+                $0.id.uuidString == backupAttempt.id
+            }) {
+                let existing = dataManager.attempts[index]
+                if backupAttempt.createdAt >= formatter.string(from: existing.createdAt) {
+                    dataManager.attempts[index] = try backupAttempt.toAttempt()
+                }
+            } else {
+                dataManager.attempts.append(try backupAttempt.toAttempt())
+            }
+        }
+
+        // Apply deletions
+        let allDeletions = dataManager.getDeletedItems() + response.deletedItems
+        let uniqueDeletions = Array(Set(allDeletions))
+        applyDeletionsToDataManager(deletions: uniqueDeletions, dataManager: dataManager)
+
+        // Save all changes
+        dataManager.saveGyms()
+        dataManager.saveProblems()
+        dataManager.saveSessions()
+        dataManager.saveAttempts()
+
+        // Update deletion records
+        dataManager.clearDeletedItems()
+        if let data = try? JSONEncoder().encode(uniqueDeletions) {
+            UserDefaults.standard.set(data, forKey: "ascently_deleted_items")
+        }
+
+        DataStateManager.shared.updateDataState()
+    }
+
+    private func applyDeletionsToDataManager(
+        deletions: [DeletedItem], dataManager: ClimbingDataManager
+    ) {
+        let deletedGymIds = Set(deletions.filter { $0.type == "gym" }.map { $0.id })
+        let deletedProblemIds = Set(deletions.filter { $0.type == "problem" }.map { $0.id })
+        let deletedSessionIds = Set(deletions.filter { $0.type == "session" }.map { $0.id })
+        let deletedAttemptIds = Set(deletions.filter { $0.type == "attempt" }.map { $0.id })
+
+        dataManager.gyms.removeAll { deletedGymIds.contains($0.id.uuidString) }
+        dataManager.problems.removeAll { deletedProblemIds.contains($0.id.uuidString) }
+        dataManager.sessions.removeAll { deletedSessionIds.contains($0.id.uuidString) }
+        dataManager.attempts.removeAll { deletedAttemptIds.contains($0.id.uuidString) }
+    }
+
+    private func syncModifiedImages(
+        modifiedProblems: [BackupProblem], dataManager: ClimbingDataManager
+    ) async throws {
+        guard !modifiedProblems.isEmpty else { return }
+
+        print("iOS DELTA SYNC: Syncing images for \(modifiedProblems.count) modified problems")
+
+        for backupProblem in modifiedProblems {
+            guard
+                let problem = dataManager.problems.first(where: {
+                    $0.id.uuidString == backupProblem.id
+                })
+            else {
+                continue
+            }
+
+            for (index, imagePath) in problem.imagePaths.enumerated() {
+                let filename = URL(fileURLWithPath: imagePath).lastPathComponent
+                let consistentFilename = ImageNamingUtils.generateImageFilename(
+                    problemId: problem.id.uuidString, imageIndex: index)
+
+                let imageManager = ImageManager.shared
+                let fullPath = imageManager.imagesDirectory.appendingPathComponent(filename).path
+
+                if let imageData = imageManager.loadImageData(fromPath: fullPath) {
+                    do {
+                        if filename != consistentFilename {
+                            let newPath = imageManager.imagesDirectory.appendingPathComponent(
+                                consistentFilename
+                            ).path
+                            try? FileManager.default.moveItem(atPath: fullPath, toPath: newPath)
+                        }
+
+                        try await uploadImage(filename: consistentFilename, imageData: imageData)
+                        print("Uploaded modified problem image: \(consistentFilename)")
+                    } catch {
+                        print("Failed to upload image \(consistentFilename): \(error)")
+                    }
+                }
+            }
+        }
+    }
+
    func uploadImage(filename: String, imageData: Data) async throws {
        guard isConfigured else {
            throw SyncError.notConfigured
@@ -246,6 +554,17 @@ class SyncService: ObservableObject {
                !serverBackup.gyms.isEmpty || !serverBackup.problems.isEmpty
                || !serverBackup.sessions.isEmpty || !serverBackup.attempts.isEmpty

+            // If both client and server have been synced before, use delta sync
+            if hasLocalData && hasServerData && lastSyncTime != nil {
+                print("iOS SYNC: Using delta sync for incremental updates")
+                try await performDeltaSync(dataManager: dataManager)
+
+                // Update last sync time
+                lastSyncTime = Date()
+                userDefaults.set(lastSyncTime, forKey: Keys.lastSyncTime)
+                return
+            }
+
            if !hasLocalData && hasServerData {
                // Case 1: No local data - do full restore from server
                print("iOS SYNC: Case 1 - No local data, performing full restore from server")
@@ -286,7 +605,6 @@ class SyncService: ObservableObject {
        }
    }

-    /// Parses ISO8601 timestamp to milliseconds for comparison
    private func parseISO8601ToMillis(timestamp: String) -> Int64 {
        let formatter = ISO8601DateFormatter()
        if let date = formatter.date(from: timestamp) {
@@ -1150,7 +1468,6 @@ class SyncService: ObservableObject {
        // Get active session IDs to protect their attempts
        let activeSessionIds = Set(
            local.compactMap { attempt in
-                // This is a simplified check - in a real implementation you'd want to cross-reference with sessions
                return attempt.sessionId
            }.filter { sessionId in
                // Check if this session ID belongs to an active session
--- a/ios/Ascently/Utils/DataStateManager.swift
+++ b/ios/Ascently/Utils/DataStateManager.swift
@@ -37,46 +37,36 @@ class DataStateManager {
        print("iOS Data state updated to: \(now)")
    }

-    /// Gets the current data state timestamp. This represents when any data was last modified
-    /// locally.
    func getLastModified() -> String {
        if let storedTimestamp = userDefaults.string(forKey: Keys.lastModified) {
            print("iOS DataStateManager returning stored timestamp: \(storedTimestamp)")
            return storedTimestamp
        }

-        // If no timestamp is stored, return epoch time to indicate very old data
-        // This ensures server data will be considered newer than uninitialized local data
        let epochTime = "1970-01-01T00:00:00.000Z"
-        print("WARNING: No data state timestamp found - returning epoch time: \(epochTime)")
+        print("No data state timestamp found - returning epoch time: \(epochTime)")
        return epochTime
    }

-    /// Sets the data state timestamp to a specific value. Used when importing data from server to
-    /// sync the state.
    func setLastModified(_ timestamp: String) {
        userDefaults.set(timestamp, forKey: Keys.lastModified)
        print("Data state set to: \(timestamp)")
    }

-    /// Resets the data state (for testing or complete data wipe).
    func reset() {
        userDefaults.removeObject(forKey: Keys.lastModified)
        userDefaults.removeObject(forKey: Keys.initialized)
        print("Data state reset")
    }

-    /// Checks if the data state has been initialized.
    private func isInitialized() -> Bool {
        return userDefaults.bool(forKey: Keys.initialized)
    }

-    /// Marks the data state as initialized.
    private func markAsInitialized() {
        userDefaults.set(true, forKey: Keys.initialized)
    }

-    /// Gets debug information about the current state.
    func getDebugInfo() -> String {
        return "DataState(lastModified=\(getLastModified()), initialized=\(isInitialized()))"
    }
--- a/ios/Ascently/Utils/ImageManager.swift
+++ b/ios/Ascently/Utils/ImageManager.swift
@@ -690,7 +690,6 @@ class ImageManager {
    }

    private func cleanupOrphanedFiles() {
-        // This would need access to the data manager to check which files are actually referenced
        print("Cleanup would require coordination with data manager")
    }

--- a/ios/Ascently/Utils/ImageNamingUtils.swift
+++ b/ios/Ascently/Utils/ImageNamingUtils.swift
@@ -108,7 +108,6 @@ class ImageNamingUtils {
        )
    }

-    /// Generates the canonical filename that should be used for a problem image
    static func getCanonicalImageFilename(problemId: String, imageIndex: Int) -> String {
        return generateImageFilename(problemId: problemId, imageIndex: imageIndex)
    }
--- a/ios/Ascently/Utils/ZipUtils.swift
+++ b/ios/Ascently/Utils/ZipUtils.swift
@@ -18,6 +18,7 @@ struct ZipUtils {
        var fileEntries: [(name: String, data: Data, offset: UInt32)] = []
        var currentOffset: UInt32 = 0

+        // Add metadata
        let metadata = createMetadata(
            exportData: exportData, referencedImagePaths: referencedImagePaths)
        let metadataData = metadata.data(using: .utf8) ?? Data()
@@ -29,6 +30,7 @@ struct ZipUtils {
            currentOffset: &currentOffset
        )

+        // Encode JSON data
        let encoder = JSONEncoder()
        encoder.outputFormatting = .prettyPrinted
        encoder.dateEncodingStrategy = .custom { date, encoder in
@@ -46,44 +48,49 @@ struct ZipUtils {
            currentOffset: &currentOffset
        )

-        print("Processing \(referencedImagePaths.count) referenced image paths")
+        // Process images in batches for better performance
+        print("Processing \(referencedImagePaths.count) images for export")
        var successfulImages = 0
+        let batchSize = 10
+        let sortedPaths = Array(referencedImagePaths).sorted()
+
+        // Pre-allocate capacity for better memory performance
+        zipData.reserveCapacity(zipData.count + (referencedImagePaths.count * 200_000))  // Estimate 200KB per image
+
+        for (index, imagePath) in sortedPaths.enumerated() {
+            if index % batchSize == 0 {
+                print("Processing images \(index)/\(sortedPaths.count)")
+            }

-        for imagePath in referencedImagePaths {
-            print("Processing image path: \(imagePath)")
            let imageURL = URL(fileURLWithPath: imagePath)
            let imageName = imageURL.lastPathComponent
-            print("Image name: \(imageName)")

-            if FileManager.default.fileExists(atPath: imagePath) {
-                print("Image file exists at: \(imagePath)")
-                do {
-                    let imageData = try Data(contentsOf: imageURL)
-                    print("Image data size: \(imageData.count) bytes")
-                    if imageData.count > 0 {
-                        let imageEntryName = "\(IMAGES_DIR_NAME)/\(imageName)"
-                        try addFileToZip(
-                            filename: imageEntryName,
-                            fileData: imageData,
-                            zipData: &zipData,
-                            fileEntries: &fileEntries,
-                            currentOffset: &currentOffset
-                        )
-                        successfulImages += 1
-                        print("Successfully added image to ZIP: \(imageEntryName)")
-                    } else {
-                        print("Image data is empty for: \(imagePath)")
-                    }
-                } catch {
-                    print("Failed to read image data for \(imagePath): \(error)")
+            guard FileManager.default.fileExists(atPath: imagePath) else {
+                continue
+            }
+
+            do {
+                let imageData = try Data(contentsOf: imageURL)
+                if imageData.count > 0 {
+                    let imageEntryName = "\(IMAGES_DIR_NAME)/\(imageName)"
+                    try addFileToZip(
+                        filename: imageEntryName,
+                        fileData: imageData,
+                        zipData: &zipData,
+                        fileEntries: &fileEntries,
+                        currentOffset: &currentOffset
+                    )
+                    successfulImages += 1
                }
-            } else {
-                print("Image file does not exist at: \(imagePath)")
+            } catch {
+                print("Failed to read image: \(imageName)")
            }
        }

-        print("Export completed: \(successfulImages)/\(referencedImagePaths.count) images included")
+        print("Export: included \(successfulImages)/\(referencedImagePaths.count) images")

+        // Build central directory
+        centralDirectory.reserveCapacity(fileEntries.count * 100)  // Estimate 100 bytes per entry
        for entry in fileEntries {
            let centralDirEntry = createCentralDirectoryEntry(
                filename: entry.name,
@@ -372,12 +379,12 @@ struct ZipUtils {
        return data
    }

-    private static func calculateCRC32(data: Data) -> UInt32 {
+    // CRC32 lookup table for faster calculation
+    private static let crc32Table: [UInt32] = {
        let polynomial: UInt32 = 0xEDB8_8320
-        var crc: UInt32 = 0xFFFF_FFFF
-
-        for byte in data {
-            crc ^= UInt32(byte)
+        var table = [UInt32](repeating: 0, count: 256)
+        for i in 0..<256 {
+            var crc = UInt32(i)
            for _ in 0..<8 {
                if crc & 1 != 0 {
                    crc = (crc >> 1) ^ polynomial
@@ -385,6 +392,19 @@ struct ZipUtils {
                    crc >>= 1
                }
            }
+            table[i] = crc
+        }
+        return table
+    }()
+
+    private static func calculateCRC32(data: Data) -> UInt32 {
+        var crc: UInt32 = 0xFFFF_FFFF
+
+        data.withUnsafeBytes { (bytes: UnsafeRawBufferPointer) in
+            for byte in bytes {
+                let index = Int((crc ^ UInt32(byte)) & 0xFF)
+                crc = (crc >> 8) ^ crc32Table[index]
+            }
        }

        return ~crc
--- a/ios/Ascently/ViewModels/ClimbingDataManager.swift
+++ b/ios/Ascently/ViewModels/ClimbingDataManager.swift
@@ -653,9 +653,6 @@ class ClimbingDataManager: ObservableObject {
        return gym(withId: mostUsedGymId)
    }

-    /// Clean up orphaned data - removes attempts that reference non-existent sessions
-    /// and removes duplicate attempts. This ensures data integrity and prevents
-    /// orphaned attempts from appearing in widgets
    private func cleanupOrphanedData() {
        let validSessionIds = Set(sessions.map { $0.id })
        let validProblemIds = Set(problems.map { $0.id })
@@ -761,8 +758,6 @@ class ClimbingDataManager: ObservableObject {
        }
    }

-    /// Validate data integrity and return a report
-    /// This can be called manually to check for issues
    func validateDataIntegrity() -> String {
        let validSessionIds = Set(sessions.map { $0.id })
        let validProblemIds = Set(problems.map { $0.id })
@@ -801,8 +796,6 @@ class ClimbingDataManager: ObservableObject {
        return report
    }

-    /// Manually trigger cleanup of orphaned data
-    /// This can be called from settings or debug menu
    func manualDataCleanup() {
        cleanupOrphanedData()
        successMessage = "Data cleanup completed"
@@ -830,12 +823,12 @@ class ClimbingDataManager: ObservableObject {
        }
    }

-    func exportData() -> Data? {
+    func exportData() async -> Data? {
        do {
+            // Create backup objects on main thread (they access MainActor-isolated properties)
            let dateFormatter = DateFormatter()
            dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSSSS"

-            // Create export data with normalized image paths
            let exportData = ClimbDataBackup(
                exportedAt: dateFormatter.string(from: Date()),
                version: "2.0",
@@ -846,19 +839,30 @@ class ClimbingDataManager: ObservableObject {
                attempts: attempts.map { BackupAttempt(from: $0) }
            )

-            // Collect actual image paths from disk for the ZIP
-            let referencedImagePaths = collectReferencedImagePaths()
-            print("Starting export with \(referencedImagePaths.count) images")
+            // Get image manager path info on main thread
+            let imagesDirectory = ImageManager.shared.imagesDirectory.path
+            let problemsForImages = problems

-            let zipData = try ZipUtils.createExportZip(
-                exportData: exportData,
-                referencedImagePaths: referencedImagePaths
-            )
+            // Move heavy I/O operations to background thread
+            let zipData = try await Task.detached(priority: .userInitiated) {
+                // Collect actual image paths from disk for the ZIP
+                let referencedImagePaths = await Self.collectReferencedImagePathsStatic(
+                    problems: problemsForImages,
+                    imagesDirectory: imagesDirectory)
+                print("Starting export with \(referencedImagePaths.count) images")

-            print("Export completed successfully")
-            successMessage = "Export completed with \(referencedImagePaths.count) images"
+                let zipData = try await ZipUtils.createExportZip(
+                    exportData: exportData,
+                    referencedImagePaths: referencedImagePaths
+                )
+
+                print("Export completed successfully")
+                return (zipData, referencedImagePaths.count)
+            }.value
+
+            successMessage = "Export completed with \(zipData.1) images"
            clearMessageAfterDelay()
-            return zipData
+            return zipData.0
        } catch {
            let errorMessage = "Export failed: \(error.localizedDescription)"
            print("ERROR: \(errorMessage)")
@@ -955,36 +959,36 @@ class ClimbingDataManager: ObservableObject {

 extension ClimbingDataManager {
    private func collectReferencedImagePaths() -> Set<String> {
+        let imagesDirectory = ImageManager.shared.imagesDirectory.path
+        return Self.collectReferencedImagePathsStatic(
+            problems: problems,
+            imagesDirectory: imagesDirectory)
+    }
+
+    private static func collectReferencedImagePathsStatic(
+        problems: [Problem], imagesDirectory: String
+    ) -> Set<String> {
        var imagePaths = Set<String>()
-        print("Starting image path collection...")
-        print("Total problems: \(problems.count)")
+        var missingCount = 0

        for problem in problems {
            if !problem.imagePaths.isEmpty {
-                print(
-                    "Problem '\(problem.name ?? "Unnamed")' has \(problem.imagePaths.count) images"
-                )
                for imagePath in problem.imagePaths {
-                    print("   - Stored path: \(imagePath)")
-
                    // Extract just the filename (migration should have normalized these)
                    let filename = URL(fileURLWithPath: imagePath).lastPathComponent
-                    let fullPath = ImageManager.shared.getFullPath(from: filename)
-                    print("   - Full disk path: \(fullPath)")
+                    let fullPath = (imagesDirectory as NSString).appendingPathComponent(filename)

                    if FileManager.default.fileExists(atPath: fullPath) {
-                        print("   ✓ File exists")
                        imagePaths.insert(fullPath)
                    } else {
-                        print("   ✗ WARNING: File not found at \(fullPath)")
-                        // Still add it to let ZipUtils handle the logging
+                        missingCount += 1
                        imagePaths.insert(fullPath)
                    }
                }
            }
        }

-        print("Collected \(imagePaths.count) total image paths for export")
+        print("Export: Collected \(imagePaths.count) images (\(missingCount) missing)")
        return imagePaths
    }

@@ -1273,7 +1277,9 @@ extension ClimbingDataManager {
        ) { [weak self] notification in
            if let updateCount = notification.userInfo?["updateCount"] as? Int {
                print("🔔 Image migration completed with \(updateCount) updates - reloading data")
-                self?.loadProblems()
+                Task { @MainActor in
+                    self?.loadProblems()
+                }
            }
        }
    }
--- a/ios/Ascently/Views/AddEdit/AddEditProblemView.swift
+++ b/ios/Ascently/Views/AddEdit/AddEditProblemView.swift
@@ -103,7 +103,6 @@ struct AddEditProblemView: View {
            setupInitialGym()
        }
        .onChange(of: dataManager.gyms) {
-            // Ensure a gym is selected when gyms are loaded or changed
            if selectedGym == nil && !dataManager.gyms.isEmpty {
                selectedGym = dataManager.gyms.first
            }
--- a/ios/Ascently/Views/SettingsView.swift
+++ b/ios/Ascently/Views/SettingsView.swift
@@ -180,10 +180,12 @@ struct DataManagementSection: View {
    private func exportDataAsync() {
        isExporting = true
        Task {
-            let data = await MainActor.run { dataManager.exportData() }
-            isExporting = false
-            if let data = data {
-                activeSheet = .export(data)
+            let data = await dataManager.exportData()
+            await MainActor.run {
+                isExporting = false
+                if let data = data {
+                    activeSheet = .export(data)
+                }
            }
        }
    }
--- a/ios/AscentlyTests/AscentlyTests.swift
+++ b/ios/AscentlyTests/AscentlyTests.swift
@@ -256,10 +256,6 @@ final class AscentlyTests: XCTestCase {
    // MARK: - Active Session Preservation Tests

    func testActiveSessionPreservationDuringImport() throws {
-        // Test that active sessions are preserved during import operations
-        // This tests the fix for the bug where active sessions disappear after sync
-
-        // Simulate an active session that exists locally but not in import data
        let activeSessionId = UUID()
        let gymId = UUID()

--- a/sync/main.go
+++ b/sync/main.go
@@ -13,7 +13,7 @@ import (
 	"time"
 )

-const VERSION = "2.0.0"
+const VERSION = "2.1.0"

 func min(a, b int) int {
 	if a < b {
@@ -39,6 +39,24 @@ type ClimbDataBackup struct {
 	DeletedItems  []DeletedItem        `json:"deletedItems"`
 }

+type DeltaSyncRequest struct {
+	LastSyncTime string               `json:"lastSyncTime"`
+	Gyms         []BackupGym          `json:"gyms"`
+	Problems     []BackupProblem      `json:"problems"`
+	Sessions     []BackupClimbSession `json:"sessions"`
+	Attempts     []BackupAttempt      `json:"attempts"`
+	DeletedItems []DeletedItem        `json:"deletedItems"`
+}
+
+type DeltaSyncResponse struct {
+	ServerTime   string               `json:"serverTime"`
+	Gyms         []BackupGym          `json:"gyms"`
+	Problems     []BackupProblem      `json:"problems"`
+	Sessions     []BackupClimbSession `json:"sessions"`
+	Attempts     []BackupAttempt      `json:"attempts"`
+	DeletedItems []DeletedItem        `json:"deletedItems"`
+}
+
 type BackupGym struct {
 	ID                     string   `json:"id"`
 	Name                   string   `json:"name"`
@@ -154,6 +172,174 @@ func (s *SyncServer) loadData() (*ClimbDataBackup, error) {
 	return &backup, nil
 }

+func (s *SyncServer) mergeGyms(existing []BackupGym, updates []BackupGym) []BackupGym {
+	gymMap := make(map[string]BackupGym)
+	for _, gym := range existing {
+		gymMap[gym.ID] = gym
+	}
+
+	for _, gym := range updates {
+		if existingGym, exists := gymMap[gym.ID]; exists {
+			// Keep newer version based on updatedAt timestamp
+			if gym.UpdatedAt >= existingGym.UpdatedAt {
+				gymMap[gym.ID] = gym
+			}
+		} else {
+			gymMap[gym.ID] = gym
+		}
+	}
+
+	result := make([]BackupGym, 0, len(gymMap))
+	for _, gym := range gymMap {
+		result = append(result, gym)
+	}
+	return result
+}
+
+func (s *SyncServer) mergeProblems(existing []BackupProblem, updates []BackupProblem) []BackupProblem {
+	problemMap := make(map[string]BackupProblem)
+	for _, problem := range existing {
+		problemMap[problem.ID] = problem
+	}
+
+	for _, problem := range updates {
+		if existingProblem, exists := problemMap[problem.ID]; exists {
+			if problem.UpdatedAt >= existingProblem.UpdatedAt {
+				problemMap[problem.ID] = problem
+			}
+		} else {
+			problemMap[problem.ID] = problem
+		}
+	}
+
+	result := make([]BackupProblem, 0, len(problemMap))
+	for _, problem := range problemMap {
+		result = append(result, problem)
+	}
+	return result
+}
+
+func (s *SyncServer) mergeSessions(existing []BackupClimbSession, updates []BackupClimbSession) []BackupClimbSession {
+	sessionMap := make(map[string]BackupClimbSession)
+	for _, session := range existing {
+		sessionMap[session.ID] = session
+	}
+
+	for _, session := range updates {
+		if existingSession, exists := sessionMap[session.ID]; exists {
+			if session.UpdatedAt >= existingSession.UpdatedAt {
+				sessionMap[session.ID] = session
+			}
+		} else {
+			sessionMap[session.ID] = session
+		}
+	}
+
+	result := make([]BackupClimbSession, 0, len(sessionMap))
+	for _, session := range sessionMap {
+		result = append(result, session)
+	}
+	return result
+}
+
+func (s *SyncServer) mergeAttempts(existing []BackupAttempt, updates []BackupAttempt) []BackupAttempt {
+	attemptMap := make(map[string]BackupAttempt)
+	for _, attempt := range existing {
+		attemptMap[attempt.ID] = attempt
+	}
+
+	for _, attempt := range updates {
+		if existingAttempt, exists := attemptMap[attempt.ID]; exists {
+			if attempt.CreatedAt >= existingAttempt.CreatedAt {
+				attemptMap[attempt.ID] = attempt
+			}
+		} else {
+			attemptMap[attempt.ID] = attempt
+		}
+	}
+
+	result := make([]BackupAttempt, 0, len(attemptMap))
+	for _, attempt := range attemptMap {
+		result = append(result, attempt)
+	}
+	return result
+}
+
+func (s *SyncServer) mergeDeletedItems(existing []DeletedItem, updates []DeletedItem) []DeletedItem {
+	deletedMap := make(map[string]DeletedItem)
+	for _, item := range existing {
+		key := item.Type + ":" + item.ID
+		deletedMap[key] = item
+	}
+
+	for _, item := range updates {
+		key := item.Type + ":" + item.ID
+		if existingItem, exists := deletedMap[key]; exists {
+			if item.DeletedAt >= existingItem.DeletedAt {
+				deletedMap[key] = item
+			}
+		} else {
+			deletedMap[key] = item
+		}
+	}
+
+	result := make([]DeletedItem, 0, len(deletedMap))
+	for _, item := range deletedMap {
+		result = append(result, item)
+	}
+	return result
+}
+
+func (s *SyncServer) applyDeletions(backup *ClimbDataBackup, deletedItems []DeletedItem) {
+	deletedMap := make(map[string]map[string]bool)
+	for _, item := range deletedItems {
+		if deletedMap[item.Type] == nil {
+			deletedMap[item.Type] = make(map[string]bool)
+		}
+		deletedMap[item.Type][item.ID] = true
+	}
+
+	if deletedMap["gym"] != nil {
+		filtered := []BackupGym{}
+		for _, gym := range backup.Gyms {
+			if !deletedMap["gym"][gym.ID] {
+				filtered = append(filtered, gym)
+			}
+		}
+		backup.Gyms = filtered
+	}
+
+	if deletedMap["problem"] != nil {
+		filtered := []BackupProblem{}
+		for _, problem := range backup.Problems {
+			if !deletedMap["problem"][problem.ID] {
+				filtered = append(filtered, problem)
+			}
+		}
+		backup.Problems = filtered
+	}
+
+	if deletedMap["session"] != nil {
+		filtered := []BackupClimbSession{}
+		for _, session := range backup.Sessions {
+			if !deletedMap["session"][session.ID] {
+				filtered = append(filtered, session)
+			}
+		}
+		backup.Sessions = filtered
+	}
+
+	if deletedMap["attempt"] != nil {
+		filtered := []BackupAttempt{}
+		for _, attempt := range backup.Attempts {
+			if !deletedMap["attempt"][attempt.ID] {
+				filtered = append(filtered, attempt)
+			}
+		}
+		backup.Attempts = filtered
+	}
+}
+
 func (s *SyncServer) saveData(backup *ClimbDataBackup) error {
 	backup.ExportedAt = time.Now().UTC().Format(time.RFC3339)

@@ -167,7 +353,6 @@ func (s *SyncServer) saveData(backup *ClimbDataBackup) error {
 		return err
 	}

-	// Ensure images directory exists
 	if err := os.MkdirAll(s.imagesDir, 0755); err != nil {
 		return err
 	}
@@ -315,6 +500,123 @@ func (s *SyncServer) handleImageDownload(w http.ResponseWriter, r *http.Request)
 	w.Write(imageData)
 }

+func (s *SyncServer) handleDeltaSync(w http.ResponseWriter, r *http.Request) {
+	if !s.authenticate(r) {
+		log.Printf("Unauthorized delta sync attempt from %s", r.RemoteAddr)
+		http.Error(w, "Unauthorized", http.StatusUnauthorized)
+		return
+	}
+
+	if r.Method != http.MethodPost {
+		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	var deltaRequest DeltaSyncRequest
+	if err := json.NewDecoder(r.Body).Decode(&deltaRequest); err != nil {
+		log.Printf("Invalid JSON from %s: %v", r.RemoteAddr, err)
+		http.Error(w, "Invalid JSON", http.StatusBadRequest)
+		return
+	}
+
+	log.Printf("Delta sync from %s: lastSyncTime=%s, gyms=%d, problems=%d, sessions=%d, attempts=%d, deletedItems=%d",
+		r.RemoteAddr, deltaRequest.LastSyncTime,
+		len(deltaRequest.Gyms), len(deltaRequest.Problems),
+		len(deltaRequest.Sessions), len(deltaRequest.Attempts),
+		len(deltaRequest.DeletedItems))
+
+	// Load current server data
+	serverBackup, err := s.loadData()
+	if err != nil {
+		log.Printf("Failed to load data: %v", err)
+		http.Error(w, "Failed to load data", http.StatusInternalServerError)
+		return
+	}
+
+	// Merge client changes into server data
+	serverBackup.Gyms = s.mergeGyms(serverBackup.Gyms, deltaRequest.Gyms)
+	serverBackup.Problems = s.mergeProblems(serverBackup.Problems, deltaRequest.Problems)
+	serverBackup.Sessions = s.mergeSessions(serverBackup.Sessions, deltaRequest.Sessions)
+	serverBackup.Attempts = s.mergeAttempts(serverBackup.Attempts, deltaRequest.Attempts)
+	serverBackup.DeletedItems = s.mergeDeletedItems(serverBackup.DeletedItems, deltaRequest.DeletedItems)
+
+	// Apply deletions to remove deleted items
+	s.applyDeletions(serverBackup, serverBackup.DeletedItems)
+
+	// Save merged data
+	if err := s.saveData(serverBackup); err != nil {
+		log.Printf("Failed to save data: %v", err)
+		http.Error(w, "Failed to save data", http.StatusInternalServerError)
+		return
+	}
+
+	// Parse client's last sync time
+	clientLastSync, err := time.Parse(time.RFC3339, deltaRequest.LastSyncTime)
+	if err != nil {
+		// If parsing fails, send everything
+		clientLastSync = time.Time{}
+	}
+
+	// Prepare response with items modified since client's last sync
+	response := DeltaSyncResponse{
+		ServerTime:   time.Now().UTC().Format(time.RFC3339),
+		Gyms:         []BackupGym{},
+		Problems:     []BackupProblem{},
+		Sessions:     []BackupClimbSession{},
+		Attempts:     []BackupAttempt{},
+		DeletedItems: []DeletedItem{},
+	}
+
+	// Filter gyms modified after client's last sync
+	for _, gym := range serverBackup.Gyms {
+		gymTime, err := time.Parse(time.RFC3339, gym.UpdatedAt)
+		if err == nil && gymTime.After(clientLastSync) {
+			response.Gyms = append(response.Gyms, gym)
+		}
+	}
+
+	// Filter problems modified after client's last sync
+	for _, problem := range serverBackup.Problems {
+		problemTime, err := time.Parse(time.RFC3339, problem.UpdatedAt)
+		if err == nil && problemTime.After(clientLastSync) {
+			response.Problems = append(response.Problems, problem)
+		}
+	}
+
+	// Filter sessions modified after client's last sync
+	for _, session := range serverBackup.Sessions {
+		sessionTime, err := time.Parse(time.RFC3339, session.UpdatedAt)
+		if err == nil && sessionTime.After(clientLastSync) {
+			response.Sessions = append(response.Sessions, session)
+		}
+	}
+
+	// Filter attempts created after client's last sync
+	for _, attempt := range serverBackup.Attempts {
+		attemptTime, err := time.Parse(time.RFC3339, attempt.CreatedAt)
+		if err == nil && attemptTime.After(clientLastSync) {
+			response.Attempts = append(response.Attempts, attempt)
+		}
+	}
+
+	// Filter deletions after client's last sync
+	for _, deletedItem := range serverBackup.DeletedItems {
+		deletedTime, err := time.Parse(time.RFC3339, deletedItem.DeletedAt)
+		if err == nil && deletedTime.After(clientLastSync) {
+			response.DeletedItems = append(response.DeletedItems, deletedItem)
+		}
+	}
+
+	log.Printf("Delta sync response to %s: gyms=%d, problems=%d, sessions=%d, attempts=%d, deletedItems=%d",
+		r.RemoteAddr,
+		len(response.Gyms), len(response.Problems),
+		len(response.Sessions), len(response.Attempts),
+		len(response.DeletedItems))
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(response)
+}
+
 func (s *SyncServer) handleSync(w http.ResponseWriter, r *http.Request) {
 	switch r.Method {
 	case http.MethodGet:
@@ -354,6 +656,7 @@ func main() {
 	}

 	http.HandleFunc("/sync", server.handleSync)
+	http.HandleFunc("/sync/delta", server.handleDeltaSync)
 	http.HandleFunc("/health", server.handleHealth)
 	http.HandleFunc("/images/upload", server.handleImageUpload)
 	http.HandleFunc("/images/download", server.handleImageDownload)
@@ -362,6 +665,8 @@ func main() {
 	fmt.Printf("Data file: %s\n", dataFile)
 	fmt.Printf("Images directory: %s\n", imagesDir)
 	fmt.Printf("Health check available at /health\n")
+	fmt.Printf("Delta sync: POST /sync/delta (incremental sync)\n")
+	fmt.Printf("Full sync: GET /sync (download all), PUT /sync (upload all)\n")
 	fmt.Printf("Image upload: POST /images/upload?filename=<name>\n")
 	fmt.Printf("Image download: GET /images/download?filename=<name>\n")