feat(v1.8.0): IMPL_016 - Server Deletion Detection

- Add DELETED_ON_SERVER to SyncStatus enum
- Add deletedOnServerCount to SyncResult
- Implement detectServerDeletions() function in WebDavSyncService
- Integrate server deletion detection in downloadRemoteNotes()
- Update UI icons in NoteCard, NoteCardGrid, NoteCardCompact
- Add string resources for deleted_on_server status
- No additional HTTP requests (uses existing PROPFIND data)
- Zero performance impact

Closes #IMPL_016

android/app/src/main/java/dev/dettmer/simplenotes/adapters/NotesAdapter.kt

@@ -89,6 +89,7 @@ class NotesAdapter(
                     SyncStatus.PENDING -> android.R.drawable.ic_popup_sync
                     SyncStatus.CONFLICT -> android.R.drawable.ic_dialog_alert
                     SyncStatus.LOCAL_ONLY -> android.R.drawable.ic_menu_save
+                    SyncStatus.DELETED_ON_SERVER -> android.R.drawable.ic_menu_delete  // 🆕 v1.8.0
                 }
                 imageViewSyncStatus.setImageResource(syncIcon)
                 imageViewSyncStatus.visibility = View.VISIBLE

android/app/src/main/java/dev/dettmer/simplenotes/models/SyncStatus.kt

@@ -1,8 +1,15 @@
 package dev.dettmer.simplenotes.models
 
+/**
+ * Sync-Status einer Notiz
+ * 
+ * v1.4.0: Initial (LOCAL_ONLY, SYNCED, PENDING, CONFLICT)
+ * v1.8.0: DELETED_ON_SERVER hinzugefügt
+ */
 enum class SyncStatus {
     LOCAL_ONLY,        // Noch nie gesynct
     SYNCED,            // Erfolgreich gesynct
     PENDING,           // Wartet auf Sync
-    CONFLICT      // Konflikt erkannt
+    CONFLICT,          // Konflikt erkannt
+    DELETED_ON_SERVER  // 🆕 v1.8.0: Server hat gelöscht, lokal noch vorhanden
 }

android/app/src/main/java/dev/dettmer/simplenotes/sync/SyncResult.kt

@@ -1,11 +1,18 @@
 package dev.dettmer.simplenotes.sync
 
+/**
+ * Ergebnis eines Sync-Vorgangs
+ * 
+ * v1.7.0: Initial
+ * v1.8.0: deletedOnServerCount hinzugefügt
+ */
 data class SyncResult(
     val isSuccess: Boolean,
     val syncedCount: Int = 0,
     val conflictCount: Int = 0,
+    val deletedOnServerCount: Int = 0,  // 🆕 v1.8.0
     val errorMessage: String? = null
 ) {
-    val hasConflicts: Boolean
+    val hasConflicts: Boolean get() = conflictCount > 0
-        get() = conflictCount > 0
+    val hasServerDeletions: Boolean get() = deletedOnServerCount > 0  // 🆕 v1.8.0
 }

android/app/src/main/java/dev/dettmer/simplenotes/sync/WebDavSyncService.kt

@@ -655,6 +655,7 @@ class WebDavSyncService(private val context: Context) {
             
             Logger.d(TAG, "📍 Step 5: Downloading remote notes")
             // Download remote notes
+            var deletedOnServerCount = 0  // 🆕 v1.8.0
             try {
                 Logger.d(TAG, "⬇️ Downloading remote notes...")
                 val downloadResult = downloadRemoteNotes(
@@ -664,10 +665,12 @@ class WebDavSyncService(private val context: Context) {
                 )
                 syncedCount += downloadResult.downloadedCount
                 conflictCount += downloadResult.conflictCount
+                deletedOnServerCount = downloadResult.deletedOnServerCount  // 🆕 v1.8.0
                 Logger.d(
                     TAG,
                     "✅ Downloaded: ${downloadResult.downloadedCount} notes, " +
-                        "Conflicts: ${downloadResult.conflictCount}"
+                        "Conflicts: ${downloadResult.conflictCount}, " +
+                        "Deleted on server: ${downloadResult.deletedOnServerCount}"  // 🆕 v1.8.0
                 )
             } catch (e: Exception) {
                 Logger.e(TAG, "💥 CRASH in downloadRemoteNotes()!", e)
@@ -724,12 +727,16 @@ class WebDavSyncService(private val context: Context) {
             if (markdownImportedCount > 0 && syncedCount > 0) {
                 Logger.d(TAG, "📝 Including $markdownImportedCount Markdown file updates")
             }
+            if (deletedOnServerCount > 0) {  // 🆕 v1.8.0
+                Logger.d(TAG, "🗑️ Detected $deletedOnServerCount notes deleted on server")
+            }
             Logger.d(TAG, "═══════════════════════════════════════")
             
             SyncResult(
                 isSuccess = true,
                 syncedCount = effectiveSyncedCount,
-                conflictCount = conflictCount
+                conflictCount = conflictCount,
+                deletedOnServerCount = deletedOnServerCount  // 🆕 v1.8.0
             )
             
         } catch (e: Exception) {
@@ -1038,9 +1045,45 @@ class WebDavSyncService(private val context: Context) {
     
     private data class DownloadResult(
         val downloadedCount: Int,
-        val conflictCount: Int
+        val conflictCount: Int,
+        val deletedOnServerCount: Int = 0  // 🆕 v1.8.0
     )
     
+    /**
+     * 🆕 v1.8.0: Erkennt Notizen, die auf dem Server gelöscht wurden
+     * 
+     * Keine zusätzlichen HTTP-Requests! Nutzt die bereits geladene
+     * serverNoteIds-Liste aus dem PROPFIND-Request.
+     * 
+     * @param serverNoteIds Set aller Note-IDs auf dem Server (aus PROPFIND)
+     * @param localNotes Alle lokalen Notizen
+     * @return Anzahl der als DELETED_ON_SERVER markierten Notizen
+     */
+    private fun detectServerDeletions(
+        serverNoteIds: Set<String>,
+        localNotes: List<Note>
+    ): Int {
+        var deletedCount = 0
+        
+        localNotes.forEach { note ->
+            // Nur SYNCED-Notizen prüfen:
+            // - LOCAL_ONLY: War nie auf Server → irrelevant
+            // - PENDING: Soll hochgeladen werden → nicht überschreiben
+            // - CONFLICT: Wird separat behandelt
+            // - DELETED_ON_SERVER: Bereits markiert
+            if (note.syncStatus == SyncStatus.SYNCED && note.id !in serverNoteIds) {
+                val updatedNote = note.copy(syncStatus = SyncStatus.DELETED_ON_SERVER)
+                storage.saveNote(updatedNote)
+                deletedCount++
+                
+                Logger.d(TAG, "Note '${note.title}' (${note.id}) " +
+                    "was deleted on server, marked as DELETED_ON_SERVER")
+            }
+        }
+        
+        return deletedCount
+    }
+    
     @Suppress("NestedBlockDepth", "LoopWithTooManyJumpStatements") 
     // Sync logic requires nested conditions for comprehensive error handling and conflict resolution
     private fun downloadRemoteNotes(
@@ -1062,6 +1105,9 @@ class WebDavSyncService(private val context: Context) {
         // Use provided deletion tracker (allows fresh tracker from restore)
         var trackerModified = false
         
+        // 🆕 v1.8.0: Collect server note IDs for deletion detection
+        val serverNoteIds = mutableSetOf<String>()
+        
         try {
             // 🆕 PHASE 1: Download from /notes/ (new structure v1.2.1+)
             val notesUrl = getNotesUrl(serverUrl)
@@ -1077,6 +1123,12 @@ class WebDavSyncService(private val context: Context) {
                 val jsonFiles = resources.filter { !it.isDirectory && it.name.endsWith(".json") }
                 Logger.d(TAG, "   📊 Found ${jsonFiles.size} JSON files on server")
                 
+                // 🆕 v1.8.0: Extract server note IDs
+                jsonFiles.forEach { resource ->
+                    val noteId = resource.name.removeSuffix(".json")
+                    serverNoteIds.add(noteId)
+                }
+                
                 for (resource in jsonFiles) {
                     
                     val noteId = resource.name.removeSuffix(".json")
@@ -1317,8 +1369,16 @@ class WebDavSyncService(private val context: Context) {
             Logger.d(TAG, "💾 Deletion tracker updated")
         }
         
+        // 🆕 v1.8.0: Server-Deletions erkennen (nach Downloads)
+        val allLocalNotes = storage.loadAllNotes()
+        val deletedOnServerCount = detectServerDeletions(serverNoteIds, allLocalNotes)
+        
+        if (deletedOnServerCount > 0) {
+            Logger.d(TAG, "$deletedOnServerCount note(s) detected as deleted on server")
+        }
+        
         Logger.d(TAG, "📊 Total: $downloadedCount downloaded, $conflictCount conflicts, $skippedDeleted deleted")
-        return DownloadResult(downloadedCount, conflictCount)
+        return DownloadResult(downloadedCount, conflictCount, deletedOnServerCount)
     }
     
     private fun saveLastSyncTimestamp() {

android/app/src/main/java/dev/dettmer/simplenotes/ui/main/components/NoteCard.kt

@@ -186,11 +186,19 @@ fun NoteCard(
                                 SyncStatus.PENDING -> Icons.Outlined.CloudSync
                                 SyncStatus.CONFLICT -> Icons.Default.Warning
                                 SyncStatus.LOCAL_ONLY -> Icons.Outlined.CloudOff
+                                SyncStatus.DELETED_ON_SERVER -> Icons.Outlined.CloudOff  // 🆕 v1.8.0
+                            },
+                            contentDescription = when (note.syncStatus) {
+                                SyncStatus.SYNCED -> stringResource(R.string.sync_status_synced)
+                                SyncStatus.PENDING -> stringResource(R.string.sync_status_pending)
+                                SyncStatus.CONFLICT -> stringResource(R.string.sync_status_conflict)
+                                SyncStatus.LOCAL_ONLY -> stringResource(R.string.sync_status_local_only)
+                                SyncStatus.DELETED_ON_SERVER -> stringResource(R.string.sync_status_deleted_on_server)  // 🆕 v1.8.0
                             },
-                            contentDescription = null,
                             tint = when (note.syncStatus) {
                                 SyncStatus.SYNCED -> MaterialTheme.colorScheme.primary
                                 SyncStatus.CONFLICT -> MaterialTheme.colorScheme.error
+                                SyncStatus.DELETED_ON_SERVER -> MaterialTheme.colorScheme.outline.copy(alpha = 0.5f)  // 🆕 v1.8.0
                                 else -> MaterialTheme.colorScheme.outline
                             },
                             modifier = Modifier.size(16.dp)

android/app/src/main/java/dev/dettmer/simplenotes/ui/main/components/NoteCardCompact.kt

@@ -187,11 +187,13 @@ fun NoteCardCompact(
                                 SyncStatus.PENDING -> Icons.Outlined.CloudSync
                                 SyncStatus.CONFLICT -> Icons.Default.Warning
                                 SyncStatus.LOCAL_ONLY -> Icons.Outlined.CloudOff
+                                SyncStatus.DELETED_ON_SERVER -> Icons.Outlined.CloudOff  // 🆕 v1.8.0
                             },
                             contentDescription = null,
                             tint = when (note.syncStatus) {
                                 SyncStatus.SYNCED -> MaterialTheme.colorScheme.primary
                                 SyncStatus.CONFLICT -> MaterialTheme.colorScheme.error
+                                SyncStatus.DELETED_ON_SERVER -> MaterialTheme.colorScheme.outline.copy(alpha = 0.5f)  // 🆕 v1.8.0
                                 else -> MaterialTheme.colorScheme.outline
                             },
                             modifier = Modifier.size(14.dp)

android/app/src/main/java/dev/dettmer/simplenotes/ui/main/components/NoteCardGrid.kt

@@ -199,11 +199,13 @@ fun NoteCardGrid(
                                 SyncStatus.PENDING -> Icons.Outlined.CloudSync
                                 SyncStatus.CONFLICT -> Icons.Default.Warning
                                 SyncStatus.LOCAL_ONLY -> Icons.Outlined.CloudOff
+                                SyncStatus.DELETED_ON_SERVER -> Icons.Outlined.CloudOff  // 🆕 v1.8.0
                             },
                             contentDescription = null,
                             tint = when (note.syncStatus) {
                                 SyncStatus.SYNCED -> MaterialTheme.colorScheme.primary
                                 SyncStatus.CONFLICT -> MaterialTheme.colorScheme.error
+                                SyncStatus.DELETED_ON_SERVER -> MaterialTheme.colorScheme.outline.copy(alpha = 0.5f)  // 🆕 v1.8.0
                                 else -> MaterialTheme.colorScheme.outline
                             },
                             modifier = Modifier.size(14.dp)

android/app/src/main/res/values/strings.xml

@@ -58,6 +58,13 @@
     <string name="sync_status_error">Sync failed</string>
     <string name="sync_already_running">Sync already in progress</string>
     
+    <!-- 🆕 v1.8.0: SyncStatus enum values -->
+    <string name="sync_status_synced">Synced with server</string>
+    <string name="sync_status_pending">Waiting for sync</string>
+    <string name="sync_status_conflict">Sync conflict detected</string>
+    <string name="sync_status_local_only">Not yet synced</string>
+    <string name="sync_status_deleted_on_server">Deleted on server</string>
+    
     <!-- ============================= -->
     <!-- DELETE DIALOGS                -->
     <!-- ============================= -->