v1.0.74: exclude OS-volatile junk (.thumbnails/.trashed-/.pending-/.sfpart) symmetrically

The .thumbnails cache was synced then DELETE_REMOTE'd every cycle: exclude
patterns were applied only to the local walk (filename-only), never to the
remote listing, so a previously-uploaded thumbnail looked local-missing and
got mirror-deleted endlessly as Android regenerates the cache.

- isExcludedPath(): path-segment-aware, hardcoded always-ignored set protects
  all existing pairs without a DB migration
- applied symmetrically to remote listing + merged path set (never upload,
  download, or delete an excluded path on either side)
- add .thumbnails to new-pair default excludePatterns
- ExcludePathTest covers cache/trash/pending/sfpart + user patterns

app/src/main/kotlin/com/syncflow/domain/sync/SyncEngine.kt

@@ -110,8 +110,15 @@ class SyncEngine @Inject constructor(
         // level (Depth:1) made every file inside a remote subfolder look "missing from remote",
         // which on a TWO_WAY/MIRROR pair triggered DELETE_LOCAL and wiped those files off the
         // device (data loss). Walk the remote tree so subfolder files are matched, not deleted.
+        // Exclusions are filtered on BOTH sides. The local walk already drops excluded files,
+        // but the remote listing did not, so any excluded path that already existed on the
+        // server (e.g. a previously-uploaded ".thumbnails" entry) looked "local-missing" and
+        // got DELETE_REMOTE'd every cycle — endless churn as Android regenerates the cache.
+        // Filtering remote + the merged path set makes excluded paths invisible to the engine:
+        // never uploaded, downloaded, or deleted on either side.
         val remoteFiles = listRemoteFilesRecursive(provider, pair.remotePath)
             .associateBy { it.path.removePrefix(pair.remotePath).trimStart('/') }
+            .filterKeys { !isExcludedPath(it, pair) }
         val localFiles = accessor.walkFiles(pair)
 
         // Self-healing: if every known-state path is absent from the current local scan but
@@ -125,7 +132,12 @@ class SyncEngine @Inject constructor(
             return performSync(pair, provider, isRetry = true, onProgress = onProgress)
         }
 
-        val allPaths = (localFiles.keys + remoteFiles.keys + knownStates.keys).toSet()
+        // knownStates may still hold records for now-excluded paths (e.g. thumbnails uploaded
+        // by an older build). Drop them from the work set so they aren't acted on; their stale
+        // state rows are harmless and ignored.
+        val allPaths = (localFiles.keys + remoteFiles.keys + knownStates.keys)
+            .filter { !isExcludedPath(it, pair) }
+            .toSet()
         val hasPriorSyncState = knownStates.isNotEmpty()
         val semaphore = Semaphore(2)  // limit concurrency to be gentle on the server
         val uploadedAtomic = AtomicInteger(0)
@@ -409,6 +421,41 @@ internal fun syncDecide(
 
 enum class SyncDecision { UPLOAD, DOWNLOAD, DELETE_LOCAL, DELETE_REMOTE, CONFLICT, SKIP }
 
+/**
+ * OS-generated, volatile paths that must NEVER sync on any pair, regardless of user exclude
+ * config. These are matched against every path SEGMENT (directory names included), so an entire
+ * subtree like "DCIM/.thumbnails/..." is ignored. Android continuously regenerates and evicts
+ * its thumbnail cache and shuffles files through .trashed-/.pending- staging dirs; syncing them
+ * produces an endless upload→evict→DELETE_REMOTE→regenerate loop. ".sfpart" is our own atomic-
+ * write temp suffix and must never be propagated either.
+ */
+private val ALWAYS_IGNORED_SEGMENTS = setOf(".thumbnails")
+private val ALWAYS_IGNORED_PREFIXES = listOf(".trashed-", ".pending-")
+private val ALWAYS_IGNORED_SUFFIXES = listOf(".sfpart")
+
+/**
+ * True if [rel] should be excluded from sync entirely. Applied symmetrically to the local walk,
+ * the remote listing, and known state so an excluded path is never uploaded, downloaded, or
+ * deleted. The always-ignored rules run on every segment; user-configured rules
+ * (skipHiddenFiles, excludePatterns, excludeExtensions) match the filename, mirroring the
+ * existing local-walk semantics in LocalAccessor.
+ */
+internal fun isExcludedPath(rel: String, pair: SyncPair): Boolean {
+    val segments = rel.replace('\\', '/').split('/').filter { it.isNotEmpty() }
+    if (segments.isEmpty()) return false
+    for (seg in segments) {
+        if (seg in ALWAYS_IGNORED_SEGMENTS) return true
+        if (ALWAYS_IGNORED_PREFIXES.any { seg.startsWith(it) }) return true
+        if (ALWAYS_IGNORED_SUFFIXES.any { seg.endsWith(it) }) return true
+    }
+    val fileName = segments.last()
+    if (pair.skipHiddenFiles && fileName.startsWith('.')) return true
+    if (pair.excludePatterns.any { pat -> fileName.matches(globToRegex(pat)) }) return true
+    val ext = fileName.substringAfterLast('.', "").lowercase()
+    if (pair.excludeExtensions.any { ext == it.lowercase().trimStart('.') }) return true
+    return false
+}
+
 /**
  * True if a relative sync path is unsafe to act on — empty, absolute, or containing a ".."
  * segment that would let a hostile remote escape the sync root via path traversal. Applied to

app/src/main/kotlin/com/syncflow/ui/addpair/AddPairViewModel.kt

@@ -47,7 +47,7 @@ data class AddPairUiState(
     val chargingOnly: Boolean = false,
     val minBatteryPct: Int = 0,
     // ── File filters ─────────────────────────────────────────────────────────
-    val excludePatterns: String = ".DS_Store\n*.tmp\n.nomedia\nThumbs.db",
+    val excludePatterns: String = ".DS_Store\n*.tmp\n.nomedia\nThumbs.db\n.thumbnails",
     val includeExtensions: String = "",
     val excludeExtensions: String = "",
     val skipHiddenFiles: Boolean = true,

app/src/test/kotlin/com/syncflow/domain/sync/ExcludePathTest.kt

@@ -0,0 +1,78 @@
+package com.syncflow.domain.sync
+
+import com.syncflow.domain.model.ConflictStrategy
+import com.syncflow.domain.model.DeleteBehavior
+import com.syncflow.domain.model.ScheduleType
+import com.syncflow.domain.model.SyncDirection
+import com.syncflow.domain.model.SyncPair
+import com.syncflow.domain.model.SyncStatus
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * Exclusion symmetry: paths excluded from the local walk must also be excluded from the remote
+ * listing and the merged work set, so a previously-uploaded excluded file is never DELETE_REMOTE'd
+ * in an endless churn loop (the ".thumbnails" cache regression).
+ */
+class ExcludePathTest {
+
+    private fun pair(
+        excludePatterns: List<String> = emptyList(),
+        excludeExtensions: List<String> = emptyList(),
+        skipHiddenFiles: Boolean = false,
+    ) = SyncPair(
+        id = 1, name = "t", localPath = "/l", remotePath = "/r", accountId = 1,
+        syncDirection = SyncDirection.TWO_WAY,
+        conflictStrategy = ConflictStrategy.KEEP_NEWEST,
+        deleteBehavior = DeleteBehavior.MIRROR,
+        recursive = true,
+        scheduleType = ScheduleType.MANUAL, scheduleIntervalMinutes = 0,
+        scheduleDailyTime = null, scheduleWeekdays = 0,
+        wifiOnly = false, wifiSsid = "", chargingOnly = false, minBatteryPct = 0,
+        excludePatterns = excludePatterns, includeExtensions = emptyList(),
+        excludeExtensions = excludeExtensions, skipHiddenFiles = skipHiddenFiles,
+        minFileSizeKb = 0, maxFileSizeKb = 0,
+        notifyOnComplete = false, notifyOnError = false,
+        isEnabled = true, lastSyncAt = null, lastSyncResult = SyncStatus.IDLE,
+        pendingConflicts = 0,
+    )
+
+    @Test fun `thumbnails cache is always excluded regardless of config`() {
+        val p = pair()
+        assertTrue(isExcludedPath("DCIM/.thumbnails/123.jpg", p))
+        assertTrue(isExcludedPath("Pictures/.thumbnails/1000020397.jpg", p))
+        assertTrue(isExcludedPath(".thumbnails/x.jpg", p))
+    }
+
+    @Test fun `android trash and pending staging dirs are excluded`() {
+        val p = pair()
+        assertTrue(isExcludedPath("DCIM/Camera/.trashed-1700000000-IMG_0001.jpg", p))
+        assertTrue(isExcludedPath("DCIM/.pending-1700000000-VID_0001.mp4", p))
+    }
+
+    @Test fun `our own atomic-write temp files are excluded`() {
+        val p = pair()
+        assertTrue(isExcludedPath("Download/.movie.mp4.sfpart", p))
+        assertTrue(isExcludedPath("a/b/.photo.jpg.sfpart", p))
+    }
+
+    @Test fun `normal media files are not excluded`() {
+        val p = pair()
+        assertFalse(isExcludedPath("DCIM/Camera/IMG_0001.jpg", p))
+        assertFalse(isExcludedPath("Pictures/cat.png", p))
+        assertFalse(isExcludedPath("اصفهان/20171023.jpg", p)) // unicode folder, real data
+    }
+
+    @Test fun `user exclude patterns and extensions still apply on filename`() {
+        assertTrue(isExcludedPath("a/Thumbs.db", pair(excludePatterns = listOf("Thumbs.db"))))
+        assertTrue(isExcludedPath("a/note.tmp", pair(excludePatterns = listOf("*.tmp"))))
+        assertTrue(isExcludedPath("a/data.log", pair(excludeExtensions = listOf("log"))))
+        assertFalse(isExcludedPath("a/keep.jpg", pair(excludeExtensions = listOf("log"))))
+    }
+
+    @Test fun `skipHiddenFiles excludes dotfiles by filename only`() {
+        assertTrue(isExcludedPath("a/.hidden", pair(skipHiddenFiles = true)))
+        assertFalse(isExcludedPath("a/.hidden", pair(skipHiddenFiles = false)))
+    }
+}

version.properties

@@ -1,2 +1,2 @@
-VERSION_NAME=1.0.73
-VERSION_CODE=73
+VERSION_NAME=1.0.74
+VERSION_CODE=74