diff --git a/app/src/test/kotlin/com/syncflow/domain/sync/UploadBackupLifecycleTest.kt b/app/src/test/kotlin/com/syncflow/domain/sync/UploadBackupLifecycleTest.kt
new file mode 100644
index 0000000..8fba158
--- /dev/null
+++ b/app/src/test/kotlin/com/syncflow/domain/sync/UploadBackupLifecycleTest.kt
@@ -0,0 +1,117 @@
+package com.syncflow.domain.sync
+
+import com.syncflow.data.db.entities.SyncFileStateEntity
+import com.syncflow.domain.model.ConflictStrategy
+import com.syncflow.domain.model.DeleteBehavior
+import com.syncflow.domain.model.RemoteFile
+import com.syncflow.domain.model.SyncDirection
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import java.time.Instant
+
+/**
+ * End-to-end decision lifecycle for the backup scenario:
+ *
+ *   "I back up my phone to the cloud, then I delete the file on the phone.
+ *    It must stay in the cloud."
+ *
+ * These walk the exact multi-cycle state the SyncEngine produces:
+ *   - a successful UPLOAD saves state with the local mtime known and remote metadata null
+ *     (SyncEngine.buildState(..., remoteAfterTransfer = null)),
+ *   - the next sync sees both sides present and unchanged, returns SKIP, and the SKIP branch
+ *     reconciles the record by filling in the remote metadata,
+ *   - then the local file is deleted and we assert what happens to the cloud copy.
+ *
+ * The decision is driven entirely by deleteBehavior, so each terminal case is asserted for
+ * KEEP, MIRROR, and ARCHIVE.
+ */
+class UploadBackupLifecycleTest {
+
+    private val T0 = 1_716_393_136_000L // exact second boundary
+
+    private fun local(ms: Long = T0, size: Long = 100L) =
+        LocalFileInfo("photo.jpg", size, ms)
+
+    private fun remote(ms: Long = T0, etag: String? = "etag1", size: Long = 100L) =
+        RemoteFile("backup/photo.jpg", "photo.jpg", false, size, Instant.ofEpochMilli(ms), etag, null)
+
+    /** Mirrors SyncEngine.buildState right after a successful UPLOAD: remote metadata still null. */
+    private fun stateAfterUpload(ms: Long = T0) = SyncFileStateEntity(
+        syncPairId = 1L, relativePath = "photo.jpg",
+        localModifiedAt = Instant.ofEpochMilli(ms), localSizeBytes = 100L, localHash = null,
+        remoteModifiedAt = null, remoteSizeBytes = 0L, remoteEtag = null,
+        lastSyncedAt = Instant.now(), syncedHash = null,
+    )
+
+    /** Mirrors the record after the next sync's SKIP reconciliation fills in remote metadata. */
+    private fun stateReconciled(ms: Long = T0, etag: String? = "etag1") = SyncFileStateEntity(
+        syncPairId = 1L, relativePath = "photo.jpg",
+        localModifiedAt = Instant.ofEpochMilli(ms), localSizeBytes = 100L, localHash = null,
+        remoteModifiedAt = Instant.ofEpochMilli(ms), remoteSizeBytes = 100L, remoteEtag = etag,
+        lastSyncedAt = Instant.now(), syncedHash = null,
+    )
+
+    private fun decide(
+        local: LocalFileInfo?,
+        remote: RemoteFile?,
+        known: SyncFileStateEntity?,
+        delete: DeleteBehavior,
+    ) = syncDecide(
+        SyncDirection.UPLOAD_ONLY, ConflictStrategy.KEEP_NEWEST, delete,
+        local, remote, known, hasPriorSyncState = known != null,
+    )
+
+    // ── Cycle 1: first backup uploads the file ───────────────────────────────
+
+    @Test fun `cycle 1 - first backup uploads regardless of delete behavior`() {
+        assertEquals(SyncDecision.UPLOAD, decide(local(), null, null, DeleteBehavior.KEEP))
+        assertEquals(SyncDecision.UPLOAD, decide(local(), null, null, DeleteBehavior.MIRROR))
+        assertEquals(SyncDecision.UPLOAD, decide(local(), null, null, DeleteBehavior.ARCHIVE))
+    }
+
+    // ── Cycle 2: file present on both sides, unchanged -> SKIP (no deletion) ──
+
+    @Test fun `cycle 2 - unchanged file skips right after upload (remote metadata still null)`() {
+        assertEquals(SyncDecision.SKIP, decide(local(), remote(), stateAfterUpload(), DeleteBehavior.KEEP))
+        assertEquals(SyncDecision.SKIP, decide(local(), remote(), stateAfterUpload(), DeleteBehavior.MIRROR))
+    }
+
+    @Test fun `cycle 2 - unchanged file skips once state is reconciled`() {
+        assertEquals(SyncDecision.SKIP, decide(local(), remote(), stateReconciled(), DeleteBehavior.KEEP))
+        assertEquals(SyncDecision.SKIP, decide(local(), remote(), stateReconciled(), DeleteBehavior.MIRROR))
+    }
+
+    // ── Cycle 3: deleted on the phone — THE scenario ─────────────────────────
+
+    @Test fun `KEEP - deleting on phone leaves the cloud copy (correct backup behavior)`() {
+        // Reconciled steady state:
+        assertEquals(SyncDecision.SKIP, decide(null, remote(), stateReconciled(), DeleteBehavior.KEEP))
+        // And even if deletion happens before the reconcile pass ran:
+        assertEquals(SyncDecision.SKIP, decide(null, remote(), stateAfterUpload(), DeleteBehavior.KEEP))
+    }
+
+    @Test fun `MIRROR - deleting on phone DELETES the cloud copy (wrong for a backup)`() {
+        assertEquals(SyncDecision.DELETE_REMOTE, decide(null, remote(), stateReconciled(), DeleteBehavior.MIRROR))
+        assertEquals(SyncDecision.DELETE_REMOTE, decide(null, remote(), stateAfterUpload(), DeleteBehavior.MIRROR))
+    }
+
+    @Test fun `ARCHIVE - deleting on phone moves the cloud copy to _Deleted (preserved)`() {
+        // syncDecide returns DELETE_REMOTE; the engine's DELETE_REMOTE branch MOVEs the file to
+        // <remote>/_Deleted/ instead of removing it when deleteBehavior == ARCHIVE.
+        assertEquals(SyncDecision.DELETE_REMOTE, decide(null, remote(), stateReconciled(), DeleteBehavior.ARCHIVE))
+    }
+
+    // ── After deletion: a brand-new remote file is NOT pulled down (upload-only) ─
+
+    @Test fun `KEEP - a new remote file never comes down to the phone (upload-only)`() {
+        // Remote-only, no state record: in upload-only this must SKIP, not DOWNLOAD.
+        assertEquals(SyncDecision.SKIP, decide(null, remote(), null, DeleteBehavior.KEEP))
+    }
+
+    // ── Re-adding / changing a file after a KEEP deletion still uploads ───────
+
+    @Test fun `KEEP - modifying the file locally still uploads the change`() {
+        val newer = local(T0 + 5_000)
+        assertEquals(SyncDecision.UPLOAD, decide(newer, remote(), stateReconciled(), DeleteBehavior.KEEP))
+    }
+}