diff --git a/cameleer-server-app/src/main/java/com/cameleer/server/app/storage/FilesystemArtifactStore.java b/cameleer-server-app/src/main/java/com/cameleer/server/app/storage/FilesystemArtifactStore.java
index 9cbc6b8e..ee20fcca 100644
--- a/cameleer-server-app/src/main/java/com/cameleer/server/app/storage/FilesystemArtifactStore.java
+++ b/cameleer-server-app/src/main/java/com/cameleer/server/app/storage/FilesystemArtifactStore.java
@@ -7,6 +7,7 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
 
 public class FilesystemArtifactStore implements ArtifactStore {
 
@@ -24,9 +25,11 @@ public class FilesystemArtifactStore implements ArtifactStore {
     public String put(ArtifactCoordinates coords, InputStream bytes, long size) throws IOException {
         Path target = pathOf(coords);
         Files.createDirectories(target.getParent());
+        Path tmp = target.resolveSibling(target.getFileName() + ".tmp");
         try (InputStream in = bytes) {
-            Files.copy(in, target, java.nio.file.StandardCopyOption.REPLACE_EXISTING);
+            Files.copy(in, tmp, StandardCopyOption.REPLACE_EXISTING);
         }
+        Files.move(tmp, target, StandardCopyOption.REPLACE_EXISTING, StandardCopyOption.ATOMIC_MOVE);
         return target.toString();
     }
 
@@ -45,12 +48,17 @@ public class FilesystemArtifactStore implements ArtifactStore {
         Path target = pathOf(coords);
         Files.deleteIfExists(target);
         // Sweep empty {appId}/v{n}/ then {appId}/ if now empty.
+        // A concurrent put of a sibling version can create v{n+1}/ mid-sweep —
+        // DirectoryNotEmptyException just means "stop sweeping," which is what
+        // "remove empty parent dirs" semantically means.
         Path versionDir = target.getParent();
         if (versionDir != null && Files.isDirectory(versionDir) && isEmpty(versionDir)) {
-            Files.delete(versionDir);
+            try { Files.delete(versionDir); }
+            catch (java.nio.file.DirectoryNotEmptyException e) { return; }
             Path appDir = versionDir.getParent();
             if (appDir != null && Files.isDirectory(appDir) && isEmpty(appDir)) {
-                Files.delete(appDir);
+                try { Files.delete(appDir); }
+                catch (java.nio.file.DirectoryNotEmptyException e) { /* leave it */ }
             }
         }
     }
diff --git a/cameleer-server-app/src/test/java/com/cameleer/server/app/storage/FilesystemArtifactStoreTest.java b/cameleer-server-app/src/test/java/com/cameleer/server/app/storage/FilesystemArtifactStoreTest.java
index 1a52e6ef..250eb9e6 100644
--- a/cameleer-server-app/src/test/java/com/cameleer/server/app/storage/FilesystemArtifactStoreTest.java
+++ b/cameleer-server-app/src/test/java/com/cameleer/server/app/storage/FilesystemArtifactStoreTest.java
@@ -58,4 +58,35 @@ class FilesystemArtifactStoreTest {
         assertThat(store.locator(c))
                 .isEqualTo(tmp.resolve("11111111-1111-1111-1111-111111111111/v7/app.jar").toString());
     }
+
+    @Test
+    void putOverwritesExistingArtifactWithDifferentContent(@TempDir Path tmp) throws Exception {
+        FilesystemArtifactStore store = new FilesystemArtifactStore(tmp.toString());
+        ArtifactCoordinates c = new ArtifactCoordinates("default", UUID.randomUUID(), 1);
+
+        store.put(c, new ByteArrayInputStream("v1-bytes".getBytes()), 8);
+        store.put(c, new ByteArrayInputStream("v2-different-bytes".getBytes()), 18);
+
+        try (InputStream in = store.get(c)) {
+            assertThat(new String(in.readAllBytes())).isEqualTo("v2-different-bytes");
+        }
+    }
+
+    @Test
+    void deleteLeavesAppDirAloneWhenSiblingVersionExists(@TempDir Path tmp) throws Exception {
+        FilesystemArtifactStore store = new FilesystemArtifactStore(tmp.toString());
+        UUID appId = UUID.randomUUID();
+        ArtifactCoordinates v1 = new ArtifactCoordinates("default", appId, 1);
+        ArtifactCoordinates v2 = new ArtifactCoordinates("default", appId, 2);
+
+        store.put(v1, new ByteArrayInputStream("a".getBytes()), 1);
+        store.put(v2, new ByteArrayInputStream("b".getBytes()), 1);
+
+        store.delete(v1);
+
+        // v1/ should be gone, but v2/ and the appId/ dir should remain (sibling lives there)
+        assertThat(Files.exists(tmp.resolve(appId.toString()).resolve("v1"))).isFalse();
+        assertThat(Files.exists(tmp.resolve(appId.toString()).resolve("v2/app.jar"))).isTrue();
+        assertThat(Files.exists(tmp.resolve(appId.toString()))).isTrue();
+    }
 }