diff --git a/l4d2web/tests/e2e/test_files_overlay.py b/l4d2web/tests/e2e/test_files_overlay.py
index f369e55..e9752df 100644
--- a/l4d2web/tests/e2e/test_files_overlay.py
+++ b/l4d2web/tests/e2e/test_files_overlay.py
@@ -336,3 +336,50 @@ def test_new_folder_then_delete(page: Page, files_overlay_server) -> None:
     assert not (overlay_root / folder_name).exists()
     # The tree refresh removes the row.
     expect(folder_row).to_have_count(0, timeout=5000)
+
+
+def test_filename_rename_on_save(page: Page, files_overlay_server) -> None:
+    """Open server.cfg, change the filename input to server-renamed.cfg,
+    and click Save. The single POST /files/save call performs an atomic
+    rename + write; the test asserts the disk reflects both the new
+    name and the original content, AND that the tree row swaps over.
+
+    This pins the rename-on-save branch in routedSaveClicked (the
+    non-is_new code path that diffs originalLeaf vs editedFilename
+    and emits `new_path`). A regression that dropped the rename
+    payload would silently leave the original file in place — the
+    "old name gone" + "new name present" assertion pair catches that.
+
+    We do NOT call __filesEditor.setContent here: the rename should
+    preserve the original textarea-seeded content. If the save handler
+    accidentally writes an empty body, the content-equality assertion
+    fails.
+    """
+    base = files_overlay_server["base_url"]
+    overlay_id = files_overlay_server["overlay_id"]
+    overlay_root = files_overlay_server["overlay_root"]
+    original_content = (overlay_root / "server.cfg").read_text()
+    _open_overlay(page, base, overlay_id)
+
+    page.click('button.file-tree-name-button[data-target-path="server.cfg"]')
+    _wait_for_routed_editor(page)
+
+    new_name = "server-renamed.cfg"
+    page.fill("input[data-editor-filename]", new_name)
+    page.click(".files-editor-save")
+
+    expect(page.locator("#modal-container")).to_be_hidden(timeout=5000)
+
+    # Disk: old name gone, new name present with the original content.
+    assert not (overlay_root / "server.cfg").exists()
+    assert (overlay_root / new_name).read_text() == original_content
+
+    # Tree refresh runs at parentOf(new_path) = "" (root) — both rows
+    # come from that same listing, so we wait for the new one and
+    # assert the old one is gone in the same refresh.
+    expect(
+        page.locator(f'.file-tree-row-file[data-target-path="{new_name}"]')
+    ).to_be_visible(timeout=5000)
+    expect(
+        page.locator('.file-tree-row-file[data-target-path="server.cfg"]')
+    ).to_have_count(0)