diff --git a/l4d2web/l4d2web/static/js/modal-router.js b/l4d2web/l4d2web/static/js/modal-router.js
index 234de70..04a00e7 100644
--- a/l4d2web/l4d2web/static/js/modal-router.js
+++ b/l4d2web/l4d2web/static/js/modal-router.js
@@ -34,6 +34,55 @@
     });
   }
 
+  function closeModal() {
+    const dlg = document.getElementById("modal-container");
+    if (dlg && dlg.open) dlg.close();
+  }
+
+  document.addEventListener("DOMContentLoaded", () => {
+    const dlg = document.getElementById("modal-container");
+    if (!dlg) return;
+
+    // Single source of truth: every close path funnels through the dialog's
+    // native 'close' event, so URL/state cleanup runs exactly once no matter
+    // who triggered the close (Esc, backdrop, dismiss button, response error,
+    // or the legacy modal.js backdrop handler).
+    dlg.addEventListener("close", () => {
+      currentModalPath = null;
+      const url = new URL(window.location.href);
+      if (url.searchParams.has("modal")) {
+        url.searchParams.delete("modal");
+        history.pushState({}, "", url.toString());
+      }
+    });
+
+    // Esc key fires 'cancel' on a <dialog>; preventDefault so we control the
+    // close path (the default action would close() too, but we want one path).
+    dlg.addEventListener("cancel", (event) => {
+      event.preventDefault();
+      dlg.close();
+    });
+
+    // Backdrop click on our own slot. The legacy modal.js handler also
+    // matches dialog.modal and closes; this listener is harmless when the
+    // legacy one wins because dialog.close() is idempotent.
+    dlg.addEventListener("click", (event) => {
+      if (event.target === dlg) dlg.close();
+    });
+  });
+
+  // Browser back/forward: re-evaluate URL state and either fetch+show a new
+  // modal or close the current one. Closing routes through dialog.close() so
+  // the close-event cleanup fires (no separate state update here).
+  window.addEventListener("popstate", () => {
+    const path = new URL(window.location.href).searchParams.get("modal");
+    if (path) {
+      fetchAndShow(path);
+    } else {
+      closeModal();
+    }
+  });
+
   document.addEventListener("click", (event) => {
     const link = event.target.closest("a[data-modal]");
     if (!link) return;
@@ -45,7 +94,28 @@
     openModal(href);
   });
 
+  // Dismiss triggers inside modal content (e.g. the editor's × and Cancel
+  // buttons render with data-modal-dismiss). Document-level delegation so
+  // HTMX-swapped content gets the behavior without re-binding.
+  document.addEventListener("click", (event) => {
+    if (event.target.closest("[data-modal-dismiss]")) {
+      event.preventDefault();
+      closeModal();
+    }
+  });
+
+  // HTMX response error (4xx/5xx from the modal fetch): close the modal so
+  // the user isn't left with an error fragment open and a stale ?modal= URL.
+  document.body.addEventListener("htmx:responseError", (event) => {
+    const target = event.detail && event.detail.target;
+    if (target && target.id === "modal-content") {
+      console.warn("[modal-router] server returned error, closing modal", event.detail.xhr && event.detail.xhr.status);
+      closeModal();
+    }
+  });
+
   // Public API — used by files-overlay.js to open the editor from row clicks
   // that aren't a literal <a data-modal> (existing event delegation).
   window.openModal = openModal;
+  window.closeModal = closeModal;
 })();