fix(web): backup age in Templates card was frozen by hx-preserve

The backups <details> carried hx-preserve="true" to survive the card's
30s poll without collapsing if the operator had it open -- but hx-preserve
freezes the whole node, so "newest X ago" inside it never updated either,
same class of bug as the Started column before it got its own JS-side
toggle state. Drop hx-preserve; track open/closed the same way (stable id,
state re-applied after every swap) so the count/age text stays live.

src/ci_orchestrator/web/static/app.js

@@ -239,6 +239,33 @@
     }
   });
 
+  // Templates card: each "N backup(s)" row is a <details> the operator may
+  // expand -- it must not collapse every 30s poll. Unlike the time-toggle
+  // buttons, its own content (backup count, "newest X ago") legitimately
+  // needs to keep updating, so this tracks only open/closed the same way
+  // (stable id, state re-applied after every swap) instead of freezing the
+  // whole node with hx-preserve, which used to freeze that text too.
+  var detailsState = {};
+
+  function wireDetails(root) {
+    var list = root.querySelectorAll
+      ? root.querySelectorAll("details.backups-details[id]")
+      : [];
+    Array.prototype.forEach.call(list, function (el) {
+      var saved = detailsState[el.id];
+      if (saved !== undefined) {
+        el.open = saved;
+      }
+      if (el.dataset.wired === "true") {
+        return;
+      }
+      el.dataset.wired = "true";
+      el.addEventListener("toggle", function () {
+        detailsState[el.id] = el.open;
+      });
+    });
+  }
+
   document.body.addEventListener("htmx:afterSwap", function (evt) {
     var target = evt.detail && evt.detail.target;
     if (!target || !target.isConnected) {
@@ -253,11 +280,13 @@
     }
     if (target) {
       restoreTimeToggles(target);
+      wireDetails(target);
     }
   });
 
   document.addEventListener("DOMContentLoaded", function () {
     observeStack();
     processSlot(document.getElementById("action-slot"));
+    wireDetails(document);
   });
 })();

src/ci_orchestrator/web/templates/partials/templates.html

@@ -35,7 +35,7 @@
           </td>
           <td>
             {% if bks %}
-            <details class="backups-details" id="backups-{{ tmpl.name }}" hx-preserve="true">
+            <details class="backups-details" id="backups-{{ tmpl.name }}">
               <summary>{{ bks | length }} backup(s) <span class="text-dim">· newest {{ bks[0].mtime | relative_time }}</span></summary>
               <ul class="backups-list">
                 {% for b in bks %}

tests/python/test_web_stage_b.py

@@ -180,6 +180,38 @@ def test_templates_route_degrades_on_probe_failure(
     assert "unavailable" in resp.text.lower()
 
 
+def test_templates_backups_details_is_not_frozen_by_hx_preserve(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    """``hx-preserve`` freezes the *whole* node across the card's 30s poll --
+    including the "newest X ago" text inside it, which must keep updating.
+    Only the <details> open/closed state should persist (via app.js, the
+    same pattern already used for the Started column's click-to-toggle)."""
+    monkeypatch.setattr(app_module, "list_templates", lambda _config: [_TEMPLATE_ROW])
+    monkeypatch.setattr(
+        app_module,
+        "backups_by_template",
+        lambda _config: {
+            "LinuxBuild2404": [
+                FileEntry(
+                    name="Template_LinuxBuild2404_20260101_000000.7z",
+                    size_bytes=2048,
+                    mtime=1_700_000_000.0,
+                )
+            ]
+        },
+    )
+    app = create_app(_make_config(tmp_path))
+    client = TestClient(app)
+
+    resp = client.get("/templates")
+
+    assert resp.status_code == 200
+    assert 'id="backups-LinuxBuild2404"' in resp.text
+    assert "newest" in resp.text
+    assert "hx-preserve" not in resp.text
+
+
 def test_templates_route_shows_running_ram_snapshot_warning(
     tmp_path: Path, monkeypatch: pytest.MonkeyPatch
 ) -> None: