Cache the watchdog payload, and stop reading trailing comments as conf values

The tab collected over SSH on every 30s poll — 8.3s a load with HOST2 down.
vv_parse_conf_scalar() captured to end of line, so a commented toggle parsed as
"true   # HOST2 back online": every threshold read right because (int) stops at
the first non-digit, and 38 booleans read wrong. The Fallback tab has been
showing failover disabled while it was on.

Plugin/unraid/api/watchdog.php

@@ -33,15 +33,41 @@
 //   Remote collection degrades per node — one unreachable partner drops that node's card and
 //   leaves the local host and every other partner intact.
 //
+//   Served from cache, collected only on a miss.
+//       vv_wd_all() SSHes to every configured partner, so its cost is set by the slowest node
+//       rather than by how much data there is. Measured at 8.3s on this host with HOST2 down —
+//       paid by every visitor, every 30 seconds, because the tab polls. The cache check happens
+//       before the heavy include, so a hit costs one file read and no SSH at all.
+//
+//       The window is deliberately wider than the poll. Watchdog state only changes when the
+//       orchestrator runs, which is every 15 minutes; polling it every 30 seconds was never
+//       reading anything new, it was just re-paying for the same answer.
+//
 // REQUEST
-//   GET, no parameters
+//   GET             served from the 300s cache when one is present
+//   GET ?live       bypass the cache and collect everything fresh
 //
 // RESPONSE
 //   vv_wd_all() verbatim — per-node watchdog state plus the resolved threshold set
 //
 // DEPENDS ON
-//   include/watchdog.php   vv_wd_all()
+//   include/config.php          vv_cache_read()
+//   include/watchdog.php        vv_wd_all()   — required only on a miss
+//   Tools/api_cache_writer.php  writes the cache this endpoint normally serves
 // ═══════════════════════════════════════════════════════════════════════════════════════════════
 header('Content-Type: application/json');
+require_once dirname(__DIR__) . '/include/config.php';
+
+if (!isset($_GET['live'])) {
+    $_vv_cached = vv_cache_read('watchdog', 300);
+    if ($_vv_cached !== null) { echo json_encode($_vv_cached); exit; }
+    unset($_vv_cached);
+}
+
 require_once dirname(__DIR__) . '/include/watchdog.php';
-echo json_encode(vv_wd_all());
+$_vv_wd = vv_wd_all();
+// Written on the miss as well as by the background writer. Without this the first visitor after
+// a restart pays the full collection and so does the next one, until the writer's next minute
+// happens to land.
+vv_cache_write('watchdog', $_vv_wd);
+echo json_encode($_vv_wd);