Resolve a peer from tailscale status before falling back to DNS

MagicDNS does not work on this mesh, so `tailscale ip -4` missed and blocked on
a system DNS lookup until it timed out: 5.04s per call against 0.010s for the
status parse, paid by every mesh operation on both hosts. Exact match first, so
no precision is traded for the speed.

Plugin/unraid/include/config.php

@@ -416,28 +416,47 @@ function vv_get_hostname(bool $flush = false): string {
     return $name;
 }
 
-// Mirror of common.sh resolve_tailscale_ip(): tries `tailscale ip -4` first (Tailscale manages
-// the mapping so this survives IP changes), falls back to parsing `tailscale status` text.
+// Mirror of common.sh resolve_tailscale_ip(): resolves a hostname to a Tailscale IPv4.
+//
+// `tailscale status` is asked first, and that ordering is the whole point. It used to try
+// `tailscale ip -4` first, on the reasoning that Tailscale owns the mapping — true, but that call
+// resolves through MagicDNS, and MagicDNS does not work here: these hosts sit on separate tailnets
+// shared into each other, so the name misses and the call falls through to a system DNS lookup
+// that times out. Measured at **5.04 seconds, every call**, against 0.010s for the status parse.
+//
+// Nine files resolve peers this way — the AI RPC, node_chat, the arr collector, the media mesh
+// view — so that was five seconds added to every mesh operation on both hosts, quietly, for as
+// long as the mesh has existed. Nothing looked broken; everything was just slow.
+//
+// Order is now: exact match, unambiguous prefix match, then the DNS path bounded to two seconds as
+// a last resort. Exactness is not given up to get the speed — `tailscale status` carries the same
+// mapping `tailscale ip` would return, and an exact name match against it is exactly as precise.
+//
+// Memoised per request: a page that resolves the same partner four times paid four lookups.
 function vv_resolve_tailscale_ip(string $hostname): string {
-    $h  = strtolower($hostname);
-    $ip = trim(shell_exec('tailscale ip -4 ' . escapeshellarg($h) . ' 2>/dev/null') ?: '');
-    if ($ip) return $ip;
+    static $cache = [];
+    $h = strtolower($hostname);
+    if (isset($cache[$h])) return $cache[$h];
 
-    // Fallback: unambiguous prefix match against tailscale status (either direction) — handles
-    // Unraid's 15-char NetBIOS hostname truncation vs. a longer name recorded in master.conf.
-    // Only accept the match when exactly one peer could qualify; never guess between multiple
-    // candidates that happen to share a prefix (e.g. server1/server10).
-    $out = shell_exec('tailscale status 2>/dev/null') ?: '';
+    $out     = shell_exec('tailscale status 2>/dev/null') ?: '';
     $matches = [];
     foreach (explode("\n", $out) as $line) {
         $cols = preg_split('/\s+/', trim($line));
         if (!isset($cols[1])) continue;
         $peerHost = strtolower(explode('.', $cols[1])[0]);
-        if (str_starts_with($peerHost, $h) || str_starts_with($h, $peerHost)) {
-            $matches[] = $cols[0];
-        }
+
+        if ($peerHost === $h) return $cache[$h] = $cols[0];
+
+        // Unambiguous prefix match, either direction — handles Unraid's 15-char NetBIOS hostname
+        // truncation against a longer name recorded in master.conf. Only accepted when exactly one
+        // peer could qualify; never a guess between candidates sharing a prefix (server1/server10).
+        if (str_starts_with($peerHost, $h) || str_starts_with($h, $peerHost)) $matches[] = $cols[0];
     }
-    return count($matches) === 1 ? $matches[0] : '';
+    if (count($matches) === 1) return $cache[$h] = $matches[0];
+
+    // Only reached when status cannot decide. Bounded, because this is the path that blocks on DNS
+    // when MagicDNS is unavailable — which is the normal case on this mesh.
+    return $cache[$h] = trim(shell_exec('timeout 2 tailscale ip -4 ' . escapeshellarg($h) . ' 2>/dev/null') ?: '');
 }
 
 // Cached alongside the others: this reads master.conf in full and is called by vv_conf_vars() on