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.

common.sh

@@ -921,26 +921,48 @@ resolve_remote_ip() {
     info "$ICON_NET Remote IP: $REMOTE_SERVER"
 }
 
-# Resolve any hostname to a Tailscale IPv4 — tries direct lookup, falls back to status parse.
+# Resolve any hostname to a Tailscale IPv4 — status parse first, DNS as a bounded last resort.
 # Usage: ip=$(resolve_tailscale_ip "hostname") — returns empty string on failure.
+#
+# `tailscale ip -4` used to be tried first, because Tailscale owns the mapping. It also resolves
+# through MagicDNS, which does not work on this mesh — the two hosts are on separate tailnets
+# shared into each other — so the name misses and the call blocks on a system DNS lookup until it
+# times out. Five seconds, every call, on every rsync, partnership check and remote collector.
+# The status parse costs ten milliseconds and carries the same mapping.
+#
+# Exactness is not traded away for the speed: an exact name match against `tailscale status` is as
+# precise as the lookup it replaces. The prefix match keeps its ambiguity guard, and the DNS path
+# still runs — bounded, and only when status cannot decide.
+#
+# Mirror of vv_resolve_tailscale_ip() in Plugin/unraid/include/config.php; the two must agree.
 resolve_tailscale_ip() {
     local hostname="${1,,}"
-    local ip
-    ip=$(tailscale ip -4 "$hostname" 2>/dev/null)
-    if [[ -n "$ip" ]]; then
-        echo "$ip"
+    local status_out exact matches count ip
+
+    status_out=$(tailscale status 2>/dev/null)
+
+    exact=$(echo "$status_out" | awk -v name="$hostname" '
+        { split(tolower($2), parts, "."); if (parts[1] == name) { print $1; exit } }')
+    if [[ -n "$exact" ]]; then
+        echo "$exact"
         return
     fi
-    # Fallback: unambiguous prefix match against tailscale status (either direction) — handles
-    # Unraid's 15-char NetBIOS hostname truncation vs. a longer name recorded in master.conf.
-    # Only accept the match when exactly one peer could qualify; never guess between multiple
-    # candidates that happen to share a prefix (e.g. server1/server10).
-    local matches count
-    matches=$(tailscale status 2>/dev/null | awk -v name="$hostname" '
+
+    # Unambiguous prefix match, either direction — handles Unraid's 15-char NetBIOS hostname
+    # truncation vs. a longer name recorded in master.conf. Only accept the match when exactly one
+    # peer could qualify; never guess between candidates that share a prefix (server1/server10).
+    matches=$(echo "$status_out" | awk -v name="$hostname" '
         { split(tolower($2), parts, "."); host = parts[1];
           if (index(host, name) == 1 || index(name, host) == 1) print $1 }')
     count=$(echo "$matches" | grep -c .)
-    [[ "$count" -eq 1 ]] && echo "$matches"
+    if [[ "$count" -eq 1 ]]; then
+        echo "$matches"
+        return
+    fi
+
+    # Last resort, and the slow one. Bounded so a broken MagicDNS costs two seconds, not five.
+    ip=$(timeout 2 tailscale ip -4 "$hostname" 2>/dev/null)
+    [[ -n "$ip" ]] && echo "$ip"
 }
 
 # Strips the "unraid-" prefix (case-insensitive) and title-cases what remains.