refactor: host pre-check probes its own socket path

The already-running check read the roster back only to learn the
socket path cmd_host had computed a few lines earlier. The roster's
presence still gates the probe: a leftover dir without one keeps
falling through to the mkdir lock and its 'party clean' hint.

party

@@ -807,13 +807,9 @@ EOF
         echo "party: $party_dir exists and is not a directory you own" >&2
         exit 1
     fi
-    if [ -d "$party_dir" ] && [ -f "$rec" ]; then
-        roster_read "$rec" 2>/dev/null || true
-        if [ -n "${RR_SOCKET:-}" ] \
-           && [ "$(party_conn_state "$RR_SOCKET")" != dead ]; then
-            echo "party: '$name' is already running" >&2
-            exit 1
-        fi
+    if [ -f "$rec" ] && [ "$(party_conn_state "$sock")" != dead ]; then
+        echo "party: '$name' is already running" >&2
+        exit 1
     fi
 
     # mkdir is the atomic acquisition primitive. POSIX mkdir(2) on an