fix: classify unauthorized by stderr presence, not denial wording

Review flagged the 'access not allowed' substring:
if tmux's denial text drifts while keeping exit 0, unauthorized
connections would classify as ok and the false-joined status/leave
misreporting would silently return. A clean authorized list-clients
writes nothing to stderr (verified 3.3a/3.5a/3.6-SunOS, incl. invited
read-only clients), so rc 0 plus any stderr output now classifies as
unauthorized: no message text consulted. Drift in any direction
degrades to a hidden party, never to a false ok.

party

@@ -343,26 +343,33 @@ is_party_alive() {
 # Classify the caller's relationship to a party socket. Prints exactly
 # one of:
 #   ok           — live tmux server, the caller is authorized.
-#   unauthorized — live tmux server, but server-access rejected us.
-#                  CAUTION, the reason this function exists: tmux
-#                  answers a non-allowlisted user with "access not
-#                  allowed" on stderr and EXIT STATUS 0 (verified live
-#                  on 3.3a and 3.5a), for every command — including
+#   unauthorized — live tmux server, but it refused us. CAUTION, the
+#                  reason this function exists: tmux answers a
+#                  non-allowlisted user with "access not allowed" on
+#                  stderr and EXIT STATUS 0 (verified live on 3.3a,
+#                  3.5a, and 3.6/SunOS), for every command — including
 #                  has-session, which then reports any target as
 #                  existing. Exit codes alone cannot distinguish
-#                  authorized from unauthorized; the message can.
+#                  authorized from unauthorized. We deliberately do NOT
+#                  match the denial text either: wording could drift
+#                  across tmux versions and silently reopen the
+#                  false-authorized paths. A clean authorized
+#                  list-clients writes nothing to stderr, so rc 0 plus
+#                  ANY stderr output classifies as unauthorized. Should
+#                  tmux ever warn on an authorized call, that degrades
+#                  to a hidden party — never to a false "ok".
 #   dead         — nothing speaking the tmux protocol at that socket
 #                  (stale roster, killed server, AF_UNIX impostor).
-# Unknown error text with nonzero rc falls through to "dead", so string
-# drift in a future tmux degrades to hidden-party behavior, never to a
-# false "ok".
 party_conn_state() {
     _cs_err=$("$PARTY_TMUX" -S "$1" list-clients 2>&1 >/dev/null) \
         && _cs_rc=0 || _cs_rc=$?
-    case "$_cs_err" in
-        *"access not allowed"*) printf 'unauthorized\n'; return 0 ;;
-    esac
-    if [ "$_cs_rc" -eq 0 ]; then printf 'ok\n'; else printf 'dead\n'; fi
+    if [ "$_cs_rc" -ne 0 ]; then
+        printf 'dead\n'
+    elif [ -n "$_cs_err" ]; then
+        printf 'unauthorized\n'
+    else
+        printf 'ok\n'
+    fi
 }
 
 # FS perms

tests/20-helpers.bats

@@ -142,9 +142,10 @@ setup() {
   cat > "$stub" <<'S'
 #!/bin/sh
 case "${MODE:-}" in
-  ok)   exit 0 ;;
-  deny) echo "access not allowed" >&2; exit 0 ;;
-  *)    echo "error connecting to /x (No such file or directory)" >&2; exit 1 ;;
+  ok)    exit 0 ;;
+  deny)  echo "access not allowed" >&2; exit 0 ;;
+  deny2) echo "connection declined by policy (hypothetical future wording)" >&2; exit 0 ;;
+  *)     echo "error connecting to /x (No such file or directory)" >&2; exit 1 ;;
 esac
 S
   chmod +x "$stub"
@@ -153,5 +154,8 @@ S
   # The trap this function exists for: tmux answers unauthorized users
   # with EXIT 0 + a stderr message, so rc alone says "authorized".
   export MODE=deny; [ "$(party_conn_state /x)" = "unauthorized" ]
+  # Classification must not depend on tmux's denial wording (adversarial
+  # review finding): rc 0 with ANY stderr output is a refusal.
+  export MODE=deny2; [ "$(party_conn_state /x)" = "unauthorized" ]
   export MODE=dead; [ "$(party_conn_state /x)" = "dead" ]
 }

tests/96-unauthorized.bats

@@ -129,3 +129,21 @@ STUB
   [[ "$output" == *"read-only"* ]]
   [[ "$output" == *"attach-session -r -t fiesta"* ]]
 }
+
+@test "unauthorized classification does not depend on tmux's denial wording" {
+  # Adversarial-review finding: matching the English "access not
+  # allowed" would silently reopen the false-authorized paths if the
+  # wording ever drifts. The classifier keys on rc 0 + any stderr
+  # output instead; this stub proves a drifted message still counts.
+  cat > "$PARTY_TMP/tmux-denied-drift" <<'STUB'
+#!/bin/sh
+echo "connection declined by policy" >&2
+exit 0
+STUB
+  chmod +x "$PARTY_TMP/tmux-denied-drift"
+  export PARTY_TMUX="$PARTY_TMP/tmux-denied-drift"
+  run "$PARTY_BIN" list
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"invite-only"* ]]
+  [[ "$output" != *"0 attendee"* ]]
+}