Add optional short alliance victory

docs/RULE_DECISIONS.md

@@ -1,5 +1,12 @@
 # Rule decision index
 
+## Optional short alliance victory — 28 October 2026
+
+The printed optional two-member alliance target is selectable at three
+strongholds. This prototype preserves the four-stronghold two-controller
+setup as a provisional precedence choice; larger alliances remain separate.
+[Scope and source](OPTIONAL_ALLIANCE_VICTORY.md).
+
 ## Conditional future-battle leader question — 28 October 2026
 
 The printed current-turn question can provisionally refer to a named native