Add three-member short alliance prototype

docs/OPTIONAL_ALLIANCE_VICTORY.md

@@ -1,5 +1,28 @@
 # Optional three-stronghold alliance victory
 
+## Three-member, three-stronghold variant — 29 October 2026
+
+**Staged Basic prototype, not a selectable game mode.** A distinct saved
+`three-short` variant allows at most three alliance members and gives both
+pairs and triples a three-stronghold target. Existing absent-variant groups
+retain their maximum of three and four-stronghold target; the separate
+`unlimited` variant retains its six-player ceiling and three-stronghold target.
+The current two-controller four-stronghold precedence and agreed target
+increases still apply. Admission, consent and departure reuse the existing
+group protocol; player controls identify this variant, and minimal bots may
+request admission to a pair. No lobby creates a group ledger and full group
+rules and complete-game acceptance remain open.
+
+Thirteen related files pass 59 cases, including an original four-seat Basic
+setup and Nexus with a staged empty ledger, actual group consent and all four
+minimal bot proposals. Later pair/triple victories use conserved forces staged
+at Collection; they are not complete played games.
+
+The user-authorized revised rulebook, physical p. 42 (printed p. 40), lists
+the three-member/three-stronghold option separately from the four-stronghold
+and unlimited options. Saved variant naming and the two-controller precedence
+are software choices, not additional publisher rulings.
+
 ## Group admission with joint commitments — 29 October 2026
 
 **Staged Basic prototype, not a selectable game mode.** The joint