v0.3.1 — multiplayer groundwork: 13 engine tests covering 2-4 player games, a seat parameter on snapshot and actionMenu so a player sees their own railroad rather than seat 0's, and the 22 opponent-directed cards held out of every deck until they are built

TODO.md

@@ -469,8 +469,15 @@ target is settled and freight carries its intended share.
       engine currently has no per-player turn within the New Train phase, so this is unbuilt rather
       than wrong.
 
-- [ ] **Action cards (10) and Space-use cards (12).** Genuinely multiplayer-only — they are played AT
-      an opponent. Rejected with `NOT_IMPLEMENTED`.
+- [ ] **THE 22 OPPONENT-DIRECTED CARDS — 10 Action, 12 Space-use — ARE OUT OF EVERY DECK UNTIL THEY
+      ARE BUILT.** Jesse's call. They were already cut from solitaire (Q6, no legal target with one
+      player); they are now cut from the competitive deck too, because `checkPlay` answers both
+      categories `NOT_IMPLEMENTED` and dealing them would make ~9% of draws reject outright. Flip
+      `opponentCardsInDeck` in `setup.ts` when they land. They are played AT another player —
+      Watertower, Derail, Railroad Crossing and so on — so they are genuinely multiplayer work, and
+      **three Enhancements are waiting on them**: Facing Point Locks, Water Column and Overpass are
+      wired and read, and fire only against these cards. Until then those three are dormant by
+      design rather than broken.
 - [ ] **Multiplayer proper.** The engine runs 2–5 player games and the bot plays them, but there is no
       server, no turn submission, and no per-player view.