Merge origin/dev into feature/cities-and-knights

Brings in open trade offers and counter-offers. Cities & Knights gets the same
flow for goods: OfferGoods may be open to the table, CounterGoods answers an
offer, and AcceptCounter / DismissCounters are shared with the base game.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_016eTor2tpxKb4dXbd8RqnvZ

docs/RULES-catan-ck.md

@@ -197,8 +197,10 @@ checked after every move and when a turn arrives.
 - **A knight that cannot find a refuge is lost**, as the almanac says of an intrigue.
 - **A claim on a metropolis with no city to carry it waits** and is made when a city is
   built.
-- **Domestic trade** may include commodities; the one-offer-at-a-time rules of the base
-  game apply.
+- **Domestic trade** works as in the base game — an offer to one seat or to the whole
+  table, asked in seat order, each seat accepting, declining or countering — and may
+  include commodities (`OfferGoods`, `CounterGoods`; accepting and dismissing counters
+  reuse the base game's `AcceptCounter` and `DismissCounters`).
 - **No Seafarers, no 5–6 player extension**, no scenario or variant of any kind.
 
 ## The computer opponent

docs/RULES-catan.md

@@ -135,17 +135,32 @@ is the same code path.
 
 ### Domestic
 
-An offer names **one** addressee and two card multisets: what the offerer gives,
-what they want. There are no counter-offers and no open auctions in v1.
+An offer is addressed to **one** seat or, with `to = null`, to **everyone**, and
+names two card multisets: what the offerer gives, what they want.
+
+Seats are asked **one at a time**, in seat order after the offerer (seats holding
+no cards are skipped; an addressed offer asks only its addressee). The seat being
+asked may:
+
+- **accept** — the trade happens at once and the offer closes (first accept wins);
+- **decline** — the offer moves on to the next seat;
+- **counter** (`CounterTrade`) — propose different terms: what they would give and
+  what they want from the offerer. A counter must differ from the offer as made
+  (that is an accept), and both sides must hold the cards. The offer moves on.
+
+When every seat has answered and nobody accepted: with no counters the offer
+simply lapses; with counters the phase becomes `TRADE_COUNTERS` and the offerer
+either **takes one** (`AcceptCounter(seat)`, still checked for affordability) or
+**turns them all down** (`DismissCounters`).
 
 An offer is legal only when the offerer's turn is in PLAYING, the addressee is
 another seat, both legs are non-empty, the two legs are not the same multiset
 (`countOf(give) != countOf(get)` — like-for-like is not a trade), and the
 offerer actually holds the cards being offered.
 
-The addressee may **accept** only if they hold what was asked and the offerer
-still holds what was promised; otherwise only **decline** is offered. A decline
-clears the table and leaves every card where it was.
+A seat may **accept** only if it holds what was asked and the offerer still holds
+what was promised; otherwise only decline (or counter) is offered. A refusal
+leaves every card where it was.
 
 Offers are free-form intents rather than enumerated moves (the space of card
 multisets is combinatorial), so they are validated structurally by
@@ -305,7 +320,7 @@ timing rules; Longest Road and Largest Army worth five; victory at ten.
 - **Year of Plenty two-of-a-kind needs the bank to hold both cards**, not one.
 - **The robber must move.** Some printings allow staying put; this engine always
   requires a different hex.
-- **Offers are one-to-one, no auctions or counter-offers** in v1.
+- **Offers may be open to the whole table** and can be countered; the first accept wins (see Trading).
 
 ## Known gaps
 
@@ -315,12 +330,8 @@ timing rules; Longest Road and Largest Army worth five; victory at ten.
   the base game so far; it is a one-constant change in `publicVictoryPoints`.
 - **A bank short of a resource pays nobody that roll**, even when only one player is owed
   it. The published ruling lets a lone claimant take what is left; Cities & Knights does.
-
-- **No domestic auction or counter-offer.** An offer is addressed to a single
-  seat. Open trading to the whole table, and counter-offers, are the obvious next
-  step and are not implemented.
-- **No player-to-player trade over the wire beyond accept/decline.** The engine
-  supports it; whether the UI surfaces it is the screen task's concern.
+- **No timer or cancel on offers.** An offer waits for each asked seat in turn; the offerer cannot withdraw it mid-round, and a player who never answers stalls the table.
+- **The AI never counters.** It accepts, declines, and picks among counters it is sent, but does not propose them.
 - **No trading away a development card.** Not part of the base game.
 - **The screen is built, not yet verified on two devices.** The Katan screen and
   setup options exist (see [UI-catan.md](UI-catan.md)); the catalogue entry is a

docs/UI-catan.md

@@ -89,7 +89,8 @@ screen's UI state. The legal-move list stays the gate.
 | Seven | **Discard** dialog (forced); then taps a hex to move the robber; a victim dialog appears only if more than one player can be robbed |
 | Main turn | arms **Road / Settlement / City** and taps a highlighted spot; **Buy card**; **Play card**; **Trade**; **End turn** |
 | Road Building | taps highlighted edges, or **Done with roads** |
-| Offered a trade | **Accept / Decline** dialog (forced) |
+| Offered a trade | **Accept / Decline / Counter…** dialog (forced); *Counter…* opens a picker pre-filled with the mirror of the offer |
+| Counter-offers received | **Counter-offers** dialog: *Accept* beside the one to take, or *No deal* |
 | Game over | result dialog |
 
 Trade offers are free-form (two card multisets), so they are validated with
@@ -165,6 +166,6 @@ Not done yet, in rough priority order:
    it does not say which hexes paid out, so that needs either a diff of two states
    or an engine addition.
 3. Art: terrain textures, resource and harbour icons, a real robber pawn.
-4. Open trade to the whole table and counter-offers (an engine limitation too).
+4. A timer or cancel button on offers (the engine has neither).
 5. A board that shows the *last* move (a faint highlight of what just changed).
 6. Landscape polish on large tablets; the right-hand panel scrolls but is plain.