feat(m4a): 增加交易库存金钱与动态定价

[变更性质]
- 本提交新增 M4a 交易能力，不扩大到 M4b、M5 或 M6。

[新增功能]
- 支持 Food 库存、买卖双方金钱转移、原子成功与拒绝结果。
- 支持基于需求、库存、性格和近期成交记忆的动态定价。

[实现方案]
- 在 Sim 中增加 TradeRequest、TradeResult、交易失败类型、交易记忆与 TradeEvent。
- 以不可变 World 更新和确定性定价保持库存、金钱及事件守恒。
- 增加交易测试，并补齐既有 NPC fixture 与 MemoryKind 穷举匹配。

[影响范围]
- 仅影响 LivingVillage.Kernel 交易逻辑及五个 M4a 相关测试项目文件。

1 files changed, 154 insertions, 0 deletions

diff --git a/src/LivingVillage.Kernel.Tests/TradeTests.fs b/src/LivingVillage.Kernel.Tests/TradeTests.fs
new file mode 100644
index 0000000..c7c8ef4
--- /dev/null
+++ b/src/LivingVillage.Kernel.Tests/TradeTests.fs
@@ -0,0 +1,154 @@
+namespace LivingVillage.Kernel.Tests
+
+open Microsoft.VisualStudio.TestTools.UnitTesting
+open LivingVillage.Kernel
+open LivingVillage.Kernel.Sim
+
+module private TradeHarness =
+
+    let private personality =
+        { Drive = 0.5f
+          Aggression = 0.0f
+          Extraversion = 0.5f
+          Honesty = 0.5f
+          Greed = 0.5f }
+
+    let private needs money hunger =
+        { Hunger = hunger
+          Energy = 100.0f
+          Social = 100.0f
+          Money = money }
+
+    let private inventory food = Map.ofList [ Food, food ]
+
+    let private npc id money hunger food memory personalityOverride =
+        { Id = NpcId id
+          Pos = { X = float32 (id * 10); Y = 0.0f }
+          Inventory = inventory food
+          Mind =
+            { Needs = needs money hunger
+              Personality = defaultArg personalityOverride personality
+              Action = Wander
+              Target = actionTarget Wander
+              ActionAge = 0L
+              EffectDone = false
+              HungerFlagged = false
+              Memory = memory } }
+
+    let world buyerMoney buyerHunger buyerFood sellerMoney sellerHunger sellerFood sellerMemory =
+        { Tick = 10L
+          Time = 0.0
+          Rng = Rng.ofSeed 7UL
+          Avatar = { Pos = { X = 0.0f; Y = 0.0f } }
+          NoHost = { Reserved = 0UL }
+          Npcs =
+            [| npc 0 buyerMoney buyerHunger buyerFood [] None
+               npc 1 sellerMoney sellerHunger sellerFood sellerMemory None |]
+          Events = [] }
+
+    let request quantity =
+        { Buyer = NpcId 0
+          Seller = NpcId 1
+          Item = Food
+          Quantity = quantity }
+
+    let withSellerGreed greed world =
+        let seller = world.Npcs.[1]
+        { world with
+            Npcs =
+                [| world.Npcs.[0]
+                   { seller with
+                       Mind =
+                         { seller.Mind with
+                             Personality = { seller.Mind.Personality with Greed = greed } } } |] }
+
+    let succeeded result =
+        match result with
+        | TradeSucceeded world -> world
+        | TradeRejected (failure, _) -> Assert.Fail($"expected success, got {failure}"); Unchecked.defaultof<World>
+
+[<TestClass>]
+type TradeTests () =
+
+    [<TestMethod>]
+    member _.SuccessfulTradeTransfersItemMoneyAndMemoryAtomically () =
+        let before = TradeHarness.world 50.0f 30.0f 0 10.0f 80.0f 3 []
+        let request = TradeHarness.request 2
+        let unitPrice = Sim.quotePrice request before |> Option.get
+        let after = Sim.trade request before |> TradeHarness.succeeded
+        let total = unitPrice * 2.0f
+
+        Assert.IsTrue(after.Npcs.[0].Inventory.[Food] = 2)
+        Assert.IsTrue(after.Npcs.[1].Inventory.[Food] = 1)
+        Assert.IsTrue(abs (after.Npcs.[0].Mind.Needs.Money - (50.0f - total)) < 1e-5f)
+        Assert.IsTrue(abs (after.Npcs.[1].Mind.Needs.Money - (10.0f + total)) < 1e-5f)
+        Assert.IsTrue(abs ((after.Npcs.[0].Mind.Needs.Money + after.Npcs.[1].Mind.Needs.Money) - 60.0f) < 1e-5f)
+        Assert.IsTrue(after.Npcs.[0].Mind.Memory |> List.exists (fun e ->
+            match e.Kind with
+            | Bought (NpcId seller, Food, quantity, price) -> seller = 1 && quantity = 2 && price = unitPrice
+            | _ -> false))
+        Assert.IsTrue(after.Npcs.[1].Mind.Memory |> List.exists (fun e ->
+            match e.Kind with
+            | Sold (NpcId buyer, Food, quantity, price) -> buyer = 0 && quantity = 2 && price = unitPrice
+            | _ -> false))
+        Assert.IsTrue(after.Events |> List.exists (fun event ->
+            match event.Kind with
+            | TradeEvent (NpcId buyer, NpcId seller, Food, quantity, price) ->
+                buyer = 0 && seller = 1 && quantity = 2 && price = unitPrice
+            | _ -> false))
+        Assert.IsTrue(before.Npcs.[0].Inventory.[Food] = 0, "trade must not mutate the input world")
+        Assert.IsTrue(before.Npcs.[1].Inventory.[Food] = 3, "trade must not mutate the input world")
+
+    [<TestMethod>]
+    member _.RejectedTradesLeaveWorldUnchanged () =
+        let before = TradeHarness.world 50.0f 30.0f 0 10.0f 80.0f 3 []
+        let cases =
+            [ TradeHarness.request 0, InvalidQuantity
+              TradeHarness.request 4, OutOfStock
+              { TradeHarness.request 1 with Seller = NpcId 0 }, SameParticipant
+              TradeHarness.request 1, InsufficientFunds ]
+        for request, expected in cases do
+            let candidate =
+                if expected = InsufficientFunds then
+                    TradeHarness.world 1.0f 30.0f 0 10.0f 80.0f 3 []
+                else before
+            match Sim.trade request candidate with
+            | TradeRejected (actual, unchanged) ->
+                if actual <> expected then Assert.Fail($"expected {expected}, got {actual}")
+                if unchanged <> candidate then Assert.Fail("rejected trade changed the world")
+            | TradeSucceeded _ -> Assert.Fail($"expected rejection {expected}")
+
+    [<TestMethod>]
+    member _.UnknownParticipantsAreRejectedWithoutChangingWorld () =
+        let before = TradeHarness.world 50.0f 30.0f 0 10.0f 80.0f 3 []
+        let missingBuyer = { TradeHarness.request 1 with Buyer = NpcId 9 }
+        let missingSeller = { TradeHarness.request 1 with Seller = NpcId 9 }
+        match Sim.trade missingBuyer before with
+        | TradeRejected (BuyerNotFound, unchanged) ->
+            if unchanged <> before then Assert.Fail("missing buyer changed the world")
+        | other -> Assert.Fail($"expected BuyerNotFound, got {other}")
+        match Sim.trade missingSeller before with
+        | TradeRejected (SellerNotFound, unchanged) ->
+            if unchanged <> before then Assert.Fail("missing seller changed the world")
+        | other -> Assert.Fail($"expected SellerNotFound, got {other}")
+
+    [<TestMethod>]
+    member _.QuoteIsDeterministicAndRespondsToNeedStockPersonalityAndRecentTrades () =
+        let request = TradeHarness.request 1
+        let baseWorld = TradeHarness.world 50.0f 100.0f 0 50.0f 100.0f 20 []
+        let urgentWorld = TradeHarness.world 50.0f 0.0f 0 50.0f 100.0f 20 []
+        let scarceWorld = TradeHarness.world 50.0f 100.0f 0 50.0f 100.0f 1 []
+        let greedySeller = TradeHarness.withSellerGreed 1.0f baseWorld
+        let recentMemory = [ { Tick = 9L; Kind = Sold(NpcId 0, Food, 1, 40.0f); Valence = 0.2f } ]
+        let recentWorld = TradeHarness.world 50.0f 100.0f 0 50.0f 100.0f 20 recentMemory
+        let p0 = Sim.quotePrice request baseWorld |> Option.get
+        let p1 = Sim.quotePrice request baseWorld |> Option.get
+        let urgent = Sim.quotePrice request urgentWorld |> Option.get
+        let scarce = Sim.quotePrice request scarceWorld |> Option.get
+        let greedy = Sim.quotePrice request greedySeller |> Option.get
+        let recent = Sim.quotePrice request recentWorld |> Option.get
+        if p0 <> p1 then Assert.Fail("same world and request must produce the same quote")
+        if urgent <= p0 then Assert.Fail("urgent buyer need must raise the quote")
+        if scarce <= p0 then Assert.Fail("scarce seller stock must raise the quote")
+        if greedy <= p0 then Assert.Fail("seller greed must affect the quote")
+        if recent <= p0 then Assert.Fail("recent transaction prices must affect the quote")