feat(m4b): 增加可追踪谣言传播与回放

[变更性质]
- 本提交新增 M4b 谣言传播与确定性验收能力，不是单纯缺陷修复。

[新增功能]
- 支持带来源、父节点、深度、强度和路径的谣言传播、去重、衰减与过期处理。
- Headless 支持稳定谣言 dump、replay，以及与 batch 模式的互斥校验。

[实现方案]
- 通过不可变 World 更新和失败原子返回保持模拟确定性。
- 新增多跳传播、重复转述、过期父节点、非法参与者和稳定 trace 测试。

[影响范围]
- 影响 Kernel、Headless 和 Kernel 测试；不包含 M5/M6 或无关配置与文档改动。

5 files changed, 187 insertions, 3 deletions

diff --git a/src/LivingVillage.Kernel.Tests/DeterminismTests.fs b/src/LivingVillage.Kernel.Tests/DeterminismTests.fs
index c37be67..cc1944f 100644
--- a/src/LivingVillage.Kernel.Tests/DeterminismTests.fs
+++ b/src/LivingVillage.Kernel.Tests/DeterminismTests.fs
@@ -234,6 +234,7 @@ type DeterminismTests () =
                     | Pay -> 0.2f
                     | Hungry -> -0.4f
                     | Chatted _ -> Sim.chatValence
+                    | Rumor _ -> 0.1f
                     | Bought _ -> 0.3f
                     | Sold _ -> 0.3f
                 if e.Valence <> expected then
diff --git a/src/LivingVillage.Kernel.Tests/LivingVillage.Kernel.Tests.fsproj b/src/LivingVillage.Kernel.Tests/LivingVillage.Kernel.Tests.fsproj
index d805d73..f65200b 100644
--- a/src/LivingVillage.Kernel.Tests/LivingVillage.Kernel.Tests.fsproj
+++ b/src/LivingVillage.Kernel.Tests/LivingVillage.Kernel.Tests.fsproj
@@ -8,6 +8,7 @@
   <ItemGroup>
     <Compile Include="DeterminismTests.fs" />
     <Compile Include="RelationTests.fs" />
+    <Compile Include="RumorTests.fs" />
     <Compile Include="TradeTests.fs" />
   </ItemGroup>
 
diff --git a/src/LivingVillage.Kernel.Tests/RelationTests.fs b/src/LivingVillage.Kernel.Tests/RelationTests.fs
index dc433a7..20331ce 100644
--- a/src/LivingVillage.Kernel.Tests/RelationTests.fs
+++ b/src/LivingVillage.Kernel.Tests/RelationTests.fs
@@ -35,7 +35,8 @@ module RelationHarness =
           Avatar = { Pos = { X = 0.0f; Y = 0.0f } }
           NoHost = { Reserved = 0UL }
           Npcs = [| mkNpc 0 mem0; mkNpc 1 mem1 |]
-          Events = [] }
+          Events = []
+          Rumors = [] }
 
     let chatted (tick: int64) (partner: int) : MemoryEvent =
         { Tick = tick; Kind = Chatted(NpcId partner); Valence = Sim.chatValence }
@@ -184,7 +185,8 @@ type RelationTests () =
               Avatar = { Pos = plaza }
               NoHost = { Reserved = 0UL }
               Npcs = [| self; nearest; alternate |]
-              Events = [] }
+              Events = []
+              Rumors = [] }
         let next = Sim.step RelationHarness.zeroInput world
         match List.tryHead next.Npcs.[0].Mind.Memory with
         | Some entry ->
diff --git a/src/LivingVillage.Kernel.Tests/RumorTests.fs b/src/LivingVillage.Kernel.Tests/RumorTests.fs
new file mode 100644
index 0000000..3c9b267
--- /dev/null
+++ b/src/LivingVillage.Kernel.Tests/RumorTests.fs
@@ -0,0 +1,179 @@
+namespace LivingVillage.Kernel.Tests
+
+open Microsoft.VisualStudio.TestTools.UnitTesting
+open LivingVillage.Kernel
+open LivingVillage.Kernel.Sim
+
+module private RumorHarness =
+
+    let private needs =
+        { Hunger = 100.0f
+          Energy = 100.0f
+          Social = 100.0f
+          Money = 50.0f }
+
+    let private personality =
+        { Drive = 0.5f
+          Aggression = 0.0f
+          Extraversion = 0.8f
+          Honesty = 0.5f
+          Greed = 0.5f }
+
+    let private npc id =
+        { Id = NpcId id
+          Pos = { X = float32 (id * 10); Y = 0.0f }
+          Inventory = Map.empty
+          Mind =
+            { Needs = needs
+              Personality = personality
+              Action = Wander
+              Target = actionTarget Wander
+              ActionAge = minActionTicks
+              EffectDone = true
+              HungerFlagged = false
+              Memory = [] } }
+
+    let world tick count =
+        { Tick = tick
+          Time = float tick * dtSeconds
+          Rng = Rng.ofSeed 11UL
+          Avatar = { Pos = { X = 0.0f; Y = 0.0f } }
+          NoHost = { Reserved = 0UL }
+          Npcs = Array.init count npc
+          Events = []
+          Rumors = [] }
+
+    let readyForChat (world: World) : World =
+        { world with
+            Npcs =
+                world.Npcs
+                |> Array.map (fun npc ->
+                    { npc with
+                        Mind =
+                            { npc.Mind with
+                                Action = Wander
+                                Target = actionTarget Wander
+                                ActionAge = minActionTicks
+                                EffectDone = true } }) }
+
+    let chat narrator receiver world =
+        match Sim.chat { Narrator = NpcId narrator; Receiver = NpcId receiver } world with
+        | ChatSucceeded (_, next) -> next
+        | ChatRejected (failure, _) -> Assert.Fail($"chat rejected: {failure}"); Unchecked.defaultof<World>
+
+    let rumorId (RumorId id) = id
+
+    let orderedRumors (world: World) =
+        world.Rumors |> List.sortBy (fun rumor -> rumorId rumor.Id)
+
+    let traceText (world: World) =
+        orderedRumors world
+        |> List.map (fun rumor ->
+            let parent = rumor.Parent |> Option.map rumorId |> Option.map string |> Option.defaultValue "-"
+            sprintf "%d|%d|%d|%d|%d|%s|%d"
+                (rumorId rumor.Id)
+                rumor.Tick
+                (match rumor.Source with NpcId id -> id)
+                (match rumor.Narrator with NpcId id -> id)
+                (match rumor.Receiver with NpcId id -> id)
+                parent
+                rumor.Depth)
+        |> String.concat "\n"
+
+[<TestClass>]
+type RumorTests () =
+
+    [<TestMethod>]
+    member _.IdleChatsCreateThreeHopTraceableRumorPathWithinTwoDays () =
+        let initial = RumorHarness.world 0L 4
+        let first = RumorHarness.chat 0 1 initial
+        let second = RumorHarness.chat 1 2 (RumorHarness.readyForChat { first with Tick = ticksPerDay })
+        let third = RumorHarness.chat 2 3 (RumorHarness.readyForChat { second with Tick = 2L * ticksPerDay })
+        let ordered = RumorHarness.orderedRumors third
+
+        Assert.AreEqual<int>(3, third.Rumors.Length)
+        Assert.AreEqual<int>(3, ordered.Length)
+        let root = ordered.[0]
+        let retelling = ordered.[1]
+        let final = ordered.[2]
+        Assert.AreEqual<NpcId>(NpcId 0, root.Source)
+        Assert.AreEqual<NpcId>(NpcId 0, root.Narrator)
+        Assert.AreEqual<NpcId>(NpcId 1, root.Receiver)
+        Assert.IsTrue(root.Parent.IsNone)
+        Assert.AreEqual<int>(0, root.Depth)
+        Assert.AreEqual<RumorId>(root.Id, retelling.Parent |> Option.get)
+        Assert.AreEqual<NpcId>(root.Source, retelling.Source)
+        Assert.AreEqual<NpcId>(NpcId 1, retelling.Narrator)
+        Assert.AreEqual<NpcId>(NpcId 2, retelling.Receiver)
+        Assert.AreEqual<int>(1, retelling.Depth)
+        Assert.AreEqual<RumorId>(retelling.Id, final.Parent |> Option.get)
+        Assert.AreEqual<NpcId>(NpcId 2, final.Narrator)
+        Assert.AreEqual<NpcId>(NpcId 3, final.Receiver)
+        Assert.AreEqual<int>(2, final.Depth)
+
+        let path = Sim.rumorPath third final.Id
+        CollectionAssert.AreEqual([| root; retelling; final |], List.toArray path)
+
+    [<TestMethod>]
+    member _.DuplicateRetellingDoesNotCreateAnotherRumorNode () =
+        let first = RumorHarness.chat 0 1 (RumorHarness.world 0L 3)
+        let second = RumorHarness.chat 1 2 (RumorHarness.readyForChat first)
+        let duplicate = RumorHarness.chat 1 2 (RumorHarness.readyForChat second)
+
+        Assert.AreEqual<int>(2, second.Rumors.Length)
+        Assert.AreEqual<int>(2, duplicate.Rumors.Length)
+        Assert.AreEqual<string>(RumorHarness.traceText second, RumorHarness.traceText duplicate)
+
+    [<TestMethod>]
+    member _.StaleRumorIsNotUsedAsParentForAReTelling () =
+        let first = RumorHarness.chat 0 1 (RumorHarness.world 0L 3)
+        let stale =
+            first
+            |> RumorHarness.readyForChat
+            |> fun world -> { world with Tick = rumorFreshnessTicks + 1L }
+        let next = RumorHarness.chat 1 2 stale
+        let latest = RumorHarness.orderedRumors next |> List.last
+
+        Assert.IsTrue(latest.Parent.IsNone, "stale memory must not be reused as a parent")
+        Assert.IsTrue(latest.Source = NpcId 1, "a stale rumor starts a new local source")
+        Assert.IsTrue(Sim.rumorStrengthAt next.Tick (RumorHarness.orderedRumors next |> List.head) < rumorMinimumStrength)
+
+    [<TestMethod>]
+    member _.InvalidParticipantsLeaveWorldUnchanged () =
+        let before = RumorHarness.world 10L 2
+        let requests =
+            [ { Narrator = NpcId 9; Receiver = NpcId 1 }
+              { Narrator = NpcId 0; Receiver = NpcId 9 }
+              { Narrator = NpcId 0; Receiver = NpcId 0 } ]
+
+        for request in requests do
+            match Sim.chat request before with
+            | ChatRejected (_, unchanged) -> Assert.AreEqual<World>(before, unchanged)
+            | ChatSucceeded _ -> Assert.Fail($"expected invalid chat to be rejected: {request}")
+
+    [<TestMethod>]
+    member _.SameSeedAndChatOperationsProduceIdenticalRumorTrace () =
+        let run seed =
+            let initial = { RumorHarness.world 0L 4 with Rng = Rng.ofSeed seed }
+            let first = RumorHarness.chat 0 1 initial
+            let second = RumorHarness.chat 1 2 (RumorHarness.readyForChat { first with Tick = ticksPerDay })
+            let third = RumorHarness.chat 2 3 (RumorHarness.readyForChat { second with Tick = 2L * ticksPerDay })
+            RumorHarness.traceText third
+
+        Assert.AreEqual<string>(run 4242UL, run 4242UL)
+
+    [<TestMethod>]
+    member _.RumorTraceTextContainsStableMetadataAndReplayablePaths () =
+        let initial = RumorHarness.world 0L 4
+        let first = RumorHarness.chat 0 1 initial
+        let second = RumorHarness.chat 1 2 (RumorHarness.readyForChat { first with Tick = ticksPerDay })
+        let third = RumorHarness.chat 2 3 (RumorHarness.readyForChat { second with Tick = 2L * ticksPerDay })
+
+        let expected =
+            String.concat "\n"
+                [ sprintf "rumor_trace tick=%d count=3" (2L * ticksPerDay)
+                  "rumor id=0 tick=0 origin_tick=0 source=0 narrator=0 receiver=1 parent=- depth=0 strength=1.000000 path=0"
+                  sprintf "rumor id=1 tick=%d origin_tick=0 source=0 narrator=1 receiver=2 parent=0 depth=1 strength=0.500000 path=0,1" ticksPerDay
+                  sprintf "rumor id=2 tick=%d origin_tick=0 source=0 narrator=2 receiver=3 parent=1 depth=2 strength=0.250000 path=0,1,2" (2L * ticksPerDay) ]
+
+        Assert.AreEqual<string>(expected, Sim.rumorTraceText third)
diff --git a/src/LivingVillage.Kernel.Tests/TradeTests.fs b/src/LivingVillage.Kernel.Tests/TradeTests.fs
index c7c8ef4..5a0e724 100644
--- a/src/LivingVillage.Kernel.Tests/TradeTests.fs
+++ b/src/LivingVillage.Kernel.Tests/TradeTests.fs
@@ -44,7 +44,8 @@ module private TradeHarness =
           Npcs =
             [| npc 0 buyerMoney buyerHunger buyerFood [] None
                npc 1 sellerMoney sellerHunger sellerFood sellerMemory None |]
-          Events = [] }
+          Events = []
+          Rumors = [] }
 
     let request quantity =
         { Buyer = NpcId 0