feat(kernel): P31 step2 story stage state machine

- Occupation.Story: three-segment arc per occupation (accept task -> visit
  households -> conclude), driven one stage per player dialogue with day
  gates derived from the same splitmix pattern as the daily task pool
  (start day = hash(seed ^ storySeed, day 0) mod 3 + 2, range [2,4]).
- relationMeanToPlayer: decayed valence mean over acquainted NPCs only
  (same decay formula as Sim.relationMatrix); no acquaintances = 0.
- Three endings (warm/plain/distant) chosen by deterministic thresholds
  (>=0.3 / >=0.0 / <0); ending text is fixed at the concluding dialogue.
- onDialogue returns (state, summary text option) for the caller to write
  into the yearbook; StoryStage itself is unchanged (0..3) and already
  roundtrips through the existing v3 occupation segment.
- 14 new kernel tests (101 -> 115); performance digest unchanged.

3 files changed, 334 insertions, 0 deletions

diff --git a/src/LivingVillage.Kernel.Tests/LivingVillage.Kernel.Tests.fsproj b/src/LivingVillage.Kernel.Tests/LivingVillage.Kernel.Tests.fsproj
index 6924012..1a36ea7 100644
--- a/src/LivingVillage.Kernel.Tests/LivingVillage.Kernel.Tests.fsproj
+++ b/src/LivingVillage.Kernel.Tests/LivingVillage.Kernel.Tests.fsproj
@@ -15,6 +15,7 @@
     <Compile Include="DailyTaskTests.fs" />
     <Compile Include="TradeBiasTests.fs" />
     <Compile Include="OccupationBiasTests.fs" />
+    <Compile Include="OccupationStoryTests.fs" />
     <Compile Include="PerformanceTests.fs" />
   </ItemGroup>
 
diff --git a/src/LivingVillage.Kernel.Tests/OccupationStoryTests.fs b/src/LivingVillage.Kernel.Tests/OccupationStoryTests.fs
new file mode 100644
index 0000000..80bc9a4
--- /dev/null
+++ b/src/LivingVillage.Kernel.Tests/OccupationStoryTests.fs
@@ -0,0 +1,230 @@
+namespace LivingVillage.Kernel.Tests
+
+open Microsoft.VisualStudio.TestTools.UnitTesting
+open LivingVillage.Kernel
+open LivingVillage.Kernel.Sim
+
+module private StoryHarness =
+
+    let seed = 42UL
+
+    let worldAtTick (tick: int64) : World =
+        { Sim.initialWorldN 4UL 4 with Tick = tick; Time = float tick * Sim.dtSeconds }
+
+    let stateOf (kind: Occupation.Kind) (stage: int) : Occupation.State =
+        { Occupation.stateOf kind with StoryStage = stage }
+
+    let dayTick (day: int64) : int64 = day * Sim.ticksPerDay
+
+    let withMemory (valence: float32) (tick: int64) (world: World) : World =
+        { world with
+            Npcs =
+                world.Npcs
+                |> Array.mapi (fun index npc ->
+                    if index = 0 then
+                        { npc with
+                            Mind =
+                                { npc.Mind with
+                                    Memory =
+                                        [ { Tick = tick; Kind = Chatted(Sim.playerId); Valence = valence } ] } }
+                    else npc) }
+
+[<TestClass>]
+type OccupationStoryTests () =
+
+    // ---- 命名：四条轻剧情线 + 四段进度 ----
+
+    [<TestMethod>]
+    member _.EachOccupationHasItsOwnStoryLineName () =
+        Assert.AreEqual<string>("雨水与年成", Occupation.Story.lineNameOf Occupation.Farmer)
+        Assert.AreEqual<string>("水位与收成", Occupation.Story.lineNameOf Occupation.Fisher)
+        Assert.AreEqual<string>("新货的路子", Occupation.Story.lineNameOf Occupation.Peddler)
+        Assert.AreEqual<string>("庙前的争论", Occupation.Story.lineNameOf Occupation.Scholar)
+
+    [<TestMethod>]
+    member _.StageNamesCoverTheThreeSegmentArc () =
+        Assert.AreEqual<string>("未开始", Occupation.Story.stageNameOf 0)
+        Assert.AreEqual<string>("已接任务", Occupation.Story.stageNameOf 1)
+        Assert.AreEqual<string>("走访中", Occupation.Story.stageNameOf 2)
+        Assert.AreEqual<string>("已收束", Occupation.Story.stageNameOf 3)
+
+    // ---- 开线日：hash(seed ^ storySeed) mod 3 + 2，纯函数、确定性 ----
+
+    [<TestMethod>]
+    member _.StartDayIsDeterministicAndInsideTwoToFour () =
+        for kind in Occupation.all do
+            for seed in [ 42UL; 7UL; 4242UL; 999UL ] do
+                let first = Occupation.Story.startDayOf seed kind
+                let second = Occupation.Story.startDayOf seed kind
+                Assert.AreEqual<int64>(first, second)
+                Assert.IsTrue(2L <= first && first <= 4L, $"{kind} start day {first} out of range")
+
+    [<TestMethod>]
+    member _.StorySeedsDifferFromDailyOccupationSeeds () =
+        // 开线日与每日任务抽取互不串线（种子常量两两不同）
+        let storySeeds = Occupation.all |> List.map Occupation.Story.storySeedOf
+        let taskSeeds = Occupation.all |> List.map Occupation.occupationSeedOf
+        Assert.AreEqual<int>(storySeeds.Length, storySeeds |> Set.ofList |> Set.count)
+        for story in storySeeds do
+            Assert.IsFalse(taskSeeds |> List.contains story, "story seed must not collide with a task seed")
+
+    // ---- 推进门控：开线日前的对话不动剧情线 ----
+
+    [<TestMethod>]
+    member _.DialogueBeforeStartDayDoesNotAdvanceTheStory () =
+        for kind in Occupation.all do
+            let state = StoryHarness.stateOf kind 0
+            let world = StoryHarness.worldAtTick (StoryHarness.dayTick 1L)
+            let nextState, summary = Occupation.Story.onDialogue StoryHarness.seed state world
+            Assert.AreEqual<int>(0, nextState.StoryStage)
+            Assert.AreEqual<string option>(None, summary)
+
+    // ---- 三段式推进：接任务 → 走访 → 收束，逐段一对话 ----
+
+    [<TestMethod>]
+    member _.StoryAdvancesOneStagePerDialogueAcrossThreeDays () =
+        for kind in Occupation.all do
+            let startDay = Occupation.Story.startDayOf StoryHarness.seed kind
+            let mutable state = StoryHarness.stateOf kind 0
+            let mutable summaries = []
+            for offset in 0L .. 2L do
+                let world = StoryHarness.worldAtTick (StoryHarness.dayTick (startDay + offset))
+                let nextState, summary = Occupation.Story.onDialogue StoryHarness.seed state world
+                state <- nextState
+                summaries <- summary :: summaries
+            Assert.AreEqual<int>(3, state.StoryStage)
+            Assert.AreEqual<int>(3, summaries.Length)
+            Assert.AreEqual<string option>(Some "走访了几户人家，改日再问。", summaries |> List.rev |> List.item 1)
+            Assert.IsTrue(
+                summaries
+                |> List.choose id
+                |> List.exists (fun text -> text.Contains("有了结果")),
+                "the third dialogue must conclude the line")
+            // 终态后不再推进
+            let world = StoryHarness.worldAtTick (StoryHarness.dayTick (startDay + 3L))
+            let nextState, summary = Occupation.Story.onDialogue StoryHarness.seed state world
+            Assert.AreEqual<int>(3, nextState.StoryStage)
+            Assert.AreEqual<string option>(None, summary)
+
+    [<TestMethod>]
+    member _.LateFirstDialogueStillAdvancesOneStageAtATime () =
+        let kind = Occupation.Fisher
+        let startDay = Occupation.Story.startDayOf StoryHarness.seed kind
+        let state = StoryHarness.stateOf kind 0
+        let world = StoryHarness.worldAtTick (StoryHarness.dayTick (startDay + 5L))
+        let stage1, summary1 = Occupation.Story.onDialogue StoryHarness.seed state world
+        Assert.AreEqual<int>(1, stage1.StoryStage)
+        Assert.IsTrue(summary1.IsSome)
+        let stage2, _ = Occupation.Story.onDialogue StoryHarness.seed stage1 world
+        Assert.AreEqual<int>(2, stage2.StoryStage)
+        let stage3, summary3 = Occupation.Story.onDialogue StoryHarness.seed stage2 world
+        Assert.AreEqual<int>(3, stage3.StoryStage)
+        Assert.IsTrue(summary3.Value.Contains("有了结果"))
+
+    // ---- 关系均值：与 relationMatrix 同口径的衰减 valence，仅计认识玩家的人 ----
+
+    [<TestMethod>]
+    member _.RelationMeanAveragesOnlyAcquaintedNpcs () =
+        let baseWorld = StoryHarness.worldAtTick 0L
+        // 单个熟识村民：Helpful 口径 0.5
+        let friendly = baseWorld |> StoryHarness.withMemory 0.5f 0L
+        Assert.AreEqual(0.5f, Occupation.Story.relationMeanToPlayer friendly, 1e-5f)
+        // 无记忆 = 0（中性，不取负）
+        Assert.AreEqual(0.0f, Occupation.Story.relationMeanToPlayer baseWorld, 1e-5f)
+        // 两名熟识村民（0.5 与 -0.4）均值 0.05
+        let mixed =
+            { friendly with
+                Npcs =
+                    friendly.Npcs
+                    |> Array.mapi (fun index npc ->
+                        if index = 1 then
+                            { npc with
+                                Mind = { npc.Mind with Memory = [ { Tick = 0L; Kind = Chatted(Sim.playerId); Valence = -0.4f } ] } }
+                        else npc) }
+        Assert.AreEqual(0.05f, Occupation.Story.relationMeanToPlayer mixed, 1e-5f)
+
+    [<TestMethod>]
+    member _.RelationMeanDecaysWithTheRelationHalfLife () =
+        let baseWorld = StoryHarness.worldAtTick Sim.ticksPerDay
+        let decayed = baseWorld |> StoryHarness.withMemory 0.5f 0L
+        // 半衰期 = 1 模拟日：一天后 0.5 → 0.25
+        Assert.AreEqual(0.25f, Occupation.Story.relationMeanToPlayer decayed, 1e-5f)
+
+    [<TestMethod>]
+    member _.DialogueMemoriesCountTowardTheRelationMean () =
+        let baseWorld = StoryHarness.worldAtTick 0L
+        let dialogued =
+            { baseWorld with
+                Npcs =
+                    baseWorld.Npcs
+                    |> Array.mapi (fun index npc ->
+                        if index = 0 then
+                            { npc with
+                                Mind =
+                                    { npc.Mind with
+                                        Memory =
+                                            [ { Tick = 0L
+                                                Kind = Dialogue(Sim.playerId, SmallTalk, Friendly)
+                                                Valence = 0.4f } ] } }
+                        else npc) }
+        Assert.AreEqual(0.4f, Occupation.Story.relationMeanToPlayer dialogued, 1e-5f)
+
+    // ---- 三种结局：由当时关系均值确定性决定（三方对照）----
+
+    [<TestMethod>]
+    member _.EndingThresholdsSeparateThreeOutcomes () =
+        Assert.AreEqual<Occupation.Story.Ending>(Occupation.Story.Warm, Occupation.Story.endingOf 0.5f)
+        Assert.AreEqual<Occupation.Story.Ending>(Occupation.Story.Warm, Occupation.Story.endingOf 0.3f)
+        Assert.AreEqual<Occupation.Story.Ending>(Occupation.Story.Plain, Occupation.Story.endingOf 0.1f)
+        Assert.AreEqual<Occupation.Story.Ending>(Occupation.Story.Plain, Occupation.Story.endingOf 0.0f)
+        Assert.AreEqual<Occupation.Story.Ending>(Occupation.Story.Distant, Occupation.Story.endingOf -0.1f)
+
+    [<TestMethod>]
+    member _.EachOccupationHasThreeDistinctEndingTexts () =
+        for kind in Occupation.all do
+            let warm = Occupation.Story.endingTextOf kind Occupation.Story.Warm
+            let plain = Occupation.Story.endingTextOf kind Occupation.Story.Plain
+            let distant = Occupation.Story.endingTextOf kind Occupation.Story.Distant
+            Assert.AreNotEqual(warm, plain, $"{kind} warm/plain must differ")
+            Assert.AreNotEqual(plain, distant, $"{kind} plain/distant must differ")
+            Assert.AreNotEqual(warm, distant, $"{kind} warm/distant must differ")
+            Assert.IsTrue(warm.Contains(Occupation.Story.lineNameOf kind))
+            // 两次调用逐字节一致
+            Assert.AreEqual<string>(warm, Occupation.Story.endingTextOf kind Occupation.Story.Warm)
+
+    [<TestMethod>]
+    member _.ConcludingStageWritesTheEndingDeterminedByTheRelationMean () =
+        for kind in Occupation.all do
+            let startDay = Occupation.Story.startDayOf StoryHarness.seed kind
+            let conclusionTick = StoryHarness.dayTick (startDay + 2L)
+            // 热络结局：收束当天熟识村民 Helpful 口径 0.5
+            let warmWorld =
+                StoryHarness.worldAtTick conclusionTick
+                |> StoryHarness.withMemory 0.5f conclusionTick
+            let state2 = StoryHarness.stateOf kind 2
+            let warmState, warmSummary = Occupation.Story.onDialogue StoryHarness.seed state2 warmWorld
+            Assert.AreEqual<int>(3, warmState.StoryStage)
+            Assert.AreEqual<string>(Occupation.Story.endingTextOf kind Occupation.Story.Warm, warmSummary.Value)
+            // 淡漠结局：收束当天熟识村民 Offended 口径 -0.4
+            let distantWorld =
+                StoryHarness.worldAtTick conclusionTick
+                |> StoryHarness.withMemory -0.4f conclusionTick
+            let distantState, distantSummary = Occupation.Story.onDialogue StoryHarness.seed state2 distantWorld
+            Assert.AreEqual<int>(3, distantState.StoryStage)
+            Assert.AreEqual<string>(Occupation.Story.endingTextOf kind Occupation.Story.Distant, distantSummary.Value)
+            // 平常结局：无关系记忆 → 均值 0
+            let plainWorld = StoryHarness.worldAtTick conclusionTick
+            let plainState, plainSummary = Occupation.Story.onDialogue StoryHarness.seed state2 plainWorld
+            Assert.AreEqual<int>(3, plainState.StoryStage)
+            Assert.AreEqual<string>(Occupation.Story.endingTextOf kind Occupation.Story.Plain, plainSummary.Value)
+
+    [<TestMethod>]
+    member _.OnDialogueIsDeterministicForTheSameInputs () =
+        let kind = Occupation.Fisher
+        let startDay = Occupation.Story.startDayOf StoryHarness.seed kind
+        let world = StoryHarness.worldAtTick (StoryHarness.dayTick startDay) |> StoryHarness.withMemory 0.5f 0L
+        let state = StoryHarness.stateOf kind 0
+        let firstState, firstSummary = Occupation.Story.onDialogue StoryHarness.seed state world
+        let secondState, secondSummary = Occupation.Story.onDialogue StoryHarness.seed state world
+        Assert.AreEqual<Occupation.State>(firstState, secondState)
+        Assert.AreEqual<string option>(firstSummary, secondSummary)
diff --git a/src/LivingVillage.Kernel/Occupation.fs b/src/LivingVillage.Kernel/Occupation.fs
index 8ce5060..00cd2e9 100644
--- a/src/LivingVillage.Kernel/Occupation.fs
+++ b/src/LivingVillage.Kernel/Occupation.fs
@@ -272,3 +272,106 @@ module Occupation =
         match kind with
         | None -> baseResponse
         | Some kind -> remapResponse kind intent baseResponse
+
+    // ---- 轻剧情线（design §5 / P-d）：三段式 接任务 → 走访 → 收束 ----
+    // 纯年鉴/对话驱动：每次玩家对话至多推进一段，产出只有（StoryStage 推进 + 年鉴摘要文本），
+    // 由调用方写入世界。全部输入 = (seed, 世界 tick, 关系状态, 职业状态)，纯函数、确定性。
+    // 开线日沿用每日任务的 (seed, profession, day) splitmix 哈希模式。
+    module Story =
+
+        type Ending =
+            | Warm
+            | Plain
+            | Distant
+
+        /// 剧情线种子：与每日任务种子同源异值，两两不撞（见测试）。
+        let storySeedOf (kind: Kind) : uint64 =
+            match kind with
+            | Farmer -> 0x5555555555555555UL
+            | Fisher -> 0x6666666666666666UL
+            | Peddler -> 0x7777777777777777UL
+            | Scholar -> 0x8888888888888888UL
+
+        let lineNameOf (kind: Kind) : string =
+            match kind with
+            | Farmer -> "雨水与年成"
+            | Fisher -> "水位与收成"
+            | Peddler -> "新货的路子"
+            | Scholar -> "庙前的争论"
+
+        /// StoryStage 语义：0 未开始 / 1 已接任务 / 2 走访中 / 3 已收束。
+        let stageNameOf (stage: int) : string =
+            match stage with
+            | 1 -> "已接任务"
+            | 2 -> "走访中"
+            | 3 -> "已收束"
+            | _ -> "未开始"
+
+        /// 开线日 = hash(seed ^ storySeed, day 0) mod 3 + 2，落在 [2, 4]。
+        let startDayOf (seed: uint64) (kind: Kind) : int64 =
+            (int64 (taskHash seed (storySeedOf kind) 0L % 3UL)) + 2L
+
+        /// 玩家与村民的关系均值：与 Sim.relationMatrix 同口径（衰减 valence），
+        /// 但只统计认识玩家的村民（有 Chatted/Dialogue 记忆者），无一认识 = 0（中性）。
+        let relationMeanToPlayer (world: Sim.World) : float32 =
+            let player = Sim.playerId
+            let mutable total = 0.0f
+            let mutable known = 0
+            for npc in world.Npcs do
+                let mutable valence = 0.0f
+                let mutable touched = false
+                for e in npc.Mind.Memory do
+                    if e.Tick <= world.Tick then
+                        let involvesPlayer =
+                            match e.Kind with
+                            | Sim.Chatted partner -> partner = player
+                            | Sim.Dialogue (actor, _, _) -> actor = player
+                            | _ -> false
+                        if involvesPlayer then
+                            touched <- true
+                            valence <- valence + e.Valence * Sim.relationDecayWeight world.Tick e.Tick
+                if touched then
+                    known <- known + 1
+                    total <- total + valence
+            if known = 0 then 0.0f else total / float32 known
+
+        /// 结局分档：均值 ≥ 0.3 热络；[0, 0.3) 平常；< 0 淡漠。纯阈值，无随机。
+        let endingOf (mean: float32) : Ending =
+            if mean >= 0.3f then Warm
+            elif mean >= 0.0f then Plain
+            else Distant
+
+        let endingTextOf (kind: Kind) (ending: Ending) : string =
+            match kind, ending with
+            | Farmer, Warm -> "雨水与年成有了结果：乡邻都说雨水匀，今年差不了。"
+            | Farmer, Plain -> "雨水与年成有了结果：雨水尚可，年成将就，照旧耕作。"
+            | Farmer, Distant -> "雨水与年成有了结果：问不出准信，年成只能看天。"
+            | Fisher, Warm -> "水位与收成有了结果：乡邻说得真切，水位稳了，收成坏不了。"
+            | Fisher, Plain -> "水位与收成有了结果：众说平常，水位尚可，收成将就。"
+            | Fisher, Distant -> "水位与收成有了结果：问了几家都淡淡的，水情还得自己看。"
+            | Peddler, Warm -> "新货的路子有了结果：乡邻热心指路，新货不愁卖。"
+            | Peddler, Plain -> "新货的路子有了结果：说法平常，先小量试卖。"
+            | Peddler, Distant -> "新货的路子有了结果：各家都淡淡的，路子还得自己闯。"
+            | Scholar, Warm -> "庙前的争论有了结果：各说各理，事有分晓。"
+            | Scholar, Plain -> "庙前的争论有了结果：众说纷纭，暂无定论。"
+            | Scholar, Distant -> "庙前的争论有了结果：无人理会，先记在册上。"
+
+        /// 用一次玩家对话推进剧情线：同输入两次结果一致。
+        /// 返回（新状态, 应写入年鉴的摘要文本 option）；无门控命中时原样返回。
+        /// 结局文本在收束瞬间按当时关系均值定格，由调用方连同世界存档（年鉴快照）持久化。
+        let onDialogue (seed: uint64) (state: State) (world: Sim.World) : State * string option =
+            let kind = state.Profile.Kind
+            let day = dayIndexOf world.Tick
+            let startDay = startDayOf seed kind
+            match state.StoryStage with
+            | 0 when day >= startDay ->
+                { state with StoryStage = 1 },
+                Some (sprintf "接了件事：%s，得去村里多问问。" (lineNameOf kind))
+            | 1 when day >= startDay + 1L ->
+                { state with StoryStage = 2 },
+                Some "走访了几户人家，改日再问。"
+            | 2 when day >= startDay + 2L ->
+                let ending = endingOf (relationMeanToPlayer world)
+                { state with StoryStage = 3 },
+                Some (endingTextOf kind ending)
+            | _ -> state, None