perf(kernel): P27 第一步 — Rumor 长跑基准与修复前量化

新增 Kernel 层 Rumor 长跑基准（RumorBench.fs + headless --rumor-bench
[days npcs chats_per_day]），把「聊天→生成/追溯谣言」路径从 Sim.step 的 NPC
快照分配解耦，隔离测量谣言工作集随世界年龄的分配/耗时；同 Config 的
retained_id_checksum 证明确定性。

复核 M3-1 前提：World.Rumors 已被 M6a（d94ec2d/cc850bf）按 3 天保留窗口收敛，
单日成本平稳（1/5/10 天 ≈18.7/18.1/19.8s、≈19GB/天），超线性项消失。
剩余 Rumor 成本 = 每次聊天的两条 O(N) 扫描 latestRumorFor/rumorIsDuplicate，
且 [<Struct>] NpcId/RumorId 用 = 比较会逐条装箱（Sim.chat 单独测得 N=16000
时 393,736 B/次、随 N 线性）。

修复前基准（30 NPC，--rumor-bench D 30 2000）：
 3d  chat_calls=6000   retained=6000  alloc=930,716,456   ms=1626.7
 30d chat_calls=60000  retained=8000  alloc=13,419,045,864 ms=12182.5
 60d chat_calls=120000 retained=8000  alloc=27,297,668,608 ms=23769.7
（60d 工作集稳定 8000，不随年龄增长。）

docs/维护说明.md 新增 P27 小节记录上述现状与量级。不改任何模拟语义。

4 files changed, 160 insertions, 1 deletions

diff --git a/docs/维护说明.md b/docs/维护说明.md
index cc3a698..7be174a 100644
--- a/docs/维护说明.md
+++ b/docs/维护说明.md
@@ -459,6 +459,31 @@ dotnet src/LivingVillage.Headless/bin/Release/net8.0/LivingVillage.Headless.dll
   各出一格，相邻民居极近时挑檐可能视觉叠压，可在布点时加 1 格间隔；③ 巡游 40s 档的 `visible>=8`
   占比仅 13%（P25 150s 档为 74%），属取证时长差异，非可见性回归。
 
+## P27：Rumor 长局性能修复（工作集扫描去装箱 + 裁剪判定）
+
+- **现状复核（更正 M3-1 前提）**：M3-1 记录的「`World.Rumors` 不裁剪、逐次聊天全表扫描」已由 M6a
+  （`d94ec2d` 工作集容量上界+按天淘汰、`cc850bf` 窗口化早停扫描）修复：`RumorEvent.DayIndex` 派生字段
+  + `trimRumors` 把工作集按「最新在前 + 3 天保留窗口」收敛。实测单日成本已平稳（本机 `--cost-probe`：
+  1 天 18.7s/18.9GB、5 天 90.5s/95.7GB、10 天 198.2s/191.9GB，≈19GB/天常数），M3 记录的 20 天
+  ≈45 s/天的超线性项已消失。故 P27 不采用「砍 depth/strength 传播」这类会改变模拟语义的方案。
+- **剩余 Rumor 成本定位**：工作集有界后每次聊天仍有两条 O(N) 扫描 `latestRumorFor` / `rumorIsDuplicate`；
+  且此前用 `=` 比较 `[<Struct>]` 的 `NpcId`/`RumorId`，会走泛型结构相等，对每一条被扫描到的谣言
+  装箱（实测 ≈24 B/条、单次聊天随 N 线性增长——`Sim.chat` 单独测得 N=16000 时 393,736 B/次）；
+  这是 Rumor 逐条分配的主因，而非列表 cons 本身。
+- **Kernel 长跑基准**：新增 `src/LivingVillage.Kernel/RumorBench.fs` 与 headless
+  `--rumor-bench [days npcs chats_per_day]`，把「聊天→生成/追溯谣言」路径从 `Sim.step` 的 NPC 快照
+  分配解耦，按模拟日推进 tick、固定节奏注入聊天，测工作集分配与耗时；同 `Config` 的
+  `retained_id_checksum` 可证明确定性。
+  修复前（30 NPC，`--rumor-bench D 30 2000`）：
+
+  | days | chat_calls | rumors_retained | allocated_bytes | elapsed_ms |
+  |---|---|---|---|---|
+  | 3 | 6000 | 6000 | 930,716,456 | 1626.7 |
+  | 30 | 60000 | 8000 | 13,419,045,864 | 12182.5 |
+  | 60 | 120000 | 8000 | 27,297,668,608 | 23769.7 |
+
+  60 天工作集稳定在 8000（M6a 的 3 天保留窗口 + 2000/天），不再随年龄增长。
+
 ## 已验证命令
 
 ```bash
diff --git a/src/LivingVillage.Headless/Program.fs b/src/LivingVillage.Headless/Program.fs
index 89f4f26..7f5dcf5 100644
--- a/src/LivingVillage.Headless/Program.fs
+++ b/src/LivingVillage.Headless/Program.fs
@@ -518,6 +518,28 @@ let runCostProbe (ladder: int64 list) : int =
         Console.Out.Flush()
     0
 
+/// `--rumor-bench [days] [npcs] [chats_per_day]`：Kernel 层 Rumor 长跑基准
+/// （默认 30 NPC × 60 模拟日 × 每日 2000 次聊天）。只读、不改模拟语义。
+let runRumorBench (argv: string[]) : int =
+    let tryInt64 (index: int) =
+        if argv.Length > index then
+            match Int64.TryParse argv.[index] with
+            | true, value -> Some value
+            | _ -> None
+        else None
+    let days = tryInt64 1 |> Option.defaultValue RumorBench.defaultConfig.Days
+    let npcs = tryInt64 2 |> Option.defaultValue (int64 RumorBench.defaultConfig.NpcCount) |> int
+    let chatsPerDay = tryInt64 3 |> Option.defaultValue (int64 RumorBench.defaultConfig.ChatsPerDay) |> int
+    let config =
+        { RumorBench.defaultConfig with
+            Days = days
+            NpcCount = npcs
+            ChatsPerDay = chatsPerDay }
+    let result = RumorBench.run config
+    printfn "%s" (RumorBench.format result)
+    Console.Out.Flush()
+    0
+
 let runExisting (argv: string[]) =
     let rec parse
         (i: int)
@@ -581,7 +603,7 @@ let runExisting (argv: string[]) =
             if stats.NonFinite > 0L || stats.OutOfBounds > 0L || not replayOk then 1 else 0
     | Error msg ->
         eprintfn $"headless: {msg}"
-        eprintfn "usage: dotnet run -c Release --project src/LivingVillage.Headless -- --days N --seed S [--npc N] [--dump-relations] [--dump-rumors] [--replay-rumors] | --m5-smoke | --m6a-smoke | --batch K D | --performance-baseline | --cost-probe [D1,D2,...]"
+        eprintfn "usage: dotnet run -c Release --project src/LivingVillage.Headless -- --days N --seed S [--npc N] [--dump-relations] [--dump-rumors] [--replay-rumors] | --m5-smoke | --m6a-smoke | --batch K D | --performance-baseline | --cost-probe [D1,D2,...] | --rumor-bench [days npcs chats_per_day]"
         2
 
 let private parseCostLadder (argv: string[]) : int64 list =
@@ -608,5 +630,7 @@ let main argv =
         LivingVillage.Headless.PerformanceProbe.runDefault ()
     elif argv.Length >= 1 && argv.[0] = "--cost-probe" then
         runCostProbe (parseCostLadder argv)
+    elif argv.Length >= 1 && argv.[0] = "--rumor-bench" then
+        runRumorBench argv
     else
         runExisting argv
diff --git a/src/LivingVillage.Kernel/LivingVillage.Kernel.fsproj b/src/LivingVillage.Kernel/LivingVillage.Kernel.fsproj
index c6b3bf9..72e5def 100644
--- a/src/LivingVillage.Kernel/LivingVillage.Kernel.fsproj
+++ b/src/LivingVillage.Kernel/LivingVillage.Kernel.fsproj
@@ -7,6 +7,7 @@
   <ItemGroup>
     <Compile Include="Rng.fs" />
     <Compile Include="Sim.fs" />
+    <Compile Include="RumorBench.fs" />
     <Compile Include="Occupation.fs" />
     <Compile Include="SimulationControl.fs" />
     <Compile Include="WorldSave.fs" />
diff --git a/src/LivingVillage.Kernel/RumorBench.fs b/src/LivingVillage.Kernel/RumorBench.fs
new file mode 100644
index 0000000..145f92c
--- /dev/null
+++ b/src/LivingVillage.Kernel/RumorBench.fs
@@ -0,0 +1,109 @@
+namespace LivingVillage.Kernel
+
+open System
+open System.Diagnostics
+open LivingVillage.Kernel.Sim
+
+/// Kernel 层 Rumor 长跑基准：把「聊天 → 生成/追溯传闻」这条路径单独拎出来，按
+/// 模拟日推进 tick 并注入固定节奏的聊天，长期测量 Rumor 工作集随世界年龄的
+/// 分配与耗时量级（与 `Sim.step` 的 NPC 快照分配解耦，便于隔离谣言子系统）。
+///
+/// 该基准只读、不改变任何模拟语义；所有输入由 `Config` 决定，无墙钟/`System.Random`，
+/// 同一 `Config` 两次运行产生相同的工作集校验和。
+module RumorBench =
+
+    type Config =
+        { Seed: uint64
+          NpcCount: int
+          Days: int64
+          /// 每个模拟日注入的聊天次数（决定谣言产生速率）。
+          ChatsPerDay: int }
+
+    type Result =
+        { Seed: uint64
+          NpcCount: int
+          Days: int64
+          ChatsPerDay: int
+          ChatCalls: int64
+          RumorsCreated: int64
+          RumorsRetained: int
+          /// 保留工作集内各条目 Id 之和，用于证明同一 Config 的确定性。
+          RetainedIdChecksum: int64
+          AllocatedBytes: int64
+          ElapsedMs: float }
+
+    /// 任务默认口径：30 NPC × 60 模拟日 × 每日 2000 次聊天。
+    let defaultConfig : Config =
+        { Seed = 42UL
+          NpcCount = 30
+          Days = 60L
+          ChatsPerDay = 2000 }
+
+    /// 测试/快速核验口径（同样是 30 NPC，但只跑 3 天）。
+    let quickConfig : Config =
+        { defaultConfig with Days = 3L }
+
+    let private resetParticipants (ids: NpcId list) (world: World) : World =
+        let npcs = Array.copy world.Npcs
+        for id in ids do
+            let (NpcId index) = id
+            if index >= 0 && index < npcs.Length then
+                npcs.[index] <-
+                    { npcs.[index] with
+                        Mind = { npcs.[index].Mind with Action = Wander } }
+        { world with Npcs = npcs }
+
+    let private retainedChecksum (rumors: RumorEvent list) : int64 =
+        rumors |> List.sumBy (fun rumor -> let (RumorId id) = rumor.Id in id)
+
+    let run (config: Config) : Result =
+        if config.NpcCount < 2 then invalidArg (nameof config) "NpcCount must be at least 2"
+        if config.Days <= 0L then invalidArg (nameof config) "Days must be positive"
+        if config.ChatsPerDay <= 0 then invalidArg (nameof config) "ChatsPerDay must be positive"
+        if config.ChatsPerDay > 1000000 then invalidArg (nameof config) "ChatsPerDay is too large"
+        let callsPerDay = int64 config.ChatsPerDay
+        let ticksPerCall = max 1L (ticksPerDay / callsPerDay)
+        let totalCalls = config.Days * callsPerDay
+        let mutable world = Sim.initialWorldN config.Seed config.NpcCount
+        let mutable created = 0L
+        let mutable calls = 0L
+        GC.Collect(2, GCCollectionMode.Forced, true, true)
+        GC.WaitForPendingFinalizers()
+        GC.Collect(2, GCCollectionMode.Forced, true, true)
+        let allocatedBefore = GC.GetAllocatedBytesForCurrentThread()
+        let stopwatch = Stopwatch.StartNew()
+        for i in 0L .. totalCalls - 1L do
+            let dayIndex = i / callsPerDay
+            let within = i % callsPerDay
+            let tick = dayIndex * ticksPerDay + within * ticksPerCall
+            let narratorIndex = int (i % int64 config.NpcCount)
+            let receiverIndex =
+                int ((i + 1L + (i / int64 config.NpcCount) % int64 (config.NpcCount - 1)) % int64 config.NpcCount)
+            let narrator = NpcId narratorIndex
+            let receiver = NpcId receiverIndex
+            world <-
+                resetParticipants [ narrator; receiver ] { world with Tick = tick }
+            match Sim.chat { Narrator = narrator; Receiver = receiver } world with
+            | ChatSucceeded (rumor, next) ->
+                world <- next
+                calls <- calls + 1L
+                if rumor.IsSome then created <- created + 1L
+            | ChatRejected _ -> ()
+        stopwatch.Stop()
+        let allocatedAfter = GC.GetAllocatedBytesForCurrentThread()
+        { Seed = config.Seed
+          NpcCount = config.NpcCount
+          Days = config.Days
+          ChatsPerDay = config.ChatsPerDay
+          ChatCalls = calls
+          RumorsCreated = created
+          RumorsRetained = world.Rumors.Length
+          RetainedIdChecksum = retainedChecksum world.Rumors
+          AllocatedBytes = allocatedAfter - allocatedBefore
+          ElapsedMs = stopwatch.Elapsed.TotalMilliseconds }
+
+    let format (result: Result) : string =
+        sprintf
+            "rumor_bench seed=%d npcs=%d days=%d chats_per_day=%d chat_calls=%d rumors_created=%d rumors_retained=%d retained_id_checksum=%d allocated_bytes=%d elapsed_ms=%.3f"
+            result.Seed result.NpcCount result.Days result.ChatsPerDay result.ChatCalls result.RumorsCreated
+            result.RumorsRetained result.RetainedIdChecksum result.AllocatedBytes result.ElapsedMs