docs(bench): the split tree, where the refactor beats the engine choice

split 树同样 15 ok / 0 failed / 零告警。两种代码风格现在都有真实三方数据。

| 场景 | mcpp | cmake | xmake |
|---|---|---|---|
| cold | 27.59s · 1.82x | 50.13s | 41.90s · 1.20x |
| noop | 0.79s · **0.44x** | 0.34s | 0.50s · 0.68x |
| touch-hub | **1.32s · 20.08x** | 26.60s | 31.68s · 0.84x |
| edit-body | 1.79s · **0.75x** | 1.35s | 1.49s · 0.91x |
| edit-comment | 24.17s · 1.09x | 26.35s | 31.28s · 0.84x |

**最重要的一条不是 mcpp 赢在哪,而是重构本身的收益盖过了引擎选择**:mcpp 的 cold
从 92.49s(combined)降到 27.59s(3.35x),而 cmake 自己也从 119.46s 降到 50.13s
(2.38x)。把实现搬出接口单元,比换构建工具更值 —— 这是这两个 pin 存在的意义,
也是这套件能给用户的最有用的一句话。

**`edit-body` 0.75x —— 这里 mcpp 比 cmake 慢。** 函数体在 `.cpp` 里,只重编一个
object、没有级联,于是场景量的是每次调用的固定开销而非图推理,和 `noop` 是同一笔
成本。在这条轴上 mcpp 没有优势,数字就该这么写。

`touch-hub` 20.08x 比 combined 的 54.96x 小,因为下游本来就没剩多少可跳的了。

Author: speak-agent

bench/README.md

@@ -226,6 +226,35 @@ mcpp LOSING:
   cmake and xmake decide by timestamp and rebuild all of them — to within 0.00s
   of each other, which is what two timestamp-driven engines should look like.
 
+
+#### The same three engines on the SPLIT tree
+
+Same project, implementations moved out of the interface units. This is the axis
+the two pins exist for, and it changes the answer more than the engine does.
+
+| scenario | **mcpp** | cmake | xmake |
+|---|---|---|---|
+| `cold` | **27.59s** · 1.82x | 50.13s · 1.00x | 41.90s · 1.20x |
+| `noop` | **0.79s** · 0.44x | 0.34s · 1.00x | 0.50s · 0.68x |
+| `touch-hub` | **1.32s** · 20.08x | 26.60s · 1.00x | 31.68s · 0.84x |
+| `edit-body` | **1.79s** · 0.75x | 1.35s · 1.00x | 1.49s · 0.91x |
+| `edit-comment` | **24.17s** · 1.09x | 26.35s · 1.00x | 31.28s · 0.84x |
+
+<sub>xlings `2026.8.13.1`, `modules-impl`, same host and payload as above. Raw
+report: `bench/results/xlings-3way-20260814/xlings-split-3way.json`.</sub>
+
+* **The refactor beats every engine choice on this workload.** `cold` falls from
+  92.49s to 27.59s for mcpp — 3.35x — and cmake's own cold falls 119.46s → 50.13s
+  (2.38x). Moving implementations out of interface units buys more than switching
+  build tool does.
+* **`edit-body` is 0.75x — mcpp is SLOWER than cmake here**, 1.79s against 1.35s.
+  With the body in a `.cpp`, one object recompiles and nothing cascades, so the
+  scenario measures per-invocation overhead rather than graph reasoning — the
+  same fixed cost `noop` shows. On this axis mcpp has no advantage to offer and
+  the number says so.
+* **`touch-hub` still pays: 20.08x.** Smaller than the combined tree's 54.96x
+  because there is simply less downstream work left to skip.
+
 #### The two code styles, mcpp against mcpp
 
 Older run, kept because it is the only side-by-side of the two pinned

bench/README.zh-CN.md

@@ -187,6 +187,33 @@ job 一个测量都没有，这个状态持续了好几周。
   上一份比,跳过 45 个导入者;cmake 与 xmake 按时间戳判断,把它们全部重建 ——
   两者相差 0.00s,这正是两个时间戳驱动的引擎该有的样子。
 
+
+## 4c. 同样三个引擎在 split 树上
+
+同一个工程,实现从接口单元里搬了出去。这正是两个 pin 存在的意义 —— 而它对结果的
+影响**比换构建工具更大**。
+
+| 场景 | **mcpp** | cmake | xmake |
+|---|---|---|---|
+| `cold` | **27.59s** · 1.82x | 50.13s · 1.00x | 41.90s · 1.20x |
+| `noop` | **0.79s** · 0.44x | 0.34s · 1.00x | 0.50s · 0.68x |
+| `touch-hub` | **1.32s** · 20.08x | 26.60s · 1.00x | 31.68s · 0.84x |
+| `edit-body` | **1.79s** · 0.75x | 1.35s · 1.00x | 1.49s · 0.91x |
+| `edit-comment` | **24.17s** · 1.09x | 26.35s · 1.00x | 31.28s · 0.84x |
+
+<sub>xlings `2026.8.13.1`,`modules-impl`,主机与载荷同上。原始报告:
+`bench/results/xlings-3way-20260814/xlings-split-3way.json`。</sub>
+
+* **在这个工作负载上,重构的收益盖过了任何引擎选择。** mcpp 的 `cold` 从 92.49s
+  降到 27.59s(3.35x),而 cmake 自己的 cold 也从 119.46s 降到 50.13s(2.38x)。
+  把实现搬出接口单元,比换构建工具更值。
+* **`edit-body` 是 0.75x —— 这里 mcpp 比 cmake 慢**(1.79s 对 1.35s)。函数体在
+  `.cpp` 里,只重编一个 object、没有级联,于是这个场景量的是**每次调用的固定
+  开销**而不是图推理 —— 和 `noop` 反映的是同一笔成本。在这条轴上 mcpp 没有优势
+  可言,数字也就这么写。
+* **`touch-hub` 仍然值:20.08x。** 比 combined 树的 54.96x 小,因为下游本来就
+  没剩多少可跳的了。
+
 ## 5. 可观测性：跑的时候看得见
 
 harness 会把进度实时打到 **stderr**（逐行 flush），stdout 留给报告：

bench/results/xlings-3way-20260814/xlings-split-3way.json

@@ -0,0 +1,241 @@
+{
+  "protocol_version": 1,
+  "started_at": "2026-08-13T18:19:51Z",
+  "host": {
+    "os": "linux",
+    "arch": "x86_64",
+    "cpu_model": "13th Gen Intel(R) Core(TM) i9-13900K",
+    "logical_cores": 32,
+    "physical_cores": 24,
+    "heterogeneous": true,
+    "ram_bytes": 67147722752,
+    "toolchain": "/home/speak/.mcpp/registry/data/xpkgs/xim-x-gcc/16.1.0/bin/g++"
+  },
+  "cells": [
+    {
+      "engine": "mcpp@2026.8.13.1",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "cold",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "mcpp 2026.8.13.1",
+      "runs": 1,
+      "median_s": 27.588,
+      "min_s": 27.588,
+      "max_s": 27.588,
+      "samples": [27.588]
+    },
+    {
+      "engine": "mcpp@2026.8.13.1",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "noop",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "mcpp 2026.8.13.1",
+      "runs": 1,
+      "median_s": 0.785,
+      "min_s": 0.785,
+      "max_s": 0.785,
+      "samples": [0.785]
+    },
+    {
+      "engine": "mcpp@2026.8.13.1",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "touch-hub",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "mcpp 2026.8.13.1",
+      "runs": 1,
+      "median_s": 1.325,
+      "min_s": 1.325,
+      "max_s": 1.325,
+      "samples": [1.325]
+    },
+    {
+      "engine": "mcpp@2026.8.13.1",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "edit-body",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "mcpp 2026.8.13.1 · perturbation: in-body",
+      "runs": 1,
+      "median_s": 1.790,
+      "min_s": 1.790,
+      "max_s": 1.790,
+      "samples": [1.790]
+    },
+    {
+      "engine": "mcpp@2026.8.13.1",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "edit-comment",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "mcpp 2026.8.13.1 · perturbation: in-body",
+      "runs": 1,
+      "median_s": 24.168,
+      "min_s": 24.168,
+      "max_s": 24.168,
+      "samples": [24.168]
+    },
+    {
+      "engine": "cmake",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "cold",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "cmake version 4.0.2 + ninja",
+      "runs": 1,
+      "median_s": 50.129,
+      "min_s": 50.129,
+      "max_s": 50.129,
+      "samples": [50.129]
+    },
+    {
+      "engine": "cmake",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "noop",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "cmake version 4.0.2 + ninja",
+      "runs": 1,
+      "median_s": 0.342,
+      "min_s": 0.342,
+      "max_s": 0.342,
+      "samples": [0.342]
+    },
+    {
+      "engine": "cmake",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "touch-hub",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "cmake version 4.0.2 + ninja",
+      "runs": 1,
+      "median_s": 26.600,
+      "min_s": 26.600,
+      "max_s": 26.600,
+      "samples": [26.600]
+    },
+    {
+      "engine": "cmake",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "edit-body",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "cmake version 4.0.2 + ninja · perturbation: in-body",
+      "runs": 1,
+      "median_s": 1.349,
+      "min_s": 1.349,
+      "max_s": 1.349,
+      "samples": [1.349]
+    },
+    {
+      "engine": "cmake",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "edit-comment",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "cmake version 4.0.2 + ninja · perturbation: in-body",
+      "runs": 1,
+      "median_s": 26.349,
+      "min_s": 26.349,
+      "max_s": 26.349,
+      "samples": [26.349]
+    },
+    {
+      "engine": "xmake",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "cold",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "xmake v3.1.0+HEAD.96ad28e, A cross-platform build utility based on Lua",
+      "runs": 1,
+      "median_s": 41.904,
+      "min_s": 41.904,
+      "max_s": 41.904,
+      "samples": [41.904]
+    },
+    {
+      "engine": "xmake",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "noop",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "xmake v3.1.0+HEAD.96ad28e, A cross-platform build utility based on Lua",
+      "runs": 1,
+      "median_s": 0.502,
+      "min_s": 0.502,
+      "max_s": 0.502,
+      "samples": [0.502]
+    },
+    {
+      "engine": "xmake",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "touch-hub",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "xmake v3.1.0+HEAD.96ad28e, A cross-platform build utility based on Lua",
+      "runs": 1,
+      "median_s": 31.676,
+      "min_s": 31.676,
+      "max_s": 31.676,
+      "samples": [31.676]
+    },
+    {
+      "engine": "xmake",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "edit-body",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "xmake v3.1.0+HEAD.96ad28e, A cross-platform build utility based on Lua · perturbation: in-body",
+      "runs": 1,
+      "median_s": 1.486,
+      "min_s": 1.486,
+      "max_s": 1.486,
+      "samples": [1.486]
+    },
+    {
+      "engine": "xmake",
+      "compiler": "gcc",
+      "profile": "release",
+      "scenario": "edit-comment",
+      "fixture": "xlings-2026.8.13.1",
+      "variant": "modules-impl",
+      "status": "ok",
+      "note": "xmake v3.1.0+HEAD.96ad28e, A cross-platform build utility based on Lua · perturbation: in-body",
+      "runs": 1,
+      "median_s": 31.281,
+      "min_s": 31.281,
+      "max_s": 31.281,
+      "samples": [31.281]
+    }
+  ]
+}