@@ -1,6 +1,6 @@
 # 商业级可用:mcpp × xlings 的裸机与嵌入式总体方案
 
-2026-09-04 · 多仓库总体方案 · **v4:P0 引擎切片已实施**(PR #550);其余批次待实施
+2026-09-04 · 多仓库总体方案 · **v5:P0 引擎切片 + B/C/D/E 四轴已实施**(PR #550、#551)
 
 前置讨论:
 [`2026-08-21-baremetal-ecosystem-assessment.md`](2026-08-21-baremetal-ecosystem-assessment.md)(七角度评估) ·
@@ -471,3 +471,42 @@ clang 对一次 float 乘法仍发出 `vmul.f32` —— 在没有 FPU 的 Cortex
 ⚠️ **软浮点行在没有 builtins 时链接不了浮点代码**(实测:`undefined symbol:
 __aeabi_fmul`),这正是 §3.1.1 把 `compiler-rt-builtins` 与 C 库并列为 P0 的理由。
 整数程序不受影响 —— e2e 332 的四行启动用例即为整数程序。
+
+---
+
+## 11. 第二轮实施(2026-09-04,PR #551)
+
+### 11.1 六轴读数的变化
+
+| 轴 | v4 | 现在 |
+|---|---|---|
+| **A 覆盖** | 🟡 引擎能编七行 | 🟡 不变(C 库源码包与板级包仍未做) |
+| **B 可信** | ❌ 零真机 | 🟢 **模拟器与真机成为同一个包的两个 feature**;真机路径可声明、可解析、判据齐备,尚无实机运行记录 |
+| **C 闭环** | ❌ 三个槽都没有 | ✅ `flash`/`monitor`/`debug` + `runner-exclusive`,四槽一读点 |
+| **D 可复现** | ❌ `--locked` 不存在 | ✅ `--locked`/`--frozen` 断言并点名漂移;关掉快路径以免空转 |
+| **E 可交付** | ❌ 全空白 | 🟢 `mcpp sbom`(CycloneDX 1.5)+ `docs/19` 支持窗口;许可闭包门与离线快照仍未做 |
+| **F 可扩展** | ✅ | ✅ 未受损:新板 = 新包,引擎 diff 为零 |
+
+### 11.2 ⭐⭐ 方案 §2.2 的判断被实施证实,§2.3 的被加强
+
+* **两值语义是对的。** `debug` 起服务端、客户端归 IDE 这条边界成立,`debug` 与
+  `monitor` 在实现里逐字段同形,没有出现方案担心的「会话协议」。
+* **`runner-exclusive` 比方案写的更必要。** 方案说它是「第一块真板挖出的一列」;
+  实施时发现它还必须**只紧不松** —— 图里任何一个包知道设备是互斥的,它就是互斥
+  的,后来的包保持沉默不得放松它。
+
+### 11.3 ⚠️ 实施挖出的、方案没有的两条
+
+1. **一条规则的第二份拷贝。** 依赖提供的 RunGlobal 条目抵达根工程走的是与
+   `apply()` **不同**的路径(`prepare.cppm` 的 BFS 之后)。只接了前者时,
+   `mcpp flash` 报「没有配置」而 `mcpp run` 找得到同一个构建程序发出的 runner。
+   两处现在都遍历槽表。
+2. **快路径会让新槽与 `--locked` 双双空转。** `try_fast_run` 直接 exec 缓存产物,
+   于是 `mcpp flash` 打印 `Running target/…/bin/p`;`try_fast_build` 跳过解析,
+   于是被改坏的锁通过了 `--locked`。两处都按**性质**设闸(槽是不是 run、是不是
+   要求断言),不是按旗标。
+
+### 11.4 仍未做
+
+`mcpplibs/picolibc` + `compiler-rt-builtins` 源码包 · 三个板级包 · `xim:probe-rs` ·
+真机 CI · 许可闭包门(`--deny-license`)· 离线整仓快照 · openarch 第四后端(P3)。
@@ -3,6 +3,61 @@
 > 本文件追踪 `mcpp-community/mcpp` 公开仓的版本演进。
 > 格式参考 [Keep a Changelog](https://keepachangelog.com/zh-CN/1.1.0/)。
 
+## [2026.9.4.2] — 2026-09-04
+
+`runner` 长出三个兄弟槽,`--locked` 成为断言,新增 `mcpp sbom`。
+
+四件事在一个工程被采用之前会被问到,而它们此前都没有答案:产物如何抵达设备、
+构建是否可复现、里面装了什么、以及模拟器与真机是一个包还是两个。
+
+### 设备槽
+
+`run` / `flash` / `monitor` / `debug` 是同一种形状 —— **板知道、工具执行**的一段
+argv。`runner` 从 2026.8.19 起就承载着这个形状;再写三个特例命令就是把它再承载
+三遍。所以**槽成了参数**:指令表各一行、一个读点、一种 CLI 形状。
+
+```toml
+[target.thumbv7em-none-eabihf]
+flash = ["probe-rs", "download", "--verify", "--chip", "STM32L475VG", "{}"]
+```
+
+⚠️ **没有任何 argv 能说出它们哪个会终止。** `run`/`flash` 跑完并交回判决;
+`monitor`/`debug` 没有自然终点,于是「进程还活着」对后者是成功、对前者是卡死。
+引擎从**槽**读出这件事,因为 `openocd -c "program … exit"` 与 `openocd -c "init"`
+的拼写直到板所选的那个参数为止都一样。
+
+⚠️ **`runner-exclusive` 是第一件物理板需要而模拟器从不需要的事。** 一块板一个探针
+是互斥锁,两个工作者去够它不会失败 —— 它们互相穿插。板自己说一次,工程永远不必
+记得 `-j1`。
+
+### 模拟器与硬件是一个 feature,不是一次分叉
+
+两者差别只在设备槽的 argv。⭐ 这**不需要任何引擎机制** —— `mcpp::has_feature()`
+本来就存在,分层按规定在起作用。
+
+### `--locked`
+
+锁一直是解析之后写、从不读回;它自己的头注释就这么说。现在它是一条**断言**:
+发生的解析必须等于记录的解析,不等则点名移动了的包与两个版本。
+
+⚠️⚠️ **而它绝不能遇上快路径。** 实测:在加上那道闸之前,一份被故意改坏的锁通过了
+`mcpp build --locked` 并打印 `Finished` —— 旗标被接受、构建正确、断言从未跑到。
+**被跳过的判据比不存在的判据更糟,因为那个绿会被当成一次验证。**
+
+### `mcpp sbom`
+
+CycloneDX 1.5,覆盖**已记录**的解析。物料清单需要的一切都已在 `mcpp.lock` 里,
+所以这是一种输出格式而不是一套机制。⚠️ 它读锁而不是重新解析 —— 一份描述了与所
+构建者不同的图的文档比没有更糟。
+
+### 两个传播点,以及先被漏掉的那一个
+
+依赖提供的 RunGlobal 条目抵达根工程,走的是与包自身指令**不同**的代码路径。只接了
+前者时,`mcpp flash` 报「no flash is configured」,而 `mcpp run` 找得到同一个构建
+程序三行之外发出的 runner。两处现在都遍历槽表,而不是各自点名 `runner`。
+
+指令协议版本 6。新增 `docs/18-devices.md` 与 `docs/19-supported-versions.md`(中英双份)。
+
 ## [2026.9.4.1] — 2026-09-04
 
 Cortex-M 落地为七个目标行,freestanding 链接开启死代码段消除。
 
@@ -0,0 +1,160 @@
+# 18 — Reaching a Device
+
+This document specifies how mcpp executes, writes, observes and debugs an
+artifact that runs somewhere other than the machine that built it, and how a
+project selects between an emulator and physical hardware.
+
+Related documents: [13 — Bare-Metal and Freestanding Targets](13-baremetal.md)
+covers the targets these actions apply to; [07 — build.mcpp](07-build-mcpp.md)
+is the reference for the directive protocol a board-support package speaks;
+[11 — Machine Output](11-machine-output.md) is the interface a debugger client
+or IDE uses.
+
+## Four actions, one shape
+
+An artifact that cannot run on the build machine needs something to stand in
+front of it. Four things are asked of such an artifact, and all four are an
+argv that a board knows and a tool performs:
+
+| Command | Slot | What it does |
+|---|---|---|
+| `mcpp run` | `runner` | executes the artifact |
+| `mcpp flash` | `flash` | writes it to the device |
+| `mcpp monitor` | `monitor` | observes what the device prints |
+| `mcpp debug` | `debug` | starts the device's debug server |
+
+Each is declared the same way, by a board-support package:
+
+```cpp
+mcpp::flash("probe-rs");
+mcpp::flash("download");
+mcpp::flash("--verify");
+mcpp::flash("--chip");
+mcpp::flash("STM32L475VG");
+```
+
+or by a project, overriding what a dependency supplied:
+
+```toml
+[target.thumbv7em-none-eabihf]
+flash = ["probe-rs", "download", "--verify", "--chip", "STM32L475VG", "{}"]
+```
+
+The artifact path is appended, or substituted for `{}` when the template
+contains it. One token per call: argv is ordered, and a single string cannot
+say where its boundaries are.
+
+The program is located by mcpp rather than by the system: a declared payload's
+`bin/` first, then `PATH`. A tool that is nowhere is an error decided before
+any process starts, rather than a fallback to bare execution.
+
+## Termination is a property of the slot
+
+The four actions differ in one way the engine must act on, and no argv can
+express it.
+
+| Semantics | Slots | Meaning |
+|---|---|---|
+| `OneShot` | `run`, `flash` | runs to completion; the exit code is the verdict |
+| `LongLived` | `monitor`, `debug` | has no natural end; the operator ends it |
+
+`openocd -c "program image.elf verify reset exit"` terminates and `openocd -c
+"init"` does not, and the two are spelled alike up to the argument the board
+chose. The engine therefore reads termination from the slot, and a board cannot
+get it wrong by writing its argv differently.
+
+`mcpp debug` starts a **server** and stops there. The client that attaches is
+the user's debugger or their IDE, which learns what it needs through the
+machine-output protocol. mcpp does not drive the client.
+
+## Absence is reported, never substituted
+
+`mcpp run` on a hosted target with no runner executes the artifact directly,
+because the host can run it. There is no corresponding reading of "no flasher":
+nothing else writes an image to a device. An undeclared `flash`, `monitor` or
+`debug` is therefore an error on every target, naming the slot and printing the
+key to paste.
+
+Succeeding at `mcpp flash` by running the program on the build host would be
+the exact failure the slot exists to prevent.
+
+## An exclusive device
+
+A physical board is a mutex; an emulator is not. `mcpp test` runs test binaries
+on a worker pool, and two processes reaching for one probe do not fail cleanly
+— they interleave, and the verdict describes neither test.
+
+The board states this about itself:
+
+```cpp
+mcpp::runner_exclusive();
+```
+
+`mcpp test` then runs one test at a time on that target, and reports that it is
+doing so. A project never has to remember `-j1`.
+
+## Emulator and hardware are one package
+
+A board reached through an emulator and the same board reached through a debug
+probe differ in the argv of their device slots and in nothing else. The linker
+script, the startup code, the memory map and the exported module are the same
+board. Publishing two packages to vary four strings duplicates all of it and
+lets the copies drift.
+
+The choice is therefore a feature of one package:
+
+```toml
+[features]
+default  = ["emulator"]
+emulator = []
+hardware = []
+```
+
+```cpp
+int main() {
+    if (mcpp::has_feature("hardware")) {
+        for (auto a : {"probe-rs", "run", "--chip", "STM32L475VG"})
+            mcpp::runner(a);
+        for (auto a : {"probe-rs", "download", "--verify", "--chip", "STM32L475VG"})
+            mcpp::flash(a);
+        mcpp::runner_exclusive();
+    } else {
+        mcpp::runner(qemu_path());
+        for (auto a : {"-machine", "mps2-an385", "-nographic", "-semihosting",
+                       "-no-reboot", "-kernel"})
+            mcpp::runner(a);
+    }
+    return 0;
+}
+```
+
+The consumer selects an environment where it selects everything else:
+
+```toml
+[dependencies]
+demo-board-rt = { version = "0.1.0", features = ["hardware"] }
+```
+
+A slot the chosen environment does not supply stays absent. An emulator has no
+debug probe, so under the emulator feature `mcpp debug` reports that none is
+configured rather than inventing one.
+
+This required no engine mechanism. The engine reads slots and knows nothing
+about emulators or probes; `mcpp::has_feature` already existed. That the
+question is answerable without adding anything is the layering working as
+specified.
+
+## Precedence and reporting
+
+Two producers exist for every slot, with ordinary precedence: what the author
+of the project wrote beats what a dependency supplied. The override is reported
+rather than applied in silence.
+
+```
+        note [target.thumbv7em-none-eabihf].flash overrides the flash a dependency supplied
+```
+
+Exactly one dependency may supply a given slot. Link flags from two
+dependencies concatenate and that is correct; two flashers cannot, and
+appending produces an argv that is neither one's. A second provider is an error
+naming both packages.
@@ -0,0 +1,90 @@
+# 19 — Supported Versions and Compatibility
+
+This document states which releases are supported, for how long, and what may
+change between them. It exists because a project adopting mcpp is asked these
+questions by its own review process, and an answer that lives only in
+maintainers' heads cannot be cited.
+
+## Versioning
+
+Releases are named `YYYY.M.D.N` — the date of the release and the ordinal of
+that day's release. The scheme carries no compatibility promise in its digits:
+`2026.9.4.1` is not "a minor release" of `2026.9.3.2`. What may and may not
+change is stated below rather than encoded in the number.
+
+## What is supported
+
+| | |
+|---|---|
+| **Supported** | the most recent release |
+| **Security-fixed** | the most recent release, and the last release of the preceding calendar month |
+| **Unsupported** | everything older |
+
+A release is superseded rather than withdrawn. Published assets and index
+entries for older versions remain in place, because a project may have pinned
+one and removing it would break a build that was working.
+
+## What may change between releases
+
+The engine's own interfaces are not all equally stable, and the difference is
+worth stating precisely.
+
+| Surface | Stability |
+|---|---|
+| `mcpp.toml` keys | Additive. An existing key keeps its meaning; an unrecognised key is reported, never silently ignored |
+| CLI commands and flags | Additive. A removed spelling is kept as an alias |
+| Machine output (`--message-format json`) | Versioned by `schemaVersion`; see [11](11-machine-output.md) |
+| `build.mcpp` directive protocol | Versioned; see `kProtocolVersion`. An engine refuses a program declaring a **higher** version rather than guessing |
+| `mcpp.lock` format | Versioned by `schemaVersion`; older files are migrated on read |
+| Target table rows | Additive. A row's tier may rise; a row is not removed while a published package targets it |
+| Build fingerprints, cache layout, `target/` contents | **Not an interface.** These change without notice, and nothing should parse them |
+
+⚠️ A `build.mcpp` calling a function its engine's bundled `mcpp` module does not
+have fails at the **compile** of the build program, not through a protocol
+error. The protocol number governs directives on the wire; the typed API is
+governed by which engine is installed. Both are stated here because the failure
+a package author sees depends on which one they crossed.
+
+## Reproducing a build
+
+`mcpp.lock` records what a build resolved. `--locked` asserts that a resolution
+matches it and fails naming the package that moved:
+
+```
+error: --locked was given and this resolution differs from mcpp.lock:
+         mcpplibs.cmdline 0.0.1 -> 0.0.2
+```
+
+A release build, an audit or a CI job should pass `--locked`. It disables the
+build fast path, so the assertion always runs.
+
+⚠️ The lock does not yet constrain resolution — it records and verifies it.
+Pinning a resolution to the lock as an input is a separate change to the
+resolver.
+
+## Bill of materials
+
+`mcpp sbom` writes a CycloneDX 1.5 document describing the **recorded**
+resolution:
+
+```bash
+mcpp sbom -o sbom.json
+```
+
+It reads `mcpp.lock` rather than resolving again, because a document describing
+a different graph from the one that was built is worse than no document. A
+component whose licence mcpp does not know is emitted as `NOASSERTION` rather
+than omitted: an absent field reads as "not examined".
+
+## Offline and air-gapped use
+
+`--offline` (or `MCPP_OFFLINE=1`) prevents every network access: index refresh,
+package download and toolchain installation. A build that would need one of
+those fails naming what it needed, rather than reaching out.
+
+## Reporting a problem
+
+Defects and security reports go to the issue tracker of the repository that
+owns the component — the engine, the package index, or the package itself. A
+report that names the version, the host, the target and the command is
+actionable; one that does not usually results in a request for those four.
@@ -20,6 +20,8 @@
 - [15 - Cross-Compilation Over openkal](15-openkal-cross.md)
 - [16 - The Target Triple](16-the-target-triple.md)
 - [17 - The Project Environment](17-the-project-environment.md)
+- [18 - Reaching a Device](18-devices.md)
+- [19 - Supported Versions and Compatibility](19-supported-versions.md)
 
 ## Specifications