docs: release verification found SHA256SUMS covers one platform of four

Checking the four published archives against the file whose name promises to
cover them: only `linux-x86_64` is in it — the aarch64, macOS and Windows
archives are absent, and have been for at least v2026.8.16.3 and v2026.8.15.1
too, so this is not something this round did.

The mechanism is structural rather than flaky: `build-release` (linux
x86_64) runs first and writes the file; the other three platforms upload
their own `.sha256` sidecars and nothing appends. Verification IS possible —
the sidecars are there — but not through the file that says SHA256SUMS.

Recorded as outstanding, not fixed: it is the release pipeline, not one of
the three axes, and this PR is already the post-release tail.

Author: speak-agent

.agents/docs/2026-08-17-windows-three-axes-final-report.md

@@ -270,7 +270,8 @@ if (b.substr(*lfanew, 4) == "PE\0\0")   // *lfanew 直接读自文件
 | 3 | `[pack] include` / `exclude` 被解析、存进 Plan,**从未被消费** | 早于本轮;文档把它们当作已有功能。属于 pack 的另一条轴,不在三条轴的范围内 |
 | 4 | Windows CI 仍用 `7z a -tzip` 手工打包 release | 那是一个自带 `registry/` 的定制布局,不是 pack 的输出。现在 `mcpp pack` 能产 zip 了,迁移是可能的,但那是发布流程的改动 |
 | 5 | **`mcpp new` + `mcpp add compat.gtest@1.15.2` 开箱即坏** —— 脚手架的 `test_smoke.cpp` 自带 `main()`,而 gtest 依赖会把 `gtest_main.o` 链进每个测试目标,`multiple definition of 'main'`。生态验证时撞到的 | **先于本轮**,已用 2026.8.16.3 在沙盒里复现过同样的失败,所以不是本次回归。它属于依赖/测试目标的链接策略,和这三条轴无关;放在这里是因为它是一条**开箱即坏**的路径,值得单独一轮 |
-| 6 | Windows 宿主 → Linux target 时 `dist::Format` 仍解析为 PE | 早于本轮。本轮的 triple 判据**只新增答案**(说不出 OS 的 triple 走原推导),刻意没有动这一条:它会改变一个正在通过的 CI job 的旗标,而对这三条轴没有好处 |
+| 6 | **release 的 `SHA256SUMS` 只覆盖 4 个平台里的 1 个** —— 里面只有 `linux-x86_64` 的两行(带版本名 + 无版本别名),aarch64 / macOS / Windows 都不在。核对发布产物时撞到的 | **先于本轮**:v2026.8.16.3 与 v2026.8.15.1 同样如此。机制很清楚 —— `build-release`(linux x86_64)最先跑并写下这个文件,另外三个平台各自上传自己的 `.sha256` 边车,但没有人往 `SHA256SUMS` 里追加。**能校验**(边车在),只是那个名字承诺了它没做到的事。属于发布流水线,不属于这三条轴 |
+| 7 | Windows 宿主 → Linux target 时 `dist::Format` 仍解析为 PE | 早于本轮。本轮的 triple 判据**只新增答案**(说不出 OS 的 triple 走原推导),刻意没有动这一条:它会改变一个正在通过的 CI job 的旗标,而对这三条轴没有好处 |
 
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