chore: bump version to 2026.8.17.1, and record what §1–§4 actually became

The design doc gains a status section per item, including the two places the
PLAN was corrected by the implementation and the one half of §4 that was
deliberately not done:

- `dist::Format` now reads the target triple before falling back to the host.
  Everything but MinGW used to ask the host, which made a Windows contract
  unassertable on the Linux runner where most of this gets reviewed. It only
  ADDS answers, so no existing build changes.
- `force_bundle` had to reach the PE system list too. ELF always worked that
  way; making the PE exclusion unconditional would have turned an explicitly
  written decision into decoration.
- The ELF closure still runs the artifact. `ldd` hands back RESOLVED PATHS
  while `DT_NEEDED` gives only names, and turning names into paths means
  reimplementing the loader's search order ($ORIGIN, DT_RPATH before
  LD_LIBRARY_PATH before DT_RUNPATH before ld.so.cache, hwcaps). Rewriting
  that under a correct, e2e-covered path is more risk than it buys — and the
  cost is stated rather than left to be discovered: cross-ARCHITECTURE ELF
  packing is still unsupported, which is the second limit §4.1 names.

`mcpp self doctor` reports the Windows SDK PER ORIGIN. One unlabelled line was
the same "one question, two answerers" shape this axis exists to close: a user
reading it would believe it applied to their pinned build, and it did not.

Author: speak-agent

.agents/docs/2026-08-16-windows-toolchain-three-axes-design.md

@@ -298,6 +298,48 @@ LD_TRACE_LOADED_OBJECTS=1 '<binary>'
 
 ---
 
+## 6.5 落地状态(2026-08-17,mcpp 2026.8.17.1)
+
+**§1 / §2 / §3 / §4 全部实现,§2.4 明确不做。** 逐条对应:
+
+| 条目 | 状态 | 落点 |
+|---|---|---|
+| §1 Origin 建模 | ✅ | `enum class Origin`(`model.cppm`)—— 放在数据模型里,让 spec 侧(`registry`)与已定位编译器侧(`msvc`)指的是**同一根轴** |
+| §1 拒绝 `gcc@system` | ✅ | `parse_toolchain_spec`,错误里同时给出 pin 与 PATH 逃生口两种写法 |
+| §1 解析一次 | ✅ | `prepare` 原先把同一个字符串**解析两遍**、各自下结论;现在一次,`origin_of()` 分发 |
+| §1 消重复:`resolve_managed_msvc` | ✅ | `registry.cppm`。"payload 在哪、为什么不能用 fetcher 的 `root`"两份手写实现,而理由只写在其中一份里 |
+| §1 消重复:sysroot 谓词 | ✅ | `needs_linux_sysroot_payloads()`。两份**不等价**,而其中一份的注释声称它们互为镜像 —— 少的是 PE 那一项 |
+| §1 解析链注释 | ✅ | 一张按 `TcOrigin` 枚举名写的表。原先两处、分别声称 3 步和 4 步,合起来点到 9 个输入里的 5 个,还互相矛盾 |
+| §2.2 SDK 按来源分流 | ✅ | `msvc::resolve_sdk_for()`;受管来源忽略 `WindowsSdkDir`/`WindowsSdkVersion` 并打印 `note:` |
+| §2.2 无 SDK payload 时 | ✅ | 退回机器 SDK 并**说出来**(可用 > 失败,但不可复现这件事必须留痕) |
+| §2.3 `ucrt@` 身份 | ✅ | `bind_windows_ucrt()`,进 `runtimeContractHash`;`runtime_provider()` 取代各处 `starts_with("glibc@")` |
+| §2.4 manifest SDK 键 | ⛔ **不做** | 理由见该节 |
+| §3.3 PE `toolchain-coupled` | ✅ | `dist::Mechanism::deployToolchainRuntime` → `CompileFlags::toolchainRuntimeDeploy` → ninja `stage_file` 边 |
+| §3.3 排除 debug CRT | ✅ | 判据只有一处(`vc_redist_dir()`),拷贝那步复用它而不是另立一条按名字的规则 |
+| §4 静态读闭包 | ✅ | `mcpp.pack.binfmt`:ELF `DT_NEEDED`、PE 导入表 **+ 延迟导入表** |
+| §4 跨 OS 打包 | ✅ | Linux 上给 Windows 产物打 zip;`mcpp.pack.zip` 自己写压缩包(没有哪个 zip 工具在每个宿主上都存在) |
+| §4.3 `pack` 读 Contract | ✅ | `cxx_runtime` 决定 toolchain runtime 目录进不进搜索集;与 `--mode` 矛盾时拒绝 |
+
+**两处对方案本身的修正**,来自实现过程:
+
+1. **`dist::Format` 改为先看 target triple、再退回宿主。** 原先除 MinGW 外一律
+   问宿主,于是"Windows 上的契约"在 Linux runner 上**根本无法断言** —— 而这轮
+   大部分 review 就发生在 Linux runner 上。只**新增**答案:说不出 OS 的 triple
+   仍走原来那条推导,现有构建一个都不变。
+2. **`force_bundle` 在 PE 上也要能覆盖系统表。** ELF 上一直如此;PE 上第一版把
+   系统排除写成了无条件的,那会让一个明确写下来的决定变成装饰。
+
+**§4 未做的一半,以及理由。** ELF 闭包**仍然**通过运行产物取得
+(`LD_TRACE_LOADED_OBJECTS`),`binfmt` 的 `DT_NEEDED` 读取只用于识别与诊断。
+原因不是懒:`ldd` 交回的是**已解析的路径**,而 `DT_NEEDED` 只有名字,把名字变
+成路径要重新实现 loader 的搜索规则(`DT_RPATH` → `LD_LIBRARY_PATH` →
+`DT_RUNPATH` → `ld.so.cache` → 默认目录,加上 `$ORIGIN` 展开与 hwcaps 子目录)。
+在一条**已经正确、且被 e2e 覆盖**的路径上重写这个,风险远大于收益。
+**代价要说清楚:跨架构的 ELF 打包(x86_64 上给 aarch64 产物打包)仍然不支持**,
+而这正是 §4.1 指出的第二个限制。PE 那条没有既有实现,所以它从一开始就是静态的。
+
+---
+
 ## 7. 落地顺序
 
 | # | 项 | 规模 | 依赖 |

mcpp.toml

@@ -1,6 +1,6 @@
 [package]
 name        = "mcpp"
-version     = "2026.8.16.3"
+version     = "2026.8.17.1"
 description = "Modern C++ build & package management tool"
 license     = "Apache-2.0"
 authors     = ["mcpp-community"]

src/build/prepare.cppm

@@ -1294,18 +1294,36 @@ prepare_build(bool print_fingerprint,
     // resolution / fingerprinting.
     fold_build_defines_into_flags(m->buildConfig);
 
-    // msvc@system: located on the machine, never resolved through xim
-    // packages. mcpp does not install the machine's Visual Studio.
+    // ORIGIN, RESOLVED ONCE.
     //
-    // A VERSIONED msvc spec is a different origin and takes the xim path
-    // below — which is the whole point: what the manifest says is what gets
+    // The spec used to be parsed TWICE from the same string a dozen lines
+    // apart — once to ask "is this msvc@system", once to get the package —
+    // and each call site drew its own conclusions from the result. Two parses
+    // of one string is two places for the answer to differ, which is the shape
+    // §1 of the three-axes design is about: a platform special case whose cost
+    // is paid at every site that has to know about it.
+    //
+    // `Origin::SystemMsvc` is located on the machine and never resolved
+    // through an xim package — mcpp does not install the machine's Visual
+    // Studio. `Origin::Managed` is everything else, including a VERSIONED
+    // msvc spec, and that is the point: what the manifest says is what gets
     // used, on every machine, instead of whatever this one happens to have.
-    bool tcSpecIsMsvc = false;
-    if (tcSpec.has_value()) {
-        if (auto s = mcpp::toolchain::parse_toolchain_spec(*tcSpec);
-            s && mcpp::toolchain::is_system_toolchain(*s))
-            tcSpecIsMsvc = true;
+    std::optional<mcpp::toolchain::ToolchainSpec> parsedSpec;
+    auto tcOriginAxis = mcpp::toolchain::Origin::Managed;
+    if (tcSpec.has_value() && *tcSpec != "system") {
+        // A parse FAILURE is not the same as an unparseable spec being
+        // absent: `gcc@system` now fails here by name (see
+        // parse_toolchain_spec), and swallowing that would put the error back
+        // where it used to happen — somewhere else, saying something else.
+        auto s = mcpp::toolchain::parse_toolchain_spec(*tcSpec);
+        if (!s) return std::unexpected(std::format(
+            "[toolchain].{} = '{}': {}", kCurrentPlatform, *tcSpec, s.error()));
+        parsedSpec   = std::move(*s);
+        tcOriginAxis = mcpp::toolchain::origin_of(*parsedSpec);
     }
+    const bool tcSpecIsMsvc =
+        parsedSpec && tcOriginAxis == mcpp::toolchain::Origin::SystemMsvc;
+
     if (tcSpecIsMsvc) {
         if (!mcpp::platform::is_windows) {
             return std::unexpected(std::format(
@@ -1319,9 +1337,9 @@ prepare_build(bool print_fingerprint,
         mcpp::ui::info("Resolved", std::format(
             "msvc@system → msvc {} ({})",
             inst->display_version(), inst->clPath.string()));
-    } else if (tcSpec.has_value() && *tcSpec != "system") {
-        auto spec = mcpp::toolchain::parse_toolchain_spec(*tcSpec);
-        if (!spec || spec->version.empty()) {
+    } else if (parsedSpec) {
+        auto spec = parsedSpec;
+        if (spec->version.empty()) {
             return std::unexpected(std::format(
                 "[toolchain].{} = '{}' is invalid; expected '<pkg>@<version>'",
                 kCurrentPlatform, *tcSpec));

src/doctor.cppm

@@ -133,13 +133,45 @@ export int doctor_report() {
             warn("msvc not detected — run `mcpp toolchain default msvc` for "
                  "setup guidance (mcpp does not install MSVC)");
         }
-        // Windows SDK (native cl.exe builds need its UCRT/um headers).
+        // Windows SDK. REPORTED PER ORIGIN, because it is chosen per origin
+        // (design §2.2): `msvc@system` searches the machine, a pinned toolset
+        // takes the payload installed with it. One unlabelled line here would
+        // be the same "one question, two answerers" shape the SDK axis exists
+        // to close — a user reading it would believe it applied to their
+        // pinned build, and it does not.
         if (auto sdk = mcpp::toolchain::msvc::find_windows_sdk()) {
-            ok(std::format("Windows SDK {} at {}", sdk->version,
+            ok(std::format("Windows SDK (msvc@system) {} at {}", sdk->version,
                            sdk->root.string()));
         } else {
-            warn("no Windows SDK found — native msvc builds will fail "
-                 "(install the 'Windows 11 SDK' VS component)");
+            warn("no Windows SDK found for msvc@system — native builds with "
+                 "the machine's Visual Studio will fail (install the "
+                 "'Windows 11 SDK' VS component)");
+        }
+        {
+            std::error_code sdkEc;
+            auto msvcRoot = mcpp::home::root()
+                / "registry" / "data" / "xpkgs" / "xim-x-msvc";
+            for (auto& v : std::filesystem::directory_iterator(msvcRoot, sdkEc)) {
+                if (!v.is_directory(sdkEc)) continue;
+                auto ver = v.path().filename().string();
+                auto inst = mcpp::toolchain::msvc::installation_at(
+                    v.path(), ver, /*identifyVersion=*/false);
+                if (!inst) continue;
+                // The SAME resolution a build performs, not a second one
+                // shaped like it: what doctor prints is what the user will
+                // believe, so the two must not be able to disagree.
+                auto choice = mcpp::toolchain::msvc::resolve_sdk_for(inst->clPath);
+                if (choice.sdk) {
+                    ok(std::format("Windows SDK (msvc@{}) {} at {}",
+                                   ver, choice.sdk->version,
+                                   choice.sdk->root.string()));
+                } else {
+                    warn(std::format(
+                        "msvc@{} has no usable Windows SDK — reinstall it to "
+                        "pull its `xim:windows-sdk` dependency", ver));
+                }
+                if (!choice.note.empty()) warn(choice.note);
+            }
         }
 
         mcpp::ui::status("Checking", "mingw (xim:mingw-gcc)");

src/version.cppm

@@ -31,6 +31,6 @@ import std;
 
 export namespace mcpp {
 
-inline constexpr std::string_view MCPP_VERSION = "2026.8.16.3";
+inline constexpr std::string_view MCPP_VERSION = "2026.8.17.1";
 
 } // namespace mcpp