diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4a27711e..27882775 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,19 @@
 
 ## [Unreleased]
 
+### 在已激活的 xlings subos 中运行时,registry 不再被重定向(2026.9.14.3)
+
+`xlings subos use <name>` 打开的 shell 导出 `XLINGS_ACTIVE_SUBOS`,xlings 解析 subos
+时它的优先级高于 home 自身的 `activeSubos`。这个变量指的是 shell 所在 xlings home
+的 subos;mcpp 的 registry 是另一个 home,mcpp 的工具路径与视图路径都从
+`subos/default` 推导。mcpp 调用自带的 xlings 时继承了它,于是 registry 把引导安装
+的工具与工程的载荷装进同名的另一个 subos:2026.9.14.2 上实测,全新 home 的
+`ninja`、`patchelf` 落在 `registry/subos/<name>/bin`,`mcpp::pkg_config_libdir()`
+指向的 pkg-config 视图为空(在 #634 的沙箱验证中发现)。现在 mcpp 对 xlings 的每次
+调用都不带这个变量,POSIX 上由命令前缀 `env -u` 去掉,Windows 上由
+`ScopedInvocationEnv` 在调用期间移除并在结束后恢复。(单测
+`XlingsInvocationEnv.TheShellsActiveSubosIsNeverInherited`,e2e 686)
+
 ### 一个框架的 CMake 对齐清单:#634 的二十一项中引擎的部分(2026.9.14.2)
 
 #634 列出 HuxerUI 从 CMake 迁到 mcpp 时仍缺的二十一项。分类与决定见设计记录
diff --git a/docs/91-toolchain-internals.md b/docs/91-toolchain-internals.md
index b153c261..f7b615cd 100644
--- a/docs/91-toolchain-internals.md
+++ b/docs/91-toolchain-internals.md
@@ -262,6 +262,12 @@ must refuse its `-rpath "$XLINGS_SUBOS_LIB"`, because that variable names the
 different physical glibc payload. mcpp emits the farm entry it derived from the
 binding it actually selected.
 
+For the same reason mcpp's own xlings invocations do not carry
+`XLINGS_ACTIVE_SUBOS` (2026.9.14.3+). A shell that ran `xlings subos use <name>`
+exports it, and xlings ranks it above a home's own `activeSubos`; inherited, it
+made the registry install mcpp's tools and a project's payloads into a SubOS of
+that name, while mcpp reads `subos/default`.
+
 ## 3. The link model (`modules/toolchain-model/src/linkmodel.cppm`)
 
 `ToolchainLinkModel` answers exactly one question — *how does mcpp compile and
diff --git a/docs/zh/91-toolchain-internals.md b/docs/zh/91-toolchain-internals.md
index e7caef4b..ec0f477f 100644
--- a/docs/zh/91-toolchain-internals.md
+++ b/docs/zh/91-toolchain-internals.md
@@ -214,6 +214,11 @@ mcpp 还会给它启动的每个进程声明 `XLINGS_SUBOS_LD_PATHS=0` —— 
 (`<mcpp home>/registry`),两者通常指向由**不同物理 glibc 载荷**支撑的不同 farm。
 mcpp 发的是自己从已选 binding 推导出来的那一条。
 
+出于同样的原因,mcpp 自己对 xlings 的调用不带 `XLINGS_ACTIVE_SUBOS`
+(2026.9.14.3+)。执行过 `xlings subos use <name>` 的 shell 会导出它,xlings 把它排在
+home 自身的 `activeSubos` 之前;被继承时,registry 会把 mcpp 的工具和工程的载荷装进
+同名的 subos,而 mcpp 读取的是 `subos/default`。
+
 ## 3. 链接模型(`modules/toolchain-model/src/linkmodel.cppm`)
 
 `ToolchainLinkModel` 只回答一个问题——*如何对该工具链的 C 库编译与链接*——
diff --git a/mcpp.toml b/mcpp.toml
index f12c17bd..55718edc 100644
--- a/mcpp.toml
+++ b/mcpp.toml
@@ -1,6 +1,6 @@
 [package]
 name        = "mcpp"
-version = "2026.9.14.2"
+version = "2026.9.14.3"
 description = "Modern C++ build & package management tool"
 license     = "Apache-2.0"
 authors     = ["mcpp-community"]
diff --git a/modules/versioning/src/version.cppm b/modules/versioning/src/version.cppm
index bbe75676..c3333d7f 100644
--- a/modules/versioning/src/version.cppm
+++ b/modules/versioning/src/version.cppm
@@ -31,6 +31,6 @@ import std;
 
 export namespace mcpp {
 
-inline constexpr std::string_view MCPP_VERSION = "2026.9.14.2";
+inline constexpr std::string_view MCPP_VERSION = "2026.9.14.3";
 
 } // namespace mcpp
diff --git a/src/xlings/xlings.cppm b/src/xlings/xlings.cppm
index e1edb836..9afb7f87 100644
--- a/src/xlings/xlings.cppm
+++ b/src/xlings/xlings.cppm
@@ -275,6 +275,15 @@ std::string build_command_prefix(const Env& env);
 // absent XLINGS_PROJECT_DIR, because xlings resolves its subos scope from that
 // variable. POSIX renders the decision into the command prefix (`env -u` and
 // `K=V`); Windows applies it to the process through ScopedInvocationEnv.
+//
+// XLINGS_ACTIVE_SUBOS IS ALWAYS ABSENT. A shell that ran `xlings subos use
+// <name>` exports it, and xlings ranks it above the home's own `activeSubos`.
+// It names a SubOS of the shell's xlings home; mcpp's registry is a different
+// home, whose paths mcpp derives from `subos/default`. Inherited, it made the
+// registry install mcpp's tools and a project's payloads into a SubOS of the
+// shell's name, where mcpp does not look (measured on 2026.9.14.2: a fresh
+// home's `ninja` and `patchelf` landed in `registry/subos/<name>/bin`, and the
+// pkg-config view `mcpp::pkg_config_libdir()` names stayed empty).
 struct InvocationVar {
     std::string name;
     std::string value;
@@ -297,9 +306,15 @@ public:
     ScopedInvocationEnv& operator=(const ScopedInvocationEnv&) = delete;
 
 private:
-    bool        active_      = false;
-    bool        hadPrevious_ = false;
-    std::string previous_;
+    // One entry per scope variable the guard applied: its name and the value
+    // it had before, if any. Plain members, not `std::optional<std::string>`,
+    // which clang on the MSVC ABI does not copy inside a vector element.
+    struct Saved {
+        std::string name;
+        bool        hadPrevious = false;
+        std::string previous;
+    };
+    std::vector<Saved> saved_;
 };
 
 // Build full xlings interface command.
@@ -1182,18 +1197,24 @@ std::vector<InvocationVar> invocation_env(const Env& env) {
     return {
         {"XLINGS_HOME", env.home.string(), true},
         {"XLINGS_PROJECT_DIR", env.projectDir.string(), !env.projectDir.empty()},
+        {"XLINGS_ACTIVE_SUBOS", "", false},
     };
 }
 
 ScopedInvocationEnv::ScopedInvocationEnv(const Env& env) {
     if constexpr (mcpp::platform::is_windows) {
+        // Every variable but XLINGS_HOME is scope: applied for the guard's
+        // lifetime and restored after it. XLINGS_HOME keeps the process-wide
+        // lifetime `build_command_prefix` gives it.
         for (auto const& var : invocation_env(env)) {
-            if (var.name != "XLINGS_PROJECT_DIR") continue;
+            if (var.name == "XLINGS_HOME") continue;
+            Saved s;
+            s.name = var.name;
             if (auto prior = mcpp::platform::env::get(var.name)) {
-                hadPrevious_ = true;
-                previous_ = *prior;
+                s.hadPrevious = true;
+                s.previous = *prior;
             }
-            active_ = true;
+            saved_.push_back(s);
             if (var.present) mcpp::platform::env::set(var.name, var.value);
             else             mcpp::platform::env::unset(var.name);
         }
@@ -1201,9 +1222,10 @@ ScopedInvocationEnv::ScopedInvocationEnv(const Env& env) {
 }
 
 ScopedInvocationEnv::~ScopedInvocationEnv() {
-    if (!active_) return;
-    if (hadPrevious_) mcpp::platform::env::set("XLINGS_PROJECT_DIR", previous_);
-    else              mcpp::platform::env::unset("XLINGS_PROJECT_DIR");
+    for (auto const& s : saved_) {
+        if (s.hadPrevious) mcpp::platform::env::set(s.name, s.previous);
+        else               mcpp::platform::env::unset(s.name);
+    }
 }
 
 std::string build_command_prefix(const Env& env) {
diff --git a/tests/e2e/686_an_activated_xlings_subos_does_not_redirect_the_registry.sh b/tests/e2e/686_an_activated_xlings_subos_does_not_redirect_the_registry.sh
new file mode 100755
index 00000000..7af2f967
--- /dev/null
+++ b/tests/e2e/686_an_activated_xlings_subos_does_not_redirect_the_registry.sh
@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+# requires: fresh-sandbox
+# 686 -- a shell's `xlings subos use <name>` does not redirect mcpp's registry.
+# That shell exports XLINGS_ACTIVE_SUBOS, which names a SubOS of the shell's
+# xlings home, and xlings ranks it above a home's own `activeSubos`. mcpp's
+# registry is a different home, and mcpp derives its tool and view paths from
+# `subos/default`. Inherited, the variable made a fresh home's bootstrap install
+# `ninja` and `patchelf` into `registry/subos/<name>/bin` (measured on
+# 2026.9.14.2), where mcpp does not look, and left the pkg-config view that
+# `mcpp::pkg_config_libdir()` names empty.
+#
+# Criteria, for a fresh home whose first command runs with the variable set:
+#   A. `registry/subos/<name>` does not exist.
+#   B. The bootstrap's tools are in `registry/subos/default/bin`. This is the
+#      denominator: a bootstrap that installed nothing would meet A vacuously.
+set -e
+
+TMP=$(mktemp -d)
+trap "rm -rf $TMP" EXIT
+
+fail() { echo "FAIL: $1"; shift; for f in "$@"; do echo "--- $f ---"; cat "$f" 2>/dev/null; done; exit 1; }
+
+export MCPP_HOME="$TMP/mcpp-home"
+cd "$TMP"
+SHELL_SUBOS=mcpp-e2e-shell-subos
+XLINGS_ACTIVE_SUBOS=$SHELL_SUBOS "$MCPP" self env > env.log 2>&1 || true
+
+SUBOS="$MCPP_HOME/registry/subos"
+[ -d "$SUBOS/default" ] || fail "the registry was not initialised" env.log
+
+# ── A ──────────────────────────────────────────────────────────────────────
+if [ -e "$SUBOS/$SHELL_SUBOS" ]; then
+    fail "A: the registry acted on the shell's SubOS (bin: $(ls "$SUBOS/$SHELL_SUBOS/bin" 2>/dev/null | tr '\n' ' '))" env.log
+fi
+
+# ── B ──────────────────────────────────────────────────────────────────────
+tools=$(ls "$SUBOS/default/bin" 2>/dev/null | grep -v -i '^xlings' | tr '\n' ' ')
+[ -n "$tools" ] || fail "B: the bootstrap placed no tool in subos/default/bin" env.log
+echo "ok: the bootstrap's tools are in subos/default/bin: $tools"
+
+echo "PASS: 686_an_activated_xlings_subos_does_not_redirect_the_registry"
diff --git a/tests/unit/test_xlings.cpp b/tests/unit/test_xlings.cpp
index 70a9f9b2..95691533 100644
--- a/tests/unit/test_xlings.cpp
+++ b/tests/unit/test_xlings.cpp
@@ -629,12 +629,40 @@ TEST(XlingsInvocationEnv, TheProcessEnvironmentIsUnchangedAfterwards) {
 #if !defined(_WIN32)
 TEST(XlingsInvocationEnv, ThePosixPrefixRendersTheDecision) {
     auto global = mcpp::xlings::build_command_prefix(xlings_env(""));
-    EXPECT_NE(global.find("env -u XLINGS_PROJECT_DIR PATH="), std::string::npos) << global;
+    EXPECT_NE(global.find("env -u XLINGS_PROJECT_DIR -u XLINGS_ACTIVE_SUBOS PATH="),
+              std::string::npos) << global;
     EXPECT_EQ(global.find("XLINGS_PROJECT_DIR="), std::string::npos) << global;
 
     auto project = mcpp::xlings::build_command_prefix(xlings_env("/work/proj"));
     EXPECT_EQ(project.find("-u XLINGS_PROJECT_DIR"), std::string::npos) << project;
+    EXPECT_NE(project.find("env -u XLINGS_ACTIVE_SUBOS PATH="), std::string::npos) << project;
     EXPECT_NE(project.find("XLINGS_PROJECT_DIR="), std::string::npos) << project;
     EXPECT_NE(project.find("/work/proj"), std::string::npos) << project;
 }
 #endif
+
+// A shell that ran `xlings subos use <name>` exports XLINGS_ACTIVE_SUBOS, which
+// names a SubOS of the shell's xlings home and not of mcpp's registry; no
+// invocation carries it, in either mode.
+TEST(XlingsInvocationEnv, TheShellsActiveSubosIsNeverInherited) {
+    auto global = decided(xlings_env(""), "XLINGS_ACTIVE_SUBOS");
+    ASSERT_EQ(global.name, "XLINGS_ACTIVE_SUBOS");
+    EXPECT_FALSE(global.present);
+    auto project = decided(xlings_env("proj-dir"), "XLINGS_ACTIVE_SUBOS");
+    ASSERT_EQ(project.name, "XLINGS_ACTIVE_SUBOS");
+    EXPECT_FALSE(project.present);
+
+    namespace env = mcpp::platform::env;
+    env::ScopedEnv keepPath("PATH", env::get("PATH"));
+    env::ScopedEnv keepHome("XLINGS_HOME", env::get("XLINGS_HOME"));
+    env::ScopedEnv prior("XLINGS_ACTIVE_SUBOS", std::string("shell-subos"));
+    {
+        auto e = xlings_env("");
+        mcpp::xlings::ScopedInvocationEnv scope(e);
+        (void)mcpp::xlings::build_command_prefix(e);
+#if defined(_WIN32)
+        EXPECT_FALSE(env::get("XLINGS_ACTIVE_SUBOS").has_value());
+#endif
+    }
+    EXPECT_EQ(env::get("XLINGS_ACTIVE_SUBOS"), std::optional<std::string>("shell-subos"));
+}