ci: 引导用的 mcpp 自带一份 xlings,而那份早于一次索引移动

一个 mcpp 发布**内嵌**一份 xlings 在 `<install>/registry/bin/xlings`,而解析
runtime binding 的是**那一份**,不是 quick_install 装的那一份。`xim:glibc` 的
latest 移到 2.44.2,而只有 xlings 2026.8.27.1 改为从索引读默认绑定
(openxlings/xlings#567)。旧的内嵌副本要 `glibc@2.44`,干净环境装出 `2.44.2`,
工具链 post-install 停住:

    error: selected RuntimeBinding glibc@2.44 requires payload
           '.../xpkgs/xim-x-glibc/2.44', but it is not installed

在每一台**新**机器上出现,在任何已存在的机器上都不出现 —— 所以它在开发机上不可见。
索引的 pkgs/g/glibc.lua 把这次失败逐字记着。

⭐ mcpp 2026.8.27.1(mcpp-community/mcpp#515)内嵌的就是 2026.8.27.1,那之后本步骤
是空操作。只在版本不同时替换,并**打印替换了什么** —— 静默替换不可能发生。
待 pin 发布后移除。

Author: speak-agent

.github/workflows/ci.yml

@@ -80,6 +80,74 @@ jobs:
           fi
           mcpp --version
           mcpp self config --mirror GLOBAL
+          # ⚠️⚠️ TRANSITION: THE BOOTSTRAP mcpp CARRIES ITS OWN xlings, AND
+          # THAT COPY PREDATES AN INDEX MOVE.
+          #
+          # An mcpp release BUNDLES an xlings at `<install>/registry/bin/xlings`
+          # (mcpp's `pinned::kXlingsVersion`), and that copy — not the one
+          # installed above — is what resolves runtime bindings for everything
+          # mcpp does. `xim:glibc`'s `latest` moved to 2.44.2, and only
+          # xlings 2026.8.27.1 reads the default binding from the index instead
+          # of a constant compiled into itself (openxlings/xlings#567). An
+          # older bundled copy asks for `glibc@2.44`, a clean environment
+          # installs `2.44.2`, and the toolchain post-install fixup stops:
+          #
+          #     error: selected RuntimeBinding glibc@2.44 requires payload
+          #            '…/xpkgs/xim-x-glibc/2.44', but it is not installed
+          #
+          # on every NEW environment and on none that already existed. The
+          # index records this failure verbatim in `pkgs/g/glibc.lua`.
+          #
+          # ⭐ REMOVE THIS ONCE THE PIN SHIPS. mcpp 2026.8.27.1 bundles
+          # 2026.8.27.1, so a bootstrap from it needs nothing here. The step is
+          # a no-op when the bundled copy is already new enough, and it says
+          # which copy it replaced so a silent substitution is not possible.
+          mcpp_home="${MCPP_HOME:-$HOME/.mcpp}"
+          bundled="$mcpp_home/registry/bin/xlings"
+          if [ -x "$bundled" ] && [ -n "$(command -v xlings)" ]; then
+            have="$("$bundled" --version 2>/dev/null | head -1)"
+            outer="$(xlings --version 2>/dev/null | head -1)"
+            if [ "$have" != "$outer" ]; then
+              cp "$(command -v xlings)" "$bundled"
+              echo "bundled xlings: $have -> $("$bundled" --version | head -1) (was older than the installed one)"
+            else
+              echo "bundled xlings: $have (already the installed one)"
+            fi
+          fi
+          # ⚠️⚠️ TRANSITION: THE BOOTSTRAP mcpp CARRIES ITS OWN xlings, AND
+          # THAT COPY PREDATES AN INDEX MOVE.
+          #
+          # An mcpp release BUNDLES an xlings at `<install>/registry/bin/xlings`
+          # (mcpp's `pinned::kXlingsVersion`), and that copy — not the one
+          # installed above — is what resolves runtime bindings for everything
+          # mcpp does. `xim:glibc`'s `latest` moved to 2.44.2, and only
+          # xlings 2026.8.27.1 reads the default binding from the index instead
+          # of a constant compiled into itself (openxlings/xlings#567). An
+          # older bundled copy asks for `glibc@2.44`, a clean environment
+          # installs `2.44.2`, and the toolchain post-install fixup stops:
+          #
+          #     error: selected RuntimeBinding glibc@2.44 requires payload
+          #            '…/xpkgs/xim-x-glibc/2.44', but it is not installed
+          #
+          # on every NEW environment and on none that already existed. The
+          # index records this failure verbatim in `pkgs/g/glibc.lua`.
+          #
+          # ⭐ REMOVE THIS ONCE THE PIN SHIPS. mcpp 2026.8.27.1 bundles
+          # 2026.8.27.1, so a bootstrap from it needs nothing here. The step is
+          # a no-op when the bundled copy is already new enough, and it says
+          # which copy it replaced so a silent substitution is not possible.
+          mcpp_home="${MCPP_HOME:-$HOME/.mcpp}"
+          bundled="$mcpp_home/registry/bin/xlings"
+          if [ -x "$bundled" ] && [ -n "$(command -v xlings)" ]; then
+            have="$("$bundled" --version 2>/dev/null | head -1)"
+            outer="$(xlings --version 2>/dev/null | head -1)"
+            if [ "$have" != "$outer" ]; then
+              cp "$(command -v xlings)" "$bundled"
+              echo "bundled xlings: $have -> $("$bundled" --version | head -1) (was older than the installed one)"
+            else
+              echo "bundled xlings: $have (already the installed one)"
+            fi
+          fi
           # ⭐⭐ CROSS-VALIDATION: BUILD THE mcpp UNDER REVIEW AND USE THAT ONE.
           #
           # Empty in the ordinary run, so this job keeps testing the RELEASED