ci: 克隆带过来的 workspace pin 指向索引里已经没有的版本

  xlings: version '2026.8.17.1' not found for 'mcpp'
    available: 2026.8.19.4

仓库根的 .xlings.json 决定那棵树里的构建用哪个 mcpp,而 mcpp 自己的 bootstrap
pin 不随发布移动 —— 它是上次动这个文件时的当前版本。把分支克隆过来,就把一个
只在那个仓库自己的 CI 里成立的 pin 一起带了过来。

改写成本 job 已经装好的那个版本,两边就一致了。它不改变被测的东西:pin 选的是
**构建 mcpp 的**工具,而被测的是构建出来的那个 mcpp。

Author: speak-agent

.github/workflows/ci.yml

@@ -131,6 +131,24 @@ jobs:
           git clone --depth 1 -b feat/import-std-capability \
             https://github.com/mcpp-community/mcpp "$RUNNER_TEMP/mcpp-src"
           cd "$RUNNER_TEMP/mcpp-src"
+          # ⚠️ THE CLONE CARRIES A WORKSPACE PIN, AND IT NAMES A VERSION THE
+          # INDEX NO LONGER HAS.
+          #
+          #     xlings: version '2026.8.17.1' not found for 'mcpp'
+          #       available: 2026.8.19.4
+          #
+          # `.xlings.json` at a repository root says which mcpp a build in that
+          # tree uses, and mcpp's own bootstrap pin does not move when mcpp is
+          # released — it is the version that was current when the pin was last
+          # touched. Cloning the branch therefore imports a pin that is only
+          # valid inside that repository's own CI, where the same file selects
+          # what gets installed.
+          #
+          # Rewriting it to the version this job already installed is what makes
+          # the two agree. It changes nothing about what is being tested: the
+          # pin selects the tool that BUILDS mcpp, and what is under test is the
+          # mcpp that comes out.
+          printf '{\n  "workspace": {\n    "mcpp": "%s"\n  }\n}\n' "$MCPP_VERSION" > .xlings.json
           mcpp build --release
           BUILT=$(find target -type f -name mcpp -perm -u+x | head -1)
           [ -n "$BUILT" ] || { echo "::error::mcpp did not build"; exit 1; }