fix: mcpp auto-resolves LLVM from global xlings when sandbox payload missing

When xlings installs a toolchain into the mcpp sandbox, the payload
may end up in xlings' own global data dir instead of the sandbox.
Add fallback: if the expected xpkg path is missing, check
~/.xlings/data/xpkgs/ and copy from there.

Remove CI workarounds: no more explicit `xlings install llvm` or
pre-seed cp -r steps. mcpp now handles this like a real user would.

Author: Sunrisepeak

.github/workflows/ci-windows.yml

@@ -56,8 +56,7 @@ jobs:
           export PATH="$USERPROFILE/.xlings/subos/default/bin:$PATH"
           echo "$USERPROFILE/.xlings/subos/default/bin" >> "$GITHUB_PATH"
           xlings.exe --version
-          xlings.exe install llvm -y || xlings.exe install llvm@20.1.7 -y
-          xlings.exe install mcpp -y || xlings.exe install mcpp@0.0.17 -y
+          xlings.exe install mcpp -y
           echo "=== Searching for mcpp binary ==="
           find "$USERPROFILE/.xlings" -name "mcpp.exe" -o -name "mcpp" 2>/dev/null | head -10
           MCPP=$(find "$USERPROFILE/.xlings" -name "mcpp.exe" -path "*/bin/*" 2>/dev/null | head -1)
@@ -76,16 +75,6 @@ jobs:
         run: |
           export MCPP_VENDORED_XLINGS="$XLINGS_BIN"
 
-          # Pre-seed mcpp sandbox with xlings LLVM (avoids redundant download)
-          MCPP_XPKGS="$USERPROFILE/.mcpp/registry/data/xpkgs"
-          XLINGS_XPKGS="$USERPROFILE/.xlings/data/xpkgs"
-          if [ -d "$XLINGS_XPKGS/xim-x-llvm" ]; then
-            mkdir -p "$MCPP_XPKGS"
-            rm -rf "$MCPP_XPKGS/xim-x-llvm"
-            cp -r "$XLINGS_XPKGS/xim-x-llvm" "$MCPP_XPKGS/xim-x-llvm"
-            echo "Pre-seeded LLVM from global xlings"
-          fi
-
           "$MCPP" build
 
           MCPP_SELF=$(find target -name "mcpp.exe" -path "*/bin/*" | head -1)

.github/workflows/release.yml

@@ -462,8 +462,7 @@ jobs:
           export PATH="$USERPROFILE/.xlings/subos/default/bin:$PATH"
           echo "$USERPROFILE/.xlings/subos/default/bin" >> "$GITHUB_PATH"
           xlings.exe --version
-          xlings.exe install llvm -y || xlings.exe install llvm@20.1.7 -y
-          xlings.exe install mcpp -y || xlings.exe install mcpp@0.0.17 -y
+          xlings.exe install mcpp -y
           MCPP=$(find "$USERPROFILE/.xlings" -name "mcpp.exe" -path "*/bin/*" 2>/dev/null | head -1)
           if [ -z "$MCPP" ]; then
             MCPP=$(find "$USERPROFILE/.xlings" -name "mcpp" -path "*/bin/*" 2>/dev/null | head -1)
@@ -481,15 +480,6 @@ jobs:
         run: |
           export MCPP_VENDORED_XLINGS="$XLINGS_BIN"
 
-          # Pre-seed mcpp sandbox with xlings LLVM (avoids redundant download)
-          MCPP_XPKGS="$USERPROFILE/.mcpp/registry/data/xpkgs"
-          if [ -d "$XLINGS_XPKGS/xim-x-llvm" ]; then
-            mkdir -p "$MCPP_XPKGS"
-            rm -rf "$MCPP_XPKGS/xim-x-llvm"
-            cp -r "$XLINGS_XPKGS/xim-x-llvm" "$MCPP_XPKGS/xim-x-llvm"
-            echo "Pre-seeded LLVM from global xlings"
-          fi
-
           "$MCPP" build
 
           MCPP_BIN=$(find target -name "mcpp.exe" -path "*/bin/*" | head -1)

src/pm/package_fetcher.cppm

@@ -605,6 +605,28 @@ Fetcher::resolve_xpkg_path(std::string_view target,
     };
 
     auto resolve = [&]() -> std::expected<XpkgPayload, CallError> {
+        if (!std::filesystem::exists(verdir)) {
+            // xlings may have installed the package into its own global home
+            // rather than the mcpp sandbox. Try to copy it from the global
+            // xlings data directory.
+            auto xlings_home_env = std::getenv("HOME");
+#if defined(_WIN32)
+            if (!xlings_home_env) xlings_home_env = std::getenv("USERPROFILE");
+#endif
+            if (xlings_home_env) {
+                auto globalXpkgs = std::filesystem::path(xlings_home_env)
+                    / ".xlings" / "data" / "xpkgs"
+                    / verdir.parent_path().filename()
+                    / verdir.filename();
+                std::error_code ec;
+                if (std::filesystem::exists(globalXpkgs, ec)) {
+                    std::filesystem::create_directories(verdir.parent_path(), ec);
+                    std::filesystem::copy(globalXpkgs, verdir,
+                        std::filesystem::copy_options::recursive
+                        | std::filesystem::copy_options::overwrite_existing, ec);
+                }
+            }
+        }
         if (!std::filesystem::exists(verdir)) {
             return std::unexpected(CallError{
                 std::format("xpkg payload missing: {}", verdir.string())});