add multi-platform CI and mcpplibs-index-add skill

CI: build & test all packages on Linux (GCC 14) and macOS (LLVM 20).
Each package × platform runs as a separate matrix job.
llmapi tests are build-only (require API key at runtime).

Skill: document full library onboarding workflow with cross-platform
C++23 toolchain reference (GCC/LLVM/MSVC setup for CI).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Sunrisepeak

.agents/skills/mcpplibs-index-add.md

@@ -14,6 +14,7 @@ This skill adds a new library from `https://github.com/mcpplibs/<name>` to the m
 - xmake package docs: https://xmake.io/mirror/manual/package_dependencies.html
 - mcpplibs org: https://github.com/mcpplibs
 - index repo: https://github.com/mcpplibs/mcpplibs-index
+- xlings CI reference (cross-platform C++23 toolchain): https://github.com/d2learn/xlings/tree/main/.github/workflows
 
 ## Step 1: Gather Library Info
 
@@ -110,7 +111,18 @@ Add an `includes()` line to `tests/xmake.lua`:
 includes("<first-letter>/<package-name>")
 ```
 
-## Step 6: Verify Build
+## Step 6: Update CI Matrix
+
+Add the new test to `.github/workflows/ci.yml` matrix:
+
+```yaml
+- name: <package-name>
+  dir: tests/<first-letter>/<package-name>
+  target: <package-name>_test
+  run: true   # false if test needs network/API keys
+```
+
+## Step 7: Verify Build
 
 ```bash
 # Clean any cached package
@@ -129,20 +141,104 @@ xmake run <package-name>_test
 
 All three commands must succeed before proceeding.
 
-## Step 7: Create Branch, Commit & Push
+## Step 8: Create Branch, Commit & Push
 
 ```bash
 git checkout -b add-<repo-name>-library
 git add packages/<first-letter>/<package-name>/xmake.lua \
        tests/<first-letter>/<package-name>/xmake.lua \
        tests/<first-letter>/<package-name>/main.cpp \
-       tests/xmake.lua
+       tests/xmake.lua \
+       .github/workflows/ci.yml
 git commit -m "add <package-name> library"
 git push -u upstream add-<repo-name>-library
 ```
 
 Use `upstream` (SSH remote) for push, not `origin` (HTTPS, no auth).
 
+## C++23 Toolchain Reference
+
+All mcpplibs packages require C++23 with modules support. Below are the toolchain configurations for each platform, referenced from [xlings CI](https://github.com/d2learn/xlings/tree/main/.github/workflows).
+
+### Linux — GCC 14 (Ubuntu 24.04)
+
+```bash
+sudo apt-get install -y gcc-14 g++-14
+sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-14 100
+sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-14 100
+xmake f -y --toolchain=gcc
+```
+
+For static/cross builds (musl-gcc 15.1.0, used by xlings):
+```bash
+xmake f -c -p linux -m release \
+  --sdk="$MUSL_SDK" \
+  --cross=x86_64-linux-musl- \
+  --cc=x86_64-linux-musl-gcc \
+  --cxx=x86_64-linux-musl-g++
+```
+
+### macOS — LLVM 20 (macOS 15)
+
+```bash
+brew install llvm@20
+xmake f -y --toolchain=llvm --sdk=/opt/homebrew/opt/llvm@20
+```
+
+For static linking of libc++ (no runtime dependency on LLVM dylibs):
+```lua
+-- in xmake.lua
+local llvm_prefix = os.getenv("LLVM_PREFIX") or "/opt/homebrew/opt/llvm@20"
+local libcxx_dir = llvm_prefix .. "/lib/c++"
+add_ldflags("-nostdlib++", {force = true})
+add_ldflags(libcxx_dir .. "/libc++.a", {force = true})
+add_ldflags(libcxx_dir .. "/libc++experimental.a", {force = true})
+add_ldflags("-lc++abi", {force = true})
+```
+
+Verify no LLVM dylib dependency: `otool -L <binary> | grep llvm`
+
+### Windows — MSVC (windows-latest)
+
+```bash
+xmake f -y   # auto-selects MSVC
+```
+
+No special configuration needed. MSVC from Visual Studio supports C++23.
+
+### Toolchain Version Summary
+
+| Platform | Compiler | Version | Runner |
+|----------|----------|---------|--------|
+| Linux | GCC | 14+ | ubuntu-24.04 |
+| Linux (static) | musl-gcc | 15.1.0 | ubuntu-24.04 |
+| macOS | LLVM/Clang | 20 | macos-15 |
+| Windows | MSVC | latest | windows-latest |
+
+### GitHub Actions Setup Pattern
+
+```yaml
+# Linux
+- os: ubuntu-24.04
+  setup: |
+    sudo apt-get update
+    sudo apt-get install -y gcc-14 g++-14
+    sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-14 100
+    sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-14 100
+  toolchain: gcc
+
+# macOS
+- os: macos-15
+  setup: brew install llvm@20
+  toolchain: llvm
+  sdk: /opt/homebrew/opt/llvm@20
+
+# Windows
+- os: windows-latest
+  setup: echo "MSVC auto-detected"
+  toolchain: msvc
+```
+
 ## Checklist
 
 - [ ] Package directory name == `package("xxx")` name
@@ -151,6 +247,7 @@ Use `upstream` (SSH remote) for push, not `origin` (HTTPS, no auth).
 - [ ] Extra headers copied in `on_install` if needed by cppm
 - [ ] Test does NOT have `add_repositories()` (top-level handles it)
 - [ ] Test registered in `tests/xmake.lua` via `includes()`
+- [ ] CI matrix updated with new test entry
 - [ ] `xmake build` succeeds
 - [ ] `xmake run` produces expected output
 - [ ] Committed and pushed to upstream

.github/workflows/ci.yml

@@ -0,0 +1,79 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        test:
+          - name: templates
+            dir: tests/t/templates
+            target: templates_test
+            run: true
+          - name: cmdline
+            dir: tests/c/cmdline
+            target: cmdline_test
+            run: true
+            run_args: test_input
+          - name: llmapi
+            dir: tests/l/llmapi
+            target: llmapi_test
+            run: false
+          - name: llmapi-capi
+            dir: tests/l/llmapi/capi
+            target: llmapi_test_c
+            run: false
+          - name: lua
+            dir: tests/l/lua
+            target: lua_test
+            run: true
+        platform:
+          - os: ubuntu-24.04
+            setup: |
+              sudo apt-get update
+              sudo apt-get install -y gcc-14 g++-14
+              sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-14 100
+              sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-14 100
+            toolchain: gcc
+          - os: macos-15
+            setup: brew install llvm@20
+            toolchain: llvm
+            sdk: /opt/homebrew/opt/llvm@20
+
+    runs-on: ${{ matrix.platform.os }}
+    name: ${{ matrix.test.name }} (${{ matrix.platform.os }})
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup xmake
+        uses: xmake-io/github-action-setup-xmake@v1
+        with:
+          xmake-version: latest
+
+      - name: Setup toolchain
+        run: ${{ matrix.platform.setup }}
+
+      - name: Configure
+        working-directory: ${{ matrix.test.dir }}
+        run: |
+          if [ -n "${{ matrix.platform.sdk }}" ]; then
+            xmake f -y --toolchain=${{ matrix.platform.toolchain }} --sdk=${{ matrix.platform.sdk }}
+          else
+            xmake f -y --toolchain=${{ matrix.platform.toolchain }}
+          fi
+
+      - name: Build
+        working-directory: ${{ matrix.test.dir }}
+        run: xmake build ${{ matrix.test.target }}
+
+      - name: Run
+        if: matrix.test.run
+        working-directory: ${{ matrix.test.dir }}
+        run: xmake run ${{ matrix.test.target }} ${{ matrix.test.run_args }}