diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c028ef7..6581727 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,6 +5,10 @@ on:
     branches: [main]
   pull_request:
 
+env:
+  XLINGS_VERSION: 0.4.51
+  MCPP_VERSION: 0.0.52
+
 jobs:
   build-linux-mcpp:
     name: build (linux x86_64, mcpp)
@@ -13,8 +17,6 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install xlings
-        env:
-          XLINGS_VERSION: 0.4.31
         run: |
           tarball="xlings-${XLINGS_VERSION}-linux-x86_64.tar.gz"
           curl -fsSL -o "/tmp/${tarball}" \
@@ -26,14 +28,14 @@ jobs:
       - name: Refresh package index
         run: xlings update
 
-      - name: Install workspace tools (.xlings.json → mcpp 0.0.13)
+      - name: Install workspace tools (.xlings.json -> mcpp ${{ env.MCPP_VERSION }})
         run: xlings install -y
 
       - name: Cache mcpp sandbox
         uses: actions/cache@v4
         with:
-          path: ~/.xlings/data/xpkgs/xim-x-mcpp/0.0.13/registry
-          key: mcpp-sandbox-${{ runner.os }}-mcpp0.0.13
+          path: ~/.xlings/data/xpkgs/xim-x-mcpp/${{ env.MCPP_VERSION }}/registry
+          key: mcpp-sandbox-${{ runner.os }}-mcpp${{ env.MCPP_VERSION }}
 
       - name: Build with mcpp
         run: mcpp build
@@ -46,15 +48,18 @@ jobs:
           "$binary" --version
 
   build-macos:
-    runs-on: macos-15
+    name: build (${{ matrix.os }}, mcpp)
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [macos-14, macos-15]
     steps:
-      - name: Checkout code
-        uses: actions/checkout@v4
+      - uses: actions/checkout@v4
 
-      - name: Install Xlings
+      - name: Install xlings
         env:
           XLINGS_NON_INTERACTIVE: 1
-          XLINGS_VERSION: 0.4.31
         run: |
           TARBALL="xlings-${XLINGS_VERSION}-macosx-arm64.tar.gz"
           curl -fSL -o "$RUNNER_TEMP/$TARBALL" "https://github.com/d2learn/xlings/releases/download/v${XLINGS_VERSION}/${TARBALL}"
@@ -63,44 +68,117 @@ jobs:
           xattr -dr com.apple.quarantine "$EXTRACT_DIR" 2>/dev/null || true
           chmod +x "$EXTRACT_DIR/bin/xlings"
           "$EXTRACT_DIR/bin/xlings" self install
-          echo "PATH=$HOME/.xlings/subos/current/bin:$PATH" >> "$GITHUB_ENV"
+          echo "$HOME/.xlings/subos/current/bin" >> "$GITHUB_PATH"
 
-      - name: Install Project Dependencies via Xlings
-        run: |
-          xlings install
-          clang --version
+      - name: Refresh package index
+        run: xlings update
 
-      - name: Configure xmake
-        run: |
-          LLVM_ROOT="$HOME/.xlings/data/xpkgs/xim-x-llvm"
-          LLVM_SDK=$(find "$LLVM_ROOT" -mindepth 1 -maxdepth 1 -type d | sort -V | tail -1)
-          test -d "$LLVM_SDK"
-          "$LLVM_SDK/bin/clang++" --version
-          xmake f -m release --toolchain=llvm --sdk="$LLVM_SDK" -y -vvD
+      - name: Install workspace tools (.xlings.json -> mcpp ${{ env.MCPP_VERSION }})
+        run: xlings install -y
 
-      - name: Build with xmake
-        run: xmake -a -j"$(sysctl -n hw.logicalcpu)"
+      - name: Build with mcpp
+        run: mcpp build
 
       - name: Verify d2x
         run: |
-          ./build/macosx/arm64/release/d2x --version
+          BIN=$(find target -name d2x -type f | head -1)
+          test -n "$BIN" || { echo "d2x binary not found"; find target -type f | head -20; exit 1; }
+          chmod +x "$BIN"
+          "$BIN" --version
 
   build-windows:
+    name: build (windows x86_64, mcpp)
     runs-on: windows-latest
+    defaults:
+      run:
+        shell: bash
+    env:
+      XLINGS_NON_INTERACTIVE: 1
     steps:
-      - name: Checkout code
-        uses: actions/checkout@v4
+      - uses: actions/checkout@v4
 
-      - name: Setup xmake
-        uses: xmake-io/github-action-setup-xmake@v1
-        with:
-          xmake-version: latest
+      # Everything in one bash step so the in-process PATH is used directly
+      # (avoids cross-step PATH translation issues for the msys/Windows mix).
+      - name: Install xlings and build with mcpp
+        run: |
+          set -e
+          ZIP="xlings-${XLINGS_VERSION}-windows-x86_64.zip"
+          curl -fSL -o "$RUNNER_TEMP/$ZIP" "https://github.com/d2learn/xlings/releases/download/v${XLINGS_VERSION}/${ZIP}"
+          unzip -q "$RUNNER_TEMP/$ZIP" -d "$RUNNER_TEMP/xl"
+          XL=$(find "$RUNNER_TEMP/xl" -name 'xlings.exe' | head -1)
+          echo "xlings: $XL"
+          "$XL" self install
+          export PATH="$HOME/.xlings/subos/current/bin:$PATH"
+          xlings update
+          xlings install -y
+          mcpp build
+          D2X=$(find target -name 'd2x.exe' -type f | head -1)
+          test -n "$D2X" || { echo "d2x.exe not found"; find target -type f | head -20; exit 1; }
+          "$D2X" --version
+
+  # Smoke test: a real `d2x checker` run against the d2mcpp course must reach
+  # and report the FIRST exercise's build error within a bounded window, rather
+  # than hanging on the init log (issue #24). The checker waits for file edits
+  # forever, so a timeout kill is the expected, healthy outcome.
+  checker-smoke:
+    name: checker smoke (linux)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
 
-      - name: Build with xmake
+      - name: Install xlings
         run: |
-          xmake f -m release -y
-          xmake -j$env:NUMBER_OF_PROCESSORS
+          tarball="xlings-${XLINGS_VERSION}-linux-x86_64.tar.gz"
+          curl -fsSL -o "/tmp/${tarball}" \
+            "https://github.com/d2learn/xlings/releases/download/v${XLINGS_VERSION}/${tarball}"
+          tar -xzf "/tmp/${tarball}" -C /tmp
+          "/tmp/xlings-${XLINGS_VERSION}-linux-x86_64/subos/default/bin/xlings" self install
+          echo "$HOME/.xlings/subos/current/bin" >> "$GITHUB_PATH"
 
-      - name: Verify d2x
+      - name: Refresh package index
+        run: xlings update
+
+      - name: Build d2x with mcpp
+        run: |
+          xlings install -y
+          mcpp build
+
+      # Use a real xmake (not the xlings `xmake` shim): d2mcpp's .xlings.json
+      # pins xmake 3.0.7, which is gone from the registry, so the shim would
+      # fail to resolve. A standalone xmake ignores .xlings.json. Put it ahead
+      # of the xlings bin on PATH.
+      - name: Install xmake
+        run: |
+          curl -fsSL https://xmake.io/shget.text | bash
+          source ~/.xmake/profile 2>/dev/null || true
+          echo "$HOME/.local/bin" >> "$GITHUB_PATH"
+          "$HOME/.local/bin/xmake" --version
+
+      - name: Checkout d2mcpp course
+        uses: actions/checkout@v4
+        with:
+          repository: mcpp-community/d2mcpp
+          path: d2mcpp
+
+      - name: Run d2x checker (must reach first exercise, not hang on load)
         run: |
-          build\windows\x64\release\d2x.exe --version
+          D2X="$PWD/$(find target -name d2x -type f | head -1)"
+          test -x "$D2X" || chmod +x "$D2X"
+          cd d2mcpp
+          # Force the print UI so output is plain text in a non-TTY runner.
+          sed -i 's/"ui_backend": *"tui"/"ui_backend": "print"/' .d2x.json || true
+          xmake f -y
+          set +e
+          timeout 120 "$D2X" checker --ui print --lang en > checker.out 2>&1
+          code=$?
+          set -e
+          echo "checker exit=$code (124 = killed by timeout while waiting for edits = expected)"
+          echo "------------------ checker output (tail) ------------------"
+          tail -n 40 checker.out || true
+          echo "-----------------------------------------------------------"
+          if grep -q "hello-mcpp" checker.out && grep -qiE "error" checker.out; then
+            echo "OK: checker reached and reported the first exercise (not stuck on the loading log)"
+          else
+            echo "FAIL: checker produced no exercise build output within the window (stuck on load?)"
+            exit 1
+          fi
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index ca1a6ab..eb1ef5c 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -9,7 +9,7 @@ on:
         type: string
 
 env:
-  XLINGS_VERSION: v0.4.0
+  XLINGS_VERSION: v0.4.51
 
 jobs:
   build-linux:
@@ -36,19 +36,29 @@ jobs:
           "$EXTRACT_DIR/bin/xlings" self install
           echo "PATH=$HOME/.xlings/subos/current/bin:$PATH" >> "$GITHUB_ENV"
 
-      - name: Install Project Dependencies via Xlings
-        run: |
-          xlings install
+      - name: Refresh package index
+        run: xlings update
+
+      - name: Install workspace tools (.xlings.json -> mcpp)
+        run: xlings install -y
+
+      - name: Build with mcpp (static)
+        run: mcpp build --static
 
-      - name: Build with xmake
+      - name: Locate & verify binary
         run: |
-          xmake f -m release -y
-          xmake -j$(nproc)
+          BIN=$(find target -name d2x -type f | head -1)
+          test -n "$BIN" || { echo "d2x binary not found"; find target -type f | head; exit 1; }
+          chmod +x "$BIN"
+          ver=$("$BIN" --version)
+          echo "built d2x version: $ver (release input: ${{ inputs.version }})"
+          test "$ver" = "${{ inputs.version }}" || { echo "ERROR: binary version ($ver) != release version (${{ inputs.version }})"; exit 1; }
+          echo "BIN=$BIN" >> "$GITHUB_ENV"
 
       - name: Create release package
         run: |
           mkdir -p d2x-${{ inputs.version }}-linux-x86_64
-          cp build/linux/x86_64/release/d2x d2x-${{ inputs.version }}-linux-x86_64/
+          cp "$BIN" d2x-${{ inputs.version }}-linux-x86_64/
           tar -czf d2x-${{ inputs.version }}-linux-x86_64.tar.gz d2x-${{ inputs.version }}-linux-x86_64
 
       - name: Upload artifact
@@ -58,7 +68,9 @@ jobs:
           path: d2x-${{ inputs.version }}-linux-x86_64.tar.gz
 
   build-macos:
-    runs-on: macos-15
+    # Built on the oldest supported macOS so the artifact also runs on newer
+    # releases. mcpp manages its own toolchain, so no SDK pinning is needed.
+    runs-on: macos-14
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
@@ -77,31 +89,29 @@ jobs:
           "$EXTRACT_DIR/bin/xlings" self install
           echo "PATH=$HOME/.xlings/subos/current/bin:$PATH" >> "$GITHUB_ENV"
 
-      - name: Install Project Dependencies via Xlings
-        run: |
-          xlings install
-          clang --version
+      - name: Refresh package index
+        run: xlings update
 
-      - name: Build with xmake
-        run: |
-          export LLVM_PREFIX=$HOME/.xlings/data/xpkgs/xim-x-llvm/20.1.7
-          xmake f -m release --toolchain=llvm --sdk=$LLVM_PREFIX -vv -y
-          xmake -j$(nproc)
+      - name: Install workspace tools (.xlings.json -> mcpp)
+        run: xlings install -y
+
+      - name: Build with mcpp
+        run: mcpp build
 
-      - name: Verify no LLVM runtime dependency
+      - name: Locate & verify binary
         run: |
-          BIN=build/macosx/arm64/release/d2x
-          if otool -L "$BIN" | grep -q "llvm"; then
-            otool -L "$BIN"
-            echo "FAIL: binary links against LLVM dylib"
-            exit 1
-          fi
-          echo "OK: binary has no LLVM runtime dependency"
+          BIN=$(find target -name d2x -type f | head -1)
+          test -n "$BIN" || { echo "d2x binary not found"; find target -type f | head; exit 1; }
+          chmod +x "$BIN"
+          ver=$("$BIN" --version)
+          echo "built d2x version: $ver (release input: ${{ inputs.version }})"
+          test "$ver" = "${{ inputs.version }}" || { echo "ERROR: binary version ($ver) != release version (${{ inputs.version }})"; exit 1; }
+          echo "BIN=$BIN" >> "$GITHUB_ENV"
 
       - name: Create release package
         run: |
           mkdir -p d2x-${{ inputs.version }}-macosx-arm64
-          cp build/macosx/arm64/release/d2x d2x-${{ inputs.version }}-macosx-arm64/
+          cp "$BIN" d2x-${{ inputs.version }}-macosx-arm64/
           tar -czf d2x-${{ inputs.version }}-macosx-arm64.tar.gz d2x-${{ inputs.version }}-macosx-arm64
 
       - name: Upload artifact
@@ -112,25 +122,39 @@ jobs:
 
   build-windows:
     runs-on: windows-latest
+    defaults:
+      run:
+        shell: bash
+    env:
+      XLINGS_NON_INTERACTIVE: 1
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
 
-      - name: Setup xmake
-        uses: xmake-io/github-action-setup-xmake@v1
-        with:
-          xmake-version: latest
-
-      - name: Build with xmake
+      - name: Install xlings and build with mcpp
         run: |
-          xmake f -m release -y
-          xmake -j$env:NUMBER_OF_PROCESSORS
-
-      - name: Create release package
+          set -e
+          VERSION_NUM="${XLINGS_VERSION#v}"
+          ZIP="xlings-${VERSION_NUM}-windows-x86_64.zip"
+          curl -fSL -o "$RUNNER_TEMP/$ZIP" "https://github.com/d2learn/xlings/releases/download/${XLINGS_VERSION}/${ZIP}"
+          unzip -q "$RUNNER_TEMP/$ZIP" -d "$RUNNER_TEMP/xl"
+          XL=$(find "$RUNNER_TEMP/xl" -name 'xlings.exe' | head -1)
+          "$XL" self install
+          export PATH="$HOME/.xlings/subos/current/bin:$PATH"
+          xlings update
+          xlings install -y
+          mcpp build
+          D2X=$(find target -name 'd2x.exe' -type f | head -1)
+          test -n "$D2X" || { echo "d2x.exe not found"; find target -type f | head; exit 1; }
+          ver=$("$D2X" --version)
+          echo "built d2x version: $ver (release input: ${{ inputs.version }})"
+          test "$ver" = "${{ inputs.version }}" || { echo "ERROR: binary version ($ver) != release version (${{ inputs.version }})"; exit 1; }
+          mkdir -p "d2x-${{ inputs.version }}-windows-x86_64"
+          cp "$D2X" "d2x-${{ inputs.version }}-windows-x86_64/"
+
+      - name: Zip release package
         shell: pwsh
         run: |
-          New-Item -ItemType Directory -Path "d2x-${{ inputs.version }}-windows-x86_64" -Force
-          Copy-Item "build\windows\x64\release\d2x.exe" -Destination "d2x-${{ inputs.version }}-windows-x86_64\"
           Compress-Archive -Path "d2x-${{ inputs.version }}-windows-x86_64" -DestinationPath "d2x-${{ inputs.version }}-windows-x86_64.zip"
 
       - name: Upload artifact
diff --git a/.gitignore b/.gitignore
index 700d111..75cc0d6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,5 @@
 build
 target
 d2x.zip
+mcpp.lock
+compile_commands.json
diff --git a/.xlings.json b/.xlings.json
index 1eb6d31..e88cf7b 100644
--- a/.xlings.json
+++ b/.xlings.json
@@ -1,8 +1,5 @@
 {
   "workspace": {
-    "mcpp": { "linux": "0.0.13" },
-    "xmake": "3.0.7",
-    "gcc": { "linux": "15.1.0" },
-    "llvm": { "macosx": "20" }
+    "mcpp": { "linux": "0.0.52", "macosx": "0.0.52", "windows": "0.0.52" }
   }
 }
diff --git a/README.md b/README.md
index 13c57d4..1e9e81f 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@
 | --- |
 
 ```cpp
-d2x version: 0.1.4
+d2x version: 0.1.5
 
 Usage: $ d2x [command] [target] [options]
 
diff --git a/mcpp.toml b/mcpp.toml
index 966fdb6..b3adb9e 100644
--- a/mcpp.toml
+++ b/mcpp.toml
@@ -1,6 +1,6 @@
 [package]
 name        = "d2x"
-version     = "0.1.2"
+version     = "0.1.5"
 description = "AI-powered development assistant for C++ projects"
 license     = "Apache-2.0"
 repo        = "https://github.com/d2learn/d2x"
diff --git a/src/cmdprocessor.cppm b/src/cmdprocessor.cppm
index 0a987de..ee8fbc9 100644
--- a/src/cmdprocessor.cppm
+++ b/src/cmdprocessor.cppm
@@ -91,7 +91,14 @@ export int run(int argc, char* argv[]) {
             .action([](const cmdline::ParsedArgs& a) {
                 apply_global_options(a);
                 auto bookdir = std::filesystem::path(platform::get_rundir()) / "book";
-                if (Config::lang() == "en") bookdir /= "en";
+                // Resolve language sub-book generically (issue #8): any language
+                // shipped by the target project as book/<lang> is supported, not
+                // just zh/en. Falls back to the default book/ when absent.
+                const auto& lang = Config::lang();
+                if (!lang.empty() && lang != "auto") {
+                    auto langdir = bookdir / lang;
+                    if (std::filesystem::exists(langdir)) bookdir = langdir;
+                }
                 std::println("Opening book: {}", bookdir.string());
                 if (std::filesystem::exists(bookdir)) {
                     platform::run_command_capture("xlings install mdbook -y");
diff --git a/src/config.cppm b/src/config.cppm
index 472c75d..8e44234 100644
--- a/src/config.cppm
+++ b/src/config.cppm
@@ -17,7 +17,7 @@ export struct EnvVars;
 export class Config;
 
 struct Info {
-    static constexpr std::string_view VERSION = "0.1.4";
+    static constexpr std::string_view VERSION = "0.1.5";
     static constexpr std::string_view REPO = "https://github.com/d2learn/d2x";
 };
 
diff --git a/src/platform/windows.cppm b/src/platform/windows.cppm
index e39bf33..e17f124 100644
--- a/src/platform/windows.cppm
+++ b/src/platform/windows.cppm
@@ -15,7 +15,8 @@ namespace platform_impl {
     export constexpr std::string_view XLINGS_INSTALL_CMD = "powershell -Command \"irm https://d2learn.org/xlings-install.ps1.txt | iex\"";
 
     export std::pair<int, std::string> run_command_capture(const std::string& cmd) {
-        FILE* pipe = _popen(cmd.c_str(), "r");
+        std::string full = cmd + " 2>&1"; // redirect stderr to stdout (match linux/macos)
+        FILE* pipe = _popen(full.c_str(), "r");
         if (!pipe) {
             return {-1, std::string{}};
         }
diff --git a/xmake.lua b/xmake.lua
deleted file mode 100644
index bef1f14..0000000
--- a/xmake.lua
+++ /dev/null
@@ -1,27 +0,0 @@
-add_rules("mode.debug", "mode.release")
-
-set_languages("c++23")
-
-add_repositories("mcpplibs-index https://github.com/mcpplibs/mcpplibs-index.git")
-
-add_requires("llmapi 0.2.5")
-add_requires("mcpplibs-tinyhttps 0.2.2")
-add_requires("mbedtls v3.6.1")
-add_requires("cmdline 0.0.2")
-add_requires("ftxui 6.1.9")
-
-target("d2x")
-    set_kind("binary")
-
-    add_files("src/main.cpp")
-    -- add common module interface units
-    add_files("src/**.cppm")
-    add_packages("ftxui", "llmapi", "mcpplibs-tinyhttps", "mbedtls", "cmdline")
-    set_policy("build.c++.modules", true)
-
-    -- platform specific settings
-    if is_plat("macosx") then
-        set_toolchains("llvm")
-    elseif is_plat("linux") then
-        add_ldflags("-static", {force = true})
-    end