diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index 5b58794..49f80a1 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -19,9 +19,15 @@ jobs:
 
       - name: Install dependencies
         run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
           sudo apt-get update -qq
           sudo apt-get install -y \
-            clang git nodejs pre-commit
+            clang-21 git nodejs pre-commit
+          for tool in clang clang++; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
 
       - uses: actions/cache@v4
         with:
@@ -57,12 +63,18 @@ jobs:
 
       - name: Install dependencies
         run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
           sudo apt-get update -qq
           sudo apt-get install -y \
-            build-essential ccache clang cmake gcc g++ \
-            libc6-dbg llvm mold ninja-build python3 valgrind zstd
+            build-essential ccache clang-21 cmake gcc g++ \
+            libc6-dbg llvm-21 lld-21 mold ninja-build python3 valgrind zstd
           sudo curl -Ls "https://dl.min.io/client/mc/release/linux-amd64/mc" \
             -o /usr/local/bin/mc && sudo chmod +x /usr/local/bin/mc
+          for tool in clang clang++ llvm-ar llvm-nm llvm-ranlib llvm-objcopy llvm-cov llvm-symbolizer lld ld.lld; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
 
       - uses: actions/cache@v4
         with:
@@ -124,14 +136,20 @@ jobs:
 
       - name: Install dependencies
         run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
           sudo apt-get update -qq
           sudo apt-get install -y \
-            biber build-essential ccache clang cmake devscripts \
-            latexmk libc6-dbg llvm mold ninja-build rpm \
+            biber build-essential ccache clang-21 cmake devscripts \
+            latexmk libc6-dbg llvm-21 lld-21 mold ninja-build rpm \
             texlive-bibtex-extra texlive-fonts-recommended \
             texlive-latex-extra texlive-pictures valgrind zstd
           sudo curl -Ls "https://dl.min.io/client/mc/release/linux-$(dpkg --print-architecture)/mc" \
             -o /usr/local/bin/mc && sudo chmod +x /usr/local/bin/mc
+          for tool in clang clang++ llvm-ar llvm-nm llvm-ranlib llvm-objcopy llvm-cov llvm-symbolizer lld ld.lld; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
 
       - uses: actions/cache@v4
         with:
@@ -212,12 +230,18 @@ jobs:
 
       - name: Install dependencies
         run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
           sudo apt-get update -qq
           sudo apt-get install -y \
-            build-essential ccache clang cmake gcovr \
-            libc6-dbg llvm mold ninja-build python3 valgrind zstd
+            build-essential ccache clang-21 cmake gcovr \
+            libc6-dbg llvm-21 lld-21 mold ninja-build python3 valgrind zstd
           sudo curl -Ls "https://dl.min.io/client/mc/release/linux-amd64/mc" \
             -o /usr/local/bin/mc && sudo chmod +x /usr/local/bin/mc
+          for tool in clang clang++ llvm-ar llvm-nm llvm-ranlib llvm-objcopy llvm-cov llvm-symbolizer lld ld.lld; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
 
       - uses: actions/cache@v4
         with: