diff --git a/.devcontainer/base/Dockerfile b/.devcontainer/base/Dockerfile
index 6194adc0..d27325f4 100644
--- a/.devcontainer/base/Dockerfile
+++ b/.devcontainer/base/Dockerfile
@@ -35,6 +35,8 @@ RUN --mount=type=bind,source=.devcontainer/base/apt-requirements.json,target=/tm
     --mount=type=cache,target=/var/log,sharing=locked \
     --mount=from=extractor,target=/src <<EOF
 
+   set -e
+
    # Install the base system with all tool dependencies
    apt-get update && apt-get install -y --no-install-recommends jq
    jq -r 'to_entries | .[] | .key + "=" + .value' /tmp/apt-requirements.json | \
diff --git a/.devcontainer/cpp/Dockerfile b/.devcontainer/cpp/Dockerfile
index 326e9f88..509a8ceb 100644
--- a/.devcontainer/cpp/Dockerfile
+++ b/.devcontainer/cpp/Dockerfile
@@ -32,6 +32,11 @@ ADD --checksum=sha256:b85cd1e0c94f249338b02a6e54b380154a5af6b5dd754121b15722125a
 # trivy:ignore:AVD-DS-0001
 FROM downloader-${TARGETARCH} AS downloader
 
+ADD --checksum=sha256:ce6eee4130298f79b0e0f09a89f93c1bc711cd68e7e3182d37c8e96c5227e2f0 \
+ https://apt.llvm.org/llvm-snapshot.gpg.key /llvm.gpg.key
+ADD --checksum=sha256:db2938ce5fd422f2db7a07508452772c945135d99274004c462190c323fefcf1 \
+ https://dl.cloudsmith.io/public/mull-project/mull-stable/gpg.41DB35380DE6BD6F.key /mull.gpg.key
+
 # Extractor stage using target architecture specific downloader
 FROM ${BASE_IMAGE} AS extractor
 
@@ -41,8 +46,11 @@ ARG XWIN_VERSION
 WORKDIR /
 
 RUN --mount=from=downloader,target=/dl <<EOF
+    set -e
     tar xJf /dl/ccache.tar.xz --strip-components=1 "ccache-${CCACHE_VERSION}-linux-$(uname -m)/ccache"
     tar xzf /dl/xwin.tar.gz --strip-components=1 "xwin-${XWIN_VERSION}-$(uname -m)-unknown-linux-musl/xwin"
+    cp /dl/llvm.gpg.key /llvm.gpg.key
+    cp /dl/mull.gpg.key /mull.gpg.key
 EOF
 
 # Final development container image
@@ -70,6 +78,7 @@ ENV CCACHE_DIR=/cache/.ccache \
 # Install the base system with all tool dependencies
 # hadolint ignore=DL3008
 RUN --mount=type=bind,source=.devcontainer/cpp/apt-requirements-base.json,target=/tmp/apt-requirements-base.json \
+    --mount=type=bind,source=.devcontainer/cpp/apt-requirements-clang.json,target=/tmp/apt-requirements-clang.json \
     --mount=type=bind,source=.devcontainer/cpp/requirements.txt,target=/tmp/requirements.txt \
     --mount=type=cache,target=/cache,sharing=locked \
     --mount=type=cache,target=/var/cache/apt,sharing=locked \
@@ -77,9 +86,10 @@ RUN --mount=type=bind,source=.devcontainer/cpp/apt-requirements-base.json,target
     --mount=type=cache,target=/var/log,sharing=locked \
     --mount=from=extractor,target=/src <<EOF
 
+    set -e
+
     # Install the base system with all tool dependencies
-    apt-get update && \
-    jq -r 'to_entries | .[] | .key + "=" + .value' /tmp/apt-requirements-base.json | \
+    apt-get update && jq -r 'to_entries | .[] | .key + "=" + .value' /tmp/apt-requirements-base.json | \
         xargs apt-get install -y --no-install-recommends
 
     # Install some tools via pip to get more recent versions, clean up afterwards
@@ -90,21 +100,18 @@ RUN --mount=type=bind,source=.devcontainer/cpp/apt-requirements-base.json,target
     # Install ccache and xwin
     cp /src/ccache /usr/local/bin/ccache
     cp /src/xwin /usr/local/bin/xwin
-EOF
 
-# Install clang toolchain and mull mutation testing framework
-RUN --mount=type=bind,source=.devcontainer/cpp/apt-requirements-clang.json,target=/tmp/apt-requirements-clang.json \
-    --mount=type=cache,target=/var/cache/apt,sharing=locked \
-    --mount=type=cache,target=/var/lib/apt,sharing=locked \
-    --mount=type=cache,target=/var/log,sharing=locked \
- wget --no-hsts -qO - https://apt.llvm.org/llvm-snapshot.gpg.key | gpg --dearmor -o /usr/share/keyrings/llvm-snapshot-keyring.gpg \
- && wget --no-hsts -qO - https://dl.cloudsmith.io/public/mull-project/mull-stable/gpg.41DB35380DE6BD6F.key | gpg --dearmor -o /usr/share/keyrings/mull-project-mull-stable-archive-keyring.gpg \
- && UBUNTU_CODENAME=$(grep '^UBUNTU_CODENAME=' /etc/os-release | cut -d= -f2) \
- && echo "deb [signed-by=/usr/share/keyrings/llvm-snapshot-keyring.gpg] http://apt.llvm.org/${UBUNTU_CODENAME}/ llvm-toolchain-${UBUNTU_CODENAME}-${CLANG_VERSION} main" | tee /etc/apt/sources.list.d/llvm.list > /dev/null \
- && echo "deb [signed-by=/usr/share/keyrings/mull-project-mull-stable-archive-keyring.gpg] https://dl.cloudsmith.io/public/mull-project/mull-stable/deb/ubuntu ${UBUNTU_CODENAME} main" | tee /etc/apt/sources.list.d/mull-project-mull-stable.list > /dev/null \
- && echo -e 'Package: *\nPin: origin "apt.llvm.org"\nPin-Priority: 1000' > /etc/apt/preferences \
- && apt-get update \
- && jq -r 'to_entries | .[] | .key + "=" + .value' /tmp/apt-requirements-clang.json | xargs apt-get install -y --no-install-recommends
+    # Install clang toolchain and mull mutation testing framework
+    cat /src/llvm.gpg.key | gpg --dearmor -o /usr/share/keyrings/llvm-snapshot-keyring.gpg
+    cat /src/mull.gpg.key | gpg --dearmor -o /usr/share/keyrings/mull-project-mull-stable-archive-keyring.gpg
+
+    UBUNTU_CODENAME=$(grep '^UBUNTU_CODENAME=' /etc/os-release | cut -d= -f2)
+    echo "deb [signed-by=/usr/share/keyrings/llvm-snapshot-keyring.gpg] http://apt.llvm.org/${UBUNTU_CODENAME}/ llvm-toolchain-${UBUNTU_CODENAME}-${CLANG_VERSION} main" | tee /etc/apt/sources.list.d/llvm-snapshot.list > /dev/null
+    echo "deb [signed-by=/usr/share/keyrings/mull-project-mull-stable-archive-keyring.gpg] https://dl.cloudsmith.io/public/mull-project/mull-stable/deb/ubuntu ${UBUNTU_CODENAME} main" | tee /etc/apt/sources.list.d/mull-project-mull-stable.list > /dev/null
+    echo -e 'Package: *\nPin: origin "apt.llvm.org"\nPin-Priority: 1000' > /etc/apt/preferences
+    apt-get update && jq -r 'to_entries | .[] | .key + "=" + .value' /tmp/apt-requirements-clang.json | \
+        xargs apt-get install -y --no-install-recommends
+EOF
 
 # Install arm-gcc toolchain
 RUN mkdir /opt/gcc-arm-none-eabi \