diff --git a/.github/actions/cryptopp/action.yaml b/.github/actions/cryptopp/action.yaml
index 700014184..4ae4a3ff5 100644
--- a/.github/actions/cryptopp/action.yaml
+++ b/.github/actions/cryptopp/action.yaml
@@ -26,7 +26,7 @@ runs:
   steps:
 
     - id: cache
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         key: ${{ runner.os }}-cryptopp-${{ inputs.version }}-${{ inputs.architecture }}-${{ inputs.runtime }}-${{ inputs.toolset }}
         path: |
@@ -71,10 +71,10 @@ runs:
     - name: Build
       if: steps.cache.outputs.cache-hit != 'true'
       run: |
-        msbuild cryptlib.vcxproj /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }}
-        msbuild cryptdll.vcxproj /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }}
-        msbuild cryptlib.vcxproj /p:Configuration=Debug /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }}
-        msbuild cryptdll.vcxproj /p:Configuration=Debug /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }}
+        msbuild cryptlib.vcxproj /m /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }}
+        msbuild cryptdll.vcxproj /m /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }}
+        msbuild cryptlib.vcxproj /m /p:Configuration=Debug /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }}
+        msbuild cryptdll.vcxproj /m /p:Configuration=Debug /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }}
       working-directory: tmp/cryptopp
       shell: cmd
 
diff --git a/.github/actions/google-test/action.yml b/.github/actions/google-test/action.yml
index ba0b2f107..55efda483 100644
--- a/.github/actions/google-test/action.yml
+++ b/.github/actions/google-test/action.yml
@@ -28,11 +28,6 @@ outputs:
 runs:
   using: composite
   steps:
-    - name: Clone Google Test
-      working-directory: tmp
-      shell: bash
-      run: |
-        git clone --depth 1 --branch release-${{ inputs.version }} https://github.com/google/googletest.git
     - id: setup
       run: |
         if ("${{ inputs.architecture }}" -eq "x64") {
@@ -45,20 +40,35 @@ runs:
         } else {
           echo "shared_libs=FALSE" >> $env:GITHUB_OUTPUT
         }
-      
-
       shell: pwsh
-    - name: Build Google Test
+
+    - id: cache
+      uses: actions/cache@v4
+      with:
+        key: ${{ runner.os }}-googletest-${{ inputs.version }}-${{ inputs.architecture }}-${{ inputs.runtime }}-${{ inputs.toolset }}
+        path: |
+          tmp/googletest/install
+
+    - name: Clone Google Test
+      if: steps.cache.outputs.cache-hit != 'true'
+      working-directory: tmp
+      shell: bash
+      run: |
+        git clone --depth 1 --branch release-${{ inputs.version }} https://github.com/google/googletest.git
+
+    - name: Configure Google Test
+      if: steps.cache.outputs.cache-hit != 'true'
       working-directory: tmp/googletest
       shell: cmd
       run: |
         cmake -S . -G "Visual Studio 17" -B build -DCMAKE_INSTALL_PREFIX=install -DBUILD_SHARED_LIBS=${{ steps.setup.outputs.shared_libs }} -T ${{ inputs.toolset }} -A ${{ steps.setup.outputs.platform }}
 
     - name: Build Google Test
+      if: steps.cache.outputs.cache-hit != 'true'
       working-directory: tmp/googletest
       shell: cmd
       run: |
-        msbuild build\INSTALL.vcxproj /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }}
+        msbuild build\INSTALL.vcxproj /m /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }}
 
     - name: Copy Google Test dlls
       if: ${{ steps.setup.outputs.shared_libs == 'TRUE' }}
diff --git a/.github/actions/lua/action.yaml b/.github/actions/lua/action.yaml
index 57db6a326..47cc2451c 100644
--- a/.github/actions/lua/action.yaml
+++ b/.github/actions/lua/action.yaml
@@ -16,7 +16,7 @@ runs:
   using: composite
   steps:
     - id: cache
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         key: ${{ runner.os }}-lua-${{ inputs.version }}
         path: |
diff --git a/.github/actions/openssl/action.yaml b/.github/actions/openssl/action.yaml
index c571d4473..6e3950f64 100644
--- a/.github/actions/openssl/action.yaml
+++ b/.github/actions/openssl/action.yaml
@@ -45,7 +45,7 @@ runs:
       shell: cmd
 
     - id: cache
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         key: ${{ runner.os }}-openssl-${{ inputs.version }}-no-shared-${{ inputs.architecture }}-${{ inputs.runtime }}
         path: |
diff --git a/.github/actions/protobuf/action.yaml b/.github/actions/protobuf/action.yaml
index 09b676c06..ad3538d7d 100644
--- a/.github/actions/protobuf/action.yaml
+++ b/.github/actions/protobuf/action.yaml
@@ -36,7 +36,7 @@ runs:
       shell: cmd
 
     - id: cache
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         key: ${{ runner.os }}-protobuf-${{ inputs.version }}-${{ inputs.architecture }}-${{ inputs.runtime }}-${{ inputs.toolset }}
         path: |
@@ -82,10 +82,10 @@ runs:
 
     - name: Build
       run: |
-        echo msbuild libprotobuf.vcxproj /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }} ${{ steps.setup.outputs.vctools_version }} ${{ steps.setup.outputs.additional_options }}
-        msbuild libprotobuf.vcxproj /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }} ${{ steps.setup.outputs.vctools_version }} ${{ steps.setup.outputs.additional_options }}
-        msbuild libprotoc.vcxproj /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }} ${{ steps.setup.outputs.vctools_version }}
-        msbuild protoc.vcxproj /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }} ${{ steps.setup.outputs.vctools_version }}
+        echo msbuild libprotobuf.vcxproj /m /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }} ${{ steps.setup.outputs.vctools_version }} ${{ steps.setup.outputs.additional_options }}
+        msbuild libprotobuf.vcxproj /m /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }} ${{ steps.setup.outputs.vctools_version }} ${{ steps.setup.outputs.additional_options }}
+        msbuild libprotoc.vcxproj /m /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }} ${{ steps.setup.outputs.vctools_version }}
+        msbuild protoc.vcxproj /m /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }} /p:PlatformToolset=${{ inputs.toolset }} ${{ steps.setup.outputs.vctools_version }}
       working-directory: tmp/protobuf-${{ inputs.version }}/build
       shell: cmd
       if: ${{ steps.cache.outputs.cache-hit != 'true' }}
diff --git a/.github/workflows/build-debian.yml b/.github/workflows/build-debian.yml
index 77113cf3b..d0d773139 100644
--- a/.github/workflows/build-debian.yml
+++ b/.github/workflows/build-debian.yml
@@ -118,7 +118,7 @@ jobs:
     - name: Build nsclient
       working-directory: tmp/nscp
       run: |
-        make
+        make -j$(nproc)
 
     - name: CPack
       working-directory: tmp/nscp
diff --git a/.github/workflows/build-redhat.yml b/.github/workflows/build-redhat.yml
index d7e05f2c8..4ae31d3f8 100644
--- a/.github/workflows/build-redhat.yml
+++ b/.github/workflows/build-redhat.yml
@@ -135,7 +135,7 @@ jobs:
     - name: Build nsclient
       working-directory: tmp/nscp
       run: |
-        make
+        make -j$(nproc)
 
     - name: CPack
       working-directory: tmp/nscp
diff --git a/.github/workflows/build-windows-legacy.yml b/.github/workflows/build-windows-legacy.yml
index 38facf247..6dc0ef131 100644
--- a/.github/workflows/build-windows-legacy.yml
+++ b/.github/workflows/build-windows-legacy.yml
@@ -155,6 +155,14 @@ jobs:
       with:
         version: ${{ ENV.MINIZ_VERSION }}
 
+    - name: Cache Boost (static)
+      id: static_boost_cache
+      uses: actions/cache@v4
+      with:
+        key: ${{ runner.os }}-boost-legacy-${{ env.BOOST_VERSION }}-${{ inputs.architecture }}-static-runtime-static-msvc141-xp
+        path: |
+          ${{ runner.workspace }}/static_boost
+
     - name: Build Boost (static)
       id: static_boost
       uses: mickem/build-boost@42c59d10fc12f919a986f7e1c2f7c752d4960190
@@ -220,7 +228,7 @@ jobs:
     - name: Build installer_lib
       working-directory: tmp/installer_lib
       run: |
-        msbuild installer_lib.sln /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }}
+        msbuild installer_lib.sln /m /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }}
   
     - name: CMake (NSCP)
       working-directory: tmp/nscp
@@ -230,7 +238,7 @@ jobs:
     - name: Build nsclient
       working-directory: tmp/nscp
       run: |
-        msbuild NSCP.sln /p:Configuration=RelWithDebInfo /p:Platform=${{ steps.setup.outputs.platform }}
+        msbuild NSCP.sln /m /p:Configuration=RelWithDebInfo /p:Platform=${{ steps.setup.outputs.platform }}
 
     - name: Run tests
       working-directory: tmp/nscp
@@ -248,7 +256,7 @@ jobs:
     - name: Build installer
       working-directory: tmp/nscp
       run: |
-        msbuild installers\installer-NSCP\installer_NSCP.vcxproj /p:Configuration=RelWithDebInfo /p:Platform=${{ steps.setup.outputs.platform }} /p:BuildProjectReferences=false
+        msbuild installers\installer-NSCP\installer_NSCP.vcxproj /m /p:Configuration=RelWithDebInfo /p:Platform=${{ steps.setup.outputs.platform }} /p:BuildProjectReferences=false
 
     - name: Post process files
       uses: ./.github/actions/post-process-windows-binaries
diff --git a/.github/workflows/build-windows.yml b/.github/workflows/build-windows.yml
index 2c62e4f3b..19a89b3f8 100644
--- a/.github/workflows/build-windows.yml
+++ b/.github/workflows/build-windows.yml
@@ -178,6 +178,14 @@ jobs:
       with:
         version: ${{ ENV.MINIZ_VERSION }}
 
+    - name: Cache Boost (static)
+      id: static_boost_cache
+      uses: actions/cache@v4
+      with:
+        key: ${{ runner.os }}-boost-${{ env.BOOST_VERSION }}-${{ inputs.architecture }}-static-runtime-static-libs-system_filesystem-${{ steps.setup.outputs.toolset }}
+        path: |
+          ${{ runner.workspace }}/static_boost
+
     - name: Build Boost (static)
       id: static_boost
       uses: mickem/build-boost@v1
@@ -190,6 +198,14 @@ jobs:
         static-runtime: 1
         directory: ${{ runner.workspace }}/static_boost
           
+    - name: Cache Boost (regular)
+      id: boost_cache
+      uses: actions/cache@v4
+      with:
+        key: ${{ runner.os }}-boost-${{ env.BOOST_VERSION }}-${{ inputs.architecture }}-shared-runtime-shared-libs-full-${{ steps.setup.outputs.toolset }}
+        path: |
+          ${{ runner.workspace }}/boost
+
     - name: Build Boost (regular)
       id: boost
       uses: mickem/build-boost@v1
@@ -256,7 +272,7 @@ jobs:
     - name: Build installer_lib
       working-directory: tmp/installer_lib
       run: |
-        msbuild installer_lib.sln /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }}
+        msbuild installer_lib.sln /m /p:Configuration=Release /p:Platform=${{ steps.setup.outputs.platform }}
   
     - name: CMake (NSCP)
       working-directory: tmp/nscp
@@ -266,7 +282,7 @@ jobs:
     - name: Build nsclient
       working-directory: tmp/nscp
       run: |
-        msbuild NSCP.sln /p:Configuration=RelWithDebInfo /p:Platform=${{ steps.setup.outputs.platform }}
+        msbuild NSCP.sln /m /p:Configuration=RelWithDebInfo /p:Platform=${{ steps.setup.outputs.platform }}
 
     - name: Run tests
       if: inputs.architecture != 'arm64'
@@ -285,7 +301,7 @@ jobs:
     - name: Build installer
       working-directory: tmp/nscp
       run: |
-        msbuild installers\installer-NSCP\installer_NSCP.vcxproj /p:Configuration=RelWithDebInfo /p:Platform=${{ steps.setup.outputs.platform }} /p:BuildProjectReferences=false
+        msbuild installers\installer-NSCP\installer_NSCP.vcxproj /m /p:Configuration=RelWithDebInfo /p:Platform=${{ steps.setup.outputs.platform }} /p:BuildProjectReferences=false
 
     - name: Post process files
       uses: ./.github/actions/post-process-windows-binaries
diff --git a/.github/workflows/tests-sanitizers.yml b/.github/workflows/tests-sanitizers.yml
index 49bc310e1..5060f6f22 100644
--- a/.github/workflows/tests-sanitizers.yml
+++ b/.github/workflows/tests-sanitizers.yml
@@ -41,14 +41,25 @@ jobs:
 
     steps:
     - name: Install dependencies
+      # archive.ubuntu.com periodically drops connections mid-fetch, which
+      # bricks CI for transient reasons. Configure apt to retry each package
+      # itself, and then wrap the whole step in a shell-level retry loop so a
+      # full mirror outage can be ridden out without re-running the workflow.
       run: |
-        apt-get update
-        DEBIAN_FRONTEND=noninteractive apt-get install -y \
-          git curl unzip cmake build-essential python3-pip \
-          libboost-all-dev libgtest-dev libgmock-dev \
-          protobuf-compiler libprotobuf-dev \
-          openssl libssl-dev libcrypto++-dev \
-          liblua5.4-dev libdbus-1-dev
+        echo 'Acquire::Retries "5";' > /etc/apt/apt.conf.d/80-retries
+        echo 'Acquire::http::Timeout "30";' >> /etc/apt/apt.conf.d/80-retries
+        echo 'Acquire::https::Timeout "30";' >> /etc/apt/apt.conf.d/80-retries
+        for attempt in 1 2 3; do
+          apt-get update && \
+          DEBIAN_FRONTEND=noninteractive apt-get install -y --fix-missing \
+            git curl unzip cmake build-essential python3-pip \
+            libboost-all-dev libgtest-dev libgmock-dev \
+            protobuf-compiler libprotobuf-dev \
+            openssl libssl-dev libcrypto++-dev \
+            liblua5.4-dev libdbus-1-dev && break
+          echo "apt attempt $attempt failed, retrying in 30s..."
+          sleep 30
+        done
 
     - uses: actions/checkout@v6