diff --git a/.github/workflows/action-tests.yml b/.github/workflows/action-tests.yml
new file mode 100644
index 0000000..6e66a94
--- /dev/null
+++ b/.github/workflows/action-tests.yml
@@ -0,0 +1,522 @@
+name: Action Tests
+on:
+  workflow_dispatch:
+    inputs:
+      debug:
+        description: "Run in debug mode."
+        type: boolean
+        required: false
+        default: false
+  push:
+    branches: [master, dev, staging]
+  pull_request:
+    types: [opened, synchronize]
+
+env:
+  DEBUG: ${{ github.event.inputs.debug || false }}
+  # Test for overrides in built in shell options (regression issue 98).
+  SHELLOPTS: errexit:pipefail
+
+jobs:
+
+  # === Core Functionality ===
+
+  list_all_versions:
+    runs-on: ubuntu-latest
+    name: List all package versions (including deps).
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: xdot=1.3-1
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-list_all_versions
+          debug: ${{ env.DEBUG }}
+      - name: Verify
+        run: |
+          echo "cache-hit = ${{ steps.execute.outputs.cache-hit }}"
+          echo "package-version-list = ${{ steps.execute.outputs.package-version-list }}"
+          echo "all-package-version-list = ${{ steps.execute.outputs.all-package-version-list }}"
+          # Verify cache miss on first run.
+          test "${{ steps.execute.outputs.cache-hit }}" = "false"
+          # Verify the main package is in the all-packages list.
+          echo "${{ steps.execute.outputs.all-package-version-list }}" | grep -q "xdot=1.3-1"
+        shell: bash
+
+  list_versions:
+    runs-on: ubuntu-latest
+    name: List package versions.
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: xdot rolldice
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-list_versions
+          debug: ${{ env.DEBUG }}
+      - name: Verify
+        run: |
+          echo "cache-hit = ${{ steps.execute.outputs.cache-hit }}"
+          echo "package-version-list = ${{ steps.execute.outputs.package-version-list }}"
+          test "${{ steps.execute.outputs.cache-hit }}" = "false"
+          echo "${{ steps.execute.outputs.package-version-list }}" | grep -q "xdot="
+          echo "${{ steps.execute.outputs.package-version-list }}" | grep -q "rolldice="
+        shell: bash
+
+  standard_workflow_install:
+    runs-on: ubuntu-latest
+    name: Standard workflow install package and cache.
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: xdot rolldice
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-standard_workflow
+          debug: ${{ env.DEBUG }}
+      - name: Verify
+        if: steps.execute.outputs.cache-hit != 'false'
+        run: |
+          echo "cache-hit = ${{ steps.execute.outputs.cache-hit }}"
+          exit 1
+        shell: bash
+
+  standard_workflow_install_with_new_version:
+    needs: standard_workflow_install
+    runs-on: ubuntu-latest
+    name: Standard workflow packages with new version.
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: xdot rolldice
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-standard_workflow_install_with_new_version
+          debug: ${{ env.DEBUG }}
+      - name: Verify
+        if: steps.execute.outputs.cache-hit != 'false'
+        run: |
+          echo "cache-hit = ${{ steps.execute.outputs.cache-hit }}"
+          exit 1
+        shell: bash
+
+  standard_workflow_restore:
+    needs: standard_workflow_install
+    runs-on: ubuntu-latest
+    name: Standard workflow restore cached packages.
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: xdot rolldice
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-standard_workflow
+          debug: ${{ env.DEBUG }}
+      - name: Verify
+        if: steps.execute.outputs.cache-hit != 'true'
+        run: |
+          echo "cache-hit = ${{ steps.execute.outputs.cache-hit }}"
+          exit 1
+        shell: bash
+
+  standard_workflow_restore_with_packages_out_of_order:
+    needs: standard_workflow_install
+    runs-on: ubuntu-latest
+    name: Standard workflow restore with packages out of order.
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: rolldice xdot
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-standard_workflow
+          debug: ${{ env.DEBUG }}
+      - name: Verify
+        if: steps.execute.outputs.cache-hit != 'true'
+        run: |
+          echo "cache-hit = ${{ steps.execute.outputs.cache-hit }}"
+          exit 1
+        shell: bash
+
+  standard_workflow_add_package:
+    needs: standard_workflow_install
+    runs-on: ubuntu-latest
+    name: Standard workflow add another package.
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: xdot rolldice distro-info-data
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-standard_workflow
+          debug: ${{ env.DEBUG }}
+      - name: Verify
+        if: steps.execute.outputs.cache-hit != 'false'
+        run: |
+          echo "cache-hit = ${{ steps.execute.outputs.cache-hit }}"
+          exit 1
+        shell: bash
+
+  standard_workflow_restore_add_package:
+    needs: standard_workflow_add_package
+    runs-on: ubuntu-latest
+    name: Standard workflow restore added package.
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: xdot rolldice distro-info-data
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-standard_workflow
+          debug: ${{ env.DEBUG }}
+      - name: Verify
+        if: steps.execute.outputs.cache-hit != 'true'
+        run: |
+          echo "cache-hit = ${{ steps.execute.outputs.cache-hit }}"
+          exit 1
+        shell: bash
+
+  # === Error Handling ===
+
+  no_packages:
+    runs-on: ubuntu-latest
+    name: No packages passed.
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: ""
+        continue-on-error: true
+      - name: Verify
+        if: steps.execute.outcome != 'failure'
+        run: |
+          echo "Expected failure but got: ${{ steps.execute.outcome }}"
+          exit 1
+        shell: bash
+
+  package_not_found:
+    runs-on: ubuntu-latest
+    name: Package not found.
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: package_that_doesnt_exist
+        continue-on-error: true
+      - name: Verify
+        if: steps.execute.outcome != 'failure'
+        run: |
+          echo "Expected failure but got: ${{ steps.execute.outcome }}"
+          exit 1
+        shell: bash
+
+  version_contains_spaces:
+    runs-on: ubuntu-latest
+    name: Version contains spaces.
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: xdot
+          version: 123 abc
+          debug: ${{ env.DEBUG }}
+        continue-on-error: true
+      - name: Verify
+        if: steps.execute.outcome != 'failure'
+        run: |
+          echo "Expected failure but got: ${{ steps.execute.outcome }}"
+          exit 1
+        shell: bash
+
+  debug_disabled:
+    runs-on: ubuntu-latest
+    name: Debug disabled.
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: xdot
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-debug_disabled
+          debug: false
+
+  # === Regression Tests ===
+
+  regression_36:
+    runs-on: ubuntu-latest
+    name: "Reinstall existing package (regression issue #36)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: libgtk-3-dev
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_36
+          debug: ${{ env.DEBUG }}
+
+  regression_37:
+    runs-on: ubuntu-latest
+    name: "Install with reported package deps not installed (regression issue #37)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: libosmesa6-dev libgl1-mesa-dev python3-tk pandoc git-restore-mtime
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_37
+          debug: ${{ env.DEBUG }}
+
+  regression_72_1:
+    runs-on: ubuntu-latest
+    name: "Cache Java CA certs package v1 (regression issue #72)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: openjdk-11-jre
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_72
+          debug: ${{ env.DEBUG }}
+
+  regression_72_2:
+    runs-on: ubuntu-latest
+    name: "Cache Java CA certs package v2 (regression issue #72)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: default-jre
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_72
+          debug: ${{ env.DEBUG }}
+
+  regression_76:
+    runs-on: ubuntu-latest
+    name: "Cache empty archive (regression issue #76)."
+    steps:
+      - uses: actions/checkout@v4
+      - run: |
+          sudo wget -O- https://apt.repos.intel.com/intel-gpg-keys/GPG-PUB-KEY-INTEL-SW-PRODUCTS.PUB | gpg --dearmor | sudo tee /usr/share/keyrings/oneapi-archive-keyring.gpg > /dev/null;
+          echo "deb [signed-by=/usr/share/keyrings/oneapi-archive-keyring.gpg] https://apt.repos.intel.com/oneapi all main" | sudo tee /etc/apt/sources.list.d/oneAPI.list;
+          sudo apt-get -qq update;
+          sudo apt-get install -y intel-oneapi-runtime-libs intel-oneapi-runtime-opencl;
+          sudo apt-get install -y opencl-headers ocl-icd-opencl-dev;
+          sudo apt-get install -y libsundials-dev;
+      - uses: ./
+        with:
+          packages: intel-oneapi-runtime-libs
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_76
+          debug: ${{ env.DEBUG }}
+
+  regression_79:
+    runs-on: ubuntu-latest
+    name: "Tar error with libboost-dev (regression issue #79)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: libboost-dev
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_79
+          debug: ${{ env.DEBUG }}
+
+  regression_81:
+    runs-on: ubuntu-latest
+    name: "Tar error with alsa-ucm-conf (regression issue #81)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: libasound2 libatk-bridge2.0-0 libatk1.0-0 libatspi2.0-0 libcups2 libdrm2 libgbm1 libnspr4 libnss3 libxcomposite1 libxdamage1 libxfixes3 libxkbcommon0 libxrandr2
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_81
+          debug: ${{ env.DEBUG }}
+
+  regression_84_literal_block_install:
+    runs-on: ubuntu-latest
+    name: "Install multiline package listing - literal block (regression issue #84)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: >
+            xdot
+            rolldice distro-info-data
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_84_literal_block
+          debug: ${{ env.DEBUG }}
+
+  regression_84_literal_block_restore:
+    needs: regression_84_literal_block_install
+    runs-on: ubuntu-latest
+    name: "Restore multiline package listing - literal block (regression issue #84)."
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: xdot rolldice distro-info-data
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_84_literal_block
+          debug: ${{ env.DEBUG }}
+      - name: Verify
+        if: steps.execute.outputs.cache-hit != 'true'
+        run: |
+          echo "cache-hit = ${{ steps.execute.outputs.cache-hit }}"
+          exit 1
+        shell: bash
+
+  regression_84_folded_block_install:
+    runs-on: ubuntu-latest
+    name: "Install multiline package listing - folded block (regression issue #84)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: |
+            xdot \
+            rolldice distro-info-data
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_84_folded_block
+          debug: ${{ env.DEBUG }}
+
+  regression_84_folded_block_restore:
+    needs: regression_84_folded_block_install
+    runs-on: ubuntu-latest
+    name: "Restore multiline package listing - folded block (regression issue #84)."
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: xdot rolldice distro-info-data
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_84_folded_block
+          debug: ${{ env.DEBUG }}
+      - name: Verify
+        if: steps.execute.outputs.cache-hit != 'true'
+        run: |
+          echo "cache-hit = ${{ steps.execute.outputs.cache-hit }}"
+          exit 1
+        shell: bash
+
+  regression_89:
+    runs-on: ubuntu-latest
+    name: "Upload logs artifact name (regression issue #89)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: libgtk-3-dev:amd64
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_89
+          debug: ${{ env.DEBUG }}
+
+  regression_98:
+    runs-on: ubuntu-latest
+    name: "Install error due to SHELLOPTS override (regression issue #98)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: git-restore-mtime libgl1-mesa-dev libosmesa6-dev pandoc
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_98
+          debug: ${{ env.DEBUG }}
+
+  regression_106_install:
+    runs-on: ubuntu-latest
+    name: "Stale apt repo - install phase (regression issue #106)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: libtk8.6
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_106
+          debug: ${{ env.DEBUG }}
+
+  regression_106_restore:
+    needs: regression_106_install
+    runs-on: ubuntu-latest
+    name: "Stale apt repo - restore phase (regression issue #106)."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: libtk8.6
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-regression_106
+          debug: ${{ env.DEBUG }}
+
+  # === Special Cases ===
+
+  multi_arch_cache_key:
+    runs-on: ubuntu-latest
+    name: "Cache packages with multi-arch cache key."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: libfuse2
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-multi_arch_cache_key
+          debug: ${{ env.DEBUG }}
+
+  virtual_package:
+    runs-on: ubuntu-latest
+    name: "Cache virtual package."
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          packages: libvips
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-virtual_package
+          debug: ${{ env.DEBUG }}
+
+  # === dpkg Registration Tests ===
+
+  dpkg_status_install:
+    runs-on: ubuntu-latest
+    name: "dpkg knows about packages after install (phase 1)."
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: rolldice
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-dpkg_status
+          debug: ${{ env.DEBUG }}
+      - name: Verify dpkg knows the package
+        run: |
+          dpkg -s rolldice | grep -q 'Status: install ok installed'
+          echo "dpkg reports rolldice as installed after fresh install."
+        shell: bash
+
+  dpkg_status_restore:
+    needs: dpkg_status_install
+    runs-on: ubuntu-latest
+    name: "dpkg knows about packages after cache restore (phase 2)."
+    steps:
+      - uses: actions/checkout@v4
+      - name: Execute
+        id: execute
+        uses: ./
+        with:
+          packages: rolldice
+          version: ${{ github.run_id }}-${{ github.run_attempt }}-dpkg_status
+          debug: ${{ env.DEBUG }}
+      - name: Verify cache hit
+        run: test "${{ steps.execute.outputs.cache-hit }}" = "true"
+        shell: bash
+      - name: Verify dpkg knows the package after cache restore
+        run: |
+          dpkg -s rolldice | grep -q 'Status: install ok installed'
+          echo "dpkg reports rolldice as installed after cache restore."
+        shell: bash
+      - name: Verify the binary works
+        run: |
+          rolldice 2d6
+          echo "rolldice binary works after cache restore."
+        shell: bash
diff --git a/install_and_cache_pkgs.sh b/install_and_cache_pkgs.sh
index 1a544ad..9c7742a 100755
--- a/install_and_cache_pkgs.sh
+++ b/install_and_cache_pkgs.sh
@@ -76,21 +76,19 @@ install_log_filepath="${cache_dir}/install.log"
 
 log "Clean installing ${package_count} packages..."
 # Zero interaction while installing or upgrading the system via apt.
-sudo DEBIAN_FRONTEND=noninteractive apt-fast --yes install ${packages} > "${install_log_filepath}"
-log "done"
-log "Installation log written to ${install_log_filepath}"
+# Explicitly check exit status since set +e (from lib.sh) is active.
+sudo DEBIAN_FRONTEND=noninteractive apt-fast --yes install ${packages} 2>&1 | tee "${install_log_filepath}"
+install_rc=${PIPESTATUS[0]}
+
+if [ "${install_rc}" -ne 0 ]; then
+  log_err "Failed to install packages. apt-fast exited with an error (see messages above)."
+  exit 5
+fi
+log "Install completed successfully."
 
 log_empty_line
 
 installed_packages=$(get_installed_packages "${install_log_filepath}")
-log "Installed package list:"
-for installed_package in ${installed_packages}; do
-  # Reformat for human friendly reading.  
-  log "- $(echo ${installed_package} | awk -F\= '{print $1" ("$2")"}')"
-done
-
-log_empty_line
-
 installed_packages_count=$(wc -w <<< "${installed_packages}")
 log "Caching ${installed_packages_count} installed packages..."
 for installed_package in ${installed_packages}; do
@@ -101,24 +99,35 @@ for installed_package in ${installed_packages}; do
     read package_name package_ver < <(get_package_name_ver "${installed_package}")
     log "  * Caching ${package_name} to ${cache_filepath}..."
 
-    # Pipe all package files (no folders), including symlinks, their targets, and installation control data to Tar.
-    tar -cf "${cache_filepath}" -C / --verbatim-files-from --files-from <(
-      { dpkg -L "${package_name}" &&
-        get_install_script_filepath "" "${package_name}" "preinst" &&
-        get_install_script_filepath "" "${package_name}" "postinst" ; } |
+    # Pipe all package files, directories, and symlinks (plus symlink targets
+    # and dpkg metadata) to Tar.  Directories are included so that tar
+    # preserves their ownership and permissions on restore — without them,
+    # tar auto-creates parent directories using the current umask, which on
+    # some runners (e.g. GPU-optimized images) defaults to 0077, leaving
+    # restored trees inaccessible to non-root users.
+    tar -cf "${cache_filepath}" -C / --no-recursion --verbatim-files-from --files-from <(
+      { dpkg -L "${package_name}" | grep -vxF -e '/.' -e '.' -e '/' &&
+        # Include all dpkg info files for this package (list, md5sums,
+        # conffiles, triggers, preinst, postinst, prerm, postrm, etc.)
+        # so dpkg recognizes the package after cache restore.
+        ls -1 /var/lib/dpkg/info/${package_name}.* 2>/dev/null &&
+        ls -1 /var/lib/dpkg/info/${package_name}:*.* 2>/dev/null ; } |
       while IFS= read -r f; do
-        if test -f "${f}" -o -L "${f}"; then
-          get_tar_relpath "${f}"
+        if [ -f "${f}" ] || [ -L "${f}" ] || [ -d "${f}" ]; then
+          echo "${f#/}"
           if [ -L "${f}" ]; then
             target="$(readlink -f "${f}")"
             if [ -f "${target}" ]; then
-              get_tar_relpath "${target}"
+              echo "${target#/}"
             fi
           fi
         fi
       done
     )
 
+    # Save the dpkg status entry so we can register the package on restore.
+    dpkg -s "${package_name}" > "${cache_dir}/${installed_package}.dpkg-status" 2>/dev/null || true
+
     log "    done (compressed size $(du -h "${cache_filepath}" | cut -f1))."
   fi
 
diff --git a/lib.sh b/lib.sh
index 755d939..b0cb54a 100755
--- a/lib.sh
+++ b/lib.sh
@@ -54,14 +54,14 @@ function get_install_script_filepath {
 #   The list of colon delimited action syntax pairs with each pair equals
 #   delimited. <name>:<version> <name>:<version>...
 ###############################################################################
-function get_installed_packages {   
+function get_installed_packages {
   local install_log_filepath="${1}"
-  local regex="^Unpacking ([^ :]+)([^ ]+)? (\[[^ ]+\]\s)?\(([^ )]+)"  
-  local dep_packages=""  
+  local regex="^Unpacking ([^ :]+)([^ ]+)? (\[[^ ]+\]\s)?\(([^ )]+)"
+  local dep_packages=""
   while read -r line; do
     # ${regex} should be unquoted since it isn't a literal.
     if [[ "${line}" =~ ${regex} ]]; then
-      dep_packages="${dep_packages}${BASH_REMATCH[1]}=${BASH_REMATCH[4]} "      
+      dep_packages="${dep_packages}${BASH_REMATCH[1]}${BASH_REMATCH[2]}=${BASH_REMATCH[4]} "
     else
       log_err "Unable to parse package name and version from \"${line}\""
       exit 2
diff --git a/pre_cache_action.sh b/pre_cache_action.sh
index 5cb64cb..7c06450 100755
--- a/pre_cache_action.sh
+++ b/pre_cache_action.sh
@@ -111,6 +111,16 @@ if [ "${cpu_arch}" != "x86_64" ]; then
   log "- Architecture '${cpu_arch}' added to value."
 fi
 
+# Include a hash of pre-installed packages so runners with different base
+# images (e.g., GPU runners with CUDA pre-installed vs plain Ubuntu) get
+# different cache keys. This prevents a cache built on runner A (where some
+# packages were already installed) from being restored on runner B (where
+# those packages are missing).
+base_pkgs_hash="$(dpkg-query -W -f='${binary:Package}\n' | sha1sum | cut -f1 -d' ')"
+value="${value} base:${base_pkgs_hash}"
+log "- Base packages hash '${base_pkgs_hash}' added to value."
+echo "::notice::Runner base image fingerprint: ${base_pkgs_hash}. Runners with different pre-installed packages produce different fingerprints and cannot share caches."
+
 log "- Value to hash is '${value}'."
 
 key="$(echo "${value}" | md5sum | cut -f1 -d' ')"
diff --git a/restore_pkgs.sh b/restore_pkgs.sh
index 4556265..b336bc7 100755
--- a/restore_pkgs.sh
+++ b/restore_pkgs.sh
@@ -50,7 +50,7 @@ for cached_filepath in ${cached_filepaths}; do
   sudo tar -xf "${cached_filepath}" -C "${cache_restore_root}" > /dev/null
   log "  done"
 
-  # Execute install scripts if available.    
+  # Execute install scripts if available.
   if test ${execute_install_scripts} == "true"; then
     # May have to add more handling for extracting pre-install script before extracting all files.
     # Keeping it simple for now.
@@ -59,3 +59,69 @@ for cached_filepath in ${cached_filepaths}; do
   fi
 done
 log "done"
+
+log_empty_line
+
+# Register packages with dpkg so they appear as installed.
+# The tar extraction restores dpkg info files (list, md5sums, etc.) but the
+# main status database (/var/lib/dpkg/status) also needs updating.
+dpkg_status_dir="${cache_dir}"
+status_files=$(ls -1 "${dpkg_status_dir}"/*.dpkg-status 2>/dev/null || true)
+if test -n "${status_files}"; then
+  log "Registering restored packages with dpkg..."
+  dpkg_status_path="${cache_restore_root}var/lib/dpkg/status"
+  for status_file in ${status_files}; do
+    pkg_name=$(grep '^Package:' "${status_file}" | head -1 | sed 's/^Package: //')
+    cached_ver=$(grep '^Version:' "${status_file}" | head -1 | sed 's/^Version: //')
+    cached_arch=$(grep '^Architecture:' "${status_file}" | head -1 | sed 's/^Architecture: //')
+
+    # Build architecture-qualified name for dpkg queries.
+    dpkg_query_name="${pkg_name}"
+    if [ -n "${cached_arch}" ] && [ "${cached_arch}" != "all" ]; then
+      dpkg_query_name="${pkg_name}:${cached_arch}"
+    fi
+
+    if dpkg -s "${dpkg_query_name}" > /dev/null 2>&1; then
+      existing_status=$(dpkg -s "${dpkg_query_name}" 2>/dev/null | grep '^Status:' | head -1)
+      existing_ver=$(dpkg -s "${dpkg_query_name}" 2>/dev/null | grep '^Version:' | head -1 | sed 's/^Version: //')
+
+      if echo "${existing_status}" | grep -q 'install ok installed'; then
+        if [ "${existing_ver}" = "${cached_ver}" ]; then
+          log "- ${dpkg_query_name} already at version ${cached_ver}, skipping."
+          continue
+        fi
+        # Package is installed at a different version (was upgraded during
+        # the original install).  Remove the old dpkg status entry so we can
+        # replace it with the cached (upgraded) version.
+        log "- ${dpkg_query_name} updating from ${existing_ver} to ${cached_ver}..."
+        sudo python3 -c "
+import sys
+pkg, arch, path = sys.argv[1], sys.argv[2], sys.argv[3]
+with open(path, 'r') as f:
+    content = f.read()
+entries = content.split('\n\n')
+kept = []
+for entry in entries:
+    if not entry.strip():
+        continue
+    lines = entry.strip().split('\n')
+    match_pkg = any(l == 'Package: ' + pkg for l in lines)
+    match_arch = any(l == 'Architecture: ' + arch for l in lines)
+    if match_pkg and match_arch:
+        continue
+    kept.append(entry.strip())
+with open(path, 'w') as f:
+    f.write('\n\n'.join(kept))
+    if kept:
+        f.write('\n\n')
+" "${pkg_name}" "${cached_arch}" "${dpkg_status_path}"
+      fi
+    fi
+
+    # Append the status entry (with blank line separator) to the dpkg database.
+    echo "" | sudo tee -a "${dpkg_status_path}" > /dev/null
+    cat "${status_file}" | sudo tee -a "${dpkg_status_path}" > /dev/null
+    log "- ${dpkg_query_name} registered."
+  done
+  log "done"
+fi