Fix dpkg not knowing about packages after cache restore

After cache restore, dpkg had no record of the installed packages because:
1. Only preinst/postinst scripts were cached from /var/lib/dpkg/info/,
   missing .list, .md5sums, .conffiles, and other metadata files
2. The dpkg status database (/var/lib/dpkg/status) was never updated

This meant dpkg -s, apt list --installed, and anything checking package
state would not see the restored packages.

Fix:
- Cache all /var/lib/dpkg/info/<package>.* files (not just install scripts)
- Save each package's dpkg status entry to a .dpkg-status file
- On restore, append status entries to /var/lib/dpkg/status (skipping
  packages that are already registered)

Adds tests verifying dpkg -s reports packages as installed after both
fresh install and cache restore.

Co-developed-by: Claude Code v2.1.58 (claude-opus-4-6)

.github/workflows/action-tests.yml

@@ -473,3 +473,50 @@ jobs:
           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

install_and_cache_pkgs.sh

@@ -101,11 +101,15 @@ 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.
+    # Pipe all package files (no folders), including symlinks, their targets,
+    # and all dpkg metadata (info files) to Tar.
     tar -cf "${cache_filepath}" -C / --verbatim-files-from --files-from <(
       { dpkg -L "${package_name}" &&
-        get_install_script_filepath "" "${package_name}" "preinst" &&
+        # Include all dpkg info files for this package (list, md5sums,
-        get_install_script_filepath "" "${package_name}" "postinst" ; } |
+        # 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}"
@@ -119,6 +123,9 @@ for installed_package in ${installed_packages}; do
       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
 

restore_pkgs.sh

@@ -59,3 +59,30 @@ 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..."
+  for status_file in ${status_files}; do
+    pkg_name=$(head -1 "${status_file}" | sed 's/^Package: //')
+    # Skip if dpkg already knows about this package (e.g., it was pre-installed).
+    if dpkg -s "${pkg_name}" > /dev/null 2>&1; then
+      existing_status=$(dpkg -s "${pkg_name}" 2>/dev/null | grep '^Status:' | head -1)
+      if echo "${existing_status}" | grep -q 'install ok installed'; then
+        log "- ${pkg_name} already registered, skipping."
+        continue
+      fi
+    fi
+    # Append the status entry (with blank line separator) to the dpkg database.
+    echo "" | sudo tee -a "${cache_restore_root}var/lib/dpkg/status" > /dev/null
+    cat "${status_file}" | sudo tee -a "${cache_restore_root}var/lib/dpkg/status" > /dev/null
+    log "- ${pkg_name} registered."
+  done
+  log "done"
+fi