diff --git a/pkg_auto/impl/pkg_auto_lib.sh b/pkg_auto/impl/pkg_auto_lib.sh
index 4342e59254..1f7b33c7bd 100644
--- a/pkg_auto/impl/pkg_auto_lib.sh
+++ b/pkg_auto/impl/pkg_auto_lib.sh
@@ -53,6 +53,7 @@ source "$(dirname "${BASH_SOURCE[0]}")/util.sh"
 source "${PKG_AUTO_IMPL_DIR}/cleanups.sh"
 source "${PKG_AUTO_IMPL_DIR}/debug.sh"
 source "${PKG_AUTO_IMPL_DIR}/gentoo_ver.sh"
+source "${PKG_AUTO_IMPL_DIR}/md5_cache_diff_lib.sh"
 
 # Sets up the workdir using the passed config. The config can be
 # created basing on the config_template file or using the
@@ -2185,9 +2186,9 @@ function handle_pkg_update() {
     local pkg_name
     pkg_name=${new_pkg#*/}
     local -a lines
-    lines=( "from ${old} to ${new}")
+    lines=( "0:from ${old} to ${new}")
     if [[ ${old_pkg} != "${new_pkg}" ]]; then
-        lines+=( "renamed from ${old_pkg}" )
+        lines+=( "0:renamed from ${old_pkg}" )
     fi
     # shellcheck disable=SC2153 # OLD_PORTAGE_STABLE is not a misspelling, it comes from globals file
     generate_ebuild_diff "${OLD_PORTAGE_STABLE}" "${NEW_PORTAGE_STABLE}" "${old_pkg}" "${new_pkg}" "${old_s}" "${new_s}" "${old}" "${new}"
@@ -2196,15 +2197,28 @@ function handle_pkg_update() {
     local hpu_update_dir hpu_update_dir_non_slot
     update_dir_non_slot "${new_pkg}" hpu_update_dir_non_slot
     update_dir "${new_pkg}" "${old_s}" "${new_s}" hpu_update_dir
+
+    local diff_report_name
+    gen_varname diff_report_name
+    diff_report_declare "${diff_report_name}"
+    generate_cache_diff_report "${diff_report_name}" "${WORKDIR}/pkg-reports/old/portage-stable-cache" "${WORKDIR}/pkg-reports/new/portage-stable-cache" "${old_pkg}" "${new_pkg}" "${old}" "${new}"
+
+    local -n diff_report_ref=${diff_report_name}
+    local -n diff_lines_ref=${diff_report_ref[${DR_LINES_IDX}]}
+    lines+=( "${diff_lines_ref[@]}" )
+    unset -n diff_lines_ref
+    unset -n diff_report_ref
+    diff_report_unset "${diff_report_name}"
+
     if [[ -s "${hpu_update_dir}/ebuild.diff" ]]; then
-        lines+=( 'TODO: review ebuild.diff' )
+        lines+=( '0:TODO: review ebuild.diff' )
     fi
     if [[ -s "${hpu_update_dir_non_slot}/other.diff" ]]; then
-        lines+=( 'TODO: review other.diff' )
+        lines+=( '0:TODO: review other.diff' )
     fi
-    lines+=( 'TODO: review occurences' )
+    lines+=( '0:TODO: review occurences' )
     if [[ ${old_pkg} != "${new_pkg}" ]]; then
-        lines+=( 'TODO: review occurences-for-old-name' )
+        lines+=( '0:TODO: review occurences-for-old-name' )
     fi
 
     local -a hpu_tags
@@ -2213,7 +2227,7 @@ function handle_pkg_update() {
     if ver_test "${new_no_r}" -gt "${old_no_r}"; then
         # version bump
         generate_changelog_entry_stub "${pkg_name}" "${new_no_r}" "${hpu_tags[@]}"
-        lines+=( 'release notes: TODO' )
+        lines+=( '0:release notes: TODO' )
     fi
 
     generate_summary_stub "${new_pkg}" "${hpu_tags[@]}" -- "${lines[@]}"
@@ -2253,12 +2267,12 @@ function handle_pkg_as_is() {
     local pkg_name
     pkg_name=${new_pkg#/}
     local -a lines
-    lines=( "still at ${v}" )
+    lines=( "0:still at ${v}" )
 
     local renamed
     renamed=
     if [[ ${old_pkg} != "${new_pkg}" ]]; then
-        lines+=( "renamed from ${old_pkg}" )
+        lines+=( "0:renamed from ${old_pkg}" )
         renamed=x
     fi
     generate_ebuild_diff "${OLD_PORTAGE_STABLE}" "${NEW_PORTAGE_STABLE}" "${old_pkg}" "${new_pkg}" "${old_s}" "${new_s}" "${v}" "${v}"
@@ -2267,12 +2281,28 @@ function handle_pkg_as_is() {
     update_dir "${new_pkg}" "${old_s}" "${new_s}" hpai_update_dir
     local modified
     modified=
+
+    local diff_report_name
+    gen_varname diff_report_name
+    diff_report_declare "${diff_report_name}"
+    generate_cache_diff_report "${diff_report_name}" "${WORKDIR}/pkg-reports/old/portage-stable-cache" "${WORKDIR}/pkg-reports/new/portage-stable-cache" "${old_pkg}" "${new_pkg}" "${v}" "${v}"
+
+    local -n diff_report_ref=${diff_report_name}
+    local -n diff_lines_ref=${diff_report_ref[${DR_LINES_IDX}]}
+    if [[ ${#diff_lines_ref[@]} -gt 0 ]]; then
+        lines+=( "${diff_lines_ref[@]}" )
+        modified=x
+    fi
+    unset -n diff_lines_ref
+    unset -n diff_report_ref
+    diff_report_unset "${diff_report_name}"
+
     if [[ -s "${hpai_update_dir}/ebuild.diff" ]]; then
-        lines+=( 'TODO: review ebuild.diff' )
+        lines+=( '0:TODO: review ebuild.diff' )
         modified=x
     fi
     if [[ -s "${hpai_update_dir_non_slot}/other.diff" ]]; then
-        lines+=( 'TODO: review other.diff' )
+        lines+=( '0:TODO: review other.diff' )
         modified=x
     fi
     if [[ -z ${renamed} ]] && [[ -z ${modified} ]]; then
@@ -2281,9 +2311,9 @@ function handle_pkg_as_is() {
     fi
     # shellcheck disable=SC2034 # ref to an external variable
     changed_ref=x
-    lines+=( 'TODO: review occurences' )
+    lines+=( '0:TODO: review occurences' )
     if [[ ${old_pkg} != "${new_pkg}" ]]; then
-        lines+=( 'TODO: review occurences-for-old-name' )
+        lines+=( '0:TODO: review occurences-for-old-name' )
     fi
 
     local -a hpai_tags
@@ -2324,24 +2354,37 @@ function handle_pkg_downgrade() {
     local pkg_name
     pkg_name=${new_pkg#*/}
     local -a lines
-    lines=( "downgraded from ${old} to ${new}" )
+    lines=( "0:downgraded from ${old} to ${new}" )
     if [[ ${old_pkg} != "${new_pkg}" ]]; then
-        lines+=( "renamed from ${old_pkg}" )
+        lines+=( "0:renamed from ${old_pkg}" )
     fi
     generate_ebuild_diff "${OLD_PORTAGE_STABLE}" "${NEW_PORTAGE_STABLE}" "${old_pkg}" "${new_pkg}" "${old_s}" "${new_s}" "${old}" "${new}"
 
     local hpd_update_dir hpd_update_dir_non_slot
     update_dir_non_slot "${new_pkg}" hpd_update_dir_non_slot
     update_dir "${new_pkg}" "${old_s}" "${new_s}" hpd_update_dir
+
+    local diff_report_name
+    gen_varname diff_report_name
+    diff_report_declare "${diff_report_name}"
+    generate_cache_diff_report "${diff_report_name}" "${WORKDIR}/pkg-reports/old/portage-stable-cache" "${WORKDIR}/pkg-reports/new/portage-stable-cache" "${old_pkg}" "${new_pkg}" "${old}" "${new}"
+
+    local -n diff_report_ref=${diff_report_name}
+    local -n diff_lines_ref=${diff_report_ref[${DR_LINES_IDX}]}
+    lines+=( "${diff_lines_ref[@]}" )
+    unset -n diff_lines_ref
+    unset -n diff_report_ref
+    diff_report_unset "${diff_report_name}"
+
     if [[ -s "${hpd_update_dir}/ebuild.diff" ]]; then
-        lines+=( 'TODO: review ebuild.diff' )
+        lines+=( '0:TODO: review ebuild.diff' )
     fi
     if [[ -s "${hpd_update_dir_non_slot}/other.diff" ]]; then
-        lines+=( 'TODO: review other.diff' )
+        lines+=( '0:TODO: review other.diff' )
     fi
-    lines+=( 'TODO: review occurences' )
+    lines+=( '0:TODO: review occurences' )
     if [[ ${old_pkg} != "${new_pkg}" ]]; then
-        lines+=( 'TODO: review occurences-for-old-name' )
+        lines+=( '0:TODO: review occurences-for-old-name' )
     fi
 
     local -a hpd_tags
@@ -2350,7 +2393,7 @@ function handle_pkg_downgrade() {
     if ver_test "${new_no_r}" -lt "${old_no_r}"; then
         # version bump
         generate_changelog_entry_stub "${pkg_name}" "${new_no_r}" "${hpd_tags[@]}"
-        lines+=( "release notes: TODO" )
+        lines+=( "0:release notes: TODO" )
     fi
 
     generate_summary_stub "${new_pkg}" "${hpd_tags[@]}" -- "${lines[@]}"
@@ -2456,10 +2499,16 @@ function generate_summary_stub() {
             printf ' [%s]' "${tags[@]}"
         fi
         printf '\n'
-        if [[ ${#} -gt 0 ]]; then
-            printf '  - %s\n' "${@}"
-            printf '\n'
-        fi
+        local indent_line indent line
+        for indent_line; do
+            indent=${indent_line%%:*}
+            line=${indent_line#*:}
+            if [[ ${indent} -gt 0 ]]; then
+                printf -- '  %.0s' $(seq 1 "${indent}")
+            fi
+            printf '  - %s\n' "${line}"
+        done
+        printf '\n'
     } >>"${REPORTS_DIR}/updates/summary_stubs"
 }
 
@@ -2565,6 +2614,32 @@ function generate_ebuild_diff() {
     xdiff --unified=3 "${old_path}" "${new_path}" >"${ged_update_dir}/ebuild.diff"
 }
 
+function generate_cache_diff_report() {
+    local diff_report_var_name=${1}; shift
+    local old_cache_dir=${1}; shift
+    local new_cache_dir=${1}; shift
+    local old_pkg=${1}; shift
+    local new_pkg=${1}; shift
+    local old=${1}; shift
+    local new=${1}; shift
+
+    source "${WORKDIR}/globals"
+
+    local old_entry=${old_cache_dir}/${old_pkg}-${old}
+    local new_entry=${new_cache_dir}/${new_pkg}-${new}
+
+    local old_cache_name new_cache_name
+    gen_varname old_cache_name
+    gen_varname new_cache_name
+    cache_file_declare "${old_cache_name}" "${new_cache_name}"
+    parse_cache_file "${old_cache_name}" "${old_entry}" "${ARCHES[@]}"
+    parse_cache_file "${new_cache_name}" "${new_entry}" "${ARCHES[@]}"
+
+    diff_cache_data "${old_cache_name}" "${new_cache_name}" "${diff_report_var_name}"
+
+    cache_file_unset "${old_cache_name}" "${new_cache_name}"
+}
+
 # Generate a report with information where the old and new packages
 # are mentioned in entire scripts repository. May result in two
 # separate reports if the package got renamed.
@@ -2936,11 +3011,11 @@ function handle_eclass() {
     if [[ -e "${OLD_PORTAGE_STABLE}/${eclass}" ]] && [[ -e "${NEW_PORTAGE_STABLE}/${eclass}" ]]; then
         mkdir -p "${REPORTS_DIR}/updates/${eclass}"
         xdiff --unified=3 "${OLD_PORTAGE_STABLE}/${eclass}" "${NEW_PORTAGE_STABLE}/${eclass}" >"${REPORTS_DIR}/updates/${eclass}/eclass.diff"
-        lines+=( 'TODO: review the diff' )
+        lines+=( '0:TODO: review the diff' )
     elif [[ -e "${OLD_PORTAGE_STABLE}/${eclass}" ]]; then
-        lines+=( 'unused, dropped' )
+        lines+=( '0:unused, dropped' )
     else
-        lines+=( 'added from Gentoo' )
+        lines+=( '0:added from Gentoo' )
     fi
     generate_summary_stub "${eclass}" -- "${lines[@]}"
 }
@@ -3014,7 +3089,7 @@ function handle_profiles() {
     done <"${out_dir}/full.diff"
     lines_to_file_truncate "${out_dir}/relevant.diff" "${relevant_lines[@]}"
     lines_to_file_truncate "${out_dir}/possibly-irrelevant-files" "${possibly_irrelevant_files[@]}"
-    generate_summary_stub profiles -- 'TODO: review the diffs'
+    generate_summary_stub profiles -- '0:TODO: review the diffs'
 }
 
 # Handles changes in license directory. Generates brief reports and
@@ -3083,15 +3158,15 @@ function handle_licenses() {
     local joined
     if [[ ${#dropped[@]} -gt 0 ]]; then
         join_by joined ', ' "${dropped[@]}"
-        lines+=( "dropped ${joined}" )
+        lines+=( "0:dropped ${joined}" )
     fi
     if [[ ${#added[@]} -gt 0 ]]; then
         join_by joined ', ' "${added[@]}"
-        lines+=( "added ${joined}" )
+        lines+=( "0:added ${joined}" )
     fi
     if [[ ${#changed[@]} -gt 0 ]]; then
         join_by joined ', ' "${changed[@]}"
-        lines+=( "updated ${joined}" )
+        lines+=( "0:updated ${joined}" )
     fi
     generate_summary_stub licenses -- "${lines[@]}"
 }
@@ -3106,7 +3181,7 @@ function handle_scripts() {
     mkdir -p "${out_dir}"
 
     xdiff --unified=3 --recursive "${OLD_PORTAGE_STABLE}/scripts" "${NEW_PORTAGE_STABLE}/scripts" >"${out_dir}/scripts.diff"
-    generate_summary_stub scripts -- 'TODO: review the diffs'
+    generate_summary_stub scripts -- '0:TODO: review the diffs'
 }
 
 fi