fix(build.func): stop a modified conffile from aborting the whole update

update_script() runs with no tty. If an update pulls a package whose conffile
the operator edited, and the new version also ships a changed copy, dpkg raises
its "modified since installation" prompt, finds nothing to read it, and exits
with "end of file on stdin at conffile prompt".

The package is then left half configured (iU) and apt returns 100, which aborts
every other pending package on that container, not just the one being updated.
The error surfaced is "APT: Package manager error (broken packages / dependency
problems)", which does not mention conffiles. The dpkg --configure -a recovery
paths run without --force-conf* and hit the same prompt, so they cannot clear
it either.

87 of 583 ct scripts run an apt upgrade inside update_script() and none pass
Dpkg::Options, so this hooks the single dispatch in start() that all of them
already funnel through, beside the existing check_container_os_guard.

The guard is scoped to the update run and removed afterwards, so an operator's
own later apt calls are unaffected. It also reports any newly appearing
.dpkg-dist / .dpkg-new files, so keeping the local version stays visible
instead of silently diverging from upstream.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: MarcvsTvllivs

misc/build.func

@@ -4109,6 +4109,65 @@ check_container_os_guard() {
 # - Otherwise: shows update/setting menu and runs update_script with cleanup
 # ------------------------------------------------------------------------------
 
+# ------------------------------------------------------------------------------
+# apt_conffile_guard_begin()
+#
+# - Makes the upgrade inside update_script non-interactive for dpkg conffiles
+# - Without this, a conffile the operator edited raises dpkg's "modified since
+#   installation" prompt. update_script has no tty, so dpkg exits with
+#   "end of file on stdin at conffile prompt", the package is left half
+#   configured (iU), and apt returns 100 - which aborts every other pending
+#   package on the container, not just the one being updated
+# - DEBIAN_FRONTEND does not cover this: the prompt comes from dpkg, not debconf
+# - Scoped to the update run only. apt_conffile_guard_end() removes the drop-in
+#   again, so an operator's own later apt calls are unaffected
+# ------------------------------------------------------------------------------
+CS_APT_CONF_DROPIN="/etc/apt/apt.conf.d/99-community-scripts-conffile"
+
+apt_conffile_guard_begin() {
+  command -v apt-get >/dev/null 2>&1 || return 0
+  [[ -d /etc/apt/apt.conf.d ]] || return 0
+
+  rm -f "$CS_APT_CONF_DROPIN"
+  cat >"$CS_APT_CONF_DROPIN" <<'EOF'
+// Added by community-scripts for the duration of an update run.
+// Keeps locally modified configuration files instead of prompting, because
+// update_script runs without a tty and dpkg would otherwise abort the upgrade.
+Dpkg::Options {
+  "--force-confdef";
+  "--force-confold";
+};
+EOF
+
+  CS_CONFFILE_BEFORE="$(_cs_list_pending_conffiles)"
+}
+
+# ------------------------------------------------------------------------------
+# apt_conffile_guard_end()
+#
+# - Removes the drop-in written by apt_conffile_guard_begin()
+# - Reports any conffile where upstream shipped a change that was not applied,
+#   so keeping the local file stays visible instead of silently diverging
+# ------------------------------------------------------------------------------
+apt_conffile_guard_end() {
+  command -v apt-get >/dev/null 2>&1 || return 0
+  rm -f "$CS_APT_CONF_DROPIN"
+
+  local after new
+  after="$(_cs_list_pending_conffiles)"
+  new="$(comm -13 <(printf '%s\n' "$CS_CONFFILE_BEFORE") <(printf '%s\n' "$after") 2>/dev/null)"
+  [[ -z "$new" ]] && return 0
+
+  msg_warn "Kept your version of these config files; upstream shipped changes alongside them:"
+  while IFS= read -r f; do
+    [[ -n "$f" ]] && msg_warn "  ${f%.dpkg-*} (new upstream version: $f)"
+  done <<<"$new"
+}
+
+_cs_list_pending_conffiles() {
+  find /etc \( -name '*.dpkg-dist' -o -name '*.dpkg-new' \) -type f 2>/dev/null | sort
+}
+
 start() {
   source <(curl -fsSL https://raw.githubusercontent.com/community-scripts/ProxmoxVE/main/misc/tools.func)
   if command -v pveversion >/dev/null 2>&1; then
@@ -4122,7 +4181,9 @@ start() {
     get_lxc_ip
     runtime_script_status_guard update || return 0
     check_container_os_guard || return 0
+    apt_conffile_guard_begin
     update_script
+    apt_conffile_guard_end
     run_addon_updates
     update_motd_ip
     cleanup_lxc
@@ -4134,7 +4195,9 @@ start() {
     get_lxc_ip
     runtime_script_status_guard update || return 0
     check_container_os_guard || return 0
+    apt_conffile_guard_begin
     update_script
+    apt_conffile_guard_end
     run_addon_updates
     update_motd_ip
     cleanup_lxc
@@ -4165,7 +4228,9 @@ start() {
     get_lxc_ip
     runtime_script_status_guard update || return 0
     check_container_os_guard || return 0
+    apt_conffile_guard_begin
     update_script
+    apt_conffile_guard_end
     run_addon_updates
     update_motd_ip
     cleanup_lxc