feat(info): show the install reason and drop the indentation

N? and `info PKG` now print three lines, none indented:

    PKG: <description>
    reason: explicitly installed | installed as a dependency | unknown | not installed
    required by: <installed dependents, comma separated> | nothing

The reason comes from a new <be>_reason backend function: apt-mark
showauto / showmanual (dpkg decides for a package in neither list), the
Install Reason of pacman -Qi, dnf repoquery --installed %{reason} (dnf4
and dnf5 words) and the Installed line of zypper info (rpm plus libzypp's
AutoInstalled when zypper is locked). A row whose old version is "-" is
not installed and the backend is not asked. The "(installed)" qualifier
moves to --help, README and DESIGN.

The rpm E2E fixture and e2e_reset now also mark su-dummy-a and su-dummy-c
as user-installed on dnf, which records plain rpm installs as "unknown",
so 1? and 2? show both reasons on all 12 distros. The verified commands
are recorded in discovery/{apt,pacman,rpm}.md.

tests/e2e/fixtures/rpm.sh

@@ -31,7 +31,10 @@
 #   so it is a pre-existing unneeded package (dnf repoquery --unneeded / zypper packages --unneeded).
 #
 # Optional (SU_FIXTURE_B_AUTO=1): su-dummy-b counts as installed as a dependency (dnf: `dnf mark
-#   remove`, zypper: /var/lib/zypp/AutoInstalled), like the pacman fixture's --asdeps.
+#   remove`, zypper: /var/lib/zypp/AutoInstalled), like the pacman fixture's --asdeps; on dnf
+#   su-dummy-a and su-dummy-c also count as installed by the user (`dnf mark install`): dnf4 reports
+#   packages installed with plain rpm as reason "unknown" (dnf5: "External User"). zypper needs
+#   nothing for them: a package that is not in AutoInstalled is user-installed.
 #
 # Re-runnable: re-running resets everything to the "1.0 installed, 2.0 available" state.
 #
@@ -198,7 +201,11 @@ fi
 if [ "${SU_FIXTURE_B_AUTO:-0}" = 1 ]; then
   case $BACKEND in
     zypper) grep -qx su-dummy-b /var/lib/zypp/AutoInstalled 2>/dev/null || echo su-dummy-b >>/var/lib/zypp/AutoInstalled ;;
-    dnf|yum) "$BACKEND" -q mark remove su-dummy-b >/dev/null ;;
+    dnf|yum)
+      # dnf4 spelling first, then dnf5's (which asks for confirmation)
+      "$BACKEND" -q mark remove su-dummy-b >/dev/null 2>&1 || "$BACKEND" -q -y mark dependency su-dummy-b >/dev/null
+      "$BACKEND" -q mark install su-dummy-a su-dummy-c >/dev/null 2>&1 || "$BACKEND" -q -y mark user su-dummy-a su-dummy-c >/dev/null
+      ;;
   esac
   log "su-dummy-b marked as installed as a dependency"
 fi

tests/e2e/helpers.bash

@@ -132,10 +132,14 @@ e2e_reset() {
 		rpm -Uvh --oldpackage --replacepkgs /var/tmp/su-fixture/RPMS/*/su-dummy-[abc]-1.0-1.*.rpm >/dev/null 2>&1
 		;;
 	esac
-	# su-dummy-b is a dependency of su-dummy-a (installed as such), on every backend
+	# su-dummy-b is a dependency of su-dummy-a (installed as such), on every backend; su-dummy-a and
+	# su-dummy-c were installed by the user (dnf records plain rpm installs as reason unknown)
 	case $BE in
 	apt) apt-mark auto su-dummy-orphan su-dummy-b >/dev/null ;;
-	dnf) dnf -q mark remove su-dummy-b >/dev/null 2>&1 ;;
+	dnf)
+		dnf -q mark remove su-dummy-b >/dev/null 2>&1 || dnf -q -y mark dependency su-dummy-b >/dev/null 2>&1
+		dnf -q mark install su-dummy-a su-dummy-c >/dev/null 2>&1 || dnf -q -y mark user su-dummy-a su-dummy-c >/dev/null 2>&1
+		;;
 	zypper) grep -qx su-dummy-b /var/lib/zypp/AutoInstalled 2>/dev/null || echo su-dummy-b >>/var/lib/zypp/AutoInstalled ;;
 	esac
 	[[ $(versions) == "a=1.0 b=1.0 c=1.0" && $(pkg_ver su-dummy-orphan) == 1.0 ]] || {

tests/e2e/skeptical-updater.bats

@@ -32,14 +32,27 @@ zypper_verb() { case $(. /etc/os-release && printf '%s' "$ID") in opensuse-tumbl
 	refute_line --regexp '^.\[4\]'
 }
 
-@test "N? prints the description; su-dummy-b is required by su-dummy-a" {
+@test "N? prints the description, the install reason and who requires it" {
+	local -a lines_=()
+	local i a=-1 b=-1
 	run skeptical-updater --no-refresh <<<$'1?\n2?\nq'
 	assert_success
 	assert_line --regexp '^su-dummy-a: .*([Dd]ummy|skeptical-updater).*$'
 	assert_line --regexp '^su-dummy-b: .*([Dd]ummy|skeptical-updater).*$'
-	# [1] su-dummy-a has no installed reverse dependency, [2] su-dummy-b is needed by su-dummy-a
-	assert_line '  required by (installed): nothing'
-	assert_line '  required by (installed): su-dummy-a'
+	# [1] su-dummy-a was installed explicitly and nothing needs it; [2] su-dummy-b was installed as
+	# a dependency of su-dummy-a - the two lines right under each description, no indentation
+	mapfile -t lines_ <<<"$output"
+	for i in "${!lines_[@]}"; do
+		case ${lines_[i]} in
+		'su-dummy-a: '*) a=$i ;;
+		'su-dummy-b: '*) b=$i ;;
+		esac
+	done
+	[[ ${lines_[a + 1]} == 'reason: explicitly installed' && ${lines_[a + 2]} == 'required by: nothing' ]] ||
+		fail "1? (su-dummy-a): got '${lines_[a + 1]}' / '${lines_[a + 2]}'"
+	[[ ${lines_[b + 1]} == 'reason: installed as a dependency' && ${lines_[b + 2]} == 'required by: su-dummy-a' ]] ||
+		fail "2? (su-dummy-b): got '${lines_[b + 1]}' / '${lines_[b + 2]}'"
+	refute_output --partial 'required by (installed)'
 	assert_line 'Quit: nothing was upgraded.'
 }
 
@@ -250,7 +263,11 @@ zypper_verb() { case $(. /etc/os-release && printf '%s' "$ID") in opensuse-tumbl
 	assert_line --partial "$BE"$'\t'"su-dummy-c"$'\t'"user"
 	run asuser skeptical-updater info su-dummy-b
 	assert_success
-	assert_line '  required by (installed): su-dummy-a'
+	assert_line 'reason: installed as a dependency'
+	assert_line 'required by: su-dummy-a'
+	run asuser skeptical-updater info su-dummy-a
+	assert_success
+	assert_line 'reason: explicitly installed'
 	run asuser skeptical-updater --dry-run --no-refresh <<<''
 	assert_success
 	assert_line --regexp "$(native_upgrade_regex)"