fix(install): mark pacman packages explicit after --needed install

pacman --needed skips a package that is already on the system as a dependency and leaves its install reason alone. A declared package can then sit as asdeps, surface as an orphan once its accidental dependent leaves, and get swept away by an orphan cleanup. expac and lm_sensors, both maintenance-console runtime deps, nearly went this way: they were asdeps on both hosts and only survived today's orphan sweep because something still depended on them.

pacman_install now marks the package explicit after a successful install. The mark never runs on a failed install, and a mark failure never fails the install. I flipped expac and lm_sensors to explicit on ratio and velox by hand since the installer only runs on fresh systems.

2 files changed, 101 insertions, 1 deletions

diff --git a/archsetup b/archsetup
index 09961aa..0349113 100755
--- a/archsetup
+++ b/archsetup
@@ -732,7 +732,12 @@ retry_install() {
 
 # Pacman Install
 pacman_install() {
-    retry_install "$1" "pacman" "pacman --noconfirm --needed -S \"$1\""
+    retry_install "$1" "pacman" "pacman --noconfirm --needed -S \"$1\"" || return $?
+    # --needed skips a package already present as a dependency and leaves
+    # its install reason alone; the package can then surface as an orphan
+    # later and get swept away (expac/lm_sensors nearly went this way,
+    # 2026-07-08). Every declared package is wanted explicitly.
+    pacman -D --asexplicit "$1" >> "$logfile" 2>&1 || true
 }
 
 # AUR Install
diff --git a/tests/installer-steps/test_pacman_install.py b/tests/installer-steps/test_pacman_install.py
new file mode 100644
index 0000000..28c9a7f
--- /dev/null
+++ b/tests/installer-steps/test_pacman_install.py
@@ -0,0 +1,95 @@
+"""Characterization tests for pacman_install's install-reason handling.
+
+pacman --needed skips a package that is already present as a dependency and
+leaves its install reason alone. A declared package can then sit as asdeps
+on an existing system, show up as an orphan once its accidental dependent
+leaves, and get swept away by an orphan cleanup (expac and lm_sensors nearly
+went this way on 2026-07-08). pacman_install therefore marks every declared
+package explicit after a successful install.
+
+Method mirrors test_orchestrators: sed-extract the real functions from
+`archsetup`, source them with `display`/`error_warn` silenced and `pacman`
+replaced by a recorder, run, and assert the recorded calls.
+
+Run from repo root:
+    python3 -m unittest tests.installer-steps.test_pacman_install
+"""
+
+import os
+import subprocess
+import textwrap
+import unittest
+
+REPO_ROOT = os.path.abspath(os.path.join(os.path.dirname(__file__), "..", ".."))
+ARCHSETUP = os.path.join(REPO_ROOT, "archsetup")
+
+
+def run_pacman_install(pkg, pacman_s_rc=0, pacman_d_rc=0):
+    """Extract retry_install + pacman_install, run against a fake pacman.
+
+    Returns (exit_code, recorded pacman calls as a list of strings).
+    """
+    script = textwrap.dedent("""
+        set -u
+        MAX_INSTALL_RETRIES=3
+        logfile=/dev/null
+        display() { :; }
+        error_warn() { return 1; }
+        pacman() {
+            echo "pacman $*" >> "$CALLS"
+            case "$1" in
+                --noconfirm) return "$PACMAN_S_RC" ;;
+                -D)          return "$PACMAN_D_RC" ;;
+            esac
+        }
+        %(functions)s
+        pacman_install "%(pkg)s"
+    """)
+    extract = subprocess.run(
+        ["sed", "-n",
+         "/^retry_install()/,/^}/p;/^pacman_install()/,/^}/p", ARCHSETUP],
+        capture_output=True, text=True, check=True)
+    calls_file = os.path.join(os.environ.get("TMPDIR", "/tmp"),
+                              f"pacman-install-calls-{os.getpid()}")
+    if os.path.exists(calls_file):
+        os.unlink(calls_file)
+    open(calls_file, "w").close()
+    env = dict(os.environ, CALLS=calls_file,
+               PACMAN_S_RC=str(pacman_s_rc), PACMAN_D_RC=str(pacman_d_rc))
+    proc = subprocess.run(
+        ["bash", "-c", script % {"functions": extract.stdout, "pkg": pkg}],
+        capture_output=True, text=True, env=env)
+    with open(calls_file) as f:
+        calls = [line.strip() for line in f if line.strip()]
+    os.unlink(calls_file)
+    return proc.returncode, calls
+
+
+class PacmanInstallTests(unittest.TestCase):
+    def test_success_marks_package_explicit(self):
+        rc, calls = run_pacman_install("expac")
+        self.assertEqual(rc, 0)
+        self.assertIn("pacman --noconfirm --needed -S expac", calls)
+        self.assertIn("pacman -D --asexplicit expac", calls)
+        # the mark comes after the install, never before
+        self.assertGreater(calls.index("pacman -D --asexplicit expac"),
+                           calls.index("pacman --noconfirm --needed -S expac"))
+
+    def test_failed_install_never_marks(self):
+        rc, calls = run_pacman_install("expac", pacman_s_rc=1)
+        self.assertNotEqual(rc, 0)
+        self.assertNotIn("pacman -D --asexplicit expac", calls)
+        # all three retry attempts happened
+        self.assertEqual(
+            calls.count("pacman --noconfirm --needed -S expac"), 3)
+
+    def test_mark_failure_does_not_fail_the_install(self):
+        # -D can fail in odd corners (readonly db mid-transaction); the
+        # install itself succeeded and must report success
+        rc, calls = run_pacman_install("expac", pacman_d_rc=1)
+        self.assertEqual(rc, 0)
+        self.assertIn("pacman -D --asexplicit expac", calls)
+
+
+if __name__ == "__main__":
+    unittest.main()