session: parse DesktopNames for XDG_CURRENT_DESKTOP, wire utmpx, fix shell

- .desktop files now parse DesktopNames: first ;-entry → XDG_SESSION_DESKTOP,
  full list with : separators → XDG_CURRENT_DESKTOP
- AddUtmpx/Close wired into spawnSession (logins appear in who/w/last)
- Credentials.Shell reads from /etc/passwd instead of hardcoded /bin/sh
- Added SetDesktopVars to env.go

src/auth/pam.go

@@ -37,9 +37,11 @@ static struct pam_conv makePAMConv(void *data) {
 import "C"
 import (
 	"fmt"
+	"os"
 	ouser "os/user"
 	"runtime"
 	"runtime/cgo"
+	"strings"
 	"unsafe"
 )
 
@@ -169,7 +171,7 @@ func Validate(user, pass, service string) (*Credentials, error) {
 		PrimaryGID: gid,
 		AllGIDs:    gids,
 		HomeDir:    u.HomeDir,
-		Shell:      "/bin/sh",
+		Shell:      shellFromPasswd(uid),
 		pamHandle:  pamh,
 		pamData:    cData,
 		pamCB:      h,
@@ -211,3 +213,21 @@ func atou32(s string) uint32 {
 	}
 	return n
 }
+
+func shellFromPasswd(uid uint32) string {
+	data, err := os.ReadFile("/etc/passwd")
+	if err != nil {
+		return "/bin/sh"
+	}
+	uidStr := fmt.Sprint(uid)
+	for _, line := range strings.Split(string(data), "\n") {
+		parts := strings.Split(line, ":")
+		if len(parts) >= 7 && parts[2] == uidStr && parts[6] != "" {
+			sh := parts[6]
+			if sh != "/sbin/nologin" && sh != "/usr/sbin/nologin" && sh != "/bin/false" {
+				return sh
+			}
+		}
+	}
+	return "/bin/sh"
+}

src/main.go

@@ -165,12 +165,16 @@ func spawnSession(res *login.Result) error {
 	session.SetSeatVars(res.Config.TTY)
 	session.SetSessionVars(creds.UID)
 	session.SetXDGCommonPaths(creds.HomeDir)
+	session.SetDesktopVars(res.Env.DesktopNames, res.Env.SessionDesktop)
 
 	sess, err := session.Spawn(&res.Env, creds.UID, creds.PrimaryGID, creds.AllGIDs, &res.Config)
 	if err != nil {
 		return fmt.Errorf("spawn: %w", err)
 	}
 
+	utmpx := auth.AddUtmpx(creds.Username, res.Config.TTY, uint32(sess.PID()))
+	defer utmpx.Close()
+
 	err = sess.Wait()
 	if err != nil {
 		log.Printf("session exited: %v", err)

src/session/env.go

@@ -57,6 +57,15 @@ func SetXDGCommonPaths(home string) {
 	setOrOwn("XDG_CONFIG_DIRS", "/etc/xdg")
 }
 
+func SetDesktopVars(currentDesktop, sessionDesktop string) {
+	if currentDesktop != "" {
+		setOrOwn("XDG_CURRENT_DESKTOP", currentDesktop)
+	}
+	if sessionDesktop != "" {
+		setOrOwn("XDG_SESSION_DESKTOP", sessionDesktop)
+	}
+}
+
 func setOrOwn(k, v string) {
 	if _, ok := os.LookupEnv(k); !ok {
 		os.Setenv(k, v)

src/session/exec.go

@@ -20,6 +20,8 @@ type PostLoginEnv struct {
 	Title            string
 	XinitrcPath      string
 	ScriptPath       string
+	DesktopNames     string // for XDG_CURRENT_DESKTOP (colon-separated)
+	SessionDesktop   string // for XDG_SESSION_DESKTOP
 }
 
 type SpawnedEnv struct {

src/session/scan.go

@@ -15,6 +15,7 @@ import (
 type DesktopEntry struct {
 	Name         string
 	Exec         string
+	DesktopNames string
 	Hidden       bool
 	NoDisplay    bool
 }
@@ -51,6 +52,8 @@ func parseDesktopEntry(path string) (*DesktopEntry, error) {
 			e.Name = v
 		case "Exec":
 			e.Exec = v
+		case "DesktopNames":
+			e.DesktopNames = v
 		case "Hidden":
 			e.Hidden = strings.EqualFold(v, "true")
 		case "NoDisplay":
@@ -97,15 +100,28 @@ func scanDesktopDir(dir, kind string, envs *[]PostLoginEnv) {
 		if err != nil || de.Hidden || de.NoDisplay {
 			continue
 		}
+		desktopNames, sessionDesktop := splitDesktopNames(de.DesktopNames, e.Name())
 		*envs = append(*envs, PostLoginEnv{
 			Kind:           kind,
 			Title:          de.Name,
 			XinitrcPath:    de.Exec,
 			ScriptPath:     de.Exec,
+			DesktopNames:   desktopNames,
+			SessionDesktop: sessionDesktop,
 		})
 	}
 }
 
+func splitDesktopNames(raw, fallback string) (currentDesktop, sessionDesktop string) {
+	if raw == "" {
+		return fallback, fallback
+	}
+	parts := strings.SplitN(raw, ";", 2)
+	sessionDesktop = strings.TrimSpace(parts[0])
+	currentDesktop = strings.ReplaceAll(raw, ";", ":")
+	return
+}
+
 func scanScriptDir(dir, kind string, envs *[]PostLoginEnv) {
 	entries, err := os.ReadDir(dir)
 	if err != nil {