fix: replace hardcoded Unix path separators with filepath.Join and os.TempDir

- cmd_daemon.go: use filepath.Join for PID/log file paths instead of string concat with "/"
- codex_home.go: use os.TempDir() instead of hardcoded "/tmp" for cross-platform fallback

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/cmd/multica/cmd_daemon.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"strconv"
 	"strings"
 	"time"
@@ -82,11 +83,11 @@ func daemonDirForProfile(profile string) string {
 }
 
 func daemonPIDPathForProfile(profile string) string {
-	return daemonDirForProfile(profile) + "/daemon.pid"
+	return filepath.Join(daemonDirForProfile(profile), "daemon.pid")
 }
 
 func daemonLogPathForProfile(profile string) string {
-	return daemonDirForProfile(profile) + "/daemon.log"
+	return filepath.Join(daemonDirForProfile(profile), "daemon.log")
 }
 
 // healthPortForProfile returns the health check port for the given profile.

server/internal/daemon/execenv/codex_home.go

@@ -87,7 +87,7 @@ func resolveSharedCodexHome() string {
 	}
 	home, err := os.UserHomeDir()
 	if err != nil {
-		return filepath.Join("/tmp", ".codex") // last resort fallback
+		return filepath.Join(os.TempDir(), ".codex") // last resort fallback
 	}
 	return filepath.Join(home, ".codex")
 }