feat(codex): include plan type in auth filename

internal/auth/codex/filename.go

@@ -0,0 +1,55 @@
+package codex
+
+import (
+	"fmt"
+	"strings"
+	"unicode"
+)
+
+// CredentialFileName returns the filename used to persist Codex OAuth credentials.
+// When planType is available (e.g. "plus", "team"), it is appended after the email
+// as a suffix to disambiguate subscriptions.
+func CredentialFileName(email, planType string, includeProviderPrefix bool) string {
+	email = strings.TrimSpace(email)
+	plan := normalizePlanTypeForFilename(planType)
+
+	prefix := ""
+	if includeProviderPrefix {
+		prefix = "codex-"
+	}
+
+	if plan == "" {
+		return fmt.Sprintf("%s%s.json", prefix, email)
+	}
+	return fmt.Sprintf("%s%s-%s.json", prefix, email, plan)
+}
+
+func normalizePlanTypeForFilename(planType string) string {
+	planType = strings.TrimSpace(planType)
+	if planType == "" {
+		return ""
+	}
+
+	parts := strings.FieldsFunc(planType, func(r rune) bool {
+		return !unicode.IsLetter(r) && !unicode.IsDigit(r)
+	})
+	if len(parts) == 0 {
+		return ""
+	}
+
+	for i, part := range parts {
+		parts[i] = titleToken(part)
+	}
+	return strings.Join(parts, "-")
+}
+
+func titleToken(token string) string {
+	token = strings.TrimSpace(token)
+	if token == "" {
+		return ""
+	}
+	lower := strings.ToLower(token)
+	runes := []rune(lower)
+	runes[0] = unicode.ToUpper(runes[0])
+	return string(runes)
+}