panel: disable demote and delete for the only global admin

Co-authored-by: Cursor <cursoragent@cursor.com>

CHANGELOG.md

@@ -21,6 +21,9 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
 
 ### Changed
 
+- panel: the user edit form disables role change and delete for the only global
+  administrator, with a short note, instead of allowing the action and showing
+  an error on submit.
 - panel: the user create/edit form hides **Assigned domains** when the role is
   global administrator, since that role manages every domain anyway.
 - panel: **Settings** shows panel credentials and DMARC aggregate reports side

internal/web/handlers/handlers_users.go

@@ -132,9 +132,18 @@ func (h *Handlers) renderUserForm(w http.ResponseWriter, r *http.Request, status
 	data["FormDomains"] = view.FormDomains
 	data["FormPassword"] = view.FormPassword
 	data["IsEdit"] = userID != 0
+	data["LastGlobalLocked"] = lastGlobalLocked(h, userID, view.FormRole)
 	h.view.Render(w, status, "user_form", data)
 }
 
+func lastGlobalLocked(h *Handlers, userID int64, formRole string) bool {
+	if userID == 0 || formRole != string(store.RoleGlobal) {
+		return false
+	}
+	n, err := h.store.CountGlobalUsers()
+	return err == nil && n <= 1
+}
+
 func (h *Handlers) submitUserCreate(w http.ResponseWriter, r *http.Request) {
 	if err := r.ParseForm(); err != nil {
 		h.renderUserForm(w, r, http.StatusBadRequest, 0, userFormView{FormErr: "Invalid form submission."})

internal/web/view/static/panel.css

@@ -193,6 +193,14 @@ button, a.btn, a.danger {
   color: var(--on-accent); background: var(--accent-fill); border: 0; border-radius: 5px; cursor: pointer;
 }
 button:hover, a.btn:hover { background: var(--accent-fill-hover); }
+button:disabled, button.danger:disabled {
+  opacity: 0.45; cursor: not-allowed;
+}
+button:disabled:hover { background: var(--accent-fill); }
+button.danger:disabled:hover { background: var(--danger-fill); }
+select:disabled {
+  opacity: 0.65; cursor: not-allowed; background: var(--code-bg);
+}
 .error { color: var(--danger-fg); margin: 0.6rem 0 0; font-weight: 600; }
 .muted { color: var(--muted); }
 /* Links take the accent. The panel never set a colour here and ran on the

internal/web/view/templates/user_form.html

@@ -14,10 +14,12 @@
     <input id="password" name="password" type="password" autocomplete="new-password" {{if not .IsEdit}}required{{end}}>
 
     <label for="role">Role</label>
-    <select id="role" name="role" data-global-role="{{.GlobalRole}}">
+    {{if .LastGlobalLocked}}<input type="hidden" name="role" value="{{.FormRole}}">{{end}}
+    <select id="role" name="role" data-global-role="{{.GlobalRole}}"{{if .LastGlobalLocked}} disabled{{end}}>
       <option value="domain_admin" {{if eq .FormRole "domain_admin"}}selected{{end}}>Domain administrator</option>
       <option value="global" {{if eq .FormRole "global"}}selected{{end}}>Global administrator</option>
     </select>
+    {{if .LastGlobalLocked}}<p class="muted">The only global administrator cannot be demoted.</p>{{end}}
 
     <fieldset id="domain-pick" data-domain-pick>
       <legend>Assigned domains</legend>
@@ -32,7 +34,8 @@
 
     <button type="submit">{{if .IsEdit}}Save{{else}}Create{{end}}</button>
     {{if .IsEdit}}
-    <button type="submit" name="action" value="delete" class="danger">Delete user</button>
+    <button type="submit" name="action" value="delete" class="danger"{{if .LastGlobalLocked}} disabled{{end}}>Delete user</button>
+    {{if .LastGlobalLocked}}<p class="muted">The only global administrator cannot be deleted.</p>{{end}}
     {{end}}
   </form>
 </div>