feat: add support for right-side composer sidebar and update related types

lib/__tests__/plugin-store.test.ts

@@ -48,6 +48,7 @@ function resetStore() {
       'email-footer': [],
       'composer-toolbar': [],
       'composer-sidebar': [],
+      'composer-sidebar-right': [],
       'sidebar-widget': [],
       'email-detail-sidebar': [],
       'settings-section': [],

lib/plugin-api.ts

@@ -612,7 +612,8 @@ export function createPluginAPI(plugin: InstalledPlugin): PluginAPI {
 
       registerComposerSidebar: (widget: SidebarWidget) => {
         requirePermission(plugin, 'ui:composer-sidebar');
-        return registerSlot(plugin.id, 'composer-sidebar', widget.render as React.ComponentType<Record<string, unknown>>, widget.order ?? 100);
+        const slot = widget.side === 'right' ? 'composer-sidebar-right' : 'composer-sidebar';
+        return registerSlot(plugin.id, slot, widget.render as React.ComponentType<Record<string, unknown>>, widget.order ?? 100);
       },
 
       registerDetailSidebar: (widget: SidebarWidget) => {

lib/plugin-types.ts

@@ -110,6 +110,7 @@ export type SlotName =
   | 'email-footer'
   | 'composer-toolbar'
   | 'composer-sidebar'
+  | 'composer-sidebar-right'
   | 'sidebar-widget'
   | 'email-detail-sidebar'
   | 'settings-section'
@@ -159,6 +160,12 @@ export interface SidebarWidget {
   label: string;
   render: React.ComponentType;
   order?: number;
+  /**
+   * For composer sidebars, choose which side of the New Message dialog the
+   * panel renders on. Defaults to `'left'` for backwards compatibility.
+   * Ignored by other sidebar slots.
+   */
+  side?: 'left' | 'right';
 }
 
 export interface ContextMenuItem {