Align group invite settings with eligibility logic (#10748)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/dms/util.ts

@@ -47,6 +47,22 @@ export function canBeAddedToGroup(profile: bsky.profile.AnyProfileView) {
   }
 }
 
+/**
+ * Resolves the effective `allowGroupInvites` value for a chat declaration.
+ * When unset, group invites follow the general DM preference
+ * (`allowIncoming`), which itself defaults to `following`. This mirrors the
+ * `undefined` fallthrough in canBeAddedToGroup, and is the single source of
+ * truth for both displaying and persisting the setting.
+ */
+export function resolveAllowGroupInvites(
+  chat: {allowIncoming?: string; allowGroupInvites?: string} | undefined,
+): 'all' | 'none' | 'following' {
+  return (chat?.allowGroupInvites ?? chat?.allowIncoming ?? 'following') as
+    | 'all'
+    | 'none'
+    | 'following'
+}
+
 export function localDateString(date: Date) {
   // can't use toISOString because it should be in local time
   const mm = date.getMonth()