An event card joins and leaves the event

PrivaPub lets a persona join another server's event (owner decision
2026-10-05). The card of a remote event shows the persona's participation
(pending, accepted, rejected) with Join or Leave, except for events by
invitation or taken on another site. Joining is public on the event's
server, so the first join asks the persona once, as reactions and votes do,
remembered apart from them (PublicAct).

The e2e joins the event SocialPub's Mobilizon scenario keeps, checks the
participant on Mobilizon and PrivaPub's answer, and leaves it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

CLAUDE.md

@@ -209,8 +209,9 @@ supplies:
 - **Services** (`Services/`): `TimelineService` (every feed as `FeedPage`s of `FeedPost`s, paged by `max_id`/`min_id`;
   circles are read as ids from `/clientapi` and hydrated through `/api/v1/statuses?id[]=`; located posts come from
   `/clientapi/post/nearby` and have no Mastodon actions), `StatusService` (publish, favourite, boost, bookmark, delete,
-  threads, mute, block, poll votes, emoji reactions through Pleroma's `/api/v1/pleroma/statuses/:id/reactions`;
-  located and group posts go through `/clientapi/post/insert`), `AccountService` (profiles, relationships, follow,
+  threads, mute, block, poll votes, emoji reactions through Pleroma's `/api/v1/pleroma/statuses/:id/reactions`, joining and
+  leaving remote events through `/api/privapub/v1/statuses/:id/join|leave`; located and group posts go through
+  `/clientapi/post/insert`), `AccountService` (profiles, relationships, follow,
   block, mute, follow requests, `/api/v2/search`, whose handles and URLs PrivaPub resolves), `ListService` (the
   persona's lists and their members; members are only accounts it follows, found with `accounts/search?following=true`),
   `FilterService` (the persona's v2 filters, their keywords and filtered posts), `DiscoveryService` (hashtags and
@@ -219,7 +220,10 @@ supplies:
   `ProvenanceService`.
 - **Reactions and votes are public** (owner decision, PrivaPub's ROADMAP): before a persona's first reaction or poll
   vote, `PublicNoticeService` asks it once (`PublicNoticeHost` in `MainLayout`) and remembers the persona in
-  localStorage (`PublicActionNotices`). Anything else that makes a persona's act visible to others gets the same notice.
+  localStorage (`PublicActionNotices`). Anything else that makes a persona's act visible to others gets the same notice,
+  with its own `PublicAct`: joining an event (owner decision 2026-10-05) is asked once more, since the event's server
+  shows who takes part. An event card shows the persona's participation (`privapub.event.participation`: pending,
+  accepted, rejected) with Join or Leave, except for events by invitation or taken on another site (`join_mode`).
 - **Profiles and search** (`Pages/Profile.razor` at `/account/{id}`, `Pages/Search.razor` at `/search?q=`): a card's
   author and a notification's account open the profile in the app; "Open original" is the only way to the remote site.
   A card in a fixed-height flex column with `overflow-hidden` needs `flex-none`, or it collapses to nothing.