Replies to a persona's posts reach its followers; personas join remote events

Two owner decisions of 2026-10-05, recorded in the roadmap.

Replies passed on ("the fediverse is broken without"): a public or unlisted
reply from another server to a persona's public, unlisted or followers-only
post goes on to the persona's followers as its author's server sent it, as
Mastodon forwards it, never to the replier's own server, never for a
local-only or group post; its edit and deletion follow. Only an activity its
own actor delivered is passed on (Arrival.Raw), so nothing forwarded is
forwarded again. The town checks it as relay.reply cells (specs/relay-five:
882 checks pass); Mastodon takes a passed-on activity only with an LD
signature, which GoToSocial and Akkoma don't add, and the checker knows it.

Events: a persona joins another server's event with a Join and leaves it with
a Leave, both to the organiser only, through
POST /api/privapub/v1/statuses/:id/join|leave; the organiser's Accept or
Reject is routed by our join id and shows as privapub.event.participation.
Events by invitation or taken on another site are refused before anything
is sent. Mobilizon's scenario joins and leaves an event (28 checks) and keeps
one for decePubClient's e2e.

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

docs/INTEROP.md

@@ -794,8 +794,10 @@ FEP-8a8e (draft) is the common reference.
   - Other: `category`, `contacts`.
   - Attachments: the online link `Link{name: Website}`; `PropertyValue`s under `mz:` keys; a banner `Document`.
   - The event is attributed to the Group.
-  - **RSVP:** `Join{object: event}` with a stable id that can be fetched; Mobilizon answers `Accept` or `Reject`;
-    `Leave`.
+  - **RSVP:** `Join{object: event}` with a stable id; Mobilizon answers `Accept` or `Reject` naming it; `Leave`. A
+    persona joins and leaves since 2026-10-05 (owner decision): its `Join` goes to the organiser alone, and Mobilizon
+    takes a participant of an open event at once (`role` `participant`) and answers `Accept`. It never fetches the
+    `Join`, so PrivaPub does not serve it. `joinMode` `invite` and `external` are refused before anything is sent.
   - The organiser (`actor` on the event) sends its Create, Update and Delete; the event is attributed to the group,
     which announces the Event itself, not the activity. PrivaPub refused the organiser's activities as misattributed
     until 2026-10-05, so an edit was lost and a deletion left the event in place; it now takes them as Mobilizon has
@@ -805,10 +807,11 @@ FEP-8a8e (draft) is the common reference.
   - Its NodeInfo names the software "Mobilizon" (NodeInfo wants lower case) and sends
     `Content-Type: application/json; profile=http://…#` with the URL unquoted, which .NET cannot parse: PrivaPub reads
     the raw media type, and lowercases software names.
-  - **Pasture evidence (2026-10-05, Mobilizon 5.2.4, `tools/pasture/scenarios/mobilizon.sh`):** 23 checks pass:
+  - **Pasture evidence (2026-10-05, Mobilizon 5.2.4, `tools/pasture/scenarios/mobilizon.sh`):** 27 checks pass:
     alice follows a group; the event its organiser makes arrives as an Event with its start, end and located place;
-    comments both ways; the organiser's edit, closing the comments (PrivaPub then refuses a reply) and deletes of a
-    comment and the event; a group post with its title; the unfollow; statistics. No RSVP yet.
+    she joins it (a participant row on Mobilizon, its `Accept` back as `privapub.event.participation: accepted`) and
+    leaves it (the row gone); comments both ways; the organiser's edit, closing the comments (PrivaPub then refuses a
+    reply) and deletes of a comment and the event; a group post with its title; the unfollow; statistics.
 - **Gancio:** a single Application actor; `location` is an **array** of `VirtualLocation` and `Place`; no RSVP.
   - **Pasture evidence (2026-10-05, Gancio 1.28.2, `tools/pasture/scenarios/gancio.sh`):** 17 checks pass: alice follows
     its actor `relay`; a published event arrives as an Event with its start, end and place; her reply is kept as one of