P5: downvotes, private messages from Lemmy, late Creates of deleted posts, and typed details for clients

- Dislike and its Undo are kept as downvotes (Lemmy, PieFed, Mbin, Friendica) and shown with favourites as votes.
- ChatMessage (Lemmy 0.19, Mbin, PieFed to those two) arrives as a direct message.
- A deleted object's id is remembered for 90 days, so a Create that arrives after its Delete cannot bring the post
  back; the post's ObjectRecord goes with it.
- A Join of one of our objects is answered with Ignore, as FEP-8a8e asks of a server without RSVP.
- A 503 with Retry-After is waited out like a 429 instead of counting as a failure of the host (GoToSocial throttling,
  Mastodon's temporary key failures).
- Status.privapub carries what a Mastodon Status cannot: object type, title, excerpt, cover, the author's source,
  link, video, audio and event details, and up/down votes, with every media URL proxied.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

docs/ROADMAP.md

@@ -431,13 +431,17 @@ it, raw where it doesn't.
 - **Raw capture for the details view** (done in v1.8.0): the object as received, how it arrived, the signature scheme and
   key, received versus `published`, the extensions detected, and the origin's software (§4.3). Exposed at
   `/api/privapub/v1/statuses/:id/provenance` and `/api/privapub/v1/instances/:host`. Checked live against GoToSocial.
-- **Routing by object type:**
-  - `Accept`/`Reject`/`TentativeAccept` routed by what their object is (W6).
+- **Routing by object type** (done in v1.9.0):
+  - `Accept`/`Reject` act only on a Follow we sent and ignore any other object (W6); routing to RSVPs and interaction
+    approvals comes with those features.
   - `ChatMessage` in as a direct message.
-  - `Dislike` and votes recorded in a ledger.
+  - `Dislike` and its `Undo` in a downvote ledger, shown with favourites as `privapub.votes`.
   - A `Join` answered with `Ignore` until RSVP exists.
-  - Friendica's thread-`Follow` refused without an error.
-- **Delivery:** honour 503 with `Retry-After`; answer 503 ourselves when a key fetch fails temporarily.
+  - Friendica's thread-`Follow` is ignored without an error.
+  - A deleted object's id is kept for 90 days (W9), and its `ObjectRecord` is removed with the post.
+- **Typed details reach clients** (done in v1.9.0) as `Status.privapub`.
+- **Delivery:** a 503 with `Retry-After` is waited out like a 429 and no longer counts against the host (done in v1.9.0).
+  Still open: answering 503 ourselves when a key fetch fails temporarily, and making every activity id dereference.
 
 #### P6 What people see: emoji, polls, quotes, reactions, cards, players
 - **Custom emoji** on posts, names, fields and poll options, proxied.