GoToSocial's interaction policies are honoured

A remote post's canReply, canLike and canAnnounce (with the older always and approvalRequired) are kept beside
canQuote and judged for each persona: let in at once when the rule names the public, the persona, the author's
followers while it follows the author, or the accounts the author follows while the author follows it; asked first
when only the manual list names it; refused (422) otherwise. Asked first, a ReplyRequest, LikeRequest or
AnnounceRequest with the interaction as its instrument goes to the author alone, and the interaction waits
(privapub.approval: pending). The author's Accept brings an authorization, verified on the author's origin as naming the
interaction and the post; the reply then goes out with replyAuthorization, the boost with announceAuthorization, the
like with likeAuthorization. A Reject leaves the reply ours alone and takes a like or a boost back. As a third party, a
reply a policy does not let in at once is kept only with an authorization that verifies. Clients see the rules as
GoToSocial's interaction_policy.

Checked live against GoToSocial 0.22.1: the scenario's nine new checks pass (64 in all), a reply and a like approved
through its interaction requests and a boost refused.

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

FEDERATION.md

@@ -176,6 +176,22 @@ An incoming `Update` without a newer `updated` only refreshes counts and details
     `Delete{stamp}`.
   - Followers-only posts and DMs can never be quoted.
 
+**Interaction policies** (GoToSocial's `canReply`, `canLike`, `canAnnounce`, with the older `always` and
+`approvalRequired`):
+- **Read** on every remote post; one left out means anyone, automatically. A persona is let in at once when the rule
+  names the public, the persona itself, the author's followers while it follows the author, or the accounts the author
+  follows while the author follows it.
+- **Shut out:** the client API answers 422 to a reply, favourite or boost the rule does not allow at all.
+- **Asked first:** a `ReplyRequest`, `LikeRequest` or `AnnounceRequest` (the interaction as its `instrument`) goes to the
+  author alone, and the interaction waits (`privapub.approval: pending`). The author's `Accept` brings an authorization
+  (`result`), which must be on the author's origin, attributed to them and naming the interaction and the post; only then
+  does the reply go out with `replyAuthorization`, the boost with `announceAuthorization` and the like with
+  `likeAuthorization`. A `Reject` leaves it ours alone (`rejected`), and takes a like or a boost back.
+- **As a third party,** a reply that a post's policy does not let in at once is kept only with an authorization that
+  verifies the same way. A rule naming a collection we cannot list (followers, following) lets the reply in.
+- **Shown** to clients as GoToSocial's `interaction_policy` (`can_favourite`, `can_reply`, `can_reblog`).
+- Our own posts state only `canQuote`: anyone may reply to, like and boost them.
+
 **Custom emoji** (`Emoji` tags) are read on posts, display names, bios and profile fields, at most 64 per object.
 **Profiles** keep their header, profile fields, `manuallyApprovesFollowers`, `published`, `movedTo`, `indexable`,
 `memorial` and avatar and header descriptions. A post's title becomes `name` and is also the first, bold line of `content`, because Mastodon does not show