React

React is a separate model with its own self-contained handler, following the same pattern as Reply. Kowloon uses a one reaction per user per target model: a React activity sets it (creating or replacing whatever was there), and an emoji-less payload clears it. There is no separate "unreact" activity type -- clearing is just React with no emoji.

Set or replace a reaction

{
  "type": "React",
  "objectType": "React",
  "to": "post:64f0...@kwln.org",
  "object": { "type": "React", "emoji": "thumbsup", "name": "thumbsup" }
}

Clear a reaction

{
  "type": "React",
  "objectType": "React",
  "to": "post:64f0...@kwln.org",
  "object": { "emoji": "" }
}

The emoji field has a three-way fallback -- omit object.type when clearing

The handler reads the emoji value as object.react || object.emoji || object.type -- a three-way fallback. object.type is deliberately optional on a clear payload specifically so a populated object.type isn't misread as the emoji value. The schema allows object.type to be absent on React, but if present it must equal "React". If you send object.type: "React" alongside an empty emoji intending to clear, that's fine -- but never rely on object.type carrying an emoji value, and match the client SDK's own behavior (below) of omitting type entirely on a clear payload.

Required: actorId, objectType (a string), object (an object), to (the target ID -- despite the schema calling it to, semantically this is the reaction target, not an audience).

Targets supported: Post, Reply, Page, Bookmark, Group, Circle.

Auth

Only gated on new/changed reactions -- clearing your own past reaction is never blocked, even if you've since been blocked (you can always clean up your own data). The gate (authorizeInteraction(..., capability: "canReact")) is currently only enforced for Post/Reply targets, checked against the root post for Reply targets. Page/Bookmark/Group/Circle react targets aren't FeedItems-backed and skip this gate -- a tracked follow-up, kowloon#40.

Side effects

• reactCount/reactPreview (top emoji)/reactSummary (all distinct emoji, concatenated) are recomputed from a live aggregate over the React collection -- never incremented/decremented by delta -- and written to whichever target model matches, plus its FeedItems cache entry. Recompute-not-delta is what keeps counts correct across add/replace/clear without needing to track prior state.
• User.reactCount (the actor's own tally of things they've reacted to) is incremented on a brand-new reaction, decremented on clear, and left untouched on a replace.
• A notification fires only on a brand-new reaction -- never on replace or clear -- respecting prefs.notifications.react.
• Federation goes to the target's host, the target author's home, and -- for Reply targets -- the parent's host too.

Response

{ activity, created: { status, react }, result: same, federation }, where status is one of reacted / replaced / unreacted / already_reacted / no_change.

Client mapping

react({ postId, emoji, name }) matches exactly, including the deliberate object.type omission on clear. There is no separate deleteReact() method; react({ postId, emoji: '' }) is the only (and correct) way to clear a reaction.