Reactions on an agent's final reply after a recap don't render #534

A reaction on an agent turn's final reply is stored and sent to the app, but the timeline doesn't show it when the turn has a recap above the final reply.

Repro (Ace from source, local channel):

1. Ask an agent something that makes it call a few tools and then reply. The turn gets a recap ("Worked for N seconds, ran N tool calls") followed by the final reply.
2. React to the final reply's entry ({ op: "react", entry: <final pi.assistant entry> } through the gateway).
3. The channel's ace.messages document has the reaction, and watch with actions: true sends a reactions event, but no reaction shows under the reply.

Found while testing seed imports (#533). It happens the same way on a channel that wasn't imported.