Show a reply's steps, and catch up on a reply whose live push was missed

A reply that works through tools now shows its latest tool step under
"is thinking…" (not its closing note, which is the answer). While a reply
is due, the open conversation checks the session's latest messages every
few seconds (api/admin/bots/session-messages) and replays any it missed
as server:bot-message, so the thread, rail and unread all take it and the
thinking row can't stay up until a reload. MCP and custom tool steps read
in words ("Using Exa search (web search exa)").

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/pages/admin/bots/[bot_id]/(functions)/post-session-api.ts

@@ -5,7 +5,7 @@ type Params = {
     /**
      * Under `/api/admin/bots/`.
      */
-    path: "list-sessions" | "new-session" | "reopen-session";
+    path: "list-sessions" | "new-session" | "reopen-session" | "session-messages";
     body: Record<string, unknown>;
 };