Add a temporary side chat like Codex /side #26454

Problem

While an agent is working, I often want to ask a quick question about the current task. For example, I might want to understand a decision or explore another approach.

Today, asking in the main thread can steer the agent or add the question and answer to its context. Starting a new thread keeps things separate, but loses the current conversation's context.

Proposed feature

Add a temporary side chat, similar to Codex's /side or Claude Code's /btw.

It should:

• Use the current thread's context.
• Let the main agent continue working.
• Keep side-chat messages out of the main thread's context.
• Be easy to open and close.

A button, keyboard shortcut, or slash command would all work. It could also allow the user to send an answer back to the main thread when useful.

Related requests

I'd like this issue to serve as an umbrella for the existing requests:

• Discussion [Feature]: Add a Codex-style /side command #7311
• Issues [Feature]: Side questions without polluting thread context (Codex /side equivalent) #9274, SideChat: temporary snapshot tabs alongside a running thread #12793 and [Feature]: Add Claude Code /btw / Codex /side style ephemeral Side Chat on Orchestrator V2 #15758
• Previous PRs feat(server): fork threads and side chats #9436 and feat: side chat and fork surfaces for web and mobile #9437, which were closed during the V2 rewrite