Proposal: Ephemeral side chats and persistent thread forks

[prrcarvalho]

Summary

I’d like to propose conversation branching in T3 Code with two complementary modes:

1. Ephemeral side chats

   • Similar to the side-chat behavior in the Codex desktop experience.
   • Start from the current thread context.
   • Allow exploring a tangent without adding those turns to the main thread.
   • Intended to be temporary and disposable.

2. Persistent thread forks

   • Create a real new thread from the current thread, optionally from a specific turn.
   • Inherit the conversation context up to the fork point.
   • Both threads continue independently.
   • The fork appears as a normal thread in the sidebar.

These solve related but different problems.

Motivation

For long-running development sessions, a thread can accumulate a lot of useful context about the repository, architecture, decisions, and current work.

Sometimes I want to explore:

• an alternative implementation;
• a different architectural direction;
• a debugging hypothesis;
• an unrelated repository question;
• a second approach to the same task.

Right now, the two obvious options both have drawbacks.

Continue in the existing thread

This preserves all accumulated context, but the tangent becomes part of the main conversation and may pollute the context for subsequent work.

Start a new thread

This keeps the conversations isolated, but loses the accumulated conversational context unless it is manually summarized or copied into the new thread.

What I’d like instead is:

                         Main thread
                             |
                ---------------------------
                |                         |
          ephemeral side chat       persistent fork
                |                         |
        temporary exploration      independent thread
        does not pollute main      appears in sidebar

[juliusmarminge]

Duplicate of the existing Ideas threads for this feature:

• [Feature]: conversation branching (fork thread from a message) #6707 — conversation branching / persistent fork from a message
• [Feature]: Add a Codex-style /side command #7311 — Codex-style /side ephemeral side chat

Same combined ask was already filed as #11818 (closed as duplicate of those). Please +1 / fold any extra detail into #6707 and #7311.

Related prior impl (closed unmerged): #9436 and #9437.