Agents: no way to open a new session beside the current one

[federicobrancasi]

Problem

In the Agents window, New (⌘N) always replaces the session in the active slot. When you're already working in a session and want to open a second one and work in both, there's no single gesture for it — you have to rearrange the grid yourself, in one of two ways:

• Take an existing session, move it to the side, and then click New; or
• Click New — which replaces what you were looking at — and then find the session you were working in and move that one to the side.

Either way it's a two-step detour, and the second one makes you lose sight of your session before you get it back.

Steps to reproduce

1. Open a session in the Agents window.
2. Press ⌘N (or click New).

Current: the composer replaces the session you were looking at.
Expected: a way to keep the current session visible and start the new one next to it, in one action.

Why it matters

The grid already supports side-by-side sessions — Alt+click on a row in the sessions list opens an existing session to the side — but there's no equivalent for creating a new one. Comparing two agents on the same task, or kicking off a second session while the first is still running, is a common flow that currently costs an extra manual rearrange.

Proposal

• A New Session to the Side command with a keybinding.
• Reachable from the New button without adding a second button — e.g. a split button, plus Alt+click to match the Alt = "to the side" convention the window already uses.

[vs-code-engineering]

Sharing media and context from merged PR #334962 for verification:

Summary

Alt+click (Option+click on macOS) on New in the Agents window opens a new session beside the current one, keeping it visible.

Regular click and existing keyboard shortcuts are unchanged. No new buttons, dropdowns, or tooltip text.

Screen.Recording.2026-09-07.at.8.13.28.PM.mov

Testing

• 143 targeted tests passing, 2 pending.
• Client type-check and scoped hygiene checks passing.

Source PR: #334962

[federicobrancasi]

Test

• With a session open, click New normally and verify it still opens in place.
• Alt/Option-click New and verify the new session composer opens next to the
  current session, which stays visible.
• With several sessions visible and a middle one active, Alt/Option-click New
  and verify the composer lands beside the active session.
• If an empty composer already exists elsewhere in the grid, Alt/Option-click
  New and verify it moves next to the active session rather than staying put.
• Verify the New button looks unchanged: no dropdown/chevron, and its tooltip
  shows only "New Session" with its shortcut.

[Caffeine19]

Federico Brancasi (@federicobrancasi)
Hi bro, can we also have a "fork chat to the side" command? Most of the time, I fork a chat from one checkpoint, then drag it to the side and reopen the previous one from the sessions view.