New worktree on an existing branch

I'd like to create a new session in a new worktree of a GitHub repo, starting from a specific branch. There doesn't seem to be a way: if I select "New worktree" in the dropdown I can only select the `master`/default branch (while if I select "Local" I can switch among the various local branches).

In theory I can create a new worktree and then checkout the branch I want, but it's time- (and token-) consuming. It should be technically simple to add this as a valid option through the UI.

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| Field | Value |
| --- | --- |
| App version | 1.0.22 |
| OS | Windows 10.0.26200 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Week 5 |

Reproduce the flow at /chat by opening the “New worktree” dropdown and compare it with the “Local” branch selector. Trace how branch choices are populated, then verify that an existing local branch can be selected and that the new worktree starts from it.

Written by the indexing model from the issue text.