I've been playing with nested sessions and I see that, of course, the parent ...

I've been playing with nested sessions and I see that, of course, the parent can see the child and viceversa, but noticed that really any session can see any other open session. So two things
1. Sometimes I may have ton of sessions and I don't want a session "tree" from being able to see another stree (or it might get confusing for that agent). Similarly, it would be great to control if sessions can see their siblings or just parent/child. A setting to control how this discovery behavior works would be awesome
2. Sometimes I've wanted a session tree to be reparented under another. Right now this forks in practice because any session can see any other so I can just tell "root A" to take charge of "root B". But this change is not really reflected in the UI. It would be cool if we could move a "tree" from one place to another

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| Field | Value |
| --- | --- |
| App version | 1.1.0 |
| OS | Windows 10.0.26200 |
| Theme | Fox |
| Path | /chat |
| Tenure | Week 3 |

Start in the /chat path and reproduce the nested-session behavior described in the issue, including visibility between unrelated sessions and the current UI after one session takes charge of another. Done means the discovery behavior can be controlled for separate trees and parent/child or sibling visibility, and moving a session tree is reflected in the UI.

索引モデルが issue の本文から書いたものです。