feat: show the Session summary as a column next to the preview

[Douglasymlai]

Pull Request

Related Issue

N/A — maintainer-directed work; no linked issue required for this PR.

Description

Draft. This branch only adds the shared plan, docs/session-split-view-plan.md, so far. The implementation for this part (§4 of the plan) will follow on this branch.

Problem

Today a Space shows one Session at a time with a fixed summary rail on the right. People want a simpler Session view, two or three things side by side in one Space, model comparison as two Sessions next to each other, and a way to open a Session on its own.

Approach

The plan splits the work into six pull requests: a simpler Session layout, Sessions that can render side by side, split view, model comparison in split view, a new Session layout, and opening a Session in its own window or tab. Each pull request carries the same plan document.

This PR

The Session summary becomes an optional column between the chat timeline and the preview, toggled from the Session header next to the preview toggle. It is closed by default and remembered per Session. On narrow windows the summary closes first, then the preview, so the chat timeline keeps a usable width.

Builds on

None.

Testing

Not started. This branch only adds the plan document. Testing will follow the acceptance list for this part in the plan (§9).

Testing Evidence (REQUIRED)

• I have included human-verified testing evidence in this PR.
• This PR includes frontend/UI changes, and I attached screenshot(s) or screen recording(s).
• No frontend/UI changes in this PR.

Not yet available: the branch currently contains only the plan document.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Contribution Guidelines Acknowledgement

• I have read and agree to the Eigent Contribution Guideline