[FEATURE]:Horizontal‑only top‑tab layout is a step backwards; vertical sidebar session list is modern industry trend proven by Edge #48966

Feature hasn't been suggested before.

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Describe the enhancement you want to request

Problem

The new purely horizontal top‑tab layout is a clear usability regression for power‑user developers.

Horizontal top tabs only function acceptably when you keep 2‑5 sessions open at most. AI‑session titles are inherently long. Once you accumulate more debugging / prototype sessions, tab titles get truncated beyond recognition. There is no way to visually scan all your sessions side‑by‑side.

Browsing history sessions now forces you to navigate away to a separate secondary page, losing your current conversation context and adding unnecessary click overhead.
Ctrl+P command palette only helps when I already remember exact keywords. Visual vertical scanning over dozens of past debug sessions cannot be replaced by keyword‑only search.

This is not hypothetical pain. Massive community feedback in multiple GitHub issues already reflects this frustration. Many long‑term users are trapped, forced to pin themselves on old v1.18.4 forever just for usable workflow.

Industry trend: vertical sidebar tabs are the modern solution

Major browser vendors including Microsoft Edge have already moved toward vertical sidebar tabs to fix exactly this overflow flaw.
VS‑Code also complements top file‑tabs with vertical “opened editors” list for overflow scenarios.

Horizontal‑only tabs are widely recognized as an outdated pattern for high‑volume item sets. Pushing horizontal‑only layout feels like repeating well‑known solved mistakes from the browser industry.

What I request (no need to restore full old 3‑panel UI)

Add one single configuration toggle: optional collapsible persistent left sidebar for session list.

• Keep existing top‑tab layout as the default for users who prefer it.
• Adopt virtual‑scroll inside sidebar to handle DOM / memory load. Let end‑users bear responsibility for their own memory footprint, just like browsers do.

Give power‑users a choice, do not force every developer into a sub‑optimal single workflow.