### Summary of Improvements
This PR replaces the custom `IntersectionObserver`-based virtualization
with the `virtua` library to significantly improve rendering performance
and UI responsiveness.
### 🚀 Performance Results
Verified using `session-performance.test.ts`:
- **Rendering**: 2000 messages rendered in **16.90ms**.
- **Huge Conversation**: 10,000 messages processed in **0.80ms**.
- **Session Switching**: Average switch time reduced to **0.58ms**
(virtually zero lag).
### 🛠️ Key Changes
- **Virtualized Message Stream**: Integrated `virtua/solid` for
efficient windowing and automatic scroll compensation.
- **Floating Scroll Controls**: Applied `position: absolute` and
`pointer-events: none` to the list controls to ensure
scroll-to-top/bottom buttons float correctly over the message area
without blocking interactions.
- **Package Synchronization**: Updated `virtua` and SDK dependencies,
with a fully synchronized `package-lock.json` for stable builds.
### 🎥 UI Verification
https://github.com/user-attachments/assets/24e483a3-8be6-4ac4-a431-d719f2015f4e
- **Smooth Scrolling**: Verified that rendering gaps are eliminated
during fast scrolls.
- **Position Retention**: Scroll positions are preserved when switching
between sessions.
> [!NOTE]
> Detailed performance gains and layout fixes are isolated to the
`virtua` implementation and core package updates, following the
requested cleanup.
---------
Co-authored-by: Shantur Rathore <i@shantur.com>
Ensure the Tauri prebuild step refreshes packages/server/public from the current UI renderer bundle so the packaged desktop app does not serve a stale folder-selection UI.
Set the same explicit AppUserModelID that the legacy Electron app used so Windows taskbar grouping and notification attribution stay consistent in the Tauri desktop build.
Match the Tauri package, Cargo, and bundle version metadata to the current legacy desktop version so About dialogs and installer artifacts stop reporting 0.1.0.
Make the legacy Electron desktop client generate and pass a per-launch auth cookie name too, so parallel desktop instances stop clobbering each other's localhost session cookie just like the Tauri client.
Drop the startup instrumentation call that leaked into the auth-cookie isolation branch. The helper is not defined on this PR branch, and the PR does not need to serialize the generated cookie name to fix the multi-instance auth collision.
Reconcile optimistic user messages by replacing the oldest synthetic pending message when the server-backed message arrives. Stop sending prompt part ids and rely on message-level replacement so v1.2.25 validation passes without duplicating optimistic content.
Disable follow-mode virtualization churn and simplify reasoning header layout so streaming thinking blocks stop nudging the scroll position while the list is pinned to bottom.
Keep visible rows mounted during follow-up measurements and clear stale refs so async message rendering no longer flickers or measures detached blocks. Coalesce per-item render notifications so content-heavy rows only trigger one remeasurement per frame.
