[Bug]: Multi-session tab switching takes 2–3 seconds, input lags, and app exits unexpectedly

### Operating system

macOS 26.3 (Build 25D125), Apple M2 Pro

### Orca version

1.4.147

### Details

**Short summary**

Orca becomes noticeably unresponsive when multiple sessions are open. Switching to another session tab takes about 2–3 seconds before the conversation content is rendered. Typing in the chat input also has obvious latency, and Orca occasionally exits unexpectedly.

**What happened?**

- Performance degrades significantly with multiple sessions open.
- After clicking a session tab, its conversation content takes roughly 2–3 seconds to appear.
- Text input is delayed while typing in the chat composer.
- Orca occasionally exits unexpectedly during normal conversation use.

**How can we reproduce it?**

1. Open and use multiple agent sessions in Orca.
2. Switch repeatedly between session tabs.
3. Continue a conversation and type into the chat input.
4. Observe the delayed transcript rendering and delayed keystrokes.
5. Continue using the sessions; the unexpected exit is intermittent.

**Expected behavior**

- Switching tabs should render the selected conversation immediately.
- Typing should remain responsive with multiple sessions open.
- The application should not exit unexpectedly.

**Additional context**

Issue #5096 appears related to general long-running UI/input lag, but this report specifically reproduces under multi-session use and includes a consistent 2–3 second conversation-render delay plus intermittent unexpected exits.