[Bug] Windows Companion crashes when opening older sessions that work in browser Dashboard

Summary

Windows Companion crashes when selecting certain older chat sessions from the session picker. The same sessions open successfully in the browser Dashboard against the same Gateway, so the session data and Gateway appear healthy and the failure seems isolated to the Windows Companion / WinUI client.

Environment

• Windows Companion / Windows Hub: v2026.9.3
• OpenClaw CLI / Gateway: v2026.9.4 (3a9d69d)
• Gateway runtime: Node v24.19.0
• Gateway URL: ws://127.0.0.1:18789
• Gateway status: running, connectivity probe OK
• Platform: Windows with OpenClaw Gateway running under WSL/systemd user service

Steps to reproduce

1. Start the OpenClaw Gateway and connect Windows Companion.
2. Open Chat in Windows Companion.
3. Open the session selector at the bottom (currently showing Main session).
4. Select one of the older sessions in the list (for example, older ragenius:... sessions).
5. Windows Companion crashes.
6. Open the browser Dashboard at http://127.0.0.1:18789/.
7. Open the same older session there.

Actual behavior

Windows Companion crashes when the older session is selected.

Expected behavior

The session should open normally in Windows Companion, as it does in the browser Dashboard.

Additional observations

• New/current chats work in Windows Companion.
• The same older chats are readable in the browser Dashboard, which strongly suggests this is a Companion-side rendering/session-loading issue rather than corrupt Gateway/session data.
• Gateway and CLI versions match (2026.9.4), and the Gateway is healthy.
• This appeared after upgrading the OpenClaw Gateway/session environment from an older installation to 2026.9.4.

Please let me know what Windows Companion crash logs or diagnostic bundle would be most useful to attach.

Start by reproducing the crash in Windows Companion v2026.9.3 with an older session, then collect the Windows Companion crash logs or diagnostic bundle requested in the issue. Compare the failing session with the same session in the browser Dashboard; done means older sessions open without crashing while current chats continue to work.