[Bug]: [Critical]: T3Code forgets complete session history

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/desktop

Steps to reproduce

I had a few sessions that we're a bit more long running research threads. They are on Worktrees usually with a fresh branch.

If I come back to the session after a few days Opus has completely forgotten about the session history and treats it as a fresh session, which means I need to copy my whole session history in a user message to be able to continue (and copying the session history in T3Code is nearly impossible if there is plan UI elements and diff UI elements in the thread).

This has happened for multiple sessions.

See screenshot.

Expected behavior

We should just be able to continue on the thread with the session history that is there.

Actual behavior

The session is treated as completely fresh

Impact

Major degradation or frequent failure

Version or commit

0.0.21 (188df6da074b)

Environment

macOS Tahoe 26.4

Logs or stack traces

Screenshots, recordings, or supporting files

Workaround

Copy the whole session history and add as user message (very annoying and hacky)

Start in apps/desktop and reproduce the report by returning to a long-running Worktree session after several days. Trace how the session history is loaded and passed to the resumed session; done means an existing thread retains its history instead of being treated as fresh, including threads containing plan and diff UI elements.