[Bug]: Settled local thread unsettles and loses merged PR# when switching back to main for pull / new branch

[sebbonit]

Before submitting

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

Area

apps/web

Steps to reproduce

1. Work in a local checkout on a feature branch.
2. Follow the usual workflow on that thread: commit → push → open PR → merge to main.
3. After the PR is merged, switch the local checkout back to main, pull, and open a new branch (or start a new thread that does this).
4. Look at the older thread that owned the merged PR.

Expected behavior

• The older thread stays settled.
• The merged PR number / PR link remains visible in the UI for that thread.

Actual behavior

• The older thread unsettles on its own.
• The merged PR # disappears from the UI for that thread.
• Happens every time with this workflow.

Impact

Minor bug or occasional failure

Version or commit

latest nightly

Environment

macOS desktop app, local checkout workflow

Logs or stack traces

Workaround

None known

Notes

This happens specifically with the local checkout path (branch → commit → push → PR → switch back to main to pull → new branch). Closest related open issues do not cover this settle + PR metadata regression (#4706, #4725, #4561, #4356).