Desktop: "Toggle pinned summary" header control missing in some sessions

On the macOS desktop app (macOS 26.5), the header control with tooltip "Toggle pinned summary" (next to the "Open in" menu and the right-panel toggle) appears in some sessions but not in others.

Expected: every session shows both "Open in" and the pinned-summary toggle.

Observed: sessions in the same workspace differ — some have the toggle, some do not, with no obvious correlation to session type (new vs resumed, local vs worktree).

Versions: at least 2.1.218 is in the mix; long-lived sessions may be running an older runtime than freshly opened ones via auto-update, but the inconsistency has not been confirmed to track version.

If this control is deliberately gated (by version, by whether a session summary exists yet, or by rollout flag), it would help to have that documented — and ideally surfaced consistently across sessions of one app instance.