[M4n5ter]

Summary

Scrolling back through a long conversation used to read the tool and activity records inside collapsed turns before reaching earlier messages. The desktop chat now pages visible history for completed native-model turns. Each collapsed turn shows activity counts and recent image previews. Opening it loads the activity on demand. Steering messages and context checkpoints stay in chronological order.

Verification

• Replayed a long conversation from a local copy of its history. The previous context checkpoint was in the first page of the new chat view, compared with 109 pages in the full transcript view.
• Passed the relevant macOS desktop, tool-history, and paging tests, plus contract and formatting checks.

The screenshots below come from the same conversation reopened in the macOS desktop test renderer against a fixture Host. The first frame shows the collapsed turn and its final reply. The second shows the original activity after expanding the turn.

AI use

• Generative tooling made a substantive contribution

Tool and scope: OpenAI Codex implemented and tested the change.

Checklist

• Tests cover the change and fail without it
• Format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes