# TASK 69 — Chat sample-preview toggle

**Status:** ☐ Queued (creator request 2026-11-11); scheduled after TASK 68 and before the gold pass.

## Request

Expose the autogenerated sample chatter as a per-ChatBox layer-control toggle, so the creator decides
whether it appears while adjusting chat font/color and previewing the layout. Keep the existing behavior
as the default: `Source.ChatPreviewEnabled` already defaults to `true`.

## Established behavior

- `ChatOverlayLayer.StartMockPreview` autogenerates sample messages for the ChatBox preview.
- A real message stops the sample loop; after the real-message fade clears the buffer, the sample loop
  starts again—even during a live session.
- Samples are preview-only: they are not inserted into the real `Messages` buffer, and the output
  renderer reads that real buffer. Viewers do not receive sample chatter.
- `ChatPreviewEnabled` is currently read by the mock-preview starter but is not persisted.

## Acceptance

- The selected ChatBox layer control exposes **Show sample chat in preview**, on by default.
- The choice persists across restart and applies to that ChatBox layer.
- Off stops/removes generated samples. It does not hide real chat messages or change the live output.
- When on, samples return in the preview when there are no real messages to show.
- One Good Dog integration test covers the toggle and persistence; pin that sample chatter never enters
  the output message buffer.