896c4bb17b
- Bounded expanded partial edit diff rendering in `formatStreamingDiff` to `previewWindowRows()` instead of an unbounded budget, preventing runaway preview growth during live updates. - Updated streaming diff tests to simulate terminal height and verify expanded previews stay full only within the viewport, then switch to a truncated tail with the `more lines above` marker when too tall. - Reinitialized in-memory `Settings` before each initial-messages test since the test suite reads global display configuration and needs isolation.