[snkmcb]

Summary

ReplayPlayer::apply backed up and restored the viewport, scale, animation clock, host slots, requested scroll offsets and input clock one field at a time. Adding a step input required editing both lists.

Group those inputs in a private StepState and restore it in one assignment on rejection before commit. Tree replacement still restores its own snapshot. This preserves the public API, recording formats, and the existing commit and close behavior.

Add a regression test that rejects a reload after scrolling, then settles another generation to verify that layout still uses the previous requested offset and that accepted steps reproduce the session.

Verification

• Windows x64 Debug build of Replay, Replay host, Replay serialization, offscreen runner and the Hierarchy / Inspector example.
• CTest replay, replay_host, replay_serialization, offscreen_runner and inspector_hierarchy passed.
• Changed-file C++ format, documentation, release metadata, and CI selection checks passed.