control-play-mode: Play always saves dirty Scenes before entering Play Mode, rewriting Scene files Unity would keep in memory

[hatayama]

Summary

uloop control-play-mode --action Play quietly saves every dirty loaded Scene (and the current Prefab Stage) before entering Play Mode from Edit Mode (ControlPlayModeUseCase.SaveDirtyEditorChangesBeforePlayStart, added in #1756). There is no way to opt out, unlike run-tests --unsaved-changes save|fail|discard, and the response does not say that anything was saved (it only reports Play mode started).

Problem

Unity itself does not block entering Play Mode when Scenes have unsaved changes; it keeps them in memory and restores them after Play Mode ends. The CLI saves them anyway, so the Scene file on disk is rewritten on every CLI Play.

This becomes a problem for Scenes that turn dirty just by being opened (for example, layout groups / CanvasScaler recomputing RectTransform values, or objects that recreate themselves in Edit Mode):

• Every CLI Play rewrites the Scene file and produces a VCS diff in a Scene the user never edited.
• If the Scene already has the user's own uncommitted changes, they get mixed with this noise and the user can no longer tell which changes are theirs.
• An agent that enters Play repeatedly for verification rewrites the file each time without noticing, because the response is silent about the save.

Repro

1. Open a Scene that becomes dirty on load (or make any change and leave it unsaved).
2. Run uloop control-play-mode --action Play.
3. The Scene file on disk is rewritten and git status shows it as modified.

Proposal

• Add --unsaved-changes to control-play-mode Play, for example:
  • keep: enter Play Mode without saving (Unity's native behavior)
  • save: current behavior
  • fail: stop with the list of unsaved Scenes / Prefab Stage
• List the saved Scenes / Prefab Stage in the response whenever a save happens, so callers notice the rewrite.
• Default value is open for discussion. keep matches Unity's native behavior; save stays available for environments where a save dialog would stall the Play start (the motivation of fix: pause-point disconnect no longer leaves Play Mode stuck; quiet-save before CLI Play #1756).

Environment

• Unity 6000.3.15f1
• Unity CLI Loop 3.7.1
• macOS

[hatayama]

Fixed by #3048: Play now defaults to --unsaved-changes keep, with save and fail available.