Real bug, caught by hand (not by any automated test): clicking Stop in
the Lingua Editor panel threw InvalidOperationException — "A system
structurally changed 'QuadRenderer' without declaring Writes<QuadRenderer>()".
Root cause: GameWorld.Restore rebuilds the world via GameObject.
AddComponent, which SystemAccessScope checks. That's fine when Restore is
called from unconstrained code — every existing WorldSnapshotTests test
calls it directly, outside any system, which is exactly why none of them
caught this. But PlayModeController.ExitPlay is called from inside
EditorPlugin's own Stage.Render system (the button click handler runs as
part of DrawUi), which correctly declares no Reads/Writes at all — it has
no compile-time knowledge of QuadRenderer or any other game's component
types. So the ambient SystemAccessScope was still active when Restore
tried to rebuild them.
SystemAccessScope's own doc comment already said "editor code... [is]
unconstrained by design" — true only when the call happened to originate
outside a system's scope, not actually true in general. Fixed with
SystemAccessScope.Suspend(), which GameWorld.Restore now wraps its entire
rebuild in: Restore is a bulk, whole-world reset regardless of who calls
it, the same category of operation Destroy already is (which never went
through the checked RemoveComponent path to begin with).
New regression test reproduces the exact shape: a system with no declared
access calling Restore, run through the real Schedule — not calling
SystemAccessScope directly, and not calling Restore outside a system
either, which is why this slipped through the first time. Passed
immediately after the fix; would have failed loudly before it.
Full suite: 87 tests.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N1qPfzq8TDCUMFMV3UwV5N
