ModeFlipGuard Module Cross-module transient state about the edit<->play mode flip: OWNED — "the layers module currently owns the mode-flip reset, so the player_spawner / camera_spawner onModeChange watchers should stand down." IN FLIGHT — "a mode-flip transition is materialising the scene right now, so the live entities are a partial rebuild of it." SESSION — "this is the play session the engine is in." The id advances every time the engine enters play, so state that belongs to one play session records the id it was armed under and compares it before it is spent. An arm its own session ended without spending names an id the engine has moved past, so it goes stale with the session that made it. Formerly `_G.__zero_layers_owns_mode_flip`. Moved off `_G` ahead of the read-only `_G` seal: the flags are RUNTIME writes (set when layers drives a mode flip), which would break under a sealed `_G`. `require()` caches modules per VM, so the upvalues are shared state across every requirer within a VM — exactly the cross-module reach the old `_G` key provided. Setters: layers.module (claims ownership before any flip; raises the in-flight signal for the span of the transition); engine.module (opens a play session from the mode-change watcher every route that changes the mode fires). Readers: player_spawner.module, camera_spawner.module (stand down while owned so the player/camera respawn happens exactly once via the layers transition's reload fan-out); playerSetupValidation.module (judges the authored scene once the transition has settled); engine.module (scopes the leave-play safeguard's deliberate discard to the play session that armed it).