Variables and state machines can reset with every scene (#164)

A shared variable or machine used to live either per object or for the
whole run. Levels need a third lifetime: shared like global, but built
fresh from the declarations whenever a scene is loaded.

- New scope `scene` for Variables assets and state machines. A missing
  field keeps the old meaning: `global` for assets, `local` for
  machines, so existing projects do not change.
- Returning to a scene that was visited before is fresh as well. There
  is no memory per scene.
- A `scene` machine announces its start state again after a scene swap,
  so `On state entered` in the new scene hears it. A global machine
  stays quiet because it never left its state.
- The rule lives in two pure functions in `sharedState.ts`
  (`carriedForward`, `restartedAssets`). BehaviorSystem only calls them.
- The inspector shows a Scope dropdown on Variables assets and a third
  step on the machine dropdown, with a note on what `scene` means.

Decisions:
- `scene` and `persistent` exclude each other (variant A). The choice
  dialog was cancelled, so this is an assumption to revisit. A
  scene-scoped asset hides the Persistent switch, and switching to
  `scene` drops the flag (undo restores it). The guard sits in
  `isPersistent` itself, so no path can save values the scope throws
  away anyway.

Findings:
- `clickText('Scene')` hits the Scene tab, not the menu entry. One e2e
  check was red because of that, and its partner was falsely green
  because it compared `undefined` with `undefined`. Both use `clickLast`
  now.

Tests:
- ./check.sh: 144 files, 2142 tests, CHECK EXIT 0 (before 143 / 2133)
- 9 new unit tests in tests/core/scene-scope.test.ts
- e2e 32 fresh: ALL PASSED, 17 checks
- e2e 1-3,17,18,26,32,35 fresh: ALL PASSED, 213 checks
- 3 new e2e checks (35: scene-scoped asset resets on swap, 32h: dropdown,
  note, hidden Persistent switch)
- Counter-checks bite: ignoring `restarted` fails 2 unit tests and the
  new check in 35, the old announcement rule fails 1, dropping the scope
  guard in `isPersistent` fails 1. Originals restored, cmp IDENTICAL.
- Check sum 1307 (1304 + 3) is computed. Last CI measurement: 1293.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/core/model/Scope.ts

@@ -1,29 +1,60 @@
 /**
- * Whether a state machine keeps its current state per behavior instance or shares one for the whole
- * run. Everything was `local` before scopes existed, so a missing field means `local` and old
- * projects load unchanged. Variables are shared by living on a Variables asset instead (#91).
+ * How long a shared value lives. `local` is one per behavior instance, `global` one for the whole
+ * run, `scene` one per scene: rebuilt from the declarations whenever a scene is loaded, so what a
+ * level counts is gone with the level while a score is not (#164).
+ *
+ * Everything was `local` before scopes existed, so a missing field means `local` and old projects
+ * load unchanged. Variables are shared by living on a Variables asset instead (#91) – that asset is
+ * shared by its nature, so a missing field means `global` there (see `sharedScopeOf`).
  */
-export type Scope = 'local' | 'global';
+export type Scope = 'local' | 'global' | 'scene';
+
+/** The scopes of something that is shared either way: a Variables asset has no `local`. */
+export type SharedScope = 'global' | 'scene';
 
 export interface Scoped {
   scope?: Scope;
 }
 
 export function scopeOf(owner: Scoped): Scope {
-  return owner.scope === 'global' ? 'global' : 'local';
+  if (owner.scope === 'global') return 'global';
+  return owner.scope === 'scene' ? 'scene' : 'local';
 }
 
-export function isGlobal(owner: Scoped): boolean {
-  return owner.scope === 'global';
+/** Whether the value is shared at all: both `global` and `scene` are one value for many instances. */
+export function isShared(owner: Scoped): boolean {
+  return owner.scope === 'global' || owner.scope === 'scene';
 }
 
-/** Reads a scope out of loaded data, where anything but the one known word means `local`. */
+/** Whether a scene swap rebuilds the value instead of handing it over. */
+export function isPerScene(owner: Scoped): boolean {
+  return owner.scope === 'scene';
+}
+
+/** Reads a scope out of loaded data, where anything but the two known words means `local`. */
 export function readScope(raw: unknown): Scope {
-  return raw === 'global' ? 'global' : 'local';
+  if (raw === 'global') return 'global';
+  return raw === 'scene' ? 'scene' : 'local';
 }
 
-/** Keeps `local` out of the document: the field is present only when it says `global`. */
+/** Keeps `local` out of the document: the field is present only when it says more than that. */
 export function setScope(owner: Scoped, scope: Scope): void {
-  if (scope === 'global') owner.scope = 'global';
+  if (scope === 'local') delete owner.scope;
+  else owner.scope = scope;
+}
+
+/** The scope of something shared by nature, where a missing field is `global` rather than `local`. */
+export function sharedScopeOf(owner: Scoped): SharedScope {
+  return owner.scope === 'scene' ? 'scene' : 'global';
+}
+
+/** Reads the scope of something shared by nature out of loaded data. */
+export function readSharedScope(raw: unknown): SharedScope {
+  return raw === 'scene' ? 'scene' : 'global';
+}
+
+/** Keeps the default out of the document the other way round: only `scene` is written. */
+export function setSharedScope(owner: Scoped, scope: SharedScope): void {
+  if (scope === 'scene') owner.scope = 'scene';
   else delete owner.scope;
 }