A state change is something the graph can react to, so the machine announces it (#53, #54, #55, #57)

Four issues that all reach for the same line: how the current state is
read and written. Splitting them into four commits would mean four
states of the tree that do not compile, so they arrive together.

#55 start state — the machine asset carries an optional `start` holding
a State node's id. Right-click a state to set or remove it, a ring in
the node's title says which one it is. A dead id (the state was deleted)
reads as "no start", so nothing has to clean up after a deletion.

#53 entered/exited — `On state entered` and `On state exited`, one exec
output per state. Every change now goes through a single `setState`
that reports it; BehaviorSystem delivers it after the exec flow that
caused it, `exited` of the old before `entered` of the new, round after
round until the queue is empty, with a cap that stops a ping-pong graph
with an endless-loop error. A local machine tells the instance that
switched, a global one tells every instance holding a matching event
node. The start state fires `entered` too: per instance for a local
machine, once per run for a global one.

#57 reading — `Current state` with `name` for showing and `id` for
comparing, `Is in state` with one boolean per state. Neither has a
`run`, so `read` learned `def` and `lookup`, and the catalog test knows
this third kind of node.

#54 seeing it — during a run the state machine tab marks every state
some instance is holding faintly, and the one held by the selected
scene object's instance strongly.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/helpers.ts

@@ -188,7 +188,12 @@ export function fakeHandle(props: PropertyBag, parent: EntityHandle | null = nul
   return { [ENTITY_HANDLE]: true, id: 'h', assetId: 'a', name: 'h', x: 0, y: 0, z: 0, props, parent };
 }
 
-export type FakeContext = NodeContext & { logs: string[]; stopped: boolean };
+/** `changes` records the state moves the context was told about, in the order they were reported. */
+export type FakeContext = NodeContext & {
+  logs: string[];
+  stopped: boolean;
+  changes: { machineId: string; from: string; to: string }[];
+};
 
 /** A NodeContext double: self/owner handles, `speed = 100`, dt 0.5, moves applied directly, `log` and `stop` recorded. */
 export function fakeContext(overrides: Partial<NodeContext> = {}): FakeContext {
@@ -199,6 +204,8 @@ export function fakeContext(overrides: Partial<NodeContext> = {}): FakeContext {
     variables: { speed: 100 },
     states: {},
     shared: emptySharedState(),
+    changes: [],
+    stateChanged: (machineId, from, to) => ctx.changes.push({ machineId, from, to }),
     time: 0,
     dt: 0.5,
     logs,