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>

src/core/store/serialize.ts

@@ -141,6 +141,8 @@ export function deserializeProject(raw: unknown, fallbackId = ''): Project {
         graph: normalizeGraph(a.graph, (def) => def.type === STATE),
       };
       if (readScope(a.scope) === 'global') machine.scope = 'global';
+      // Kept as written even where it names no state any more: the same as a deleted start.
+      if (typeof a.start === 'string' && a.start !== '') machine.start = a.start;
       assets.push(machine);
     } else if (type === 'shader') {
       assets.push({ id, type, name, props, graph: shaderGraphs.get(id) ?? createEmptyGraph() });