Let a Start input or a variable name the state machine it carries

A sub-behavior that gets its machine through a Start input had no
state ports on Is in state, Set state and the other state nodes.
Their ports came only from an inline pick or a State machine literal,
so a machine handed in from outside left them empty.

- A statemachine port of a Start node can now name a machine
  (DeclaredPort.machine). The inspector shows the pick next to the
  port name. SetPortMachineCommand sets it with undo.
- machineIdOf follows an edge from such a port to that machine, so
  the state nodes it feeds offer its states.
- A Run behavior node has the machine picked in advance on that input.
- A different pick there is allowed, but the node warns, because the
  called graph asks for the states of its own machine.
- A statemachine variable of a Variables node can name a machine
  the same way, picked next to the variable's row.
- The inspector signature of a node now includes the picked machine.
  Before, the pick changed the ports but the dropdown kept its text
  until the node was selected again.
- A local machine handed in still starts in no state every call.
  That rule from #229 is unchanged.

Tests:
- tests/core/start-machine.test.ts (7): ports with and without a
  machine and undo, save and load, the preset value moving a shared
  machine through the call, the warning, a port of another kind,
  the inspector signature, a Variables node.
- Counter checks: without the new branch in machineIdOf 2 tests
  fail, without the machine in the signature 1 test fails.
- Gate on melektaus-atx: 239 files, 3599 tests, CHECK EXIT 0.

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

src/core/graph/nested.ts

@@ -156,8 +156,9 @@ export function isFlowPort(port: DeclaredPort): boolean {
  */
 export function portDefOf(port: DeclaredPort): PortDef {
   const def: PortDef = { key: port.key, label: port.key, type: declaredPortType(port.kind) };
+  // The machine a start node's input carries is what the field offers before anyone picks.
   return isTaggedKind(port.kind) && port.kind !== 'object'
-    ? { ...def, field: flatDef(port.key, port.kind) }
+    ? { ...def, field: flatDef(port.key, port.kind, { value: port.machine }) }
     : def;
 }
 
@@ -360,6 +361,20 @@ export function callProblem(node: GraphNode, lookup: GraphLookup, ownerId = ''):
   const program = lookup.behavior(id);
   if (!program) return 'That behavior is gone';
   if (callEntries(program.graph).length === 0) return 'No start or On start node – does nothing';
+  return otherMachineProblem(node, program.graph, lookup);
+}
+
+/**
+ * A machine picked here other than the one the start node's input carries: the called graph asks for
+ * the states of its own, so every one of them would read as never entered.
+ */
+function otherMachineProblem(node: GraphNode, graph: Graph, lookup: GraphLookup): string | null {
+  for (const port of terminalNode(graph, BEHAVIOR_START)?.ports ?? []) {
+    const picked = textOf(node.params[port.key] ?? '');
+    if (port.kind !== 'statemachine' || !port.machine || !picked || picked === port.machine) continue;
+    const machine = lookup.machine(port.machine);
+    return `"${port.key}" expects ${machine ? `"${machine.name}"` : 'a machine that is gone'}`;
+  }
   return null;
 }