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/editor/inspector/nodeSection.ts

@@ -25,7 +25,7 @@ import {
 } from '../../core/graph';
 import type { GraphAsset } from '../../core/model/Asset';
 import { graphLookup } from '../../core/model/graphLookup';
-import { findGraphAsset, type Project } from '../../core/model/Project';
+import { findAssetOf, findGraphAsset, type Project } from '../../core/model/Project';
 import { type PropertyValue, textOf } from '../../core/model/Properties';
 import {
   isListNode,
@@ -62,7 +62,14 @@ export function nodeSignature(project: Project, assetId: string, nodeId: string)
         .filter((p) => edgesInto(asset.graph, node.id, p.key).length > 0)
         .map((p) => p.key)
     : [];
-  const declared = (node.ports ?? []).map((p) => `${p.key}:${p.kind}${p.write ? ':set' : ''}`).join(',');
+  // The machine a port carries is drawn as the picker's text, its name included.
+  const machineOf = (id: string) => findAssetOf(project, id, 'statemachine')?.name ?? '';
+  const declared = (node.ports ?? [])
+    .map(
+      (p) =>
+        `${p.key}:${p.kind}${p.write ? ':set' : ''}${p.machine ? `:${p.machine}:${machineOf(p.machine)}` : ''}`,
+    )
+    .join(',');
   // They decide which rows the inspector builds, and two behaviors may share a name in the title.
   const target = `${textOf(node.params[OBJECT_TYPE_PARAM] ?? '')}:${textOf(node.params[OBJECT_BEHAVIOR_PARAM] ?? '')}`;
   // The transition rows and the picked name are drawn, not filled in by `refreshNodeSection`, so

src/editor/inspector/portSection.ts

@@ -6,6 +6,7 @@ import {
   RemovePortCommand,
   RenamePortCommand,
   RepointPortCommand,
+  SetPortMachineCommand,
   SetPortWriteCommand,
 } from '../../core/commands/portCommands';
 import {
@@ -32,6 +33,7 @@ import {
 import { isPrivateVariable } from '../../core/model/Asset';
 import { findAssetOf, findGraphAsset, type Project } from '../../core/model/Project';
 import { textOf } from '../../core/model/Properties';
+import { assetRefChoices, NO_ASSET_LABEL } from '../../core/properties/assetRef';
 import { DECLARED_PORT_KINDS, VARIABLE_KINDS } from '../../core/properties/kinds';
 import { allShaderParamRows, type PropertyDef, schemaForAsset } from '../../core/properties/PropertySchema';
 import {
@@ -187,7 +189,12 @@ function buildPickedPortSection(
   else if (ports.length === 0) addNote(host, `No ${plural} picked yet. Each one adds a port.`);
 
   for (const port of ports) {
-    const toggle = writeToggle(host, assetId, node, port);
+    // A machine a variable holds is a running value; which one its states come from is picked here.
+    const carries = noun === 'Variable' && port.kind === 'statemachine';
+    const toggle = [
+      ...(carries ? [machinePick(host, assetId, node, port)] : []),
+      ...writeToggle(host, assetId, node, port),
+    ];
     if (custom) {
       portRow(host, assetId, node, port, portNameField(host, assetId, node, port), toggle);
       continue;
@@ -266,7 +273,14 @@ export function buildPortSection(
     );
 
   const blocks = ports.map((port) =>
-    portRow(host, assetId, node, port, portNameField(host, assetId, node, port)),
+    portRow(
+      host,
+      assetId,
+      node,
+      port,
+      portNameField(host, assetId, node, port),
+      onStart && port.kind === 'statemachine' ? [machinePick(host, assetId, node, port)] : [],
+    ),
   );
   sortBlocks(blocks, (from, to) => host.state.execute(new MovePortCommand(assetId, node.id, from, to)));
 }
@@ -280,6 +294,32 @@ function portNameField(host: InspectorHost, assetId: string, node: GraphNode, po
   });
 }
 
+/**
+ * Which machine a start node's input or a Variables node's variable carries: what the state nodes
+ * behind it offer, and for a start node what a node running the behavior has picked before anyone
+ * picks there.
+ */
+function machinePick(host: InspectorHost, assetId: string, node: GraphNode, port: DeclaredPort): Dropdown {
+  const project = host.state.project;
+  const machine = port.machine ? findAssetOf(project, port.machine, 'statemachine') : undefined;
+  const gone = port.machine !== undefined && machine === undefined;
+  const pick = new Dropdown(machine?.name ?? (gone ? 'Gone' : NO_ASSET_LABEL), {
+    variant: gone ? 'danger' : 'default',
+  });
+  const set = (id: string) => host.state.execute(new SetPortMachineCommand(assetId, node.id, port.key, id));
+  pick.onClick = () => {
+    const items: MenuItem[] = [
+      { label: NO_ASSET_LABEL, onSelect: () => set('') },
+      ...assetRefChoices(project, ['statemachine']).map((a) => ({
+        label: a.name,
+        onSelect: () => set(a.id),
+      })),
+    ];
+    new Menu(items).openBelow(pick);
+  };
+  return pick;
+}
+
 function writeToggle(host: InspectorHost, assetId: string, node: GraphNode, port: DeclaredPort): Widget[] {
   const box = new Checkbox(port.write === true);
   box.onChange = (on) => host.state.execute(new SetPortWriteCommand(assetId, node.id, port.key, on));