Make a call node say why it does nothing, and easier to place

A behavior node that cannot run looked exactly like a healthy one: no
start node, no behavior picked, a deleted behavior or a self-call were
all silently skipped. The call still had to be forgiving at runtime -- a
dangling reference must not abort a game -- so the fix is diagnosis, not
an exception: describeProblem() names the one reason, the node draws it
in red under its title, and the inspector repeats it where you pick the
behavior. A missing end node is deliberately not a problem: a call is
always synchronous, and the end node only decides which values come back.

Two ways in: a behavior dragged from the asset panel lands in the graph
under the pointer, and double-clicking a call node opens the graph it
runs. Both reuse machinery that already existed -- the asset panel
already starts the drag, and list views already report double clicks.

The e2e module needed its assets at the head of the asset list: after 18
modules the list is long enough that a newly appended row scrolls out of
view, and the press then lands on the panel behind it, starting no drag
at all. That looked exactly like a rejected drop and cost two full runs.

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

src/editor/inspector/nodeSection.ts

@@ -1,5 +1,6 @@
 import { RemoveNodeCommand, SetNodeParamCommand } from '../../core/commands/graphCommands';
 import {
+  callProblem,
   edgesInto,
   type GraphNode,
   inlineInputDef,
@@ -32,7 +33,7 @@ export function nodeSignature(project: Project, assetId: string, nodeId: string)
         .map((p) => p.key)
     : [];
   const declared = (node.ports ?? []).map((p) => `${p.key}:${p.kind}`).join(',');
-  return `${portSignature(node, lookup)}|${declared}|${connected.join(',')}|${asset.variables
+  return `${portSignature(node, lookup, assetId)}|${declared}|${connected.join(',')}|${asset.variables
     .map((v) => v.key)
     .join(',')}`;
 }
@@ -48,6 +49,8 @@ export function buildNodeSection(host: InspectorHost, assetId: string, nodeId: s
   addTitle(host, `${def.category.toUpperCase()} NODE`);
   host.body.add(new Label(def.label, { style: 'bodyBold' }));
   addNote(host, def.description);
+  const problem = callProblem(node, behaviorLookup(host.state.project), assetId);
+  if (problem) addNote(host, problem, 'warning');
   if (isTerminalNode(node)) buildPortSection(host, assetId, node);
 
   if (def.params.length > 0) addTitle(host, 'SETTINGS');