Let a behavior be a node in another graph

A behavior that has a Start and an End node can now be dropped into any
other graph as a node of its own. What is declared on the start node
becomes the inputs of that node, what hangs on the end node its outputs;
the port list is derived from the sub graph, not copied, so declaring a
port in one graph grows the node in the other without touching it. The
node carries the behavior's name and the palette lists behaviors by
name, so a call is one grab instead of a node plus a dropdown.

An embedded behavior has no object and therefore no place for
variables: every call starts on the asset defaults and communicates
only through its ports. That is the conservative direction - state can
still be added later, and shared state already has a home in a behavior
object in the scene. Node ids are unique per graph only, so each call
gets its own pulse cache; without that, two graphs would collide.

Renaming a port used to silently drop the value typed on the calling
node. It is carried along now, project wide, like the edges.

tests/core/graph.test.ts

@@ -18,6 +18,7 @@ import {
   dropTargetPort,
   findNode,
   firstPortFor,
+  NO_BEHAVIORS,
   type PortType,
   portsCompatible,
   requireNodeDef,
@@ -512,7 +513,7 @@ describe('dropping an edge on a node', () => {
   it('picks the first compatible input', () => {
     const { graph, number, clamp } = fixtureWithClamp();
     const from = { nodeId: number.id, port: 'value', isOutput: true };
-    expect(dropTargetPort(graph, from, clamp.id)).toEqual({
+    expect(dropTargetPort(graph, from, clamp.id, NO_BEHAVIORS)).toEqual({
       nodeId: clamp.id,
       port: 'value',
       isOutput: false,
@@ -524,7 +525,7 @@ describe('dropping an edge on a node', () => {
     const other = edit.addNode('Number');
     edit.connect(other, 'value', clamp, 'value');
     const from = { nodeId: number.id, port: 'value', isOutput: true };
-    expect(dropTargetPort(graph, from, clamp.id)?.port).toBe('min');
+    expect(dropTargetPort(graph, from, clamp.id, NO_BEHAVIORS)?.port).toBe('min');
   });
 
   it('falls back to the last compatible input once every one is taken', () => {
@@ -532,7 +533,7 @@ describe('dropping an edge on a node', () => {
     for (const port of ['value', 'min', 'max']) edit.connect(edit.addNode('Number'), 'value', clamp, port);
     const from = { nodeId: number.id, port: 'value', isOutput: true };
     // Not free, but the drop still connects – it replaces the edge, as dropping on the port would.
-    expect(dropTargetPort(graph, from, clamp.id)?.port).toBe('max');
+    expect(dropTargetPort(graph, from, clamp.id, NO_BEHAVIORS)?.port).toBe('max');
   });
 
   it('keeps offering an exec input, which is never exclusive', () => {
@@ -543,26 +544,26 @@ describe('dropping an edge on a node', () => {
     const move = edit.addNode('SetPosition');
     edit.connect(edit.addNode('OnKeyHeld'), 'exec', move, 'exec');
     const from = { nodeId: held.id, port: 'exec', isOutput: true };
-    expect(dropTargetPort(behavior.graph, from, move.id)?.port).toBe('exec');
+    expect(dropTargetPort(behavior.graph, from, move.id, NO_BEHAVIORS)?.port).toBe('exec');
   });
 
   it('refuses a node that offers nothing compatible, and the node itself', () => {
     const { graph, edit, number, clamp } = fixtureWithClamp();
     const boolean = edit.addNode('Boolean');
     const from = { nodeId: number.id, port: 'value', isOutput: true };
-    expect(dropTargetPort(graph, from, boolean.id)).toBeNull();
-    expect(dropTargetPort(graph, from, number.id)).toBeNull();
+    expect(dropTargetPort(graph, from, boolean.id, NO_BEHAVIORS)).toBeNull();
+    expect(dropTargetPort(graph, from, number.id, NO_BEHAVIORS)).toBeNull();
     // A pair that is already wired is not offered again either.
     edit.connect(number, 'value', clamp, 'value');
     edit.connect(number, 'value', clamp, 'min');
     edit.connect(number, 'value', clamp, 'max');
-    expect(dropTargetPort(graph, from, clamp.id)).toBeNull();
+    expect(dropTargetPort(graph, from, clamp.id, NO_BEHAVIORS)).toBeNull();
   });
 
   it('resolves a drag started at an input to an output', () => {
     const { graph, number, clamp } = fixtureWithClamp();
     const from = { nodeId: clamp.id, port: 'value', isOutput: false };
-    expect(dropTargetPort(graph, from, number.id)).toEqual({
+    expect(dropTargetPort(graph, from, number.id, NO_BEHAVIORS)).toEqual({
       nodeId: number.id,
       port: 'value',
       isOutput: true,