Let variables, fields, ports and list items be dragged into order (#310)

Variables of a behavior, the fields of a struct, the ports of a start
or end node and the items of a list could only be added and removed.
Changing their order meant removing and adding them again. Now each of
them is dragged by the mark in front of its row.

- sortBlocks (ui/blockDrag.ts) makes the rows of one column sortable.
  A block is every row it covers, so a struct moves with its fields and
  a list item with its nested list. The block is dimmed while it is
  carried, an accent line shows where it lands, and a scrolled panel
  follows the pointer at its edge. Less than 4 px stays a click.
- The arithmetic is pure and lives in ui/sortable.ts: blockGap,
  gapLineY, dropSlot and edgeScroll. dropIndex of the tile strip moved
  there too, so the reorder maths sits in one file.
- MoveVariableCommand, MoveStructFieldCommand and MovePortCommand
  build on the existing MoveCommand. Undo moves back.
- Lists need no command. InlineList replaces the list as a whole, as
  it does for every other edit of its items.
- The grip is the kind mark, for a list item its number. Moving only
  happens among siblings: a field stays in its struct.
- On a Struct asset the move runs through WithStructTypes. Typed
  variables, Pack/Expand ports and split outputs follow the new order.
- Values and edges hang on names, so only the order changes. Nodes
  running a behavior read their ports from the start node, the new
  order reaches them without a copy.
- Not sortable by design: the variables of a placed object, the fields
  of a typed struct (moved on the Struct asset) and the picked ports
  of Variables/Properties nodes.
- Test hook __gm.inspectorMark(label) finds the mark of a row.

Tests:
- Gate on melektaus-atx: 235 files, 3572 tests, CHECK EXIT 0 (+9).
- tests/core/reorder.test.ts: a variable, a field two levels deep, a
  Struct asset reaching a typed variable and Pack, and start ports
  reaching the calling node with edges and result kept.
- e2e 22: ALL PASSED, 39 checks (+4, sum 1739). 22f-iii drags a
  variable past a struct of several rows, then a field inside it.
- Counter-probes: dropSlot by top edge instead of middle and a field
  move that ignores its path fail 3 unit tests. With sortBlocks
  switched off, the three order checks of 22f-iii fail.

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

tests/core/reorder.test.ts

@@ -0,0 +1,178 @@
+/**
+ * Reordering what the inspector lets be dragged (#310): variables, the fields of a struct at any
+ * depth, a Struct asset's fields with every place of its type, and the declared ports of a start node.
+ * Only the order may change – values, edges and what runs stay as they were.
+ */
+import { describe, expect, it } from 'vitest';
+import { CreateAssetCommand, SetAssetPropertyCommand } from '../../src/core/commands/assetCommands';
+import { CommandError } from '../../src/core/commands/Command';
+import { AddPortCommand, MovePortCommand } from '../../src/core/commands/portCommands';
+import { SetStructTypeCommand, WithStructTypes } from '../../src/core/commands/structTypeCommands';
+import {
+  AddStructFieldCommand,
+  AddVariableCommand,
+  MoveStructFieldCommand,
+  MoveVariableCommand,
+} from '../../src/core/commands/variableCommands';
+import {
+  BEHAVIOR_END,
+  BEHAVIOR_PARAM,
+  BEHAVIOR_START,
+  GraphInterpreter,
+  RUN_BEHAVIOR,
+  resolveDef,
+} from '../../src/core/graph';
+import type { BehaviorAsset, StructAsset } from '../../src/core/model/Asset';
+import { graphLookup } from '../../src/core/model/graphLookup';
+import type { StructDef } from '../../src/core/properties/PropertySchema';
+import { fakeContext, fire, graphEditor, makeBehavior, makeProject, type ProjectFixture } from '../helpers';
+
+const keys = (list: readonly { key: string }[] | undefined) => (list ?? []).map((item) => item.key);
+
+describe('reordering variables and struct fields', () => {
+  it('moves a variable and leaves the values alone; undo moves it back', () => {
+    const f = makeProject();
+    const behavior = makeBehavior(f, 'B', ['a', 'b', 'c']);
+    const props = structuredClone(behavior.props);
+    f.stack.execute(new MoveVariableCommand(behavior.id, 0, 2));
+    expect(keys(behavior.variables)).toEqual(['b', 'c', 'a']);
+    expect(behavior.props).toEqual(props);
+    f.stack.undo();
+    expect(keys(behavior.variables)).toEqual(['a', 'b', 'c']);
+  });
+
+  it('refuses a place the list does not have', () => {
+    const f = makeProject();
+    const behavior = makeBehavior(f, 'B', ['a', 'b']);
+    expect(() => new MoveVariableCommand(behavior.id, 0, 2).execute(f.project)).toThrow(CommandError);
+    expect(keys(behavior.variables)).toEqual(['a', 'b']);
+  });
+
+  it('moves a field inside a struct inside a struct, the rest of the declaration as it was', () => {
+    const f = makeProject();
+    const behavior = makeBehavior(f, 'B');
+    f.stack.execute(new AddVariableCommand(behavior.id, 'hero', 'struct'));
+    for (const field of ['name', 'pos'])
+      f.stack.execute(
+        new AddStructFieldCommand(
+          behavior.id,
+          'hero',
+          field === 'pos' ? { key: field, kind: 'struct', fields: [] } : { key: field, kind: 'text' },
+        ),
+      );
+    for (const field of ['x', 'y', 'z'])
+      f.stack.execute(
+        new AddStructFieldCommand(behavior.id, 'hero', { key: field, kind: 'number' }, ['pos']),
+      );
+    const hero = () => behavior.variables[0] as StructDef;
+    const pos = () => hero().fields.find((field) => field.key === 'pos') as StructDef;
+    const value = structuredClone(behavior.props.hero);
+
+    f.stack.execute(new MoveStructFieldCommand(behavior.id, 'hero', 2, 0, ['pos']));
+    expect(keys(pos().fields)).toEqual(['z', 'x', 'y']);
+    expect(keys(hero().fields)).toEqual(['name', 'pos']);
+    expect(behavior.props.hero).toEqual(value);
+
+    f.stack.execute(new MoveStructFieldCommand(behavior.id, 'hero', 1, 0));
+    expect(keys(hero().fields)).toEqual(['pos', 'name']);
+    f.stack.undo();
+    f.stack.undo();
+    expect(keys(hero().fields)).toEqual(['name', 'pos']);
+    expect(keys(pos().fields)).toEqual(['x', 'y', 'z']);
+  });
+});
+
+/** `Loot` = { Name: "Coin", Amount: 1 } */
+function lootType(f: ProjectFixture): StructAsset {
+  const create = new CreateAssetCommand('struct', 'Loot');
+  f.stack.execute(create);
+  const id = create.asset.id;
+  f.stack.execute(new AddVariableCommand(id, 'Name', 'text'));
+  f.stack.execute(new AddVariableCommand(id, 'Amount', 'number'));
+  f.stack.execute(new SetAssetPropertyCommand(id, 'Amount', 1));
+  return create.asset as StructAsset;
+}
+
+describe('reordering the fields of a Struct asset', () => {
+  it('reaches every place of the type: typed variables and the ports of Pack, edges kept', () => {
+    const f = makeProject();
+    const loot = lootType(f);
+    const chest = makeBehavior(f, 'Chest');
+    f.stack.execute(new AddVariableCommand(chest.id, 'drop', 'struct'));
+    f.stack.execute(
+      new SetStructTypeCommand({ kind: 'variable', ownerId: chest.id, key: 'drop', path: [] }, loot.id),
+    );
+    const g = graphEditor(f, chest);
+    const pack = g.addNode('PackStruct');
+    f.stack.execute(new SetStructTypeCommand({ kind: 'node', assetId: chest.id, nodeId: pack.id }, loot.id));
+    const number = g.addNode('Number');
+    g.connect(number, 'value', pack, 'Amount');
+    const drop = () => chest.variables[0] as StructDef;
+
+    f.stack.execute(new WithStructTypes(new MoveVariableCommand(loot.id, 1, 0)));
+    expect(keys(loot.variables)).toEqual(['Amount', 'Name']);
+    expect(keys(drop().fields)).toEqual(['Amount', 'Name']);
+    expect(keys(pack.ports)).toEqual(['Amount', 'Name']);
+    expect(chest.graph.edges.map((e) => `${e.from.port}>${e.to.port}`)).toEqual(['value>Amount']);
+    expect(chest.props.drop).toEqual({ Name: '', Amount: 1 });
+
+    f.stack.undo();
+    expect(keys(drop().fields)).toEqual(['Name', 'Amount']);
+    expect(keys(pack.ports)).toEqual(['Name', 'Amount']);
+  });
+});
+
+/** Hands `a - b` back: two inputs whose order matters to the arithmetic, not to the wiring. */
+function subtracter(f: ProjectFixture): BehaviorAsset {
+  const asset = makeBehavior(f, 'Subtract');
+  const edit = graphEditor(f, asset);
+  const start = edit.addNode(BEHAVIOR_START);
+  const end = edit.addNode(BEHAVIOR_END);
+  f.stack.execute(new AddPortCommand(asset.id, start.id, { key: 'a', kind: 'number' }));
+  f.stack.execute(new AddPortCommand(asset.id, start.id, { key: 'b', kind: 'number' }));
+  f.stack.execute(new AddPortCommand(asset.id, end.id, { key: 'out1', kind: 'number' }));
+  const minus = edit.addNode('Subtract');
+  edit.wire([
+    [start, 'exec', end, 'exec'],
+    [start, 'a', minus, 'a'],
+    [start, 'b', minus, 'b'],
+    [minus, 'result', end, 'out1'],
+  ]);
+  return asset;
+}
+
+describe('reordering the ports of a start node', () => {
+  it('changes the order on the calling node and nothing else: edges, values and result stay', () => {
+    const f = makeProject();
+    const callee = subtracter(f);
+    const caller = makeBehavior(f, 'Caller', ['result']);
+    const edit = graphEditor(f, caller);
+    const onStart = edit.addNode('OnStart');
+    const call = edit.addNode(RUN_BEHAVIOR, { [BEHAVIOR_PARAM]: callee.id, a: 10, b: 3 });
+    const set = edit.variables(['result'], { write: true });
+    edit.wire([
+      [onStart, 'exec', call, 'exec'],
+      [call, 'exec', set, 'exec'],
+      [call, 'out1', set, 'result'],
+    ]);
+    const start = callee.graph.nodes.find((n) => n.type === BEHAVIOR_START)!;
+    const edges = structuredClone(callee.graph.edges);
+    const inputs = () => keys(resolveDef(call, caller.graph, graphLookup(f.project))!.inputs);
+    const run = () => {
+      const ctx = fakeContext({ variables: { result: 0 } });
+      fire(new GraphInterpreter(caller.graph, graphLookup(f.project)), 'OnStart', ctx);
+      return ctx.variables.result;
+    };
+    expect(inputs()).toEqual(['exec', 'a', 'b']);
+
+    f.stack.execute(new MovePortCommand(callee.id, start.id, 1, 0));
+    expect(keys(start.ports)).toEqual(['b', 'a']);
+    expect(inputs()).toEqual(['exec', 'b', 'a']);
+    expect(callee.graph.edges).toEqual(edges);
+    expect(call.params).toMatchObject({ a: 10, b: 3 });
+    expect(run()).toBe(7);
+
+    f.stack.undo();
+    expect(inputs()).toEqual(['exec', 'a', 'b']);
+  });
+});