feat(bgm): model setup as ordered placements

Replace the path->parts setup map with an ordered list of placements, each moving its parts to a path. Entries apply in order, so a part listed in a later placement ends up on that placement's path.

packages/bgm/src/__fixtures__/harbor/harbor.md

@@ -103,6 +103,8 @@ surfaces:
   - board#harbor
   - board#player
 setup:
-  /dock/0: harbor:token#wood
-  /deck: harbor:token#grain
+  - path: /dock/0
+    parts: harbor:token#wood
+  - path: /deck
+    parts: harbor:token#grain
 ```

packages/bgm/src/__fixtures__/vite-build/games/azul/azul.md

@@ -48,5 +48,6 @@ role: setup
 type: game
 id: main
 setup:
-  /factory/0: azul:tile#blue
+  - path: /factory/0
+    parts: azul:tile#blue
 ```

packages/bgm/src/__fixtures__/vite-build/games/harbor/harbor.md

@@ -53,6 +53,8 @@ role: setup
 type: game
 id: main
 setup:
-  /dock/0: harbor:token#wood
-  /deck: harbor:token#grain
+  - path: /dock/0
+    parts: harbor:token#wood
+  - path: /deck
+    parts: harbor:token#grain
 ```

packages/bgm/src/collect.test.ts

@@ -55,10 +55,10 @@ describe('collectPackages', () => {
     expect([...harbor.setups.keys()]).toEqual(['game#main']);
     const setup = harbor.setups.get('game#main')!;
     expect(setup.surfaces).toEqual(['board#harbor', 'board#player']);
-    expect(setup.setup).toEqual({
-      '/dock/0': 'harbor:token#wood',
-      '/deck': 'harbor:token#grain',
-    });
+    expect(setup.setup).toEqual([
+      { path: '/dock/0', parts: 'harbor:token#wood' },
+      { path: '/deck', parts: 'harbor:token#grain' },
+    ]);
   });
 
   it('scopes include patterns to the package declaration directory', () => {

packages/bgm/src/schemas.ts

@@ -60,11 +60,18 @@ const surfaceSchema = z.object({
   layout: z.array(route),
 });
 
+const setupValue = z.union([z.string(), z.array(z.string())]);
+
+const setupPlacement = z.object({
+  path: z.string(),
+  parts: setupValue,
+});
+
 const setupSchema = z.object({
   type: z.string().min(1),
   id: z.string().min(1),
   surfaces: z.array(z.string()).optional(),
-  setup: z.record(z.string(), z.union([z.string(), z.array(z.string())])),
+  setup: z.array(setupPlacement),
 });
 
 const packageSchema = z.object({

packages/bgm/src/types.ts

@@ -157,13 +157,25 @@ export interface Surface {
 
 export type SetupValue = string | string[];
 
-/** Seeds the state store: the enabled surfaces and a map from path to parts. */
+/**
+ * One setup placement: move `parts` to `path`. Entries are applied in order,
+ * so a part listed in a later entry ends up on that entry's path.
+ */
+export interface SetupPlacement {
+  /** The path key to place the parts on. */
+  path: string;
+  /** Parts to place: a part id, a bare type (expands to all of that type), or a list of either. */
+  parts: SetupValue;
+}
+
+/** Seeds the state store: the enabled surfaces and an ordered list of placements. */
 export interface Setup {
   type: string;
   id: string;
   /** Surfaces (`type#id` refs) enabled at the start; omitted = all enabled. */
   surfaces?: string[];
-  setup: Record<string, SetupValue>;
+  /** Ordered placements; each moves its parts to its path. */
+  setup: SetupPlacement[];
 }
 
 export type Role = 'package' | 'part' | 'surface' | 'setup';