fix(bgm): resolve include patterns relative to package dir

The default include matched every yaml across the games root, so a
package could absorb a sibling game's defs (e.g. two game#main setups).
Resolve patterns against the package declaration's directory instead;
a leading slash marks a pattern as root-relative.

packages/bgm/src/collect.test.ts

@@ -4,6 +4,7 @@ import { fileURLToPath } from 'node:url';
 import { loadDefs, collectPackages } from './collect.js';
 
 const fixtureRoot = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '__fixtures__', 'harbor');
+const multiRoot = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '__fixtures__', 'vite-build', 'games');
 
 describe('collectPackages', () => {
   it('collects the harbor package from markdown code blocks', () => {
@@ -60,6 +61,23 @@ describe('collectPackages', () => {
     });
   });
 
+  it('scopes include patterns to the package declaration directory', () => {
+    // Two packages share a games root. Each uses the default `./**/*.yaml`
+    // include, which must resolve relative to its own folder so neither
+    // absorbs the other's defs (both define a `game#main` setup).
+    const defMap = loadDefs('', multiRoot);
+    const packages = collectPackages(defMap, multiRoot);
+
+    expect(packages).toHaveLength(2);
+    const azul = packages.find((p) => p.meta.id === 'azul')!;
+    const harbor = packages.find((p) => p.meta.id === 'harbor')!;
+
+    expect([...azul.parts.keys()]).toEqual(['tile#blue']);
+    expect([...azul.setups.keys()]).toEqual(['game#main']);
+    expect([...harbor.parts.keys()]).toEqual(['token#wood']);
+    expect([...harbor.setups.keys()]).toEqual(['game#main']);
+  });
+
   it('throws on a duplicate type#id', () => {
     const defMap = loadDefs('', fixtureRoot);
     // Inject a duplicate part into the map under a new file name.