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.

docs/bgm-format.md

@@ -104,6 +104,13 @@ package. **Defaults to `./**/*.yaml`**, so all yaml in the same and sub
 folders is discovered with no configuration. This also matches the package
 declaration itself, which is fine — it's the package, not a part.
 
+Patterns are resolved **relative to the package declaration's own directory**,
+not the games root. So a package declared in `carcassonne/carcassonne.md`
+with the default `./**/*.yaml` only picks up yaml under `carcassonne/` — it
+never absorbs defs from a sibling game. To reach outside its folder, a
+package can use a `../`-relative pattern or an absolute-from-root pattern
+(e.g. `**/shared/*.yaml`).
+
 ---
 
 ## 3. Roles

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.

packages/bgm/src/collect.ts

@@ -101,7 +101,8 @@ export function collectPackages(defMap: DefMap, rootDir: string): Package[] {
       const role = def.value['role'] as Role;
       if (role === 'package') {
         const pkg = asPackage(def, file);
-        accs.push(new PackageAcc(pkg, defMap, rootDir));
+        const baseDir = path.posix.dirname(file).replace(/^\/+/, '');
+        accs.push(new PackageAcc(pkg, defMap, rootDir, baseDir));
       }
     }
   }
@@ -125,6 +126,8 @@ class PackageAcc {
     readonly pkg: PackageDef,
     private readonly defs: DefMap,
     private readonly rootDir: string,
+    /** Path-style directory of the package declaration, e.g. `carcassonne`. */
+    private readonly baseDir: string,
   ) {}
 
   collect() {
@@ -152,10 +155,17 @@ class PackageAcc {
   private expandIncludes(patterns: string[]): string[] {
     // Match include patterns against the parsed definitions' names, which
     // cover both real files and markdown code blocks. Patterns are relative
-    // to the games root (e.g. `./**/*.yaml`).
+    // to the package declaration's own directory (e.g. `./**/*.yaml` means
+    // this package's folder and below), so a package never absorbs defs from
+    // a sibling game. A leading `/` marks a pattern as root-relative.
+    // Def names carry a leading `/` (from the empty games root), so resolved
+    // patterns are prefixed to match.
     const names = new Set<string>();
     for (const pattern of patterns) {
-      const matcher = picomatch(pattern, { dot: true });
+      const resolved = pattern.startsWith('/')
+        ? pattern
+        : `/${path.posix.join(this.baseDir, pattern)}`;
+      const matcher = picomatch(resolved, { dot: true });
       for (const name of this.defs.defs.keys()) {
         if (matcher(name)) names.add(name);
       }