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.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);
       }