fix: harden empty-parent pruning boundary and cleanup

Use a path-boundary check instead of a string prefix so sibling dirs
(e.g. _bmad2) can't match the bmad root, and make the walk best-effort
so a dir that vanishes or fills in mid-walk never aborts the install.
Move the test fixture cleanup into finally so failures don't leak temp
dirs.

test/test-installation-components.js

@@ -3278,8 +3278,9 @@ async function runTests() {
   // ============================================================
   console.log(`${colors.yellow}Test Suite 45: cleanup prunes empty skill-group dirs${colors.reset}\n`);
 
+  let root45;
   try {
-    const root45 = await fs.mkdtemp(path.join(os.tmpdir(), 'bmad-cleanup-test-'));
+    root45 = await fs.mkdtemp(path.join(os.tmpdir(), 'bmad-cleanup-test-'));
     const bmadDir45 = path.join(root45, '_bmad');
     await fs.ensureDir(path.join(bmadDir45, '_config'));
 
@@ -3307,12 +3308,12 @@ async function runTests() {
     assert(!(await fs.pathExists(path.join(bmadDir45, 'bmm', '1-analysis', 'research'))), 'empty nested skill-group dir is pruned');
     assert(await fs.pathExists(path.join(bmadDir45, 'bmm', 'config.yaml')), 'module-level files are preserved');
     assert(await fs.pathExists(bmadDir45), 'bmad root is never removed');
-
-    await fs.remove(root45);
   } catch (error) {
     console.log(`${colors.red}Test Suite 45 setup failed: ${error.message}${colors.reset}`);
     console.log(error.stack);
     failed++;
+  } finally {
+    if (root45) await fs.remove(root45).catch(() => {});
   }
 
   console.log('');

tools/installer/core/installer.js

@@ -426,17 +426,24 @@ class Installer {
 
   /**
    * Remove now-empty parent directories left behind after skill dir cleanup.
-   * Walks up from dir, stopping at (and never removing) bmadDir.
+   * Walks up from dir, stopping at (and never removing) bmadDir. Best-effort:
+   * a directory that vanishes or fills in mid-walk just ends the walk.
    * @param {string} dir - Directory to start walking up from
    * @param {string} bmadDir - BMAD installation directory (boundary)
    */
   async _removeEmptyParents(dir, bmadDir) {
     let current = dir;
-    while (current.startsWith(bmadDir) && current !== bmadDir) {
+    while (true) {
-      if (!(await fs.pathExists(current))) break;
+      // Path-boundary check (not a string prefix, so siblings like _bmad2 don't match).
-      const entries = await fs.readdir(current);
+      const rel = path.relative(bmadDir, current);
-      if (entries.length > 0) break;
+      if (rel === '' || rel.startsWith('..') || path.isAbsolute(rel)) break;
-      await fs.rmdir(current);
+      try {
+        const entries = await fs.readdir(current);
+        if (entries.length > 0) break;
+        await fs.rmdir(current);
+      } catch {
+        break;
+      }
       current = path.dirname(current);
     }
   }