fix(test): make GET /api/sessions/:id/files error-path test deterministic (#241)

Race condition fix surfaced by the post-merge CI on dc8a4a5: macOS
arm64 Node 24 lost the race between fs.rmSync and the PTY exit callback,
so the session was removed from the Map before the GET landed and we got
404 instead of the 500 the route returns when readdirSync fails.
Switching from rm to rename keeps the inode alive (PTY happy) while
still making the path-based readdir fail. 1199/1199 tests still pass
locally.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: dorlugasigal

test/server/routes.test.js

@@ -4216,11 +4216,13 @@ describe('Routes', () => {
     after(async () => {
       inst?.shutdown();
       await safeCleanup(path.join(process.cwd(), '.termbeam-test-files-err'));
+      await safeCleanup(path.join(process.cwd(), '.termbeam-test-files-err-moved'));
     });
 
     it('should return 500 when session cwd no longer exists', async () => {
       inst = await startServer({ password: null });
       const tmpDir = path.join(process.cwd(), '.termbeam-test-files-err');
+      const movedDir = path.join(process.cwd(), '.termbeam-test-files-err-moved');
       fs.mkdirSync(tmpDir, { recursive: true });
 
       const body = JSON.stringify({ name: 'files-err', cwd: tmpDir });
@@ -4239,7 +4241,13 @@ describe('Routes', () => {
       );
       const sessionId = JSON.parse(createRes.data).id;
 
-      fs.rmSync(tmpDir, { recursive: true, force: true });
+      // Rename (don't rm) so the PTY's cwd inode stays alive — otherwise on
+      // fast macOS arm64 the shell exits before the GET arrives, removing the
+      // session and yielding a 404 instead of the 500 we want to assert.
+      try {
+        fs.rmSync(movedDir, { recursive: true, force: true });
+      } catch {}
+      fs.renameSync(tmpDir, movedDir);
 
       const res = await httpRequest({
         hostname: '127.0.0.1',