fix: move prompt temp file outside workingDirectory to prevent race condition

The .prompt-tmp file was written inside workingDirectory, which gets deleted
by afterAll cleanup. With --concurrent --retry, afterAll can interleave with
retries, causing "No such file or directory" crashes at 0s (seen in
review-design-lite and office-hours-spec-review).

Fix: write prompt file to os.tmpdir() with a unique suffix so it survives
directory cleanup. Also convert review-design-lite from describeE2E to
describeIfSelected for proper diff-based test selection.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

test/helpers/session-runner.ts

@@ -161,8 +161,10 @@ export async function runSkillTest(options: {
     '--allowed-tools', ...allowedTools,
   ];
 
-  // Write prompt to a temp file and pipe it via shell to avoid stdin buffering issues
-  const promptFile = path.join(workingDirectory, '.prompt-tmp');
+  // Write prompt to a temp file OUTSIDE workingDirectory to avoid race conditions
+  // where afterAll cleanup deletes the dir before cat reads the file (especially
+  // with --concurrent --retry). Using os.tmpdir() + unique suffix keeps it stable.
+  const promptFile = path.join(os.tmpdir(), `.prompt-${process.pid}-${Date.now()}-${Math.random().toString(36).slice(2)}`);
   fs.writeFileSync(promptFile, prompt);
 
   const proc = Bun.spawn(['sh', '-c', `cat "${promptFile}" | claude ${args.map(a => `"${a}"`).join(' ')}`], {