fix(3597): bug-1974 windows EPERM — retry rmSync on tmpDir teardown

Test spawns a fire-and-forget subprocess; on Windows the child may still
hold a handle on tmpDir when afterEach runs, producing EPERM from
fs.rmSync. Match helpers.cleanup() retry budget (20 × 250ms = 5s) to
absorb the deferred-handle window without pulling in the helper (this
suite predates it).

Closes the Windows test (windows-latest, 24/26) lane failure on #3649.

tests/bug-1974-context-exhaustion-record.test.cjs

@@ -99,7 +99,10 @@ describe('#1974 context exhaustion auto-record', () => {
   });
 
   afterEach(() => {
-    fs.rmSync(tmpDir, { recursive: true, force: true });
+    // Windows: AV/file-indexer/not-yet-exited fire-and-forget subprocess may
+    // still hold a handle on tmpDir at teardown. Match the helpers.cleanup()
+    // retry budget (20 × 250ms = 5s) to absorb the deferred-handle window.
+    fs.rmSync(tmpDir, { recursive: true, force: true, maxRetries: 20, retryDelay: 250 });
     // Clean up bridge files
     try {
       const warnPath = path.join(os.tmpdir(), `claude-ctx-${sessionId}-warned.json`);