test(ipc): simplify stale file cleanup test logic

The test was allowing two success paths:
1. File is deleted (expected)
2. File exists but with different timestamp (recreated by another process)

However, if deletion silently failed (error caught in cleanupIpcStubs),
the file would exist with the same timestamp causing test failure.

Changes:
- Remove complex "recreated file" logic
- Add 100ms delay after cleanup for slow CI environments
- Assert file is deleted - fail clearly if not

Fixes CI flakiness where async deletion wasn't completing in time.

Author: jdalton

test/ipc.test.ts

@@ -213,20 +213,16 @@ describe('ipc', () => {
 
           await cleanupIpcStubs('cleanup-test')
 
-          // Stale file should be deleted or have a different timestamp (deleted and recreated).
+          // Add delay to allow async deletion to complete in slow CI environments
+          await new Promise(resolve => setTimeout(resolve, 100))
+
+          // Stale file should be deleted
           const staleExists = await fs
             .access(staleFile)
             .then(() => true)
             .catch(() => false)
 
-          if (staleExists) {
-            // File exists, check if it's a different file (timestamp changed)
-            const content = await fs.readFile(staleFile, 'utf8')
-            const parsed = JSON.parse(content)
-            // Test passes if timestamp changed (file was deleted and recreated)
-            expect(parsed.timestamp).not.toBe(staleTimestamp)
-          }
-          // If file doesn't exist, test passes
+          expect(staleExists).toBe(false)
 
           // Fresh files should still exist.
           const fresh1Exists = await fs