[Tech Debt] Replace vendored RetryOperationHelper with inline retry logic — good to have

[gladjohn]

Task type

Tech Debt — Good to have

Context

RetryOperationHelper in Microsoft.Identity.Client/Utils/ is vendored retry logic originally copied from an external repo. It has only 2 consumers. Replacing it reduces the internal API surface and removes code no one actively owns.

Priority

🟢 Low priority / Good to have — Not urgent, not blocking any work. Suitable for spare cycles.

Proposed fix

1. Identify the 2 call sites
2. Inline the retry loop directly at each call site (simple for loop with try/catch and Task.Delay)
3. Preserve exception filtering and callback semantics
4. Delete RetryOperationHelper.cs
5. Update/remove RetryOperationHelperTest.cs accordingly

Note: Polly is likely overkill for just 2 call sites. Simple inline retry is preferred.

Risk assessment

🟡 Medium — Retry semantics must be preserved exactly. Verify with existing tests.