Copilot round 1: the new EMA regression test constructed its inner provider's
storage with `as unknown as OAuthStorage`, an unjustified double cast — the
rule in AGENTS.md is that such a cast must carry a justification or be replaced.
Replaced with the genuine article: `OAuthStorageBase` over an
`OAuthMemoryStore` and a no-op persist backend, so the stub type-checks against
the real interface the provider is handed and a future `OAuthStorage` contract
change cannot pass silently. Reusing `emaConfig.storage`, as suggested, would
not have addressed the objection — that value is itself a cast, and typed as
`EmaFlowConfig["storage"]` rather than `OAuthStorage`.
The test's assertion is unchanged and was re-verified to fail against pre-fix
code (`expected 'corp-idp' to be null`).
Signed-off-by: cliffhall <cliff@futurescale.com>
362e2f419d