## What changed
- The retry test now uses the same streaming SSE test server used by
production-style tests instead of a wiremock sequence.
- The fixture is resolved via `find_resource!`, and the test asserts
that exactly two outbound requests were sent.
## Why this fixes the flake
- The old wiremock sequence approximated early-close behavior, but it
did not reproduce the same streaming semantics the real client sees.
- That meant the retry path depended on mock implementation details
instead of on the actual transport behavior we care about.
- Switching to the streaming SSE helper makes the test exercise the real
early-close/retry contract, and counting requests directly verifies that
we retried exactly once rather than merely hoping the sequence aligned.
## Scope
- Test-only change.
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