Cut C's headline cross-process proof. The TS `serve` peer already tore its
listener down the instant it finished broadcasting, so nothing could dial it
late; it gains `--linger-ms` to hold the listener open afterward instead. The
interop harness starts that provider, runs a throwaway `dial` peer that
receives every frame and disconnects (the provider requires a first peer
before it broadcasts at all, so this is also what proves broadcasting
finished), then only after that dials with the C# native connector and
asserts the frame it gets is the retained one, by payload, not just
non-empty. New `NativeConnectorReceivesTheRetainedFrameWhenJoiningLate` in
GameCult.Mesh.Quic.Native.Tests carries the assertion; the existing
`NativeConnectorReceivesFromExternalProvider` is untouched. Windows-only,
matching the native connector under test.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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