whep-client/main.go: minimal Pion subscriber that POSTs a recvonly
offer, applies the answer, and waits for one RTP packet on each of
the video and audio tracks. Used as M1's end-to-end verifier.
whep-client/main_test.go: in-process e2e wiring — stands up Source,
Registry, PeerFactory and WHEPHandler behind an httptest server,
injects synthetic PT=102/111 RTP on the Source's UDP port and calls
Subscribe. Validates the full egress pipeline without requiring
FFmpeg or external network. Skipped under -short.
