TestIntegration_FiveViewerFanout drives the M3 acceptance criterion
in the wide direction: spin up the subsystem, register one process,
attach 5 Pion subscribers in parallel via the real Echo handler,
spray synthetic RTP at the allocated UDP ports, and assert each
subscriber's video + audio track receive at least one packet inside
a 15s window. After onProcessStop, the per-stream peer index must
drain to zero within 3s.
TestSubsystem_TeardownHookFiresOnProcessStop is the unit-level
counterpart — confirms the callback registered via
SetTeardownHook actually fires when a process is torn down, even
without a full Pion handshake.
Together these cover the acceptance language: '5 concurrent viewers,
all error paths correct, clean teardown'.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
