The 'already in channel' server response (code 0x0302) is treated as a
successful join by _onJoinChannel: the user stays in the channel and
local state is updated to reflect the joined target. But the underlying
voiceJoin call still raises BridgeError_ServerRejected, which the
joinVoiceChannelWithIosAudioSession helper used to interpret as a join
failure and deactivate the iOS audio session. Result: the UI shows the
user as joined while the audio session is dead and capture/playback
remain silent.
Add an isJoinSuccess predicate to the ordering helper. When the
predicate matches, the helper rethrows (so the caller can still run its
success-on-already-joined branch) without deactivating the session.
Wire _onJoinChannel to pass _isAlreadyInChannel as the predicate so the
0x0302 path keeps the session active.
Adds two regression tests covering the success-on-rethrow and the
predicate-false-still-deactivates paths.