feat: let the viewer pick the audio track

The streaming path mapped 0:a:0 unconditionally, so a dubbed film played in
whichever language was muxed first and the others were unreachable. The node
now enumerates the tracks in stream_init and honours audio_track in
stream_req; switching is the seek path, since one ffmpeg carries one track.

MNP 3.2, additive: the player draws its selector from the node's own list and
never from a version number, so an older node is never asked for a track it
would ignore. MNP_MIN_SUPPORTED does not move.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 14 insertions, 13 deletions

diff --git a/packages/meshbay-node/tests/test_stream_audio_transcode.py b/packages/meshbay-node/tests/test_stream_audio_transcode.py
index 959cc91..92518ba 100644
--- a/packages/meshbay-node/tests/test_stream_audio_transcode.py
+++ b/packages/meshbay-node/tests/test_stream_audio_transcode.py
@@ -150,15 +150,15 @@ async def test_probe_video_reports_aac_regardless_of_source_audio_codec(tmp_path
     clip = tmp_path / "clip.mkv"
     _make_clip(clip, acodec="eac3", channels=6)
 
-    codec, duration, has_audio, width, height, raw_codec = await _probe_video(str(clip))
+    probe = await _probe_video(str(clip))
 
-    assert has_audio is True
-    assert duration > 0
-    assert codec is not None
-    assert "eac3" not in codec and "ec-3" not in codec
-    assert "mp4a.40.2" in codec
-    assert (width, height) == (320, 240)
-    assert raw_codec == "h264"
+    assert probe.has_audio is True
+    assert probe.duration > 0
+    assert probe.codec is not None
+    assert "eac3" not in probe.codec and "ec-3" not in probe.codec
+    assert "mp4a.40.2" in probe.codec
+    assert (probe.width, probe.height) == (320, 240)
+    assert probe.raw_codec_name == "h264"
 
 
 async def test_probe_video_handles_no_audio_track(tmp_path):
@@ -170,10 +170,11 @@ async def test_probe_video_handles_no_audio_track(tmp_path):
         check=True, capture_output=True,
     )
 
-    codec, duration, has_audio, width, height, raw_codec = await _probe_video(str(clip))
+    probe = await _probe_video(str(clip))
 
-    assert has_audio is False
-    assert codec is not None and "," not in codec, \
+    assert probe.has_audio is False
+    assert probe.audio_tracks == []
+    assert probe.codec is not None and "," not in probe.codec, \
         "no audio track must not produce a dangling ',' or a fake audio codec"
-    assert (width, height) == (320, 240)
-    assert raw_codec == "h264"
+    assert (probe.width, probe.height) == (320, 240)
+    assert probe.raw_codec_name == "h264"