Stop throwing away the audio Whisper has to read

The single encode at save time was %mp3(bitrate=16), and the comment said why:
it matched what Liquidsoap pushes to Icecast. That was the wrong thing to
match. Icecast is the LISTENING path and 16 kbps is a bandwidth budget for a
live stream; this file is the ACCURACY path -- it is what Whisper transcribes,
and CLAUDE.md is explicit that everything downstream is hostage to it. P25 has
already been through a vocoder, so 16 kbps MP3 stacked a second lossy stage on
the one copy that had to stay faithful.

FLAC instead. Lossless, so the bytes Whisper receives are the bytes PulseAudio
captured. ~1.3 MB/min against 120 KB/min, which keeps a 600 s call (the time
cap) around 13 MB -- inside Whisper's 25 MB request cap and well inside
upload_max_bytes. Icecast's own 16 kbps stream is untouched; nothing about
live listening changes.

Capture, buffering, silence detection and the byte-offset trim are all
unchanged: they operate on raw PCM and never saw the encode. The sample rate
stays pinned to pcm.SAMPLE_RATE so the encode remains a straight pass -- the
trim arithmetic depends on that, and Whisper resamples to 16 kHz itself.

encode_mp3 is now encode_recording, the upload sends audio/flac, and the test
that pinned the old contract now pins losslessness instead, including an
assertion that no bitrate constant comes back.

This is the before/after boundary for STT quality. Last night's window is the
16 kbps baseline.

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

drb-edge-node/tests/test_call_recorder.py

@@ -59,7 +59,7 @@ def encodes(monkeypatch):
         path.write_bytes(audio)
         return True
 
-    monkeypatch.setattr(recorder_mod, "encode_mp3", _encode)
+    monkeypatch.setattr(recorder_mod, "encode_recording", _encode)
     return calls
 
 
@@ -412,21 +412,31 @@ async def test_a_failed_encode_leaves_no_file_and_no_recording(recorder, monkeyp
     async def _fail(audio, path):
         return False
 
-    monkeypatch.setattr(recorder_mod, "encode_mp3", _fail)
+    monkeypatch.setattr(recorder_mod, "encode_recording", _fail)
     ingest(recorder, T0, T0 + 5.0)
     await recorder.start_recording("call-1", start_epoch=T0 + 1.0)
 
     assert await recorder.stop_recording(end_epoch=T0 + 3.0) is None
-    assert list(recorder._recordings_dir.glob("*.mp3")) == []
+    assert list(recorder._recordings_dir.glob("*.flac")) == []
 
 
 def test_encoder_command_contract_matches_what_c2_expects():
     """
-    /upload has always received mono MP3 at 22050 Hz / 16 kbps, and Whisper
-    consumes it downstream. The single encode must not quietly change that.
+    The saved file is what Whisper transcribes, so the encode must stay
+    LOSSLESS and must not resample. It was 16 kbps MP3 — a bitrate copied from
+    Icecast's live stream, i.e. the listening path's budget applied to the
+    accuracy path — which put a second lossy stage on top of the P25 vocoder.
+
+    The sample rate must equal pcm.SAMPLE_RATE or the encode stops being a
+    straight pass and the byte-offset trim arithmetic no longer lines up.
     """
-    assert recorder_mod.MP3_SAMPLE_RATE == str(pcm.SAMPLE_RATE) == "22050"
-    assert recorder_mod.MP3_BITRATE == "16k"
+    assert recorder_mod.AUDIO_SAMPLE_RATE == str(pcm.SAMPLE_RATE) == "22050"
+    assert recorder_mod.AUDIO_FORMAT == "flac"
+    assert recorder_mod.AUDIO_SUFFIX == ".flac"
+    assert recorder_mod.AUDIO_MIME == "audio/flac"
+    # No bitrate constant should exist: a bitrate on a lossless codec would mean
+    # someone reintroduced lossy encoding.
+    assert not hasattr(recorder_mod, "MP3_BITRATE")
 
 
 # ---------------------------------------------------------------------------
@@ -523,7 +533,7 @@ async def test_discard_drops_the_audio_without_writing_anything(recorder, encode
 
     assert not recorder.is_recording
     assert encodes == []
-    assert list(recorder._recordings_dir.glob("*.mp3")) == []
+    assert list(recorder._recordings_dir.glob("*.flac")) == []
     # ...and the recorder is immediately reusable.
     assert await recorder.start_recording("call-next", start_epoch=T0 + 2.0) is True