refactor: break up _record_utterance() into focused helpers (#572)

Co-authored-by: Kimi Agent <kimi@timmy.local>
Co-committed-by: Kimi Agent <kimi@timmy.local>

tests/timmy/test_voice_loop.py

@@ -15,7 +15,7 @@ except ImportError:
     np = None
 
 try:
-    from timmy.voice_loop import VoiceConfig, VoiceLoop, _strip_markdown
+    from timmy.voice_loop import VoiceConfig, VoiceLoop, _rms, _strip_markdown
 except ImportError:
     pass  # pytestmark will skip all tests anyway
 
@@ -147,6 +147,31 @@ class TestStripMarkdown:
         assert "*" not in result
 
 
+class TestRms:
+    def test_silent_block(self):
+        block = np.zeros(1600, dtype=np.float32)
+        assert _rms(block) == pytest.approx(0.0, abs=1e-7)
+
+    def test_loud_block(self):
+        block = np.ones(1600, dtype=np.float32)
+        assert _rms(block) == pytest.approx(1.0, abs=1e-5)
+
+
+class TestFinalizeUtterance:
+    def test_returns_none_for_empty(self):
+        assert VoiceLoop._finalize_utterance([], min_blocks=5, sample_rate=16000) is None
+
+    def test_returns_none_for_too_short(self):
+        chunks = [np.zeros(1600, dtype=np.float32) for _ in range(3)]
+        assert VoiceLoop._finalize_utterance(chunks, min_blocks=5, sample_rate=16000) is None
+
+    def test_returns_audio_for_sufficient_chunks(self):
+        chunks = [np.ones(1600, dtype=np.float32) for _ in range(6)]
+        result = VoiceLoop._finalize_utterance(chunks, min_blocks=5, sample_rate=16000)
+        assert result is not None
+        assert len(result) == 6 * 1600
+
+
 class TestThink:
     def test_think_returns_response(self):
         loop = VoiceLoop()