fix: --bars now suppresses early EOS until target bar count is reached

Previously the model could emit EOS before reaching n_bars because the
EOS-suppression was only applied via the n_bars break, not the grammar
bias. Fixed by masking EOS to -inf in the logit bias while
bars_completed < n_bars.

Added _EosHungryModel fixture and test_generate_bars_overrides_early_eos
to catch this regression class.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_generate.py

@@ -28,6 +28,21 @@ class _UniformModel(nn.Module):
         return logits
 
 
+class _EosHungryModel(nn.Module):
+    """Strongly prefers EOS at every step — simulates a model that wants to stop early."""
+    def __init__(self, vocab_size: int = len(VOCAB), max_seq_len: int = 512):
+        super().__init__()
+        self.max_seq_len = max_seq_len
+        self._vocab_size = vocab_size
+        self._dummy = nn.Parameter(torch.zeros(1))
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        b, s = x.shape
+        logits = torch.zeros(b, s, self._vocab_size, device=x.device)
+        logits[:, :, _EOS] = 1000.0   # model desperately wants to emit EOS
+        return logits
+
+
 def test_encode_prefix_chord_only():
     # "Cmaj7" in C major (shift=0) → ROOT_C QUAL_maj7 EXT_none BASS_root
     ids, n_pos = _encode_prefix(["Cmaj7"], shift=0)
@@ -117,6 +132,17 @@ def test_generate_bars_with_prefix():
     assert len(period.bars) == 4
 
 
+def test_generate_bars_overrides_early_eos():
+    # Model desperately wants EOS — n_bars must prevent it from stopping early
+    model = _EosHungryModel()
+    period = generate_period(
+        model=model, mode="major", time="4/4", subdivision=4,
+        style="H1K0", function="verse", key="C_major",
+        n_bars=4, seed=0,
+    )
+    assert len(period.bars) == 4
+
+
 def test_generate_no_bars_arg_still_works():
     # Without n_bars the model generates until EOS or max_tokens
     model = _UniformModel()