test(tools): cover export_onnx with tiny synthetic models

tests/tools/test_export_onnx.py

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+"""Validate tools.export_onnx with a tiny synthetic model."""
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+import pytest
+import torch
+
+from tools.export_onnx import (
+    _check_flow_parity,
+    _check_scroll_parity,
+    export_flow_model,
+    export_scroll_decoder,
+)
+
+
+@pytest.fixture
+def tiny_flow_ckpt(tmp_path: Path) -> Path:
+    """A flow model with seq_len=8, d_model=16, 1 layer — small but valid."""
+    from tools.models import TrajectoryFlowModel
+
+    cfg = {
+        "seq_len": 8,
+        "d_model": 16,
+        "nhead": 2,
+        "num_layers": 1,
+        "dim_feedforward": 32,
+        "cond_dim": 3,
+    }
+    model = TrajectoryFlowModel(**cfg, dropout=0.0)
+    model.eval()
+    out = tmp_path / "flow_ckpt"
+    out.mkdir()
+    torch.save(model.state_dict(), out / "flow_model.pt")
+    (out / "train_config.json").write_text(json.dumps(cfg))
+    return out
+
+
+@pytest.fixture
+def tiny_scroll_ckpt(tmp_path: Path) -> Path:
+    """A scroll model with seq_len=4, latent=4, hidden=8."""
+    from tools.scroll.models import ScrollCVAE
+
+    cfg = {"seq_len": 4, "latent_dim": 4, "hidden": 8, "cond_dim": 7}
+    model = ScrollCVAE(**cfg)
+    model.eval()
+    out = tmp_path / "scroll_ckpt"
+    out.mkdir()
+    torch.save(model.state_dict(), out / "scroll_model.pt")
+    (out / "scroll_config.json").write_text(json.dumps(cfg))
+    return out
+
+
+def test_export_flow_model_parity(tiny_flow_ckpt: Path, tmp_path: Path) -> None:
+    out_dir = tmp_path / "out"
+    onnx_path = export_flow_model(tiny_flow_ckpt, out_dir)
+    assert onnx_path.exists()
+    _check_flow_parity(tiny_flow_ckpt, onnx_path)  # raises on failure
+
+
+def test_export_scroll_decoder_parity(tiny_scroll_ckpt: Path, tmp_path: Path) -> None:
+    out_dir = tmp_path / "out"
+    onnx_path = export_scroll_decoder(tiny_scroll_ckpt, out_dir)
+    assert onnx_path.exists()
+    _check_scroll_parity(tiny_scroll_ckpt, onnx_path)