test(agents/routing): regression tests for MRI/EEG/BBB routing heuristic

All 5 tests pass on existing code — the bare-directory-without-slash case
already works because Path.exists() resolves relative to cwd, which
monkeypatch.chdir() sets correctly in the test. No routing.py change needed.

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

tests/agents/test_routing.py

@@ -0,0 +1,44 @@
+"""Tests for src.agents.routing — deterministic workflow-guard fallbacks."""
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from src.agents.routing import route_pipeline_input
+
+
+class TestRoutePipelineInput:
+    def test_smiles_routes_to_bbb(self) -> None:
+        assert route_pipeline_input("CCO") == (
+            "run_bbb_pipeline",
+            {"smiles": "CCO", "top_k": 5},
+        )
+
+    def test_eeg_path_routes_to_eeg(self) -> None:
+        name, args = route_pipeline_input("data/raw/sample.fif")
+        assert name == "run_eeg_pipeline"
+        assert args == {"input_path": "data/raw/sample.fif"}
+
+    def test_nifti_path_routes_to_mri_with_parent_dir(self) -> None:
+        name, args = route_pipeline_input("data/raw/subjects/subject_0.nii.gz")
+        assert name == "run_mri_pipeline"
+        assert args["input_dir"] == "data/raw/subjects"
+
+    def test_existing_local_dir_without_slash_routes_to_mri(
+        self, tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        monkeypatch.chdir(tmp_path)
+        (tmp_path / "subject_dir").mkdir()
+        name, args = route_pipeline_input("subject_dir")
+        assert name == "run_mri_pipeline"
+        assert args["input_dir"] == "subject_dir"
+
+    def test_bare_string_with_no_matching_dir_still_routes_to_bbb(
+        self, tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        monkeypatch.chdir(tmp_path)
+        # Nothing on disk named "Aspirin" — should be treated as a SMILES-like token
+        name, args = route_pipeline_input("Aspirin")
+        assert name == "run_bbb_pipeline"
+        assert args == {"smiles": "Aspirin", "top_k": 5}