test(dse): adopt canonical v3 tests + criteria/GT/validation

Replace the reconstructed test_dse_agent.py with the canonical version and add
the companion unit tests (classification_gate, embedding_recall) covering the
recovered v3 modules. Include the curated DSE criteria backup + changelog
(legal-note rationale per control), the v1 validation writeup, and the
multi-company DSE ground-truth fulltexts (elli/eto/mercedes/safetykon) used
for threshold calibration.

18 DSE tests green offline (DB/embedding/LLM stubbed).

dev-only, no deploy.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend-compliance/compliance/tests/test_dse_classification_gate.py

@@ -0,0 +1,59 @@
+"""Tests fuer das DSE-Applicability-Gate (_classification_gate).
+
+Deckt die reine Split-Logik (apply_gate) und das defensive Verhalten von
+load_dse_gate ohne DB ab. Die DB-Abfrage selbst ist I/O und wird hier nicht
+gegen eine echte DB getestet (defensiver Pfad: kein DSN -> leeres Dict)."""
+
+import asyncio
+import os
+
+from compliance.services.specialist_agents.dse._classification_gate import (
+    apply_gate,
+    load_dse_gate,
+)
+
+
+def test_apply_gate_splits_findings_and_organizational():
+    controls = [
+        {"control_id": "AUTH-2051-A02", "title": "Speicherdauer nennen"},
+        {"control_id": "AUTH-2049-A01", "title": "VVT fuehren"},
+    ]
+    gate = {
+        "AUTH-2049-A01": {
+            "obligation_type": "EVIDENCE",
+            "check_intent": "DIRECT_EVIDENCE",
+            "applicable_artifacts": ["VVT", "AUDIT"],
+            "reference_allowed": "NO",
+        }
+    }
+    kept, organizational = apply_gate(controls, gate)
+    assert [c["control_id"] for c in kept] == ["AUTH-2051-A02"]
+    assert len(organizational) == 1
+    org = organizational[0]
+    assert org["control_id"] == "AUTH-2049-A01"
+    assert org["title"] == "VVT fuehren"
+    assert org["applicable_artifacts"] == ["VVT", "AUDIT"]
+    assert org["check_intent"] == "DIRECT_EVIDENCE"
+
+
+def test_apply_gate_empty_gate_keeps_all():
+    controls = [{"control_id": "X-1"}, {"control_id": "X-2"}]
+    kept, organizational = apply_gate(controls, {})
+    assert len(kept) == 2
+    assert organizational == []
+
+
+def test_load_dse_gate_without_dsn_is_defensive():
+    """Kein DSN + keine Env -> leeres Dict (kein Filter), kein Fehler."""
+    saved = (
+        os.environ.pop("DATABASE_URL", None),
+        os.environ.pop("COMPLIANCE_DATABASE_URL", None),
+    )
+    try:
+        result = asyncio.run(load_dse_gate(""))
+        assert result == {}
+    finally:
+        if saved[0] is not None:
+            os.environ["DATABASE_URL"] = saved[0]
+        if saved[1] is not None:
+            os.environ["COMPLIANCE_DATABASE_URL"] = saved[1]