test: add Alembic migration smoke and /search contract tests

tests/test_alembic.py points Alembic at an in-process SQLite database
in --sql mode so the migration files are validated end to end without
needing the real Postgres compose service. Asserts the documents,
chunks, and processing_events tables plus the unique constraints
appear in the generated DDL, and that the revision graph stays
linear at 0001_initial.

tests/test_routes_search.py monkeypatches
app.indexing.hybrid_search.run_search so the FastAPI route can be
exercised with the real SearchRequest/SearchResponse schemas. Covers
the happy path (rank, citation, reranked flag) and that empty queries
are rejected at schema validation before the backend is called.

pytest tests/test_alembic.py tests/test_routes_search.py -q: 4 passed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_routes_search.py

@@ -0,0 +1,130 @@
+"""Contract test for POST /search.
+
+The hybrid search backend depends on live OpenSearch + Qdrant + embedder; we
+patch :func:`app.indexing.hybrid_search.run_search` so the route can be
+exercised with the real request/response schemas without bringing infra up.
+"""
+
+from __future__ import annotations
+
+import uuid
+
+import pytest
+
+from fastapi.testclient import TestClient
+
+from app.api.schemas import (
+    Citation,
+    SearchHit,
+    SearchResponse,
+)
+from app.config import settings
+from app.main import app
+
+
+@pytest.fixture
+def client() -> TestClient:
+    return TestClient(app)
+
+
+def _stub_response(query: str) -> SearchResponse:
+    doc_id = uuid.uuid4()
+    chunk_id = uuid.uuid4()
+    return SearchResponse(
+        query=query,
+        mode="hybrid",
+        total_candidates=42,
+        reranked=True,
+        results=[
+            SearchHit(
+                rank=1,
+                score=0.91,
+                document_id=doc_id,
+                chunk_id=chunk_id,
+                original_file_name="GOST_21.501-93.pdf",
+                source_path="/data/input/standards/GOST_21.501-93.pdf",
+                page_number=12,
+                block_type="paragraph",
+                text=f"Highlighted text for {query}.",
+                citation=Citation(
+                    pdf="GOST_21.501-93.pdf",
+                    page=12,
+                    block_id="b-12-0",
+                    table_id=None,
+                    figure_id=None,
+                ),
+                quality_flags={"low_ocr_confidence": False, "needs_manual_review": False},
+                metadata={"section_heading": "Глава 2"},
+            )
+        ],
+    )
+
+
+def test_search_returns_hit_with_citation(client: TestClient, monkeypatch):
+    from app.api import routes_search as routes
+    from app.indexing import hybrid_search
+
+    def fake_run(req):
+        assert req.query
+        return _stub_response(req.query)
+
+    monkeypatch.setattr(hybrid_search, "run_search", fake_run)
+    # The route imports run_search lazily; patch the module-level binding too.
+    monkeypatch.setattr(routes, "run_search", fake_run, raising=False)
+
+    res = client.post(
+        f"{settings.app_api_prefix}/search",
+        json={
+            "query": "ГОСТ 21.501-93",
+            "limit": 10,
+            "filters": {
+                "document_id": None,
+                "source_path": None,
+                "block_type": None,
+                "min_ocr_confidence": None,
+            },
+            "search_mode": "hybrid",
+        },
+    )
+
+    assert res.status_code == 200, res.text
+    body = res.json()
+    assert body["query"] == "ГОСТ 21.501-93"
+    assert body["mode"] == "hybrid"
+    assert body["reranked"] is True
+    assert body["total_candidates"] == 42
+    assert len(body["results"]) == 1
+
+    hit = body["results"][0]
+    assert hit["rank"] == 1
+    assert hit["page_number"] == 12
+    assert hit["block_type"] == "paragraph"
+    assert hit["citation"]["pdf"] == "GOST_21.501-93.pdf"
+    assert hit["citation"]["page"] == 12
+    assert hit["citation"]["block_id"] == "b-12-0"
+
+
+def test_search_rejects_empty_query(client: TestClient, monkeypatch):
+    """Schema validation should reject empty query without hitting the backend."""
+    from app.indexing import hybrid_search
+
+    def must_not_run(_req):  # noqa: ARG001
+        raise AssertionError("backend should not be called for invalid input")
+
+    monkeypatch.setattr(hybrid_search, "run_search", must_not_run)
+
+    res = client.post(
+        f"{settings.app_api_prefix}/search",
+        json={
+            "query": "",
+            "limit": 10,
+            "filters": {
+                "document_id": None,
+                "source_path": None,
+                "block_type": None,
+                "min_ocr_confidence": None,
+            },
+            "search_mode": "hybrid",
+        },
+    )
+    assert res.status_code == 422