feat(fase2): expose retriever as citation-bearing data source

tests/test_datasource.py

@@ -0,0 +1,55 @@
+"""Step 7 tests — the retriever exposed as a citation-bearing data source.
+
+The in-process GA tool path and the (GA-present) MCP path both wrap the same retrieve()
+core, so their structuredContent shape is identical and every chunk maps into a
+provenance.Citation. Pattern: tests/test_retrieval.py + tests/test_backends.py.
+"""
+
+import pytest
+
+from agent_framework import FunctionTool
+
+from portfolio_optimiser.datasource import (
+    build_mcp_server,
+    chunk_dict_to_citation,
+    make_retrieval_tool,
+    retrieve_chunks,
+)
+from portfolio_optimiser.provenance import Citation
+
+
+@pytest.fixture()
+def docs(tmp_path):
+    d = tmp_path / "docs"
+    d.mkdir()
+    (d / "asphalt.txt").write_text(
+        "Asphalt Ab11 unit rate renegotiation reduced the paving cost on the school stretch.",
+        encoding="utf-8",
+    )
+    return d
+
+
+def test_in_process_tool_returns_citation_ready_chunks(docs) -> None:
+    chunks = retrieve_chunks("asphalt paving cost", str(docs), top_k=3)
+    assert chunks  # at least one citation-ready chunk
+    for d in chunks:
+        assert set(d) >= {"file", "locator", "snippet", "score"}
+        cit = chunk_dict_to_citation(d)
+        assert isinstance(cit, Citation)
+        assert cit.locator.start_index <= cit.locator.end_index
+        assert cit.snippet
+
+
+def test_make_retrieval_tool_builds_ga_function_tool(docs) -> None:
+    t = make_retrieval_tool(str(docs))
+    assert isinstance(t, FunctionTool)
+    assert t.name == "retrieve_cost_docs"
+
+
+async def test_mcp_wrapper_returns_same_structuredcontent_shape(docs) -> None:
+    query = "asphalt paving cost"
+    expected = retrieve_chunks(query, str(docs), top_k=3)
+    server = build_mcp_server(str(docs), top_k=3)
+    _content, structured = await server.call_tool("retrieve_cost_docs", {"query": query})
+    # FastMCP wraps a list return as {"result": [...]} structuredContent.
+    assert structured["result"] == expected