csv-parser: add _validate_mapping helper

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

tests/test_llm_csv_parser.py

@@ -96,3 +96,59 @@ def test_detect_dialect_empty_raises():
 
     with pytest.raises(LLMParseError):
         _detect_dialect(b"")
+
+
+def test_validate_mapping_accepts_well_formed():
+    from app.services.llm_csv_parser import _validate_mapping
+
+    headers = ["Symbol", "Quantity", "Avg Price", "Currency"]
+    first_row = ["AAPL", "100", "150.25", "USD"]
+    mapping = {
+        "ticker_col": "Symbol",
+        "qty_col": "Quantity",
+        "cost_col": "Avg Price",
+        "currency_col": "Currency",
+        "name_col": None,
+    }
+    _validate_mapping(mapping, headers, first_row)  # no raise
+
+
+def test_validate_mapping_missing_ticker_raises():
+    from app.services.llm_csv_parser import LLMParseError, _validate_mapping
+
+    headers = ["Symbol", "Quantity"]
+    first_row = ["AAPL", "100"]
+    mapping = {"ticker_col": None, "qty_col": "Quantity"}
+    with pytest.raises(LLMParseError, match="ticker"):
+        _validate_mapping(mapping, headers, first_row)
+
+
+def test_validate_mapping_missing_qty_raises():
+    from app.services.llm_csv_parser import LLMParseError, _validate_mapping
+
+    headers = ["Symbol", "Quantity"]
+    first_row = ["AAPL", "100"]
+    mapping = {"ticker_col": "Symbol", "qty_col": None}
+    with pytest.raises(LLMParseError, match="qty"):
+        _validate_mapping(mapping, headers, first_row)
+
+
+def test_validate_mapping_unknown_column_raises():
+    from app.services.llm_csv_parser import LLMParseError, _validate_mapping
+
+    headers = ["Symbol", "Quantity"]
+    first_row = ["AAPL", "100"]
+    mapping = {"ticker_col": "Symbol", "qty_col": "NotARealColumn"}
+    with pytest.raises(LLMParseError, match="NotARealColumn"):
+        _validate_mapping(mapping, headers, first_row)
+
+
+def test_validate_mapping_non_numeric_qty_raises():
+    from app.services.llm_csv_parser import LLMParseError, _validate_mapping
+
+    headers = ["Symbol", "Description"]
+    first_row = ["AAPL", "Apple Inc"]
+    # Mapping says qty is "Description", but "Apple Inc" can't parse as a number.
+    mapping = {"ticker_col": "Symbol", "qty_col": "Description"}
+    with pytest.raises(LLMParseError, match="numeric"):
+        _validate_mapping(mapping, headers, first_row)