fix(salary): require corroboration before accepting a header row (#415)

* fix(salary): require corroboration before accepting a header row

Header-row detection accepted the first row (of the first 10) where any
cell merely contained a company-pattern word - no check that the row
actually looked like a header. A source-citation row above the real
header table (standard in real Danish union/statistics exports, e.g.
"Kilde: ... opdelt efter arbejdsgiver ...") tripped it purely because
"arbejdsgiver" appeared in prose. The real header row then parsed as
data (its "Firma" cell became a bogus company), and every genuine
company silently lost all its salary data - exit 0, no warning.

A candidate row is now only accepted when a second cell also matches a
city/count/index pattern, and a sheet that ends up with zero detected
salary columns prints a warning instead of reporting success silently.

Fixes #414.

* fix(salary): require cross-cell corroboration, fall back for untyped columns

Two edge cases found in review of the corroboration fix:

- Same-cell corroboration wasn't enough: a citation sentence can pack a
  count-pattern word into the same sentence as the company-pattern one
  ("...opdelt efter arbejdsgiver, antal svar 1234"), which still passed
  the gate. Corroboration must now come from a different cell.

- The corroboration requirement itself broke sheets whose only real
  header has purely untyped salary columns (e.g. "Base pay 2025" /
  "Bonus 2025" - neither matches a known city/count/index pattern), so
  header detection found nothing at all. Falls back to the original
  any-cell-mentions-company rule when the strict pass finds no row in
  the first 10.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_convert_salary_excel.py

@@ -1,4 +1,6 @@
+import io
 import unittest
+from contextlib import redirect_stderr
 from types import SimpleNamespace
 
 from tools.convert_salary_excel import (
@@ -286,6 +288,85 @@ class DetectColumnTypeTests(unittest.TestCase):
         self.assertEqual(categories["a"], {"count": 10, "index": 100.0})
         self.assertEqual(categories["b"], {"count": 20, "index": 200.0})
 
+    def test_parse_sheet_ignores_citation_row_mentioning_company_pattern_word(self):
+        # A title/source-citation row above the real header - standard in
+        # real Danish union/statistics exports - can contain a stray
+        # company-pattern word ("arbejdsgiver" = employer) in running prose.
+        # It must not be mistaken for the header: that misreads the real
+        # header row as data (producing a bogus "Firma" company) and drops
+        # every real company's salary data (issue #414).
+        ws = FakeWorksheet([
+            ("Lønstatistik 2025",),
+            ("Kilde: Medlemsundersøgelse opdelt efter arbejdsgiver og branche",),
+            (),
+            ("Firma", "By", "Antal alle", "Lønindeks alle"),
+            ("Novo Nordisk A/S", "Bagsværd", 500, 108.5),
+            ("Ørsted A/S", "Fredericia", 200, 105.2),
+        ])
+
+        companies = parse_sheet(ws)
+
+        self.assertEqual(len(companies), 2)
+        self.assertEqual(companies[0]["company"], "Novo Nordisk A/S")
+        self.assertEqual(companies[0]["city"], "Bagsværd")
+        self.assertEqual(companies[0]["categories"]["alle"], {"count": 500, "index": 108.5})
+        self.assertEqual(companies[1]["company"], "Ørsted A/S")
+
+    def test_parse_sheet_rejects_citation_row_with_count_word_in_same_cell(self):
+        # Corroboration must come from a DIFFERENT cell than the company
+        # match. A single free-text sentence can pack both a company-pattern
+        # word and a count-pattern word together (e.g. "... opdelt efter
+        # arbejdsgiver, antal svar 1234") - same-cell corroboration must not
+        # be enough, or this citation row reintroduces the bogus-header bug.
+        ws = FakeWorksheet([
+            ("Lønstatistik 2025",),
+            ("Kilde: undersøgelse opdelt efter arbejdsgiver, antal svar 1234",),
+            (),
+            ("Firma", "By", "Antal alle", "Lønindeks alle"),
+            ("Novo Nordisk A/S", "Bagsværd", 500, 108.5),
+        ])
+
+        companies = parse_sheet(ws)
+
+        self.assertEqual(len(companies), 1)
+        self.assertEqual(companies[0]["company"], "Novo Nordisk A/S")
+        self.assertEqual(companies[0]["categories"]["alle"], {"count": 500, "index": 108.5})
+
+    def test_parse_sheet_falls_back_when_no_row_has_cross_cell_corroboration(self):
+        # A header with only untyped salary columns (no header matches a
+        # known city/count/index pattern - "Base pay"/"Bonus" don't) has
+        # nothing to corroborate against in any row. The strict cross-cell
+        # check must fall back to the original any-cell-mentions-company
+        # rule rather than failing to find a header at all.
+        ws = FakeWorksheet([
+            ("Company", "Base pay 2025", "Bonus 2025"),
+            ("Example Corp", 55000, 5000),
+        ])
+
+        companies = parse_sheet(ws)
+
+        self.assertEqual(len(companies), 1)
+        self.assertEqual(companies[0]["company"], "Example Corp")
+        self.assertEqual(companies[0]["categories"]["base_pay_2025"], {"index": 55000.0})
+        self.assertEqual(companies[0]["categories"]["bonus_2025"], {"index": 5000.0})
+
+    def test_parse_sheet_warns_when_no_salary_columns_detected(self):
+        # A header row with only company/city columns and no salary data
+        # is a strong signal something is wrong (a misdetected header row,
+        # or a sheet with no salary data at all) - it should be flagged,
+        # not silently reported as a successful conversion.
+        ws = FakeWorksheet([
+            ("Company", "City"),
+            ("Example Corp", "Aarhus"),
+        ])
+
+        stderr = io.StringIO()
+        with redirect_stderr(stderr):
+            companies = parse_sheet(ws)
+
+        self.assertEqual(companies[0]["categories"], {})
+        self.assertIn("No salary data columns detected", stderr.getvalue())
+
 
 if __name__ == "__main__":
     unittest.main()