Harden resource cost evidence contract

tests/test_ledger.py

@@ -1,4 +1,6 @@
 import sqlite3
+import os
+import shutil
 from pathlib import Path
 
 import pytest
@@ -11,6 +13,7 @@ from fin_hub.services.ledger import (
     monthly_burn_series,
     monthly_summary,
     record_engagement_price,
+    reverse_financial_fact,
     set_opening_balance,
 )
 
@@ -44,6 +47,86 @@ def test_ledger_import_skips_unchanged_file(tmp_path: Path):
     assert second.rows_imported == 0
 
 
+def test_ledger_import_is_idempotent_when_file_is_renamed_or_touched(tmp_path: Path):
+    ledger = tmp_path / "ledger.db"
+    source = tmp_path / "costs.csv"
+    shutil.copy(FIXTURES / "cloud-costs.csv", source)
+    renamed = tmp_path / "renamed.csv"
+
+    first = import_csv(source, "cloud", ledger_path=ledger)
+    os.utime(source, (source.stat().st_atime, source.stat().st_mtime + 1))
+    touched = import_csv(source, "cloud", ledger_path=ledger)
+    shutil.copy(source, renamed)
+    delivered_again = import_csv(renamed, "cloud", ledger_path=ledger)
+
+    assert first.rows_imported == 3
+    assert touched.rows_imported == 0
+    assert delivered_again.rows_imported == 0
+    assert monthly_summary(ledger_path=ledger)[0].entry_count == 3
+
+
+def test_changed_fact_requires_and_applies_one_correction(tmp_path: Path):
+    ledger = tmp_path / "ledger.db"
+    source = tmp_path / "costs.csv"
+    source.write_text(
+        "service,amount,currency,period_month\ncompute,10.00,EUR,2026-07\n",
+        encoding="utf-8",
+    )
+    import_csv(source, "cloud", ledger_path=ledger)
+    source.write_text(
+        "service,amount,currency,period_month\ncompute,12.00,EUR,2026-07\n",
+        encoding="utf-8",
+    )
+
+    with pytest.raises(ValueError, match="explicit correction"):
+        import_csv(source, "cloud", ledger_path=ledger)
+    corrected = import_csv(source, "cloud", ledger_path=ledger, force=True)
+    duplicate = import_csv(source, "cloud", ledger_path=ledger, force=True)
+
+    assert corrected.rows_imported == 1
+    assert duplicate.rows_imported == 0
+    rollup = monthly_summary(ledger_path=ledger)[0]
+    assert rollup.total == 12.0
+    assert rollup.entry_count == 1
+    with sqlite3.connect(ledger) as conn:
+        facts = conn.execute(
+            "SELECT correction_of, is_current FROM ledger_entries ORDER BY id"
+        ).fetchall()
+    assert facts[0][1] == 0
+    assert facts[1][0] is not None
+    assert facts[1][1] == 1
+
+
+def test_financial_fact_reversal_is_append_only_and_zeroes_effective_total(tmp_path: Path):
+    ledger = tmp_path / "ledger.db"
+    source = tmp_path / "costs.csv"
+    source.write_text(
+        "service,amount,currency,period_month\ncompute,10.00,EUR,2026-07\n",
+        encoding="utf-8",
+    )
+    import_csv(source, "cloud", ledger_path=ledger)
+    with sqlite3.connect(ledger) as conn:
+        fact_id = conn.execute(
+            "SELECT financial_fact_id FROM ledger_entries"
+        ).fetchone()[0]
+
+    reversal_id = reverse_financial_fact(
+        fact_id, source="provider-credit-note", ledger_path=ledger
+    )
+
+    rollup = monthly_summary(ledger_path=ledger)[0]
+    assert rollup.total == 0.0
+    with sqlite3.connect(ledger) as conn:
+        rows = conn.execute(
+            "SELECT financial_fact_id, correction_of, adjustment_kind, is_current "
+            "FROM ledger_entries ORDER BY id"
+        ).fetchall()
+    assert rows == [
+        (fact_id, None, "charge", 0),
+        (reversal_id, fact_id, "reversal", 1),
+    ]
+
+
 def test_ledger_import_preserves_client_attribution(tmp_path: Path):
     source = tmp_path / "attributed.csv"
     source.write_text(