fix(connectors): retain exact CSV source evidence

Release v0.1.27. Coordinated integrity review: GovOPlaN/govoplan-core#298.

tests/test_migrations.py

@@ -2,16 +2,45 @@ from __future__ import annotations
 
 import tempfile
 import unittest
+from datetime import UTC, datetime
 from pathlib import Path
 
+from alembic import command
 from alembic.runtime.migration import MigrationContext
-from sqlalchemy import create_engine, inspect
+from sqlalchemy import MetaData, Table, create_engine, inspect, select
 
 from govoplan_connectors.backend.manifest import get_manifest
-from govoplan_core.db.migrations import migrate_database
+from govoplan_core.db.migrations import alembic_config, migrate_database
 
 
 class ConnectorsMigrationTests(unittest.TestCase):
+    def test_csv_evidence_upgrade_preserves_legacy_snapshot_without_inventing_source(self) -> None:
+        with tempfile.TemporaryDirectory(prefix="govoplan-connectors-csv-migration-") as directory:
+            url = f"sqlite:///{Path(directory) / 'connectors.db'}"
+            config = alembic_config(database_url=url, enabled_modules=("connectors",), manifest_factories=(get_manifest,))
+            command.upgrade(config, "c0f1a2b3c4d5")
+            engine = create_engine(url)
+            try:
+                table = Table("connector_tabular_sources", MetaData(), autoload_with=engine)
+                now = datetime.now(UTC)
+                with engine.begin() as connection:
+                    connection.execute(table.insert().values(
+                        id="legacy-csv", tenant_id="tenant-1", provider="snapshot",
+                        source_name="legacy", name="Legacy", status="active", schema_version=1,
+                        schema=[{"name": "id", "data_type": "integer", "nullable": False}],
+                        rows=[{"id": 1}], fingerprint="a" * 64, row_count=1, byte_count=10,
+                        metadata={"original_label": "CSV"}, created_at=now, updated_at=now,
+                    ))
+                    before = dict(connection.execute(select(table)).mappings().one())
+                command.upgrade(config, "d2a4c6e8f0b1")
+                upgraded = Table("connector_tabular_sources", MetaData(), autoload_with=engine)
+                with engine.connect() as connection:
+                    after = dict(connection.execute(select(upgraded)).mappings().one())
+                self.assertIsNone(after.pop("csv_source"))
+                self.assertEqual(before, after)
+            finally:
+                engine.dispose()
+
     def test_baseline_creates_connector_tables_and_head(self) -> None:
         with tempfile.TemporaryDirectory(prefix="govoplan-connectors-migration-") as directory:
             url = f"sqlite:///{Path(directory) / 'connectors.db'}"
@@ -24,7 +53,7 @@ class ConnectorsMigrationTests(unittest.TestCase):
             try:
                 with engine.connect() as connection:
                     self.assertIn(
-                        "c0f1a2b3c4d5",
+                        "d2a4c6e8f0b1",
                         set(MigrationContext.configure(connection).get_current_heads()),
                     )
                     self.assertTrue(