From a638c469e08fd9e60541f0a2414e637579dc832b Mon Sep 17 00:00:00 2001
From: Bryan Van Deusen <bryan.vandeusen@fabledsword.com>
Date: Fri, 15 May 2026 15:48:29 -0400
Subject: [PATCH] feat(fc2c-i): migration 0004 enables tsm_system_rows

---
 .../versions/0004_fc2c_i_tsm_system_rows.py   | 23 ++++++++++++++++
 tests/test_migration_0004.py                  | 27 +++++++++++++++++++
 2 files changed, 50 insertions(+)
 create mode 100644 alembic/versions/0004_fc2c_i_tsm_system_rows.py
 create mode 100644 tests/test_migration_0004.py

diff --git a/alembic/versions/0004_fc2c_i_tsm_system_rows.py b/alembic/versions/0004_fc2c_i_tsm_system_rows.py
new file mode 100644
index 0000000..e8bd920
--- /dev/null
+++ b/alembic/versions/0004_fc2c_i_tsm_system_rows.py
@@ -0,0 +1,23 @@
+"""fc2c-i: enable tsm_system_rows for scalable random sampling
+
+Revision ID: 0004
+Revises: 0003
+Create Date: 2026-05-15
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+
+revision: str = "0004"
+down_revision: Union[str, None] = "0003"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.execute("CREATE EXTENSION IF NOT EXISTS tsm_system_rows")
+
+
+def downgrade() -> None:
+    op.execute("DROP EXTENSION IF EXISTS tsm_system_rows")
diff --git a/tests/test_migration_0004.py b/tests/test_migration_0004.py
new file mode 100644
index 0000000..7975d0c
--- /dev/null
+++ b/tests/test_migration_0004.py
@@ -0,0 +1,27 @@
+"""Integration: the tsm_system_rows extension is installed by migration 0004.
+
+Needs a real Postgres (CI does not provision one), so integration-marked.
+"""
+
+import pytest
+from sqlalchemy import text
+
+pytestmark = pytest.mark.integration
+
+
+@pytest.mark.asyncio
+async def test_tsm_system_rows_extension_present(db):
+    row = (
+        await db.execute(
+            text("SELECT 1 FROM pg_extension WHERE extname = 'tsm_system_rows'")
+        )
+    ).first()
+    assert row is not None
+
+
+@pytest.mark.asyncio
+async def test_system_rows_sampling_is_usable(db):
+    # Should parse and execute even on an empty table.
+    await db.execute(
+        text("SELECT * FROM image_record TABLESAMPLE SYSTEM_ROWS(1)")
+    )