feat: sql writer with dedup insert and apply call

Adds SqlWriter: a pyodbc-backed writer that dedup-inserts into
dbo.SyncQueue (IF NOT EXISTS guarded by UX_SyncQueue_Dedup), invokes
dbo.usp_SyncApply, and reports applied SourceLogIDs.

Connection is opened with autocommit=True per the controller revision:
usp_SyncApply manages its own transaction internally (BEGIN/ROLLBACK),
and an outer pyodbc transaction would conflict on ROLLBACK (SQL error
266). The dedup IF NOT EXISTS...INSERT is a single atomic statement.

Integration test self-cleans via SourceFile='sqlw_test.accdb' marker;
conn_str comes from the gitignored config.yaml (no hardcoded creds).

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

tests/test_sql_writer.py

@@ -0,0 +1,55 @@
+"""Integration test for sync.sql_writer.SqlWriter.
+
+Validates the dedup INSERT (same SourceLogID is only ever enqueued once), the
+``applied_log_ids`` query (rows flipped to ``applied`` come back in order), and
+that ``call_apply`` invokes the proc without raising.
+
+conn_str is read from the gitignored ``config.yaml`` via ``load_config``; no
+credentials are hardcoded here. The test self-cleans using a throwaway
+``SourceFile='sqlw_test.accdb'`` marker so no residue is left on SyncQueue.
+"""
+import os
+import pytest
+
+from sync.sql_writer import SqlWriter, QueueRow
+from sync.config import load_config
+
+
+@pytest.mark.integration
+def test_insert_dedup_and_applied_ids():
+    if not os.environ.get("RUN_INTEGRATION"):
+        pytest.skip("integration")
+    cfg = load_config("config.yaml")
+    w = SqlWriter(cfg.sql_server.conn_str, "dbo.SyncQueue")
+    try:
+        cur = w._conn.cursor()
+        cur.execute("DELETE dbo.SyncQueue WHERE SourceFile='sqlw_test.accdb'")
+        qr = QueueRow(
+            source_file="sqlw_test.accdb",
+            source_table="T",
+            record_id="7",
+            target_schema="sync_test",
+            target_table="T_YEAR2026",
+            source_log_id=100,
+            operate_type="Insert",
+            row_data='{"ID":7}',
+        )
+        w.insert_queue_row(qr)
+        w.insert_queue_row(qr)  # duplicate must be deduped (ignored)
+        cur.execute(
+            "SELECT COUNT(*) FROM dbo.SyncQueue "
+            "WHERE SourceFile='sqlw_test.accdb' AND SourceLogID=100"
+        )
+        assert cur.fetchone()[0] == 1
+
+        # call_apply must run without error (proc logic validated elsewhere).
+        w.call_apply(max_retries=5)
+
+        cur.execute(
+            "UPDATE dbo.SyncQueue SET Status='applied' "
+            "WHERE SourceFile='sqlw_test.accdb'"
+        )
+        assert w.applied_log_ids("sqlw_test.accdb") == [100]
+    finally:
+        cur.execute("DELETE dbo.SyncQueue WHERE SourceFile='sqlw_test.accdb'")
+        w.close()