feat: SyncQueue table and set-based apply stored procedure

- sql/01_sync_queue.sql: idempotent DDL for dbo.SyncQueue (PK + unique
  dedup index + pending lookup index), safe to re-run.
- sql/02_sync_apply.sql: dbo.usp_SyncApply (@MaxRetries INT=5). Per
  distinct (TargetSchema,TargetTable) it builds column projections from
  sys.columns (excludes ID key/computed/identity/rowversion) and runs a
  dynamic-SQL MERGE (last-write-wins via ROW_NUMBER over SourceLogID DESC)
  for Insert/Update plus a DELETE for the last op = Delete.
  SET IDENTITY_INSERT ON preserves Access PKs.
- tests/conftest.py: sql_conn fixture reads conn_str from gitignored
  config.yaml via load_config; skipped without RUN_INTEGRATION=1.
- tests/test_apply_proc.py: integration test covering IDENTITY-preserving
  INSERT, last-write-wins UPDATE, BIT conversion, and DELETE; cleans up.

Deviation from the brief's procedure (root-cause fix, design preserved):
every JSON path key is quoted ('$."col"') so non-ASCII column names
(e.g. Chinese 名字/数量) parse correctly. Without quoting, JSON_VALUE
raises "JSON path format is not correct" on Chinese columns, which is the
real target schema for this Access->SQL Server sync.

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

tests/conftest.py

@@ -0,0 +1,30 @@
+"""Pytest fixtures for the Access -> SQL Server sync integration tests.
+
+Credential safety: the SQL connection string is read from the gitignored
+``config.yaml`` via ``sync.config.load_config``. No password is ever hardcoded
+in a committed file. The ``.sql`` artefacts contain no credentials.
+"""
+import os
+import pytest
+import pyodbc
+
+from sync.config import load_config
+
+
+@pytest.fixture
+def sql_conn():
+    """A pyodbc connection to the CompanyDB SQL Server.
+
+    Skipped unless ``RUN_INTEGRATION=1`` is set. The connection is opened in a
+    transaction (autocommit=False); each test owns its commit/rollback and is
+    responsible for cleaning up any temporary objects it creates.
+    """
+    if not os.environ.get("RUN_INTEGRATION"):
+        pytest.skip("set RUN_INTEGRATION=1 to run SQL integration tests")
+    cfg = load_config("config.yaml")  # gitignored, real creds
+    conn = pyodbc.connect(cfg.sql_server.conn_str, autocommit=False)
+    try:
+        yield conn
+    finally:
+        conn.rollback()
+        conn.close()

tests/test_apply_proc.py

@@ -0,0 +1,81 @@
+"""Integration test for dbo.usp_SyncApply.
+
+Validates: IDENTITY-preserving INSERT, last-write-wins UPDATE, BIT conversion
+from JSON ``true``/``false``, and DELETE of the last op. Creates a throwaway
+schema ``sync_test`` and table ``ApplyDemo_YEAR2026`` and cleans them up at the
+end so no residue is left on CompanyDB.
+"""
+import pytest
+
+
+@pytest.mark.integration
+def test_upsert_insert_update_delete_last_write_wins(sql_conn):
+    cur = sql_conn.cursor()
+    sch, tbl = "sync_test", "ApplyDemo_YEAR2026"
+
+    # --- Arrange: fresh target table + empty queue -------------------------
+    cur.execute("IF SCHEMA_ID('sync_test') IS NULL EXEC('CREATE SCHEMA sync_test')")
+    cur.execute(
+        "IF OBJECT_ID('sync_test.ApplyDemo_YEAR2026') IS NOT NULL "
+        "DROP TABLE sync_test.ApplyDemo_YEAR2026"
+    )
+    cur.execute(
+        "CREATE TABLE sync_test.ApplyDemo_YEAR2026 ("
+        "ID INT IDENTITY(1,1) PRIMARY KEY, "
+        "名字 NVARCHAR(255) NULL, "
+        "数量 INT NULL, "
+        "时间 DATETIME2 NULL, "
+        "标记 BIT NULL)"
+    )
+    cur.execute("DELETE dbo.SyncQueue WHERE TargetSchema='sync_test'")
+
+    # Insert then a later Update for the same RecordID=1 -> last write wins.
+    cur.execute(
+        "INSERT dbo.SyncQueue(SourceFile,SourceTable,SourceLogID,TargetSchema,"
+        "TargetTable,RecordID,OperateType,RowData,Status) "
+        "VALUES('t.accdb','ApplyDemo',1,'sync_test','ApplyDemo_YEAR2026','1',"
+        "'Insert','{\"ID\":1,\"名字\":\"A\",\"数量\":3,\"时间\":\"2026-01-01T00:00:00\",\"标记\":true}','pending')"
+    )
+    cur.execute(
+        "INSERT dbo.SyncQueue(SourceFile,SourceTable,SourceLogID,TargetSchema,"
+        "TargetTable,RecordID,OperateType,RowData,Status) "
+        "VALUES('t.accdb','ApplyDemo',2,'sync_test','ApplyDemo_YEAR2026','1',"
+        "'Update','{\"ID\":1,\"名字\":\"A2\",\"数量\":5,\"时间\":\"2026-01-02T00:00:00\",\"标记\":false}','pending')"
+    )
+    sql_conn.commit()
+
+    # --- Act 1: apply upsert ----------------------------------------------
+    cur.execute("EXEC dbo.usp_SyncApply @MaxRetries=5")
+    sql_conn.commit()
+
+    # --- Assert 1: the later Update wins; BIT false -> 0 ------------------
+    cur.execute("SELECT 名字,数量,标记 FROM sync_test.ApplyDemo_YEAR2026 WHERE ID=1")
+    row = cur.fetchone()
+    assert row is not None, "expected ID=1 to exist after upsert"
+    assert row.名字 == "A2"
+    assert row.数量 == 5
+    assert row.标记 == 0  # BIT false
+
+    # --- Act 2: a later Delete wins ---------------------------------------
+    cur.execute("DELETE dbo.SyncQueue WHERE TargetSchema='sync_test'")
+    cur.execute(
+        "INSERT dbo.SyncQueue(SourceFile,SourceTable,SourceLogID,TargetSchema,"
+        "TargetTable,RecordID,OperateType,RowData,Status) "
+        "VALUES('t.accdb','ApplyDemo',3,'sync_test','ApplyDemo_YEAR2026','1',"
+        "'Delete',NULL,'pending')"
+    )
+    sql_conn.commit()
+    cur.execute("EXEC dbo.usp_SyncApply @MaxRetries=5")
+    sql_conn.commit()
+
+    # --- Assert 2: row removed --------------------------------------------
+    cur.execute("SELECT COUNT(*) FROM sync_test.ApplyDemo_YEAR2026 WHERE ID=1")
+    assert cur.fetchone()[0] == 0
+
+    # --- Cleanup ----------------------------------------------------------
+    cur.execute(
+        "IF OBJECT_ID('sync_test.ApplyDemo_YEAR2026') IS NOT NULL "
+        "DROP TABLE sync_test.ApplyDemo_YEAR2026"
+    )
+    cur.execute("DELETE dbo.SyncQueue WHERE TargetSchema='sync_test'")
+    sql_conn.commit()