feat(backend): add automatic DB migrations

Add a lightweight migration runner with schema_migrations tracking, run pending migrations during backend startup before the scheduler, and keep a manual backend-migrate entrypoint.

The change also moves the existing lockout and task-thread-ID schema steps into shared migration modules, updates docs, and archives the OpenSpec change.

apps/backend/migration_steps/task_thread_id.py

@@ -0,0 +1,98 @@
+from __future__ import annotations
+
+import json
+
+from sqlalchemy import text
+from sqlalchemy.engine import Connection
+
+
+def _table_columns(conn: Connection, table_name: str) -> set[str]:
+    rows = conn.execute(text(f"PRAGMA table_info({table_name})")).fetchall()
+    return {str(row[1]) for row in rows}
+
+
+def _table_indexes(conn: Connection, table_name: str) -> set[str]:
+    rows = conn.execute(text(f"PRAGMA index_list({table_name})")).fetchall()
+    return {str(row[1]) for row in rows}
+
+
+def _has_thread_id_uniqueness(conn: Connection) -> bool:
+    indexes = conn.execute(text("PRAGMA index_list(check_in_tasks)")).fetchall()
+    for row in indexes:
+        is_unique = bool(row[2])
+        if not is_unique:
+            continue
+        index_name = str(row[1])
+        columns = conn.execute(text(f"PRAGMA index_info({index_name})")).fetchall()
+        column_names = [str(column[2]) for column in columns]
+        if column_names == ["user_id", "thread_id"]:
+            return True
+    return False
+
+
+def _extract_thread_id(payload_config: str | None) -> str | None:
+    if not payload_config:
+        return None
+    try:
+        payload = json.loads(payload_config)
+    except json.JSONDecodeError:
+        return None
+    if not isinstance(payload, dict):
+        return None
+    thread_id = payload.get("ThreadId")
+    value = str(thread_id).strip() if thread_id is not None else ""
+    return value or None
+
+
+def apply(conn: Connection) -> None:
+    columns = _table_columns(conn, "check_in_tasks")
+
+    if "thread_id" not in columns:
+        conn.execute(text("ALTER TABLE check_in_tasks ADD COLUMN thread_id VARCHAR(100)"))
+        conn.commit()
+
+    full_rows = conn.execute(
+        text("SELECT id, user_id, payload_config FROM check_in_tasks")
+    ).fetchall()
+    invalid_ids: list[int] = []
+    seen: dict[tuple[int, str], int] = {}
+    duplicate_ids: list[int] = []
+
+    for row in full_rows:
+        thread_id = _extract_thread_id(row.payload_config)
+        if not thread_id:
+            invalid_ids.append(row.id)
+            continue
+        key = (row.user_id, thread_id)
+        if key in seen:
+            duplicate_ids.append(row.id)
+        else:
+            seen[key] = row.id
+
+    if invalid_ids or duplicate_ids:
+        messages = []
+        if invalid_ids:
+            messages.append(f"payload_config 缺少有效 ThreadId 的任务: {invalid_ids}")
+        if duplicate_ids:
+            messages.append(f"同用户 ThreadId 重复的任务: {duplicate_ids}")
+        raise RuntimeError("；".join(messages))
+
+    rows = conn.execute(text("SELECT id, payload_config FROM check_in_tasks")).fetchall()
+    for row in rows:
+        thread_id = _extract_thread_id(row.payload_config)
+        if thread_id:
+            conn.execute(
+                text("UPDATE check_in_tasks SET thread_id = :thread_id WHERE id = :id"),
+                {"thread_id": thread_id, "id": row.id},
+            )
+    conn.commit()
+
+    indexes = _table_indexes(conn, "check_in_tasks")
+    if "ix_task_user_thread_id_unique" not in indexes and not _has_thread_id_uniqueness(conn):
+        conn.execute(
+            text(
+                "CREATE UNIQUE INDEX ix_task_user_thread_id_unique "
+                "ON check_in_tasks (user_id, thread_id)"
+            )
+        )
+        conn.commit()