fix(backup): refuse another schema before reading the dump; tests read settings directly (#5815)

- restore_in_place checks the backup's migration heads before pg_restore
  writes anything, so a backup from another schema is refused at once.
- The integration tests read their own setting rows directly:
  get_all_settings knows only Steward's own keys.
- check.py: drop an import left unused by the move to pgdata.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

steward/backup/check.py

@@ -35,7 +35,7 @@ from sqlalchemy.ext.asyncio import create_async_engine
 
 from .contents import (ACTIVITY, ACTIVITY_EVERYWHERE, AREAS, EXCLUDED, HAND_SET_ONLY,
                        STATE_SETTINGS)
-from .dump import BackupError, read_backup
+from .dump import read_backup
 from .pgdata import async_url as _async_url
 from .pgdata import copy_rows, restore_script, script_tables
 

steward/backup/restore.py

@@ -321,17 +321,20 @@ async def restore_in_place(path: Path, database_url: str, *,
     from .contents import ACTIVITY, STATE_SETTINGS
     from .pgdata import restore_script, script_blocks
 
-    with tempfile.TemporaryDirectory() as tmp:
-        info, dump, key = await asyncio.to_thread(read_backup, path, Path(tmp))
-        blocks = script_blocks(await restore_script(dump))
     engine = create_async_engine(_async_url(database_url))
     try:
-        async with engine.connect() as conn:
-            heads = sorted((await conn.execute(text("SELECT version_num FROM alembic_version"))).scalars())
+        # The schema first: a backup that can't go in place is refused before
+        # anything else is read.
+        with tempfile.TemporaryDirectory() as tmp:
+            info, dump, key = await asyncio.to_thread(read_backup, path, Path(tmp))
+            async with engine.connect() as conn:
+                heads = sorted((await conn.execute(text("SELECT version_num FROM alembic_version"))).scalars())
             backup_heads = sorted(info.get("migration_heads") or [])
             schema = schema_of(backup_heads, heads, known_revisions(plugin_dirs))
             if schema != "same":
                 raise NotSameSchema(schema, backup_heads, heads)
+            blocks = script_blocks(await restore_script(dump))
+        async with engine.connect() as conn:
             present = set((await conn.execute(text(
                 "SELECT tablename FROM pg_tables WHERE schemaname = 'public'"))).scalars())
             tables = sorted(t for t in blocks if t not in EXCLUDED and t in present)