fix(backup)!: read the instance from one engine-name set, and trust it

Two shapes fell through the inline regex, which knew `database`, `db` and
`postgres` only. A container named exactly after its engine - what a compose
file writes as `container_name: postgres` - carries no separator before the
token, so it resolved to nothing and 6.0.0 stopped dumping it without saying
so. And a swarm task of a central MariaDB reads `mariadb_mariadb.1.<id>`,
where `_mariadb` was no token at all, so that database has never been dumped
under swarm at all.

ENGINE_NAMES states the set once and serves both readings: carried as a
suffix it makes the rest the instance, being one outright makes the container
its own instance.

backup_mariadb_or_postgres stops calling an application container a database.
container_engine recognises an engine by its client tools, which an
application image often ships, so refusing the dump alone would have recorded
the volume as `database: true, dumped: false` - the exact shape a restore
drill reads as a database that was missed. Without an instance there is no
database to record.

BREAKING CHANGE: `mariadb` and `mysql` join the suffix tokens, so a container
named `<app>-mariadb` resolves to the instance `<app>` rather than to its own
name. A databases.csv keyed on the full container name has to move to the
application name, or name the container in --database-containers.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/baudolo/backup/db.py

@@ -16,13 +16,18 @@ if TYPE_CHECKING:
 
 log = logging.getLogger(__name__)
 
+ENGINE_NAMES = ("database", "postgres", "mariadb", "mysql", "db")
+_SUFFIX_RE = re.compile(rf"(_|-)({'|'.join(ENGINE_NAMES)})")
+
 
 def get_instance(container: str, database_containers: list[str]) -> str | None:
     """The databases.csv instance a container serves, or None for no database.
 
-    A declared container is its own instance. Every other name is normalised by
-    stripping a database suffix token, which maps both `<app>-database` from
-    compose and `<app>_database.1.<task>` from swarm onto the same instance.
+    A declared container is its own instance. Every other name is read against
+    ENGINE_NAMES: carrying one as a suffix makes the rest the instance, which
+    maps `<app>-database` from compose and `<app>_database.1.<task>` from swarm
+    onto the same one; being one outright makes the container its own instance,
+    the shape a compose file writes as `container_name: postgres`.
 
     Args:
         container: the running container's name.
@@ -30,14 +35,16 @@ def get_instance(container: str, database_containers: list[str]) -> str | None:
             declared engines whatever they are called.
 
     Returns:
-        The instance name, or None when the name carries no database token: an
-        application container is not an engine, even when it ships the client
-        tools that would let a dump command start.
+        The instance name, or None when the name neither carries nor is an
+        engine name: an application container is not an engine, even when it
+        ships the client tools that would let a dump command start.
     """
     if container in database_containers:
         return container
-    parts = re.split(r"(_|-)(database|db|postgres)", container)
-    return parts[0] if len(parts) > 1 else None
+    parts = _SUFFIX_RE.split(container)
+    if len(parts) > 1:
+        return parts[0]
+    return container if container in ENGINE_NAMES else None
 
 
 def fallback_pg_dumpall(

src/baudolo/backup/dumps.py

@@ -10,7 +10,7 @@ from pandas.errors import EmptyDataError
 
 from baudolo.databases import COLUMNS, DELIMITER
 
-from .db import backup_database
+from .db import backup_database, get_instance
 from .docker import has_tool, image_id
 
 DUMP_TOOLS: tuple[tuple[str, str], ...] = (
@@ -76,6 +76,8 @@ def backup_mariadb_or_postgres(
     engine = container_engine(container)
     if engine is None:
         return VolumeOutcome(database=False, dumped=False)
+    if get_instance(container, database_containers) is None:
+        return VolumeOutcome(database=False, dumped=False)
     db_type, dump_tool = engine
     dumped = backup_database(
         container=container,

tests/e2e/test_e2e_app_container_ships_client_tools.py

@@ -13,10 +13,11 @@ by its own launcher and ships pg_dumpall, so a dump command starts there and
 writes a file that looks like a backup and holds none of the data.
 """
 
+import json
 import unittest
 from pathlib import Path
 
-from baudolo.generation import DUMP_SUFFIX, FILES_DIR, SQL_DIR
+from baudolo.generation import DUMP_SUFFIX, FILES_DIR, MANIFEST_FILE, SQL_DIR
 
 from .helpers import (
     POSTGRES_DATA_DIR,
@@ -158,6 +159,26 @@ class TestE2EAppContainerShipsClientTools(unittest.TestCase):
         self.assertTrue(marker.is_file(), f"expected a file backup at {marker}")
         self.assertIn(MARKER, marker.read_text(encoding="utf-8"))
 
+    def test_the_manifest_does_not_call_the_application_volume_a_database(self) -> None:
+        manifest = json.loads(
+            (self.volume_dir(self.app_volume).parent / MANIFEST_FILE).read_text(
+                encoding="utf-8"
+            )
+        )
+        entry = manifest["volumes"][self.app_volume]
+        self.assertFalse(entry["database"], entry)
+        self.assertFalse(entry["dumped"], entry)
+
+    def test_the_manifest_records_the_engine_volume_as_dumped(self) -> None:
+        manifest = json.loads(
+            (self.volume_dir(self.engine_volume).parent / MANIFEST_FILE).read_text(
+                encoding="utf-8"
+            )
+        )
+        entry = manifest["volumes"][self.engine_volume]
+        self.assertTrue(entry["database"], entry)
+        self.assertTrue(entry["dumped"], entry)
+
 
 if __name__ == "__main__":
     unittest.main()

tests/unit/backup/test_get_instance.py

@@ -24,12 +24,21 @@ class TestDeclaredContainers(unittest.TestCase):
             get_instance("shop-database", ["shop-database"]), "shop-database"
         )
 
-    def test_an_undeclared_central_engine_resolves_to_nothing(self) -> None:
-        """`postgres-central` has no separator before its token, so nothing is
-        stripped - a central engine has to be declared to be found."""
+    def test_a_qualified_central_name_still_has_to_be_declared(self) -> None:
         self.assertIsNone(get_instance("postgres-central", []))
 
 
+class TestContainersNamedAfterTheirEngine(unittest.TestCase):
+    def test_a_bare_engine_name_is_its_own_instance(self) -> None:
+        for name in ("postgres", "mariadb", "mysql", "db", "database"):
+            with self.subTest(container=name):
+                self.assertEqual(get_instance(name, []), name)
+
+    def test_a_swarm_task_of_such_a_container_keeps_the_instance(self) -> None:
+        self.assertEqual(get_instance("postgres_postgres.1.k3f9x2", []), "postgres")
+        self.assertEqual(get_instance("mariadb_mariadb.1.k3f9x2", []), "mariadb")
+
+
 class TestDedicatedEngines(unittest.TestCase):
     def test_compose_names_the_container_with_a_hyphen(self) -> None:
         self.assertEqual(get_instance("discourse-database", []), "discourse")
@@ -49,6 +58,10 @@ class TestDedicatedEngines(unittest.TestCase):
     def test_mariadb_uses_the_same_suffix(self) -> None:
         self.assertEqual(get_instance("matomo-database", []), "matomo")
 
+    def test_an_engine_named_suffix_is_stripped_too(self) -> None:
+        self.assertEqual(get_instance("shop-mariadb", []), "shop")
+        self.assertEqual(get_instance("shop-mysql", []), "shop")
+
 
 class TestApplicationContainers(unittest.TestCase):
     def test_a_bare_application_name_is_not_a_database(self) -> None: