fix(backup): detect the engine by its dump tool, not by the image name

36b2336 matched postgres and mariadb against the image's repository path. That name is not a property of the software: a dedicated Postgres inside an app's own stack is tagged <app>-database or postgis/postgis and carries no engine token at all, so it was never recognised, never dumped, and its data directory was copied as files without a single warning - the fallback notice hangs on found_db, which stayed false.

The container is now asked what it can run. pg_dumpall, mariadb-dump and mysqldump are probed by executing them, not by asking a shell for them, because a distroless image has no shell and would deny every tool it ships. The verdict is cached per image ID rather than per container, so replicas of one image cost a single probe.

Because the probe names the tool it found, the dump uses it instead of the hardcoded /usr/bin/mariadb-dump, which makes an image that ships only mysqldump dumpable rather than silently file-copied.

image_name and has_image are gone with their registry-host and tag stripping; the trap they worked around cannot occur when nothing reads the name. get_image_info stays, since the --images-* lists match exact references.

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

tests/unit/backup/test_db_mariadb_dump.py

@@ -13,7 +13,7 @@ def _df(rows):
     )
 
 
-def _capture_commands(*, db_type, rows, container):
+def _capture_commands(*, db_type, rows, container, dump_tool="mariadb-dump"):
     captured = []
 
     def _capture(cmd):
@@ -28,6 +28,7 @@ def _capture_commands(*, db_type, rows, container):
             container=container,
             volume_dir=td,
             db_type=db_type,
+            dump_tool=dump_tool,
             databases_df=_df(rows),
             database_containers=[container],
         )
@@ -57,6 +58,19 @@ class TestMariaDBDumpUsesTCP(unittest.TestCase):
         self.assertIn("-ps3cret", cmd)
         self.assertIn(" appdb", cmd)
 
+    def test_the_probed_client_is_the_one_invoked(self):
+        captured = _capture_commands(
+            db_type="mariadb",
+            rows=[("mariadb", "appdb", "appuser", "s3cret")],
+            container="mariadb",
+            dump_tool="mysqldump",
+        )
+        dump_cmds = [c for c in captured if "mysqldump" in c]
+        self.assertEqual(
+            len(dump_cmds), 1, f"expected one dump command, got: {captured}"
+        )
+        self.assertNotIn("mariadb-dump", dump_cmds[0])
+
     def test_postgres_dump_unaffected(self):
         captured = _capture_commands(
             db_type="postgres",