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_dumps_engine_detection.py

@@ -0,0 +1,138 @@
+import unittest
+from unittest.mock import patch
+
+import pandas
+
+from baudolo.backup import dumps as dumps_mod
+
+
+def _df(rows):
+    return pandas.DataFrame(
+        rows, columns=["instance", "database", "username", "password"]
+    )
+
+
+class _Probe:
+    def __init__(self, available, image="sha256:aaa"):
+        self.available = set(available)
+        self.image = image
+        self.calls = []
+
+    def has_tool(self, container, tool):
+        self.calls.append((container, tool))
+        return tool in self.available
+
+    def image_id(self, container):
+        return self.image if isinstance(self.image, str) else self.image[container]
+
+
+def _detect(probe, container="c1"):
+    dumps_mod._ENGINE_BY_IMAGE.clear()
+    with (
+        patch.object(dumps_mod, "has_tool", probe.has_tool),
+        patch.object(dumps_mod, "image_id", probe.image_id),
+    ):
+        return dumps_mod.container_engine(container)
+
+
+class TestContainerEngine(unittest.TestCase):
+    def test_a_postgres_is_found_by_its_dump_tool(self):
+        self.assertEqual(_detect(_Probe(["pg_dumpall"])), ("postgres", "pg_dumpall"))
+
+    def test_a_mariadb_is_found_by_its_dump_tool(self):
+        self.assertEqual(_detect(_Probe(["mariadb-dump"])), ("mariadb", "mariadb-dump"))
+
+    def test_an_image_with_only_mysqldump_is_dumped_with_mysqldump(self):
+        self.assertEqual(_detect(_Probe(["mysqldump"])), ("mariadb", "mysqldump"))
+
+    def test_a_container_without_either_tool_is_no_database(self):
+        self.assertIsNone(_detect(_Probe([])))
+
+    def test_the_probe_stops_at_the_first_tool_it_finds(self):
+        probe = _Probe(["pg_dumpall", "mariadb-dump"])
+        _detect(probe)
+        self.assertEqual(probe.calls, [("c1", "pg_dumpall")])
+
+    def test_the_image_name_does_not_decide_the_engine(self):
+        """The trap the old substring test fell into, from both directions."""
+        probe = _Probe(["pg_dumpall"], image="svc-db-mariadb-mgr-01:5000/pg_custom")
+        self.assertEqual(_detect(probe), ("postgres", "pg_dumpall"))
+
+        probe = _Probe(["mariadb-dump"], image="discourse-database:17")
+        self.assertEqual(_detect(probe), ("mariadb", "mariadb-dump"))
+
+
+class TestProbeCache(unittest.TestCase):
+    def test_replicas_of_one_image_are_probed_once(self):
+        probe = _Probe(["pg_dumpall"])
+        dumps_mod._ENGINE_BY_IMAGE.clear()
+        with (
+            patch.object(dumps_mod, "has_tool", probe.has_tool),
+            patch.object(dumps_mod, "image_id", probe.image_id),
+        ):
+            first = dumps_mod.container_engine("replica-1")
+            second = dumps_mod.container_engine("replica-2")
+        self.assertEqual(first, second)
+        self.assertEqual(len(probe.calls), 1)
+
+    def test_a_second_image_is_probed_separately(self):
+        probe = _Probe(["pg_dumpall"], image={"pg": "sha256:aaa", "app": "sha256:bbb"})
+        dumps_mod._ENGINE_BY_IMAGE.clear()
+        with (
+            patch.object(dumps_mod, "has_tool", probe.has_tool),
+            patch.object(dumps_mod, "image_id", probe.image_id),
+        ):
+            self.assertEqual(
+                dumps_mod.container_engine("pg"), ("postgres", "pg_dumpall")
+            )
+            probe.available = set()
+            self.assertIsNone(dumps_mod.container_engine("app"))
+
+
+class TestBackupDispatch(unittest.TestCase):
+    def test_the_probed_tool_reaches_the_dump(self):
+        probe = _Probe(["mysqldump"])
+        seen = {}
+
+        def _fake_backup_database(**kwargs):
+            seen.update(kwargs)
+            return True
+
+        dumps_mod._ENGINE_BY_IMAGE.clear()
+        with (
+            patch.object(dumps_mod, "has_tool", probe.has_tool),
+            patch.object(dumps_mod, "image_id", probe.image_id),
+            patch.object(dumps_mod, "backup_database", _fake_backup_database),
+        ):
+            is_db, dumped = dumps_mod.backup_mariadb_or_postgres(
+                container="c1",
+                volume_dir="/tmp",
+                databases_df=_df([("c1", "appdb", "u", "p")]),
+                database_containers=["c1"],
+            )
+
+        self.assertTrue(is_db)
+        self.assertTrue(dumped)
+        self.assertEqual(seen["db_type"], "mariadb")
+        self.assertEqual(seen["dump_tool"], "mysqldump")
+
+    def test_a_non_database_container_is_left_to_the_file_backup(self):
+        probe = _Probe([])
+        dumps_mod._ENGINE_BY_IMAGE.clear()
+        with (
+            patch.object(dumps_mod, "has_tool", probe.has_tool),
+            patch.object(dumps_mod, "image_id", probe.image_id),
+        ):
+            self.assertEqual(
+                dumps_mod.backup_mariadb_or_postgres(
+                    container="c1",
+                    volume_dir="/tmp",
+                    databases_df=_df([]),
+                    database_containers=[],
+                ),
+                (False, False),
+            )
+
+
+if __name__ == "__main__":
+    unittest.main()