feat(backup): write database dumps gzip-compressed

Dumps stream through gzip into <db>.backup.sql.gz; no uncompressed copy touches the disk. Restore reads gzip and plain dumps by their magic bytes, verifies a gzip dump to its end before anything is dropped, and still finds the uncompressed names of older generations. The manifest names the compression.

🎯 Fix: 92 %
💥 Break: 20 %
💸 Cost: –
⏱️ Time: –
🛡️ Security: ~100 %
🏆 Score: 74
🚦 Gate: ⛔ break 20 % > 5

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

tests/e2e/test_e2e_only_sql_fallback_to_files.py

@@ -1,14 +1,24 @@
 import json
 import unittest
 
-from baudolo.generation import FILES_DIR, MANIFEST_FILE, MANIFEST_SCHEMA, SQL_DIR
+from baudolo.generation import (
+    CLUSTER_SUFFIX,
+    DUMP_COMPRESSION,
+    DUMP_SUFFIX,
+    FILES_DIR,
+    MANIFEST_FILE,
+    MANIFEST_SCHEMA,
+    SQL_DIR,
+)
 
 from .helpers import (
     POSTGRES_DATA_DIR,
     POSTGRES_IMAGE,
+    assert_dumps_in_sees_both_suffixes,
     backup_path,
     cleanup_docker,
     create_minimal_compose_dir,
+    dumps_in,
     ensure_empty_dir,
     latest_version_dir,
     require_docker,
@@ -143,7 +153,7 @@ class TestE2EOnlySqlFallbackToFiles(unittest.TestCase):
         self.assertTrue(p.is_dir(), f"Expected files backup dir at: {p}")
 
     def test_sql_dump_not_present(self) -> None:
-        # There should be no sql dumps because databases.csv had no matching entry.
+        assert_dumps_in_sees_both_suffixes(self, f"/tmp/{self.prefix}")
         sql_dir = (
             backup_path(
                 self.backups_dir,
@@ -151,16 +161,10 @@ class TestE2EOnlySqlFallbackToFiles(unittest.TestCase):
                 self.version,
                 self.pg_volume,
             )
-            / "sql"
+            / SQL_DIR
         )
-        # Could exist (dir created) in some edge cases, but should contain no *.sql dumps.
-        if sql_dir.exists():
-            dumps = list(sql_dir.glob("*.sql"))
-            self.assertEqual(
-                len(dumps),
-                0,
-                f"Did not expect SQL dump files, found: {dumps}",
-            )
+        dumps = dumps_in(sql_dir)
+        self.assertEqual(dumps, [], f"Did not expect SQL dump files, found: {dumps}")
 
     def manifest(self) -> dict:
         generation = backup_path(
@@ -183,6 +187,9 @@ class TestE2EOnlySqlFallbackToFiles(unittest.TestCase):
         self.assertTrue((volume_dir / layout["files_dir"]).is_dir())
         self.assertEqual(layout["files_dir"], FILES_DIR)
         self.assertEqual(layout["sql_dir"], SQL_DIR)
+        self.assertEqual(layout["dump_suffix"], DUMP_SUFFIX)
+        self.assertEqual(layout["cluster_suffix"], CLUSTER_SUFFIX)
+        self.assertEqual(layout["dump_compression"], DUMP_COMPRESSION)
 
     def test_the_manifest_states_a_schema_a_reader_can_check(self) -> None:
         self.assertEqual(self.manifest()["schema"], MANIFEST_SCHEMA)