fix(backup): fallback to file backup in dump-only mode when no DB dump is possible

- Change DB backup helpers to return whether a dump was actually produced
- Detect DB containers without successful dumps in --dump-only mode
- Fallback to file backups with a warning instead of skipping silently
- Refactor DB dump logic to return boolean status
- Add E2E test covering dump-only fallback when databases.csv entry is missing

https://chatgpt.com/share/6951a659-2b0c-800f-aafa-3e89ae1eb697

src/baudolo/backup/db.py

@@ -3,9 +3,8 @@ from __future__ import annotations
 import os
 import pathlib
 import re
-
-import pandas
 import logging
+import pandas
 
 from .shell import BackupException, execute_shell_command
 
@@ -18,9 +17,7 @@ def get_instance(container: str, database_containers: list[str]) -> str:
     return re.split(r"(_|-)(database|db|postgres)", container)[0]
 
 
-def fallback_pg_dumpall(
-    container: str, username: str, password: str, out_file: str
-) -> None:
+def fallback_pg_dumpall(container: str, username: str, password: str, out_file: str) -> None:
     cmd = (
         f"PGPASSWORD={password} docker exec -i {container} "
         f"pg_dumpall -U {username} -h localhost > {out_file}"
@@ -35,20 +32,25 @@ def backup_database(
     db_type: str,
     databases_df: "pandas.DataFrame",
     database_containers: list[str],
-) -> None:
+) -> bool:
+    """
+    Returns True if at least one dump file was produced, else False.
+    """
     instance_name = get_instance(container, database_containers)
     entries = databases_df.loc[databases_df["instance"] == instance_name]
     if entries.empty:
-        log.warning("No entry found for instance '%s'", instance_name)
-        return
+        log.warning("No entry found for instance '%s' (skipping DB dump)", instance_name)
+        return False
 
     out_dir = os.path.join(volume_dir, "sql")
     pathlib.Path(out_dir).mkdir(parents=True, exist_ok=True)
 
-    for row in entries.iloc:
-        db_name = row["database"]
-        user = row["username"]
-        password = row["password"]
+    produced = False
+
+    for row in entries.itertuples(index=False):
+        db_name = row.database
+        user = row.username
+        password = row.password
 
         dump_file = os.path.join(out_dir, f"{db_name}.backup.sql")
 
@@ -58,13 +60,15 @@ def backup_database(
                 f"-u {user} -p{password} {db_name} > {dump_file}"
             )
             execute_shell_command(cmd)
+            produced = True
             continue
 
         if db_type == "postgres":
             cluster_file = os.path.join(out_dir, f"{instance_name}.cluster.backup.sql")
+
             if not db_name:
                 fallback_pg_dumpall(container, user, password, cluster_file)
-                return
+                return True
 
             try:
                 cmd = (
@@ -72,6 +76,7 @@ def backup_database(
                     f"pg_dump -U {user} -d {db_name} -h localhost > {dump_file}"
                 )
                 execute_shell_command(cmd)
+                produced = True
             except BackupException as e:
                 print(f"pg_dump failed: {e}", flush=True)
                 print(
@@ -79,4 +84,7 @@ def backup_database(
                     flush=True,
                 )
                 fallback_pg_dumpall(container, user, password, cluster_file)
+                produced = True
             continue
+
+    return produced