feat(manifest)!: record per volume what the run established

A finished generation cannot show whether a volume held a database, nor whether a dump was produced for it: under --only-sql a failed dump falls back to a file copy, and the resulting files/ tree looks like any other copy. The run knows both and threw the knowledge away as a printed warning, leaving every reader to guess from file names.

Each generation now carries a manifest.json stating its layout and, per volume, database / dumped / engine. baudolo.generation is the single place those names are spelled; restore/paths.py, backup/db.py and backup/volume.py stop repeating them. It is deliberately import-free so a consumer can read the manifest with nothing but json, on hosts where this package is not installed.

BREAKING CHANGE: BackupException is renamed BackupError. The rename is atomic across the ten modules that define or import it, three of which also carry the manifest change, so it lands in this commit rather than a separate one that could not import.

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

src/baudolo/backup/app.py

@@ -2,9 +2,9 @@
 
 from __future__ import annotations
 
-import os
 from contextlib import ExitStack
 from datetime import datetime
+from pathlib import Path
 
 from .cli import parse_args
 from .compose import handle_docker_compose_services
@@ -14,12 +14,13 @@ from .docker import (
     docker_volume_names,
     filter_stoppable,
 )
-from .dumps import backup_dumps_for_volume, load_databases_df
+from .dumps import VolumeOutcome, backup_dumps_for_volume, load_databases_df
 from .layout import (
     create_version_directory,
     create_volume_directory,
     get_machine_id,
     stamp_directory,
+    write_manifest,
 )
 from .policy import requires_stop, volume_is_fully_ignored
 from .snapshot import snapshot_source, volume_snapshot
@@ -34,13 +35,15 @@ def main() -> int:
     # order new ones before the existing ones wherever the offset is positive.
     backup_time = datetime.now().strftime("%Y%m%d%H%M%S")  # noqa: DTZ005
 
-    versions_dir = os.path.join(args.backups_dir, machine_id, args.repo_name)
+    versions_dir = str(Path(args.backups_dir) / machine_id / args.repo_name)
     version_dir = create_version_directory(versions_dir, backup_time)
 
     databases_df = None if args.only_files else load_databases_df(args.databases_csv)
 
     print("💾 Start volume backups...", flush=True)
 
+    outcomes: dict[str, VolumeOutcome] = {}
+
     with ExitStack() as stack:
         resolve_source = None
         if args.snapshot:
@@ -69,17 +72,18 @@ def main() -> int:
 
             vol_dir = create_volume_directory(version_dir, volume_name)
 
-            found_db = dumped_any = False
+            outcome = VolumeOutcome(database=False, dumped=False)
             if not args.only_files:
-                found_db, dumped_any = backup_dumps_for_volume(
+                outcome = backup_dumps_for_volume(
                     containers=containers,
                     vol_dir=vol_dir,
                     databases_df=databases_df,
                     database_containers=args.database_containers,
                 )
+            outcomes[volume_name] = outcome
 
-            if args.only_sql and found_db:
-                if not dumped_any:
+            if args.only_sql and outcome.database:
+                if not outcome.dumped:
                     print(
                         f"WARNING: only-sql requested but no DB dump was produced for DB volume '{volume_name}'. "
                         "Falling back to file backup.",
@@ -129,6 +133,7 @@ def main() -> int:
                 if not args.shutdown:
                     change_containers_status(stoppable, "start")
 
+    write_manifest(version_dir, outcomes)
     stamp_directory(version_dir)
     print("Finished volume backups.", flush=True)