get_filtered_book missing eager-load for custom_column_* relationships — DetachedInstanceError when editing book metadata

[captain-marlow]

Describe the bug

When saving book metadata via the edit form, the following error appears if a concurrent CWA background operation (e.g. the ingest watcher triggering a db reconnect) fires during the request:

Error editing book: Parent instance <Books at 0x...> is not bound to a Session;
lazy load operation of attribute 'custom_column_1' cannot proceed

Steps to reproduce

1. Have one or more custom columns defined in the Calibre library (e.g. "Translators", "Editors")
2. Open a book's edit page and save metadata
3. If a db reconnect fires concurrently (ingest watcher, reconnect-db endpoint, etc.), the error occurs

Root cause

get_filtered_book() in cps/db.py uses joinedload to eagerly load all standard relationships (authors, tags, data, series, etc.) specifically to guard against this detached-instance scenario. However, the dynamically-registered custom_column_* relationships are not included in that list. When the session is invalidated before edit_all_cc_data() accesses book.custom_column_1, the lazy-load fails.

Suggested fix

Dynamically add joinedload for each registered custom column relationship in get_filtered_book():

for cc_id in cc_classes:
    cc_rel = getattr(Books, "custom_column_" + str(cc_id), None)
    if cc_rel is not None:
        load_opts.append(joinedload(cc_rel))

Environment

• CWA image: crocodilestick/calibre-web-automated:latest
• Custom columns: text type (but affects all types since all use relationships)

Workaround

Retrying the Save on a book edit works — the error is non-destructive (no data is lost).