Fix 3,063 lists with subjects failing to index into solr

[cdrini]

Part of #11650

Was noticing errors for some lists that had subjects without the "/subjects" prefix.

Technical

Was noticing errors of this nature during the reindex:

2026-06-07 11:50:01,966 [ERROR] Failed to update '/people/serenahm/lists/OL131113L'
Traceback (most recent call last):
  File "openlibrary/solr/update.py", line 123, in openlibrary.solr.update.update_keys
  File "/openlibrary/openlibrary/solr/updater/list.py", line 28, in update_key
    lst = ListSolrBuilder(list, await fetch_seeds_facets(seeds))
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/openlibrary/openlibrary/solr/updater/list.py", line 39, in fetch_seeds_facets
    seeds_by_type[seed_key_to_seed_type(seed)].append(seed)
                  ~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/openlibrary/openlibrary/plugins/openlibrary/lists.py", line 194, in seed_key_to_seed_type
    match key.split("/")[1]:
          ~~~~~~~~~~~~~~^^^
IndexError: list index out of range

Testing

Screenshot

Stakeholders

[Copilot]

Pull request overview

This PR addresses Solr reindex failures for certain lists whose seed subjects are stored as subject pseudo-keys (e.g. subject:foo, place:bar) rather than /subjects/... paths, preventing errors during list indexing in the Solr updater.

Changes:

• Harden seed_key_to_seed_type() to handle empty/non-path seed formats instead of crashing on key.split("/")[1].
• Update list Solr faceting to skip/log unrecognized seed key types rather than failing the whole update.
• Add parametrized tests covering supported and invalid seed key formats.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
openlibrary/solr/updater/list.py	Adds warning + skip logic for invalid/unknown seed keys during seed facet grouping.
openlibrary/plugins/openlibrary/tests/test_lists.py	Adds parametrized tests for seed_key_to_seed_type() behavior across multiple seed formats.
openlibrary/plugins/openlibrary/lists.py	Adds validation/branching in seed_key_to_seed_type() to avoid IndexError on non-path seed formats.