fix: drop latin-1 decode in source title and userIds

[kyteinsky]

fixing this issue:

2026-05-28T07:53:19+0000: [ERROR|utils]: original traceback of embed_sources (PID 22239, exitcode: 0): Traceback (most recent call last):
  File "/app/context_chat_backend/utils.py", line 138, in exception_wrap
    value = None if fun is None else fun(*args, **kwargs)
                                     ^^^^^^^^^^^^^^^^^^^^
  File "/app/context_chat_backend/chain/ingest/injest.py", line 407, in embed_sources
    'source_ids': [
                  ^
  File "/app/context_chat_backend/chain/ingest/injest.py", line 408, in <listcomp>
    f'{source.reference} ({_decode_latin_1(source.title)})'
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/context_chat_backend/chain/ingest/injest.py", line 395, in _decode_latin_1
    return s.encode('latin-1').decode('utf-8')
           ^^^^^^^^^^^^^^^^^^^
UnicodeEncodeError: 'latin-1' codec can't encode character '\u2013' in position 27: ordinal not in range(256)

[marcelklehr]

So we encode a string in latin-1 and decode using utf-8 again. Why do we do that?

[kyteinsky]

I had forgotten too 🙈
blaming the lines points to this issue for which the fix was made: #71
and it was probably related to the issue that the title was transported from context_chat PHP to backend in the headers which only support latin-1 mostly, finding back the sources for it, these two links pop up:
python/cpython#105505 (comment)
https://stackoverflow.com/questions/4400678/what-character-encoding-should-i-use-for-a-http-header/4410331#4410331

now that we don't have that limitation after reversal of the indexing direction, it can be dropped.

thanks for the enquiry :)

[kyteinsky]

after dropping the conversion, it seems to work fine:

ccb=# select cmetadata from langchain_pg_embedding ;
                                                   cmetadata                                                    
----------------------------------------------------------------------------------------------------------------
 {"type": "application/pdf", "title": "files/河马.pdf", "source": "files__default: 19455", "start_index": 0}
 {"type": "application/pdf", "title": "files/河马.pdf", "source": "files__default: 19455", "start_index": 1365}
 {"type": "application/pdf", "title": "files/河马.pdf", "source": "files__default: 19455", "start_index": 2907}
 {"type": "application/pdf", "title": "files/河马.pdf", "source": "files__default: 19455", "start_index": 4138}
 {"type": "application/pdf", "title": "files/河马.pdf", "source": "files__default: 19455", "start_index": 5963}
 {"type": "application/pdf", "title": "files/河马.pdf", "source": "files__default: 19455", "start_index": 7259}
(6 rows)