* fix(proxy): link passthrough success spans to the SERVER root OTEL span
Passthrough requests never wired user_api_key_dict.parent_otel_span into the
logging metadata, so on success the litellm_request span orphaned into its own
trace and the "Received Proxy Server Request" root span was never ended. Setting
it once in _init_kwargs_for_pass_through_endpoint fixes both the non-streaming
and streaming paths, since update_environment_variables copies that metadata onto
the logging object's model_call_details, which is what the OTEL handler reads.
Resolves LIT-3443
* fix(proxy): set passthrough parent span after client metadata merge
Greptile flagged that litellm_parent_otel_span was assigned before the
_metadata.update() calls that merge request-body metadata, so a client body
mirroring the internal key could overwrite the real span with a JSON scalar
and null the fix for that request. Move the assignment after the merge and
add a regression test that fails on the old ordering.
* fix(proxy): also set user_api_key after client metadata merge
Per Greptile, user_api_key had the same clobber window as the parent span: a
passthrough request body mirroring the key could overwrite the authenticated
value in the logged metadata. Move it into the same post-merge block and add a
deterministic contract test asserting both internal keys resist client-supplied
metadata.
c754c560dd