* feat(vector-stores): forward per-request params to Vertex AI Search
The vertex_ai/search_api search transform hardcoded the request body to
query plus pageSize 10, dropping max_num_results and extra_body. Map
max_num_results to pageSize and merge extra_body through with precedence,
so callers can send native Discovery Engine fields such as dataStoreSpecs.
Resolves LIT-3506
* fix(vector-stores): log effective query when extra_body overrides it
When a caller passes a query inside extra_body, the outbound Vertex Search
request used that value but model_call_details recorded the original, so the
echoed search_query was stale. Log the effective query from the request body.
* fix(vector-stores): allowlist Vertex AI Search extra_body fields
Raw-merging extra_body let callers set dataStoreSpecs/branch to search a
different Discovery Engine data store with the proxy's Vertex credentials,
bypassing the vector_store_id path authorization. Reject target-selecting
fields and forward only allowlisted per-request tuning fields.
Resolves LIT-3506
* refactor(vector-stores): split Vertex AI Search extra_body allowlists by mode
Data-store and engine/app serving configs accept different SearchRequest
fields, so derive two TypedDicts (VertexSearchDataStoreExtraBody and
VertexSearchEngineExtraBody) in types/vector_stores.py and make
_filter_extra_body mode-aware via vertex_engine_id.
dataStoreSpecs and numResultsPerDataStore now pass through in engine/app
mode (where an app fans out across stores) and are rejected in data-store
mode. branch/servingConfig/entity remain rejected in both modes.
* fix(vector-stores): raise BadRequestError (400) for invalid Vertex Search extra_body
Rejecting unsupported or target-selecting extra_body fields previously
raised a bare ValueError, which the vector store error path mapped to a
generic APIConnectionError (HTTP 500). Raise litellm.BadRequestError so
invalid per-request input surfaces as HTTP 400 with a clear message.
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