Fix Helm reranker endpoint configuration

[nvwizhu]

Description

The Retriever service supports nim_endpoints.rerank_invoke_url and nim_endpoints.rerank_model_name, but the Helm chart did not expose or render corresponding values. As a result, reranker settings supplied through Helm were not included in retriever-service.yaml, and /v1/query requests with rerank=true could return HTTP 400.

This change:

• adds serviceConfig.nimEndpoints.rerankInvokeUrl and serviceConfig.nimEndpoints.rerankModelName
• renders them as nim_endpoints.rerank_invoke_url and nim_endpoints.rerank_model_name
• covers standalone and all split service ConfigMaps
• fails Helm rendering when a model is configured without a reranker URL
• adds structured Helm render regression coverage and documents the two values

Validation

• helm lint --strict nemo_retriever/helm
• pytest -q nemo_retriever/tests/test_helm_rerank_endpoint.py — 5 passed
• full Helm and Helm harness test suite — 171 passed, 32 subtests passed
• git diff --check

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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[greptile-apps]

Greptile Summary

The PR exposes remote reranker endpoint and model settings through Helm, renders them into every service topology, and rejects model-only configurations before deployment.

• Adds reranker URL and model defaults and documentation.
• Renders both fields in standalone and split ConfigMaps.
• Adds regression coverage for supported configurations and the invalid model-only case.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains; the prior model-only configuration now fails during Helm rendering for both missing and whitespace-only endpoints.

Important Files Changed

Filename	Overview
nemo_retriever/helm/templates/configmap.yaml	Renders reranker settings across all service ConfigMaps and fail-fast rejects the previously reported model-only configuration.
nemo_retriever/helm/values.yaml	Adds empty defaults for the two new user-configurable reranker values.
nemo_retriever/helm/README.md	Documents the endpoint/model relationship and explicitly states that the endpoint is not auto-resolved.
nemo_retriever/tests/test_helm_rerank_endpoint.py	Covers standalone and split rendering, URL-only configuration, and absent or whitespace-only endpoints paired with a model.

_{Reviews (2): Last reviewed commit: "Validate Helm reranker model configurati..." | Re-trigger Greptile}