Fix distributed (multi-GPU) PDLP dispatch for the gRPC server

[ramakrishnap-nv]

The gRPC worker built its GPU problem directly and called the base solve_lp overload, which has no distributed dispatch at all (unlike the C API path fixed in #1958). This routes run_lp_solve through the mps_data_model_t based overload when distributed PDLP is requested, and adds use_distributed_pdlp/distributed_pdlp_partitioner to the gRPC field registry so they can be set over the wire (proto message, converters, and MCP schema regenerated; num_gpus was already present).

Verified: GRPC_CLIENT_TEST mapper round-trip tests pass locally, including the extended PDLPSettingsAllFields case.

Related to #1931, and complements #1957/#1961/#1958.

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📝 Walkthrough

Walkthrough

Changes

The PR adds distributed PDLP settings and partitioner values. Eligible solves use the distributed solve_lp overload. gRPC tests verify that the new settings survive proto conversion.

Distributed PDLP support

Layer / File(s)	Summary
Distributed PDLP settings contract cpp/src/grpc/codegen/field_registry.yaml, cpp/tests/linear_programming/grpc/grpc_client_test.cpp	The settings registry adds distributed PDLP enablement and partitioner selection. The round-trip test verifies the RoundRobin value.
Distributed solve routing cpp/src/grpc/server/grpc_worker.cpp	run_lp_solve routes distributed PDLP configurations through the host-resident mps_data_model_t overload. Other LP configurations retain the existing overload.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Suggested reviewers: mlubin

Merge Risk: 🟡 Moderate · up to fd830

The routing fix appears consistent with solver semantics, but its multi-GPU gRPC behavior lacks the required regression coverage and should be tested before merging.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files. (1 skipped: 1…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: correcting distributed multi-GPU PDLP dispatch in the gRPC server.
Description check	✅ Passed	The description directly explains the dispatch fix, the added gRPC settings, regenerated artifacts, and test coverage. It is relevant to the changeset.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files. (1 skipped: 1 unsupported.)

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Inline comments:
In `@cpp/tests/linear_programming/grpc/grpc_client_test.cpp`:
- Around line 2280-2281: Add a server-dispatch regression test near the existing
mapper test that configures method_t::PDLP, enables use_distributed_pdlp, and
supplies an eligible GPU count, then invokes the RPC or worker dispatch path and
asserts the distributed solve succeeds. Keep the existing protobuf-mapping
coverage unchanged, and ensure the test exercises run_lp_solve through the
method-based dispatch rather than only the problem-based overload.

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📥 Commits

Reviewing files that changed from the base of the PR and between fae0b3c and fd830cd.

⛔ Files ignored due to path filters (5)

• cpp/src/grpc/codegen/generated/cuopt_mcp_schema.json is excluded by !**/generated/**
• cpp/src/grpc/codegen/generated/cuopt_remote_data.proto is excluded by !**/generated/**
• cpp/src/grpc/codegen/generated/generated_enum_converters_settings.inc is excluded by !**/generated/**
• cpp/src/grpc/codegen/generated/generated_pdlp_settings_to_proto.inc is excluded by !**/generated/**
• cpp/src/grpc/codegen/generated/generated_proto_to_pdlp_settings.inc is excluded by !**/generated/**

📒 Files selected for processing (3)

• cpp/src/grpc/codegen/field_registry.yaml
• cpp/src/grpc/server/grpc_worker.cpp
• cpp/tests/linear_programming/grpc/grpc_client_test.cpp

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