fix(client): support protobuf 6 runtimes

[zhengluo-nv]

Summary

• widen the ModelExpress client runtime constraint to protobuf>=5.27,<7
• keep checked-in Python stubs generated with the pinned protobuf-5-era toolchain so they remain usable on both protobuf 5 and 6
• move grpcio-tools out of the test extra into an explicit codegen extra
• run the full Python CI suite against both protobuf 5 and protobuf 6

Why

Current TensorRT-LLM images require protobuf 6.x, while ModelExpress declares protobuf<6. A normal ModelExpress install therefore conflicts with the TRT-LLM runtime or requires --no-deps, leaving compatibility unverified. The generated protobuf 5 bindings already run correctly on protobuf 6; the blocker is the package constraint and same-major-only test guard.

User impact

ModelExpress can be installed normally into qualified TensorRT-LLM images without downgrading their protobuf stack. Existing protobuf 5 users remain supported. Contributors changing p2p.proto use pip install -e ".[codegen]" to preserve dual-runtime bindings.

Validation

• 184 metadata, client, source-selection, publisher, and TRT-LLM tests passed with protobuf 5.29.6
• the same 184 tests passed with protobuf 6.33.6
• protobuf compatibility tests: 11 passed on each major
• source distribution and wheel build succeeded; wheel metadata contains protobuf>=5.27,<7
• uv lock --check
• GitHub workflow YAML parse
• git diff --check

Summary by CodeRabbit

• Compatibility

  • Expanded supported Python protobuf runtime versions to include major versions 5 and 6.
  • Updated compatibility checks to better support generated bindings across supported runtime versions.

• Documentation

  • Clarified installation steps by separating development tools from optional protobuf code-generation tools.
  • Documented supported protobuf version requirements and when code-generation dependencies are needed.

• Testing

  • CI now validates the Python package against multiple supported protobuf versions.

[coderabbitai]

Walkthrough

The Python package now supports protobuf runtime versions 5 and 6, uses protobuf 5 generated bindings, separates code-generation tooling, and tests both runtime versions in CI.

Changes

Protobuf compatibility

Layer / File(s)	Summary
Dependency and code-generation contract .github/workflows/ci.yml, modelexpress_client/python/README.md, modelexpress_client/python/pyproject.toml	The package permits protobuf versions below 7. Code-generation tooling uses a separate codegen extra with grpcio-tools pinned to 1.66.2.
CI runtime compatibility validation .github/workflows/ci.yml, modelexpress_client/python/tests/test_types.py	CI runs the Python tests with protobuf versions 5 and 6. The compatibility test requires protobuf 5 generated bindings and allows runtime major versions 5 or 6.

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

Poem

A rabbit checks the protobuf gate,
Five and six arrive in a matrix state.
Gencode five hops through the test,
Codegen tools wear a pinned vest.
“All green,” says the rabbit, “that’s best!”

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding support for protobuf 6 runtimes.
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.

---

_{Comment @coderabbitai help to get the list of available commands.}

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@modelexpress_client/python/pyproject.toml`:
- Line 31: Raise the protobuf minimum to >=5.27.2 in
modelexpress_client/python/pyproject.toml and
modelexpress_client/python/README.md, and update the protobuf 5 CI constraint in
.github/workflows/ci.yml accordingly. Add a CI job testing protobuf==5.27.2 to
validate the declared minimum version.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: a614398b-6b1e-4441-a3c9-d4ddd22b77da

📥 Commits

Reviewing files that changed from the base of the PR and between a5982b1 and d2af351.

⛔ Files ignored due to path filters (1)

• modelexpress_client/python/uv.lock is excluded by !**/*.lock

📒 Files selected for processing (4)

• .github/workflows/ci.yml
• modelexpress_client/python/README.md
• modelexpress_client/python/pyproject.toml
• modelexpress_client/python/tests/test_types.py

[AndyDai-nv]

lgtm