fix(packaging): include prefill-router in the Python sdist

[nachiketb-nvidia]

What

• Include the optional prefill-router crate and the pinned Rust toolchain in Python source distributions.
• Smoke install the generated source distribution before it can be uploaded.

Why

The generated archive contained switchyard-runner, but omitted its local prefill-router dependency. Cargo therefore failed during package metadata generation. The archive also omitted the repository's pinned toolchain, which could leave clean builds below the declared Rust version.

How

Maturin now includes only the prefill crate files needed to resolve and build the workspace dependency. The existing source-distribution job installs its generated archive in an isolated Python 3.10 environment and imports the native extension.

Validation

• Built nemo_switchyard-0.2.0.tar.gz with Maturin.
• Confirmed the archive contains the prefill manifest, build script, Rust sources, embedded Python source, and rust-toolchain.toml.
• Installed that archive outside the checkout in an isolated Python 3.10 environment.
• Imported switchyard_rust._switchyard_rust from the installed archive.
• actionlint passed for the release workflow.

Fixes SWITCH-1427.

Summary by CodeRabbit

• Chores

  • Source distributions now include all required build configuration and source files, improving reliability when building from source.

• Tests

  • Added an automated smoke test that installs the source distribution in an isolated Python environment and verifies the compiled extension can be imported successfully.

[github-actions]

PR Preview Action v1.8.1
🚀 View preview at https://NVIDIA-NeMo.github.io/Switchyard/pr-preview/pr-706/
Built to branch gh-pages at 2026-09-15 18:56 UTC. Preview will be ready when the GitHub Pages deployment is complete.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 3807ff0 and 9615475.

📒 Files selected for processing (2)

• .github/workflows/publish.yml
• pyproject.toml

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Walkthrough

The source distribution now includes required Rust build inputs. The publish workflow smoke-installs the distribution in isolated Python 3.10 and imports the Rust extension before upload.

Changes

Source Distribution Validation

Layer / File(s)	Summary
Source distribution build inputs pyproject.toml	The maturin source distribution includes the Rust toolchain and prefill-router files.
Source distribution smoke installation .github/workflows/publish.yml	The workflow installs the source distribution in isolated Python 3.10 and imports switchyard_rust._switchyard_rust.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to 96154

The source distribution includes the required build inputs and is smoke-installed and imported in isolation before upload.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 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: including the optional prefill-router crate in the Python source distribution.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
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.

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_{A rabbit packs the Rust files tight
Into the source bundle overnight
Python hops into a clean new pen
The extension loads, then hops again
The publish path shines bright with delight}

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