Fix Rust and C++ release verification regressions

[codeshaunted]

Summary

• make the canonical C++ variant template compile under MSVC by isolating the nested pack expansion
• build only the runtime_smoke CMake target so verification does not compile unused full protobuf targets
• derive Rust verifier runners from the toolchain platform contract, matching the glibc used by shipped CLI artifacts
• run generated Rust sync calls outside the Tokio runtime while still exercising the async entry point

Fixes the Rust and C++ failures in https://github.com/BoundaryML/baml/actions/runs/29884885305.

Testing

• actionlint .github/workflows/verify-rust-sdk.reusable.yaml .github/workflows/verify-cpp-sdk.reusable.yaml
• RUSTC_WRAPPER= cargo test -p baml_release platforms --locked (9 passed)
• canonical/deduplicated baml::variant C++17 compile smoke
• configured protobuf 31.1 and built the exact runtime_smoke CMake target
• pre-commit hooks, including Cargo fmt, Clang format, Clippy, and YAML validation

Summary by CodeRabbit

• Tests
  • Improved C++ SDK verification by enforcing a 10-minute timeout and explicitly building the runtime_smoke target for Unix/musl/Windows, running the Release binary on Windows.
  • Improved Rust SDK verification by generating the platform matrix dynamically.
  • Enhanced the C++ runtime smoke harness with stronger failure reporting and clearer progress output.
  • Stabilized the Rust consumer smoke entry point by switching to a synchronous main.
• Refactor
  • Refined internal C++ variant type canonicalization (no behavior change).
• Chores
  • Updated protobuf FetchContent to align MSVC runtime behavior with downstream consumers.

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Project	Deployment	Actions	Updated (UTC)
beps	Ready	Preview, Comment	Jul 22, 2026 6:02am
promptfiddle	Ready	Preview, Comment	Jul 22, 2026 6:02am
promptfiddle2	Ready	Preview, Comment	Jul 22, 2026 6:02am

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 04b870d0-c3d1-4d68-9565-bf90957157ca

📥 Commits

Reviewing files that changed from the base of the PR and between 32cf365 and 828157d.

📒 Files selected for processing (3)

• .github/workflows/verify-cpp-sdk.reusable.yaml
• baml_language/sdks/cpp/bridge_cpp/include/baml/detail/loader.h
• baml_language/sdks/cpp/bridge_cpp/tests/runtime_smoke.cc

---

📝 Walkthrough

Walkthrough

C++ SDK smoke builds explicitly select runtime_smoke across platforms, use updated runtime loading and failure reporting, and align protobuf linkage. Rust verification derives its matrix from release metadata, adds an MSRV entry, and uses a manually constructed Tokio runtime.

Changes

SDK verification

Layer / File(s)	Summary
C++ runtime verification .github/workflows/verify-cpp-sdk.reusable.yaml, baml_language/sdks/cpp/bridge_cpp/tests/run.sh, baml_language/sdks/cpp/bridge_cpp/tests/runtime_smoke.cc	C++ verification explicitly builds runtime_smoke on supported environments, enforces a 10-minute timeout, and reports smoke-test progress while replacing assertions with runtime checks.
C++ runtime compatibility baml_language/sdks/cpp/bridge_cpp/include/baml/detail/loader.h, baml_language/sdks/cpp/bridge_cpp/cmake/fetch_protobuf.cmake, baml_language/sdks/cpp/bridge_cpp/include/baml/variant.h	The loader uses platform-specific symbol resolution, protobuf uses the dynamic MSVC runtime, and canonical variant type aliases are reused during type construction.
Dynamic Rust verification matrix .github/workflows/verify-rust-sdk.reusable.yaml	A platform-matrix job derives eligible Linux and macOS targets from release/platforms.json, adds the Rust 1.91.1 MSRV entry, and supplies the matrix to verify.
Synchronous Rust consumer runtime baml_language/sdks/rust/verify/consumer_main.rs	The consumer changes to synchronous main and executes rt_int_async with a current-thread Tokio runtime and block_on.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Sequence Diagram(s)

sequenceDiagram
  participant platform_matrix
  participant platforms_json
  participant verify
  participant consumer_main
  platform_matrix->>platforms_json: Read release platform metadata
  platforms_json-->>platform_matrix: Return eligible verification entries
  platform_matrix->>verify: Supply JSON matrix
  verify->>consumer_main: Run Rust consumer checks
  consumer_main->>consumer_main: block_on rt_int_async

Loading

Possibly related PRs

• BoundaryML/baml#4004: Modifies the C++ SDK verification workflow and runtime_smoke build/run steps.
• BoundaryML/baml#4033: Introduces the Rust bridge verification flow extended by the dynamic matrix changes.
• BoundaryML/baml#4041: Defines the versioned CFFI function-table ABI used by the updated C++ loader.

Poem

A bunny builds smoke tests bright,
Through Unix, musl, Windows night.
Rust hops through matrices anew,
Tokio runs its task right through.
Hoppy reviews make SDKs glow!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% 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 matches the main change: fixing Rust and C++ release verification regressions.
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.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/rust-cpp-release-verification

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 Checkov (3.3.8)

.github/workflows/verify-cpp-sdk.reusable.yaml

Traceback (most recent call last):
File "/usr/local/bin/checkov", line 2, in
from checkov.main import Checkov
ModuleNotFoundError: No module named 'checkov'

---

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[github-actions]

⏭️ Performance benchmarks were skipped

Perf benchmarks (CodSpeed) are opt-in on pull requests — they no longer run on every push. They always run automatically after merge to canary/main.

To run them on this PR, do any of the following, then push a commit (or re-run CI):

• Add RUN_CODSPEED=1 to the PR description, or
• Include run-perf or /perf in the PR title or any commit message.

[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 @.github/workflows/verify-rust-sdk.reusable.yaml:
- Around line 53-54: Add a job-level permissions block to platform-matrix
granting only contents: read, ensuring the job can check out the repository
without inheriting broader token permissions.

🪄 Autofix (Beta)

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: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 27ff2dcc-ab5f-4e56-a410-0deb5b2216a4

📥 Commits

Reviewing files that changed from the base of the PR and between 6951c86 and 5cd63b6.

📒 Files selected for processing (5)

• .github/workflows/verify-cpp-sdk.reusable.yaml
• .github/workflows/verify-rust-sdk.reusable.yaml
• baml_language/sdks/cpp/bridge_cpp/include/baml/variant.h
• baml_language/sdks/cpp/bridge_cpp/tests/run.sh
• baml_language/sdks/rust/verify/consumer_main.rs

[github-actions]

Binary size checks passed

✅ 7 passed

	Artifact	Platform	File	Gzip	Gated on	Baseline	Delta	Status
✅	baml-cli	Linux	🔒 25.6 MB	10.8 MB	file	25.3 MB	+275.0 KB (+1.1%)	OK
✅	packed-program	Linux	🔒 17.2 MB	7.1 MB	file	17.0 MB	+153.1 KB (+0.9%)	OK
✅	baml-cli	macOS	🔒 19.8 MB	9.4 MB	file	19.6 MB	+231.5 KB (+1.2%)	OK
✅	packed-program	macOS	🔒 13.4 MB	6.2 MB	file	13.2 MB	+198.3 KB (+1.5%)	OK
✅	baml-cli	Windows	🔒 21.3 MB	9.7 MB	file	21.1 MB	+230.9 KB (+1.1%)	OK
✅	packed-program	Windows	🔒 14.3 MB	6.3 MB	file	14.2 MB	+150.5 KB (+1.1%)	OK
✅	bridge_wasm	WASM	16.3 MB	🔒 4.4 MB	gzip	4.4 MB	+19.2 KB (+0.4%)	OK

🔒 = the size this artifact is GATED on (ceiling + delta). Binaries gate on file size (installed binary); WASM gates on gzip (download size). The other size is shown for information only.

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Generated by cargo size-gate · workflow run