Skip windows-2025 Swift 6.1/6.2 in CI matrix (MSVC 14.51 STL needs Clang 20)

[leogdion]

Problem

The build-windows job fails on windows-2025 with Swift 6.1 and 6.2. It's an environmental toolchain incompatibility, not a MistKit code bug:

• The windows-2025 runner image now resolves the newest installed Visual Studio toolset (MSVC 14.51, VS18) via vswhere. Its STL header yvals_core.h hard-asserts STL1000: Unexpected compiler version, expected Clang 20 or newer.
• Swift 6.1 and 6.2 bundle Clang 19, so the assert fires when swift-crypto's CCryptoBoringSSL includes <memory>. Swift 6.3 bundles Clang 20, so it passes.
• windows-2022 defaults to an older 14.4x toolset compatible with Clang 19, so it builds all three Swift versions fine.

In a recent run, the only red Windows jobs were windows-2025 × 6.1-RELEASE and windows-2025 × 6.2-RELEASE; everything else was green.

Change

Add a matrix exclude for windows-2025 × {6.1, 6.2}. Resulting Windows coverage:

Runner	Swift
windows-2022	6.1, 6.2, 6.3
windows-2025	6.3

Swift 6.1/6.2 stay covered on windows-2022; Swift 6.3 still exercises the new 14.51 toolset on windows-2025. No package or shared-action changes.

Why not pin an older toolset

Pinning windows-2025 to the VS2022/14.44 toolset would keep 6.1/6.2 coverage there, but it's a fragile env workaround (depends on the Swift/clang driver honoring an injected INCLUDE/LIB over vswhere's latest, and on the older toolset staying installed). The exclude is a zero-risk config change with full passing evidence on windows-2022.

Follow-up: GitHub will eventually retire windows-2022. When that happens (or 6.1/6.2 are dropped), revisit — toolset-pinning or -D_ALLOW_COMPILER_AND_STL_VERSION_MISMATCH becomes the fallback.

🤖 Generated with Claude Code

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[claude]

Review: Skip windows-2025 Swift 6.1/6.2 in CI matrix

A small, well-scoped CI workflow change. Summary by category:

Code quality / correctness

• The exclude entries correctly repeat both 'version' and 'build' for the nested 'swift' object, giving an exact match against the full object as defined in the swift list above. This matters: GitHub Actions exclude matching on object-typed matrix values requires the excluded value to equal the whole object, not a subset of its keys. (The existing wasm/wasm-embedded exclude earlier in this same file only specifies 'swift: { version: "6.1" }', which works only because that matrix swift objects happen to have a single key -- an exact match by coincidence. The new windows exclude does it correctly/defensively for a two-key object.)
• Indentation and structure are consistent with the existing exclude block style in this file.
• The explanatory comment (MSVC 14.51 STL requiring Clang 20+, Swift 6.1/6.2 shipping Clang 19, windows-2022 unaffected) is clear and gives future maintainers enough context to revisit the decision without re-deriving it.

Potential issues

• Minor maintainability nit: the excluded version/build pairs duplicate values already declared in the swift list a few lines above, so a future bump of the Swift version matrix requires updating both places in sync. Not really avoidable given GitHub Actions exclude semantics, and the PR description already flags follow-up options (toolset pinning, -D_ALLOW_COMPILER_AND_STL_VERSION_MISMATCH) once windows-2022 is retired or 6.1/6.2 support is dropped, so this is already tracked rather than a blocking concern.
• No functional risk: this only narrows the windows-2025 matrix; windows-2022 keeps full 6.1/6.2/6.3 coverage, and windows-2025 still exercises the newer toolset via 6.3.

Performance

• Net positive: drops 2 of 6 Windows matrix jobs (the ones failing for environmental reasons), reducing CI minutes without losing meaningful coverage (6.1/6.2 still build on windows-2022).

Security

• None -- pure CI matrix configuration, no secrets, permissions, or new actions/inputs introduced.

Test coverage

• N/A for a workflow-only change; the real validation is the resulting CI run on this PR -- worth confirming the windows-2025 x 6.1/6.2 jobs are absent and the remaining 4 Windows jobs (windows-2022 x 6.1/6.2/6.3, windows-2025 x 6.3) are green before merging.

Overall: looks correct and low-risk. No changes requested.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.03%. Comparing base (9894d48) to head (1ee77cf).

Additional details and impacted files

@@                Coverage Diff                @@
##           v1.0.0-beta.3     #418      +/-   ##
=================================================
+ Coverage          71.82%   72.03%   +0.21%     
=================================================
  Files                168      156      -12     
  Lines               3844     3698     -146     
=================================================
- Hits                2761     2664      -97     
+ Misses              1083     1034      -49     

Flag	Coverage Δ
mistdemo-spm-macos	?
mistdemo-swift-6.2-jammy	?
mistdemo-swift-6.2-noble	?
mistdemo-swift-6.3-jammy	?
mistdemo-swift-6.3-noble	?
spm	71.76% <ø> (+0.24%)	⬆️
swift-6.1-jammy	71.73% <ø> (ø)
swift-6.1-noble	71.59% <ø> (-0.28%)	⬇️
swift-6.2-jammy	71.59% <ø> (-0.06%)	⬇️
swift-6.2-noble	71.59% <ø> (ø)
swift-6.3-jammy	71.54% <ø> (ø)
swift-6.3-noble	71.89% <ø> (+0.29%)	⬆️

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