ci(windows): add Windows MSVC CI jobs

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Summary

Add Windows MSVC CI jobs to validate Windows-supported Rust crates on pull requests and keep the Windows build cache warm on main. Build release binaries after merges to main, without publishing them.

Related Issue

No issue required: localized CI infrastructure work following #2496.

Changes

• add a pull-request job that runs strict Clippy on Windows-sensitive crates and tests the supported Rust workspace on windows-2025
• add a cache-seeding job on main that runs the same lint and test workload to keep pull-request caches warm
• add a dependent job on main that builds Windows release binaries without publishing them
• use prebuilt Z3 archives instead of compiling Z3 from source
• cache Cargo target artifacts and use the GitHub Actions sccache backend
• scope Unix-only and test-only Rust code so Windows Clippy passes with -D warnings and no blanket warning allowances
• document the Windows CI scope and cache behavior
• enable the OpenTelemetry in-memory exporter explicitly for tests

Testing

• mise run pre-commit passes
• cargo test -p openshell-otel passes
• target-cache and sccache experiments completed on windows-2025
• fully warm sccache achieved 62/62 compiler-cache hits with no errors
• hosted Windows strict Clippy and tests pass
• Branch Checks, E2E, Helm, and required aggregate gates pass
• E2E tests added/updated (not applicable; CI-only change)

Detailed timing and cache measurements are recorded in the PR comments.

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated

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Auto-sync is disabled for draft pull requests in this repository. Workflows must be run manually.

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Windows MSVC cache experiments

I ran the hosted windows-2025 workflow repeatedly while changing one major cache/build variable at a time. Times below are end-to-end workflow/job times and can vary slightly with runner setup and GitHub cache transfer latency.

Configuration	Cache state	Runtime	Notes
Original workflow / bundled Z3	effectively cold	~75m48s–78m22s	Baseline; Z3 compiled from source and the Rust target tree was not providing a useful warm reuse path. run, repeat
Cargo target cache / bundled Z3	cold	~75m16s	Populated the target archive. run
Cargo target cache / bundled Z3	warm	~18m39s	Large improvement; target artifacts were the most effective cache layer. run
sccache only / bundled Z3	cold	~80m47s	Target cache disabled to isolate sccache. Remote writes made the cold run slower. run
sccache only / bundled Z3	warm	~67m55s	1,157 hits / 122 misses (90.46% hit rate), but linking, non-cacheable crate types, Z3 work, and remote reads left total time high. run
Cargo target cache + prebuilt Z3	cold	~37m28s	z3-sys downloaded the pinned official prebuilt Z3 archive instead of compiling Z3 via CMake/MSBuild. run
Cargo target cache + prebuilt Z3	warm	~16m24s	Check 1m14s, release build 6m36s, tests 4m46s, focused test 2m12s; target restore ~58s. run
Target cache + prebuilt Z3 + sccache	target warm, sccache cold	~17m09s	62 misses, 62 successful writes, 0 errors; cache writes took 32.6s. run
Target cache + prebuilt Z3 + sccache	both warm	~15m45s	62/62 sccache hits, 0 misses/errors; check 1m07s, release build 5m19s, tests 5m06s, focused test 2m25s. run
Warm hybrid cache, redundant focused test removed	both warm	~12m33s	Check 1m01s, release build 5m07s, full tests 4m58s. The full suite already includes the Windows unsupported-driver contract test. run

Conclusions

• Cargo target caching was the largest win: roughly 75 minutes cold to roughly 19 minutes warm with bundled Z3.
• Prebuilt Z3 materially improved cold builds: the cold target-cache run dropped from roughly 75 minutes to roughly 37 minutes.
• sccache alone was not competitive, despite a high hit rate. It does not cache final linking or several Rust crate types, and GitHub remote reads still cost time.
• sccache is useful as a secondary layer on top of the target cache: it reduced the warm release build from roughly 6m36s to 5m19s and produced a clean 100% hit rate for the 62 cacheable compiler requests in the measured run.
• The best measured stack is Cargo target cache + prebuilt Z3 + sccache, with the redundant focused test removed.
• The PR/main split is intended to keep PR validation focused on Windows Clippy + Rust tests, run that same workload on main to warm the exact PR cache namespaces, and build (but not upload/publish) release binaries after the seed succeeds.

Current validation note

The earlier single-job hybrid workflow is proven by the successful runs above. The new multi-job split currently receives an opaque GitHub startup_failure before any job is created, on both manual dispatch and the PR mirror. actionlint reports the workflow as valid, and a temporary ref at the last known-good commit starts normally, so I am continuing to isolate the workflow-graph difference before treating the split as ready.

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Validation update: the opaque pre-job startup_failure was isolated to jdx/mise-action v4.2.4 on windows-2025. Restoring the previously measured v4.2.0 pin fixes workflow startup. The PR mirror is now running PR lint and test (x64), and a manual dispatch is independently running Seed cache (x64) followed by Build binaries (x64). The newer Swatinem/rust-cache v2.9.2 pin remains in place.

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Pausing this PR until the compute-driver refactor stack lands:

• refactor(compute): unify gateway restart reconciliation #2743 — unify gateway restart reconciliation
• refactor(compute): support external driver parity #2744 — negotiate external driver behavior
• refactor(compute): register compiled drivers #2786 — register compiled drivers and move first-party driver composition into the new openshell-gateway crate

#2786 overlaps 8 of the 18 files changed here and establishes a cleaner Windows boundary by keeping first-party driver dependencies out of openshell-core and openshell-server. The current strict Windows Clippy fixes add 65 cfg attributes, many of which are likely to become unnecessary after that refactor. Continuing now would create avoidable code and rebase churn.

After the stack merges, the plan is to:

1. Rebase this PR again.
2. Keep the Windows PR/main/cache-seed job split, target cache, sccache, and prebuilt Z3 work.
3. Update lint/build coverage for the new openshell-gateway composition crate.
4. Remove obsolete platform-scoping changes and handle any remaining Kubernetes or UDS boundaries at module level where possible.
5. Rerun the hosted Windows timing and cache validation.

The branch is currently rebased onto main; local mise run pre-commit passes.