refactor: extract shared primitives into vite_powershell crate

[fengmk2]

Summary

• New vite_powershell crate owns the platform-shared primitives previously inlined in vite_task_plan::ps1_shim: POWERSHELL_PREFIX, powershell_host() (LazyLock-cached pwsh.exe/powershell.exe lookup), and find_ps1_sibling() (case-insensitive .cmd → sibling .ps1 resolution).
• vite_task_plan::ps1_shim keeps its task-specific layers — workspace + node_modules/.bin scope check, cwd-relative arg conversion, Arc<AbsolutePath> / Arc<[Str]> return types — and now imports the primitives from vite_powershell.
• No behavior change. All existing snapshot/unit/integration tests pass.

Why

vite-plus is adding vite_command::ps1_shim (see voidzero-dev/vite-plus#1489) to fix the same Ctrl+C terminal-corruption symptom for package-manager-routed commands (vp dlx, vp add, vp update, etc.). Without this extraction it would have to copy the constant, the host-discovery LazyLock, and the sibling-.ps1 check. With this extraction both task scripts (vite-task) and pm commands (vp) compose the same primitives with their own scope rules.

The two callers diverge intentionally and don't share enough to merge into one helper:

• vite-task's wrapper produces (Arc<AbsolutePath>, Arc<[Str]>) with cwd-relative .ps1 paths because the args become part of the task graph's spawn fingerprint and must stay portable across machines.
• vite-plus's wrapper (in vp's vite_command) produces (AbsolutePathBuf, Vec<OsString>) with absolute .ps1 paths because there's no cache fingerprint at spawn time.

Test plan

• cargo test -p vite_powershell — 5 new tests pass (sibling found, case-insensitive .CMD, no-sibling, non-.cmd, no-extension)
• cargo test -p vite_task_plan — 39 unit + 45 integration tests pass; the existing rewrite snapshot tests are preserved
• cargo clippy -p vite_powershell -p vite_task_plan --all-targets — clean
• Companion vp PR to switch vite_command::ps1_shim to depend on vite_powershell once this lands and a new vite-task SHA is pinned

---

Note

Low Risk
Mostly a dependency extraction/refactor with tests; behavior should remain the same aside from potential edge-case differences in .cmd/.ps1 detection on Windows.

Overview
Extracts the Windows .cmd→.ps1 PowerShell-shim primitives into a new vite_powershell crate, including the POWERSHELL_PREFIX args, cached pwsh.exe/powershell.exe host discovery, and sibling-.ps1 lookup.

Updates vite_task_plan::ps1_shim to depend on and call these shared helpers while keeping its workspace/node_modules/.bin scoping and cwd-relative argument rewrite logic, and adds unit tests for the new crate. Workspace Cargo.toml/Cargo.lock are updated to include the new crate and dependency.

^{Reviewed by Cursor Bugbot for commit 1e2b791. Configure here.}

[fengmk2]

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^{Reviewed by Cursor Bugbot for commit 1e2b791. Configure here.}