fix(core): bypass Windows Git lookup - #43998

AI code review — automated review for reference; please use your judgment.

1. packages/core/src/util/git-executable.ts:4 — which("git") runs once at module import and is frozen for the process lifetime. If git is installed after startup, or the effective PATH changes (per-server/project env overrides flow through these spawns), every git call keeps using the stale-or-missing resolution with no way to refresh. Why it matters: a wrong pin silently persists across the whole session. Suggestion: memoize lazily behind a function (getGitExecutable()) with an explicit invalidation (or short TTL), so env changes and first-use timing are handled and tests can stub it.

2. packages/core/src/util/git-executable.ts:4 — Resolution uses process.env.PATH, but the call sites pass per-invocation env with extendEnv: true; a deployment that intentionally puts a specific git first in the spawn env is now ignored in favor of the host-wide lookup. Why it matters: behavior change for env-customized setups, undocumented. Suggestion: either key the cache by the resolved PATH value or document that only the launcher's PATH decides which git runs.

3. packages/util/src/cross-spawn-spawner.ts:265 — The native-vs-cross-spawn predicate (win32 && !shell && absolute && .exe/.com) embeds real security-relevant decisions (deliberately excluding .bat/.cmd) but is inline and untested, and CI likely never runs it. Suggestion: extract shouldSpawnNativeWindows(command, opts) as an exported pure function and add table tests covering extension casing, relative paths, shell opt, and non-win32.

4. packages/core/src/util/git-executable.ts:6 — Falling back to "git" keeps today's failure mode, which is fine, but a one-time warning when which() finds nothing on Windows would turn "commands fail mysteriously" into a diagnosable setup error. Suggestion: log once (guarded by a module flag).

5. packages/core/src/git.ts:318 (nit) — Worth adding a guardrail against regressions: a lint rule (no-restricted-syntax) or CI grep asserting no new ChildProcess.make("git", …) literals sneak back in now that gitExecutable exists — the diff touches four call sites, and a fifth already exists somewhere else is exactly how this class of fix rots.

— automated review (ox-alpha, round2)

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