Windows: host git guard refuses repos under 8.3 short-name paths #1381

What happens

On Windows, a branch-strategy or merge-to-head run whose repo sits under an 8.3 short-name path (for example C:\Users\RUNNER~1\AppData\Local\Temp\...) can fail with:

HostGitError: Refusing to run git on the host…

The host git guard compares paths, and the short-name form (RUNNER~1) doesn't match the long-name form git or Node resolves (runneradmin), so the guard refuses a repo it should accept.

Evidence

Seen on 2026-11-01 in the windows CI job of #1380 (test migration of the structured output tests). The new e2e tests created their repo under os.tmpdir(), which on the GitHub Windows runner is a short-name path. Resolving the temp dir with fs.realpathSync.native first made the runs pass. That change is in the test only; the product code is unchanged.

Expected

A run started from a short-name path behaves the same as one started from the long-name path. Normalising both sides with realpathSync.native before comparing is the likely fix (not yet confirmed).

Repro (sketch)

On Windows, create a repo under %TEMP% without resolving the short name, then run({ branchStrategy: { type: "branch", branch: "x" }, ... }) with noSandbox().

This issue was AI-generated (Claude Code) on behalf of @mattpocock.