Checkout Pull Request in Worktree fails for PRs from forks ("Failed to execute git")

[colluca]

Bug

"Checkout Pull Request in Worktree" fails with a generic Failed to create worktree: Failed to execute git error whenever the pull request comes from a fork.

Root cause

checkoutPRInWorktree in src/github/worktree.ts always fetches the PR's head branch from the base repo's remote:

const remoteName = pullRequestModel.remote.remoteName;
...
await repositoryToUse.fetch({ remote: remoteName, ref: branchName });

pullRequestModel.remote is the remote for the repository the PR was opened against (typically origin). For a PR opened from a fork, the head branch only exists on the fork's remote/clone URL, not on origin, so the fetch fails with something like:

fatal: couldn't find remote ref <branch-name>

That underlying git error isn't surfaced — it's swallowed into the generic "Failed to execute git" message shown to the user, which makes the bug very hard to diagnose without extension logs.

Note the extension's regular (non-worktree) checkout path already handles this correctly: PullRequestGitHelper.fetchAndCheckout detects isFork (pull.head.repositoryCloneUrl.owner !== pull.base.repositoryCloneUrl.owner) and, when true, calls checkoutFromFork, which creates (or reuses) a remote pointing at the fork's clone URL before fetching. The worktree checkout path bypasses all of this.

Repro steps

1. Open a repo where you have origin pointing at the upstream repository.
2. Open a pull request from a fork (i.e. head.repo.owner != base.repo.owner) in the Pull Requests view.
3. Use "Checkout Pull Request in Worktree".
4. Observe the notification: Failed to create worktree: Failed to execute git.
5. In the Git output channel / Git.log, the actual command run is:

   > git fetch origin <fork-branch-name>
   fatal: couldn't find remote ref <fork-branch-name>
   

Expected behavior

Worktree checkout should succeed for fork PRs the same way regular checkout does, by fetching from a remote associated with the fork (creating one if necessary) instead of always using the base repo's remote.

Environment

• GitHub Pull Requests extension (recent version, confirmed via extension logs on 2026-09-24)
• VS Code Server (remote/SSH), Linux

Fix

I have a small fix ready and will open a PR shortly that mirrors the existing fork-detection logic from PullRequestGitHelper.fetchAndCheckout/checkoutFromFork inside checkoutPRInWorktree.