Log().IncludingAllRefs().ExcludingRemoteTrackingRefs() reports commits the remote already has as "exist only here" when git maintenance prefetch is on (refs/prefetch is swept in by --all) #254

Symptom

The README's "Checking for Work That Exists Nowhere Else" query lists commits that came from the remote whenever the repository has refs/prefetch/*. That means every repository registered with git maintenance start or Scalar. Their hourly prefetch task fetches into refs/prefetch/remotes/<remote>/*, a namespace that is deliberately outside refs/remotes. --all includes those refs, and --not --remotes does not exclude them.

Reproduction (git 2.43)

1. Clone a repository and leave main in sync with origin/main.
2. From another clone, push a new commit ("remote-new").
3. In the first clone, run git maintenance run --task=prefetch. This creates refs/prefetch/remotes/origin/main and does not move origin/main.
4. Run the query:

var atRisk = await repo.Log().IncludingAllRefs().ExcludingRemoteTrackingRefs().ExecuteAsync();
// unpushed: 0ae62ea remote-new   <- authored elsewhere, already on the remote

git status -sb shows ## main...origin/main, so nothing is ahead. The query still flags the commit, and a caller deciding whether a working copy is safe to delete gets a false "has unpushed work". The same mechanism also lets any other non-refs/remotes mirror of remote state through.

Where

• GitIntegration/Builders/GitLogBuilder.cs L193-218 (permalink) emits --all and then --not --remotes --not.
• The IncludingAllRefs remarks (L47-62) and the README (L370-396) present this as the check to run before discarding a working copy.

Fix / acceptance criteria

• Treat refs/prefetch/* as remote evidence. Both of these drop the false positive and keep genuine local-only commits (checked against git 2.43):
  • --not --remotes --glob=refs/prefetch/* --not
  • --exclude=refs/prefetch/* --all (--exclude must come before --all).
• Add an integration test:
  • a commit reachable only from refs/prefetch/remotes/origin/main is not reported
  • a commit on a local branch or a detached HEAD still is.
• Update the remarks and the README to say which non-remote namespaces count as remote copies.