Push().WithBranch(x).DeletingRemoteBranch() deletes the remote tag x when no branch x exists; push/pull WithBranch can act on tags because operands aren't qualified as refs/heads/ #258

What's wrong

GitPushBuilder and GitPullBuilder take the branch as a GitBranchName, but they pass it to git as a bare short name:

• GitIntegration/Builders/GitPushBuilder.cs:260: AppendOperands(arguments, _remote.WeakString, _branch.WeakString)
• GitIntegration/Builders/GitPullBuilder.cs:272: the same call

Git resolves a bare refspec by DWIM against every ref namespace, not only refs/heads/. So the API promises a branch, but git can act on a tag instead.

Reproduced on git 2.43 against a local bare remote

1. Delete removes a tag. The remote has tag v1 and no branch v1.
   • Call: Push().ToRemote(origin).WithBranch("v1").DeletingRemoteBranch()
   • Command run: git push --porcelain --delete --end-of-options origin v1
   • Result: git exits 0 and prints - :refs/tags/v1 [deleted]. The remote tag is gone, ExecuteAsync reports success, and HasRejections is false.
   • git push origin :<tag> is git's documented way to delete a tag, so git is behaving as designed. A method named DeletingRemoteBranch should never do this.
2. Pull fast-forwards to a tag. The remote has tag onlytag and no branch of that name.
   • Call: Pull().FromRemote(origin).WithBranch("onlytag").FastForwardOnly()
   • Result: git prints * tag onlytag -> FETCH_HEAD, fast-forwards the current branch to the tag's commit, and exits 0.
   • Without FastForwardOnly(), the same call merges the tag.
3. Push fails, or pushes a tag, when names collide locally. This is the case Branches()/Tags() report "heads/v1" / "tags/v1" when a branch and a tag share a name, so the name can't be passed back to git #137 handled for listing.
   • A local branch and a local tag are both named v2: Push().ToRemote(origin).WithBranch("v2") fails with error: src refspec v2 matches more than one. There are no porcelain records, so it surfaces as a generic GitCommandException.
   • Only a local tag v2 exists, with no branch: the tag is pushed.

Related: a delete with no branch isn't validated

DeletingRemoteBranch() without WithBranch(...) builds git push --delete origin, which dies with fatal: --delete doesn't make sense without any refs. AppendRefspec (GitPushBuilder.cs:238-261) already refuses a branch with no remote in BuildArguments, but it doesn't refuse a delete with no branch.

Suggested fix

• Push: emit refs/heads/<name> as the source refspec, with no :dst, so git still updates the remote branch of the same name. For --delete, emit refs/heads/<name>. Checked on git 2.43:
  • git push --porcelain --set-upstream origin refs/heads/v2 still sets branch.v2.remote and branch.v2.merge.
  • git push --delete origin refs/heads/v1 leaves refs/tags/v1 alone.
  • Porcelain output already prints full ref names, so GitPushParser needs no change.
• Pull: emit refs/heads/<name>. git pull origin refs/heads/onlytag correctly fails with couldn't find remote ref refs/heads/onlytag.
• Validation: throw InvalidOperationException from BuildArguments when DeletingRemoteBranch() is set without WithBranch(...). This matches the existing branch-without-remote guard.

Acceptance criteria

• Builder tests assert the qualified refspec for WithBranch:
  • on push, without DeletingRemoteBranch
  • on push, with DeletingRemoteBranch
  • on pull
• Integration tests in GitRemoteSyncTests:
  • DeletingRemoteBranch on a name that exists only as a remote tag leaves the tag in place and doesn't report a deletion.
  • Push WithBranch(x) succeeds when a local branch and a local tag are both named x.
  • Pull WithBranch(x) fails, rather than merging, when only a remote tag x exists.
• DeletingRemoteBranch() without WithBranch throws InvalidOperationException from BuildArguments.