test sweep: finish src/git/ (T-91)

Closes out the three remaining files in src/git/ following the
client.dart batch:

operations.dart (25 new tests):
- GitException.toString
- GitLogEntry.toJson (body present + absent)
- gitStage / gitUnstage / gitStashPop / gitPush / gitPull error
  paths (no remote, empty stash, bogus path)
- gitUnstage with empty paths (unstage everything)
- gitStageHunk + gitUnstageHunk via _applyPatch
- _applyPatch surfaces stderr in GitException on a bad patch
- gitBranches happy + non-repo
- gitCheckout happy + unknown-branch error
- gitPull + gitPush round-trip against a local bare remote
- gitLog / gitCurrentBranch / gitBranches non-repo fallbacks
- gitDiscard with empty list short-circuit
- gitBin resolver

diff.dart (7 new tests):
- gitDiff with paths argument and non-repo fallback
- GitHunk.toPatch round-tripping header + every DiffLineKind
- GitDiff.toJson with / without oldPath
- parseDiffOutput edge cases: pre-diff garbage skipped, "\ No newline"
  marker captured as a header line, malformed @@ header skipped via
  _parseHunk null return

status.dart (4 new tests):
- branch.upstream + branch.ab populated from a local bare remote
- non-git directory returns an empty branchless status
- rename in porcelain output captures the original path
- parsePorcelainV1 short-part / empty-part / empty-input edge cases

Coverage: src/git/diff.dart 106/124 -> 124/124 (100%);
src/git/operations.dart 88/155 -> 148/155 (95% — remaining 7 lines
are gitPull/gitPush variants that need credentials, and the
gitBranches non-zero stderr path);
src/git/status.dart 86/98 -> 95/98 (97% — remaining 3 are the
ProcessException-during-call catch branches, only reachable if git
crashes mid-call).

Total coverage 76.04% -> 77.05%; floor bumped to 77.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/git/status_test.dart

@@ -92,4 +92,45 @@ void main() {
     expect(status.ahead, isZero);
     expect(status.behind, isZero);
   });
+
+  test('branch.upstream + branch.ab populate upstream/ahead/behind', () async {
+    final remote = await Directory.systemTemp.createTemp('clide-status-remote-');
+    addTearDown(() => remote.deleteSync(recursive: true));
+    await Process.run('git', ['init', '--bare'], workingDirectory: remote.path);
+    await Process.run('git', ['remote', 'add', 'origin', remote.path], workingDirectory: sandbox.path);
+    await Process.run('git', ['push', '-u', 'origin', 'HEAD'], workingDirectory: sandbox.path);
+    // Add a commit so we have ahead > 0.
+    await File('${sandbox.path}/ahead.txt').writeAsString('x');
+    await Process.run('git', ['add', '.'], workingDirectory: sandbox.path);
+    await Process.run('git', ['commit', '-m', 'ahead'], workingDirectory: sandbox.path);
+    final s = await gitStatus(sandbox);
+    expect(s.upstream, contains('origin/'));
+    expect(s.ahead, 1);
+    expect(s.behind, 0);
+  });
+
+  test('gitStatus on a non-git directory returns an empty branchless status', () async {
+    final notGit = await Directory.systemTemp.createTemp('clide-status-not-');
+    addTearDown(() => notGit.deleteSync(recursive: true));
+    final s = await gitStatus(notGit);
+    expect(s.entries, isEmpty);
+  });
+
+  test('rename in porcelain output captures the original path', () async {
+    await File('${sandbox.path}/a.txt').writeAsString('content\n');
+    await Process.run('git', ['add', '.'], workingDirectory: sandbox.path);
+    await Process.run('git', ['commit', '-m', 'add a'], workingDirectory: sandbox.path);
+    await Process.run('git', ['mv', 'a.txt', 'renamed.txt'], workingDirectory: sandbox.path);
+    final s = await gitStatus(sandbox);
+    final renamed = s.entries.firstWhere((e) => e.path == 'renamed.txt');
+    expect(renamed.origPath, 'a.txt');
+  });
+
+  test('parsePorcelainV1 handles empty input + short / empty parts', () {
+    expect(parsePorcelainV1(''), isEmpty);
+    // 'X' is too short (< 4 chars), should be skipped.
+    expect(parsePorcelainV1('X\x00'), isEmpty);
+    // Empty token-only input — skipped.
+    expect(parsePorcelainV1('\x00'), isEmpty);
+  });
 }