Round-3 review on PR #891 (no blockers):
- Add test_encode_dav_path_encodes_exactly_once pinning the documented
decoded-input precondition ("already%20encoded.pdf" -> "already%2520...").
- format_exception_group: proper singular/plural ("1 sub-exception" vs
"N sub-exceptions") instead of "(s)".
- oauth_sync: use `if doc_task is not None:` to match processor_task's guard.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>