A V4A `*** Add File:` operation is meant to create a new file. The apply
path called `write_file` unconditionally and `_validate_operations` had no
pre-check for ADD, so an Add targeting a path that already existed
overwrote the file with only the patch's `+` lines, returned success, and
emitted a `--- /dev/null` diff that hid what was lost. Models frequently
confuse Add with Update, so this destroyed existing file contents with no
error. The MOVE path already guards its destination against clobbering;
ADD now follows the same rule.
Makes a V4A `Add File` operation fail when its target already exists,
instead of silently overwriting the existing file. Validation now rejects
the operation before any write happens, so the two-phase
validate-then-apply contract ("no files were modified" on a validation
failure) holds for ADD as it already does for UPDATE/MOVE/DELETE. A
matching re-check in the apply phase closes the validate-to-apply race.
N/A
- [x] 🐛 Bug fix (non-breaking change that fixes an issue)
- `tools/patch_parser.py`: add an ADD branch in `_validate_operations`
that errors when `read_file_raw` finds an existing file, and a
defensive existence re-check in `_apply_add` before `write_file`,
mirroring the existing MOVE destination guard.
- `tests/tools/test_patch_parser.py`: add a test asserting an Add onto an
existing path fails validation and leaves the original bytes unwritten;
add `read_file_raw` to three ADD-path LSP fakes so they match the real
`file_ops` interface now exercised on ADD.
1. Build a V4A patch with `*** Add File: <path>` where `<path>` already
exists on disk.
2. Apply it via `apply_v4a_operations`. Before this change the file is
overwritten with the patch's `+` lines and the result is success;
after, the result is a validation failure and the file is untouched.
3. Run `scripts/run_tests.sh tests/tools/test_patch_parser.py` —
`TestApplyOperations::test_add_onto_existing_file_fails_and_preserves_contents`
covers the regression.
- [x] I've read the [Contributing Guide](https://github.com/NousResearch/hermes-agent/blob/main/CONTRIBUTING.md)
- [x] My commit messages follow [Conventional Commits](https://www.conventionalcommits.org/) (`fix(scope):`, `feat(scope):`, etc.)
- [x] I searched for [existing PRs](https://github.com/NousResearch/hermes-agent/pulls) to make sure this isn't a duplicate
- [x] My PR contains **only** changes related to this fix/feature (no unrelated commits)
- [x] I've run `pytest tests/ -q` and all tests pass
- [x] I've added tests for my changes (required for bug fixes, strongly encouraged for features)
- [x] I've tested on my platform: macOS 15 (Darwin 25.5.0)
- [x] I've updated relevant documentation (README, `docs/`, docstrings) — or N/A
- [x] I've updated `cli-config.yaml.example` if I added/changed config keys — or N/A
- [x] I've updated `CONTRIBUTING.md` or `AGENTS.md` if I changed architecture or workflows — or N/A
- [x] I've considered cross-platform impact (Windows, macOS) per the [compatibility guide](https://github.com/NousResearch/hermes-agent/blob/main/CONTRIBUTING.md#cross-platform-compatibility) — or N/A
- [x] I've updated tool descriptions/schemas if I changed tool behavior — or N/A
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