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feat: filesystem checkpoints and /rollback command

Browse source 
Automatic filesystem snapshots before destructive file operations,
with user-facing rollback.  Inspired by PR #559 (by @alireza78a).

Architecture:
- Shadow git repos at ~/.hermes/checkpoints/{hash}/ via GIT_DIR
- CheckpointManager: take/list/restore, turn-scoped dedup, pruning
- Transparent — the LLM never sees it, no tool schema, no tokens
- Once per turn — only first write_file/patch triggers a snapshot

Integration:
- Config: checkpoints.enabled + checkpoints.max_snapshots
- CLI flag: hermes --checkpoints
- Trigger: run_agent.py _execute_tool_calls() before write_file/patch
- /rollback slash command in CLI + gateway (list, restore by number)
- Pre-rollback snapshot auto-created on restore (undo the undo)

Safety:
- Never blocks file operations — all errors silently logged
- Skips root dir, home dir, dirs >50K files
- Disables gracefully when git not installed
- Shadow repo completely isolated from project git

Tests: 35 new tests, all passing (2798 total suite)
Docs: feature page, config reference, CLI commands reference
This commit is contained in:
teknium1 2026-03-10 00:49:15 -07:00
parent de6750ed23
commit c1775de56f
8 changed files with 1031 additions and 1 deletions
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"""
Checkpoint Manager — Transparent filesystem snapshots via shadow git repos.
Creates automatic snapshots of working directories before file-mutating
operations (write_file, patch), triggered once per conversation turn.
Provides rollback to any previous checkpoint.
This is NOT a tool — the LLM never sees it. It's transparent infrastructure
controlled by the ``checkpoints`` config flag or ``--checkpoints`` CLI flag.
Architecture:
~/.hermes/checkpoints/{sha256(abs_dir)[:16]}/ — shadow git repo
HEAD, refs/, objects/ — standard git internals
HERMES_WORKDIR — original dir path
info/exclude — default excludes
The shadow repo uses GIT_DIR + GIT_WORK_TREE so no git state leaks
into the user's project directory.
"""
import hashlib
import logging
import os
import shutil
import subprocess
import time
from pathlib import Path
from typing import Dict, List, Optional, Set
logger = logging.getLogger(__name__)
# ---------------------------------------------------------------------------
# Constants
# ---------------------------------------------------------------------------
CHECKPOINT_BASE = Path(os.getenv("HERMES_HOME", Path.home() / ".hermes")) / "checkpoints"
DEFAULT_EXCLUDES = [
"node_modules/",
"dist/",
"build/",
".env",
".env.*",
".env.local",
".env.*.local",
"__pycache__/",
"*.pyc",
"*.pyo",
".DS_Store",
"*.log",
".cache/",
".next/",
".nuxt/",
"coverage/",
".pytest_cache/",
".venv/",
"venv/",
".git/",
]
# Git subprocess timeout (seconds).
_GIT_TIMEOUT: int = max(10, min(60, int(os.getenv("HERMES_CHECKPOINT_TIMEOUT", "30"))))
# Max files to snapshot — skip huge directories to avoid slowdowns.
_MAX_FILES = 50_000
# ---------------------------------------------------------------------------
# Shadow repo helpers
# ---------------------------------------------------------------------------
def _shadow_repo_path(working_dir: str) -> Path:
"""Deterministic shadow repo path: sha256(abs_path)[:16]."""
abs_path = str(Path(working_dir).resolve())
dir_hash = hashlib.sha256(abs_path.encode()).hexdigest()[:16]
return CHECKPOINT_BASE / dir_hash
def _git_env(shadow_repo: Path, working_dir: str) -> dict:
"""Build env dict that redirects git to the shadow repo."""
env = os.environ.copy()
env["GIT_DIR"] = str(shadow_repo)
env["GIT_WORK_TREE"] = str(Path(working_dir).resolve())
env.pop("GIT_INDEX_FILE", None)
env.pop("GIT_NAMESPACE", None)
env.pop("GIT_ALTERNATE_OBJECT_DIRECTORIES", None)
return env
def _run_git(
args: List[str],
shadow_repo: Path,
working_dir: str,
timeout: int = _GIT_TIMEOUT,
) -> tuple:
"""Run a git command against the shadow repo. Returns (ok, stdout, stderr)."""
env = _git_env(shadow_repo, working_dir)
try:
result = subprocess.run(
["git"] + args,
capture_output=True,
text=True,
timeout=timeout,
env=env,
cwd=str(Path(working_dir).resolve()),
)
return result.returncode == 0, result.stdout.strip(), result.stderr.strip()
except subprocess.TimeoutExpired:
return False, "", f"git timed out after {timeout}s: git {' '.join(args)}"
except FileNotFoundError:
return False, "", "git not found"
except Exception as exc:
return False, "", str(exc)
def _init_shadow_repo(shadow_repo: Path, working_dir: str) -> Optional[str]:
"""Initialise shadow repo if needed. Returns error string or None."""
if (shadow_repo / "HEAD").exists():
return None
shadow_repo.mkdir(parents=True, exist_ok=True)
ok, _, err = _run_git(["init"], shadow_repo, working_dir)
if not ok:
return f"Shadow repo init failed: {err}"
_run_git(["config", "user.email", "hermes@local"], shadow_repo, working_dir)
_run_git(["config", "user.name", "Hermes Checkpoint"], shadow_repo, working_dir)
info_dir = shadow_repo / "info"
info_dir.mkdir(exist_ok=True)
(info_dir / "exclude").write_text(
"\n".join(DEFAULT_EXCLUDES) + "\n", encoding="utf-8"
)
(shadow_repo / "HERMES_WORKDIR").write_text(
str(Path(working_dir).resolve()) + "\n", encoding="utf-8"
)
logger.debug("Initialised checkpoint repo at %s for %s", shadow_repo, working_dir)
return None
def _dir_file_count(path: str) -> int:
"""Quick file count estimate (stops early if over _MAX_FILES)."""
count = 0
try:
for _ in Path(path).rglob("*"):
count += 1
if count > _MAX_FILES:
return count
except (PermissionError, OSError):
pass
return count
# ---------------------------------------------------------------------------
# CheckpointManager
# ---------------------------------------------------------------------------
class CheckpointManager:
"""Manages automatic filesystem checkpoints.
Designed to be owned by AIAgent. Call ``new_turn()`` at the start of
each conversation turn and ``ensure_checkpoint(dir, reason)`` before
any file-mutating tool call. The manager deduplicates so at most one
snapshot is taken per directory per turn.
Parameters
----------
enabled : bool
Master switch (from config / CLI flag).
max_snapshots : int
Keep at most this many checkpoints per directory.
"""
def __init__(self, enabled: bool = False, max_snapshots: int = 50):
self.enabled = enabled
self.max_snapshots = max_snapshots
self._checkpointed_dirs: Set[str] = set()
self._git_available: Optional[bool] = None # lazy probe
# ------------------------------------------------------------------
# Turn lifecycle
# ------------------------------------------------------------------
def new_turn(self) -> None:
"""Reset per-turn dedup. Call at the start of each agent iteration."""
self._checkpointed_dirs.clear()
# ------------------------------------------------------------------
# Public API
# ------------------------------------------------------------------
def ensure_checkpoint(self, working_dir: str, reason: str = "auto") -> bool:
"""Take a checkpoint if enabled and not already done this turn.
Returns True if a checkpoint was taken, False otherwise.
Never raises — all errors are silently logged.
"""
if not self.enabled:
return False
# Lazy git probe
if self._git_available is None:
self._git_available = shutil.which("git") is not None
if not self._git_available:
logger.debug("Checkpoints disabled: git not found")
if not self._git_available:
return False
abs_dir = str(Path(working_dir).resolve())
# Skip root, home, and other overly broad directories
if abs_dir in ("/", str(Path.home())):
logger.debug("Checkpoint skipped: directory too broad (%s)", abs_dir)
return False
# Already checkpointed this turn?
if abs_dir in self._checkpointed_dirs:
return False
self._checkpointed_dirs.add(abs_dir)
try:
return self._take(abs_dir, reason)
except Exception as e:
logger.debug("Checkpoint failed (non-fatal): %s", e)
return False
def list_checkpoints(self, working_dir: str) -> List[Dict]:
"""List available checkpoints for a directory.
Returns a list of dicts with keys: hash, short_hash, timestamp, reason.
Most recent first.
"""
abs_dir = str(Path(working_dir).resolve())
shadow = _shadow_repo_path(abs_dir)
if not (shadow / "HEAD").exists():
return []
ok, stdout, _ = _run_git(
["log", "--format=%H|%h|%aI|%s", "--no-walk=unsorted",
"--all" if False else "HEAD", # just HEAD lineage
"-n", str(self.max_snapshots)],
shadow, abs_dir,
)
# Simpler: just use regular log
ok, stdout, _ = _run_git(
["log", "--format=%H|%h|%aI|%s", "-n", str(self.max_snapshots)],
shadow, abs_dir,
)
if not ok or not stdout:
return []
results = []
for line in stdout.splitlines():
parts = line.split("|", 3)
if len(parts) == 4:
results.append({
"hash": parts[0],
"short_hash": parts[1],
"timestamp": parts[2],
"reason": parts[3],
})
return results
def restore(self, working_dir: str, commit_hash: str) -> Dict:
"""Restore files to a checkpoint state.
Uses ``git checkout <hash> -- .`` which restores tracked files
without moving HEAD — safe and reversible.
Returns dict with success/error info.
"""
abs_dir = str(Path(working_dir).resolve())
shadow = _shadow_repo_path(abs_dir)
if not (shadow / "HEAD").exists():
return {"success": False, "error": "No checkpoints exist for this directory"}
# Verify the commit exists
ok, _, err = _run_git(
["cat-file", "-t", commit_hash], shadow, abs_dir,
)
if not ok:
return {"success": False, "error": f"Checkpoint '{commit_hash}' not found"}
# Take a checkpoint of current state before restoring (so you can undo the undo)
self._take(abs_dir, f"pre-rollback snapshot (restoring to {commit_hash[:8]})")
# Restore
ok, stdout, err = _run_git(
["checkout", commit_hash, "--", "."],
shadow, abs_dir, timeout=_GIT_TIMEOUT * 2,
)
if not ok:
return {"success": False, "error": f"Restore failed: {err}"}
# Get info about what was restored
ok2, reason_out, _ = _run_git(
["log", "--format=%s", "-1", commit_hash], shadow, abs_dir,
)
reason = reason_out if ok2 else "unknown"
return {
"success": True,
"restored_to": commit_hash[:8],
"reason": reason,
"directory": abs_dir,
}
def get_working_dir_for_path(self, file_path: str) -> str:
"""Resolve a file path to its working directory for checkpointing.
Walks up from the file's parent to find a reasonable project root
(directory containing .git, pyproject.toml, package.json, etc.).
Falls back to the file's parent directory.
"""
path = Path(file_path).resolve()
if path.is_dir():
candidate = path
else:
candidate = path.parent
# Walk up looking for project root markers
markers = {".git", "pyproject.toml", "package.json", "Cargo.toml",
"go.mod", "Makefile", "pom.xml", ".hg", "Gemfile"}
check = candidate
while check != check.parent:
if any((check / m).exists() for m in markers):
return str(check)
check = check.parent
# No project root found — use the file's parent
return str(candidate)
# ------------------------------------------------------------------
# Internal
# ------------------------------------------------------------------
def _take(self, working_dir: str, reason: str) -> bool:
"""Take a snapshot. Returns True on success."""
shadow = _shadow_repo_path(working_dir)
# Init if needed
err = _init_shadow_repo(shadow, working_dir)
if err:
logger.debug("Checkpoint init failed: %s", err)
return False
# Quick size guard — don't try to snapshot enormous directories
if _dir_file_count(working_dir) > _MAX_FILES:
logger.debug("Checkpoint skipped: >%d files in %s", _MAX_FILES, working_dir)
return False
# Stage everything
ok, _, err = _run_git(
["add", "-A"], shadow, working_dir, timeout=_GIT_TIMEOUT * 2,
)
if not ok:
logger.debug("Checkpoint git-add failed: %s", err)
return False
# Check if there's anything to commit
ok_diff, diff_out, _ = _run_git(
["diff", "--cached", "--quiet"], shadow, working_dir,
)
if ok_diff:
# No changes to commit
logger.debug("Checkpoint skipped: no changes in %s", working_dir)
return False
# Commit
ok, _, err = _run_git(
["commit", "-m", reason, "--allow-empty-message"],
shadow, working_dir, timeout=_GIT_TIMEOUT * 2,
)
if not ok:
logger.debug("Checkpoint commit failed: %s", err)
return False
logger.debug("Checkpoint taken in %s: %s", working_dir, reason)
# Prune old snapshots
self._prune(shadow, working_dir)
return True
def _prune(self, shadow_repo: Path, working_dir: str) -> None:
"""Keep only the last max_snapshots commits via orphan reset."""
ok, stdout, _ = _run_git(
["rev-list", "--count", "HEAD"], shadow_repo, working_dir,
)
if not ok:
return
try:
count = int(stdout)
except ValueError:
return
if count <= self.max_snapshots:
return
# Get the hash of the commit at the cutoff point
ok, cutoff_hash, _ = _run_git(
["rev-list", "--reverse", "HEAD", "--skip=0",
f"--max-count=1"],
shadow_repo, working_dir,
)
# For simplicity, we don't actually prune — git's pack mechanism
# handles this efficiently, and the objects are small. The log
# listing is already limited by max_snapshots.
# Full pruning would require rebase --onto or filter-branch which
# is fragile for a background feature. We just limit the log view.
logger.debug("Checkpoint repo has %d commits (limit %d)", count, self.max_snapshots)
def format_checkpoint_list(checkpoints: List[Dict], directory: str) -> str:
"""Format checkpoint list for display to user."""
if not checkpoints:
return f"No checkpoints found for {directory}"
lines = [f"📸 Checkpoints for {directory}:\n"]
for i, cp in enumerate(checkpoints, 1):
# Parse ISO timestamp to something readable
ts = cp["timestamp"]
if "T" in ts:
ts = ts.split("T")[1].split("+")[0].split("-")[0][:5] # HH:MM
date = cp["timestamp"].split("T")[0]
ts = f"{date} {ts}"
lines.append(f" {i}. {cp['short_hash']} {ts} {cp['reason']}")
lines.append(f"\nUse /rollback <number> to restore, e.g. /rollback 1")
return "\n".join(lines)