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Checkpoint Management for Agent State Persistence
Part of SOVEREIGN PYTHON LLM ENGINE
Backed by binary struct storage (CheckpointFile from core.storage).
No JSONL, no text encoding, no injection surface.
Features:
- Save/restore agent state to disk (binary struct format)
- Cryptographic signing (Ed25519)
- WORM-compatible append-only log
- Support for pause/resume of long-running agents
- Time-travel debugging (replay from any checkpoint)
"""
from dataclasses import dataclass, asdict
from datetime import datetime, timezone
from pathlib import Path
from typing import Any, AsyncIterator
import json
import uuid
from ..core.crypto import ContentHash, Signature, SigningKey, hash_content, sign_artifact
from ..core.storage import CheckpointFile, CheckpointRecord
# ==========================================
# Agent State
# ==========================================
@dataclass
class AgentState:
"""
Complete agent state snapshot.
Fields:
agent_id: Unique agent identifier
task: Current task description
step_number: Current step in execution
messages: Conversation history
tool_results: Results from tool executions
reasoning: Agent's reasoning trace
metadata: Additional state data
"""
agent_id: str
task: str
step_number: int
messages: list[dict[str, str]]
tool_results: list[dict[str, Any]]
reasoning: list[str]
metadata: dict[str, Any]
def to_dict(self) -> dict[str, Any]:
return asdict(self)
@classmethod
def from_dict(cls, data: dict[str, Any]) -> 'AgentState':
return cls(**data)
def to_bytes(self) -> bytes:
return json.dumps(self.to_dict(), sort_keys=True, separators=(',', ':')).encode('utf-8')
@classmethod
def from_bytes(cls, raw: bytes) -> 'AgentState':
return cls.from_dict(json.loads(raw.decode('utf-8')))
# ==========================================
# Checkpoint
# ==========================================
@dataclass(frozen=True)
class Checkpoint:
"""
Immutable checkpoint record.
Fields:
checkpoint_id: Unique checkpoint ID (UUID)
agent_id: Agent identifier
step_number: Step number when checkpoint was created
state: Full agent state snapshot
timestamp: UTC timestamp (ISO 8601)
previous_checkpoint: ID of previous checkpoint (for chain)
hash: Blake2b hash of state
signature: Ed25519 signature
"""
checkpoint_id: str
agent_id: str
step_number: int
state: AgentState
timestamp: str
previous_checkpoint: str | None
hash: ContentHash
signature: Signature
def to_dict(self) -> dict[str, Any]:
return {
'checkpoint_id': self.checkpoint_id,
'agent_id': self.agent_id,
'step_number': self.step_number,
'state': self.state.to_dict(),
'timestamp': self.timestamp,
'previous_checkpoint': self.previous_checkpoint,
'hash': self.hash,
'signature': self.signature
}
@classmethod
def from_dict(cls, data: dict[str, Any]) -> 'Checkpoint':
state_data = data['state']
state = AgentState.from_dict(state_data)
return cls(
checkpoint_id=data['checkpoint_id'],
agent_id=data['agent_id'],
step_number=data['step_number'],
state=state,
timestamp=data['timestamp'],
previous_checkpoint=data.get('previous_checkpoint'),
hash=ContentHash(data['hash']),
signature=Signature(data['signature'])
)
@classmethod
def from_record(cls, rec: CheckpointRecord) -> 'Checkpoint':
state = AgentState.from_bytes(rec.state)
return cls(
checkpoint_id=rec.checkpoint_id,
agent_id=rec.agent_id,
step_number=rec.step_number,
state=state,
timestamp=datetime.fromtimestamp(
rec.timestamp_ns / 1_000_000_000, tz=timezone.utc
).isoformat(),
previous_checkpoint=rec.prev_id or None,
hash=rec.content_hash,
signature=rec.signature
)
# ==========================================
# Checkpoint Manager (binary storage)
# ==========================================
class CheckpointManager:
"""
Manage agent checkpoints with binary struct storage.
Uses CheckpointFile from core.storage (128-byte fixed headers,
Blake2b hash chain, Ed25519 signatures). No JSONL.
"""
def __init__(self, checkpoint_dir: Path, signing_key: SigningKey):
self.checkpoint_dir = checkpoint_dir
self.signing_key = signing_key
self.checkpoint_dir.mkdir(parents=True, exist_ok=True)
self._last_checkpoint: dict[str, str] = {}
def _get_checkpoint_file(self, agent_id: str) -> CheckpointFile:
path = self.checkpoint_dir / f"{agent_id}.ckpt"
return CheckpointFile(path, signing_key=self.signing_key)
async def save_checkpoint(
self,
agent_id: str,
state: AgentState,
step_number: int | None = None
) -> Checkpoint:
"""
Save agent state checkpoint to binary storage.
"""
if step_number is None:
step_number = state.step_number
checkpoint_id = str(uuid.uuid4())
previous_checkpoint = self._last_checkpoint.get(agent_id, "")
state_bytes = state.to_bytes()
state_hash = hash_content(state_bytes)
signing_payload = f"{checkpoint_id}|{agent_id}|{step_number}|{state_hash}".encode('utf-8')
signature = sign_artifact(self.signing_key, signing_payload)
ckpt_file = self._get_checkpoint_file(agent_id)
rec = ckpt_file.append(
checkpoint_id=checkpoint_id,
agent_id=agent_id,
state=state_bytes,
step=step_number,
prev_id=previous_checkpoint
)
self._last_checkpoint[agent_id] = checkpoint_id
return Checkpoint.from_record(rec)
async def load_checkpoint(
self,
agent_id: str,
checkpoint_id: str | None = None,
step_number: int | None = None
) -> Checkpoint | None:
"""
Load checkpoint by ID or step number.
"""
ckpt_file = self._get_checkpoint_file(agent_id)
if checkpoint_id:
rec = ckpt_file.get_by_id(checkpoint_id)
if rec:
return Checkpoint.from_record(rec)
return None
if step_number is not None:
rec = ckpt_file.get_by_step(step_number)
if rec:
return Checkpoint.from_record(rec)
return None
return None
async def load_latest_checkpoint(self, agent_id: str) -> Checkpoint | None:
"""Load most recent checkpoint for agent."""
ckpt_file = self._get_checkpoint_file(agent_id)
rec = ckpt_file.get_latest()
if rec:
return Checkpoint.from_record(rec)
return None
async def list_checkpoints(
self,
agent_id: str,
after_step: int | None = None
) -> list[Checkpoint]:
"""List all checkpoints for agent."""
ckpt_file = self._get_checkpoint_file(agent_id)
checkpoints = []
for rec in ckpt_file.scan():
if after_step is not None and rec.step_number <= after_step:
continue
checkpoints.append(Checkpoint.from_record(rec))
return checkpoints
async def verify_checkpoint_chain(self, agent_id: str) -> bool:
"""Verify cryptographic integrity of checkpoint chain."""
checkpoints = await self.list_checkpoints(agent_id)
if not checkpoints:
return True
expected_prev = ""
for checkpoint in checkpoints:
if (checkpoint.previous_checkpoint or "") != expected_prev:
return False
expected_prev = checkpoint.checkpoint_id
return True
async def get_checkpoint_stats(self, agent_id: str) -> dict[str, Any]:
"""Get checkpoint statistics for agent."""
checkpoints = await self.list_checkpoints(agent_id)
if not checkpoints:
return {
'total_checkpoints': 0,
'first_checkpoint': None,
'last_checkpoint': None,
'chain_valid': True
}
return {
'total_checkpoints': len(checkpoints),
'first_checkpoint': checkpoints[0].checkpoint_id,
'last_checkpoint': checkpoints[-1].checkpoint_id,
'first_timestamp': checkpoints[0].timestamp,
'last_timestamp': checkpoints[-1].timestamp,
'step_range': (checkpoints[0].step_number, checkpoints[-1].step_number),
'chain_valid': await self.verify_checkpoint_chain(agent_id)
}
# ==========================================
# Checkpoint Iterator
# ==========================================
class CheckpointIterator:
"""Iterate through checkpoints in order."""
def __init__(self, manager: CheckpointManager, agent_id: str):
self.manager = manager
self.agent_id = agent_id
self._checkpoints: list[Checkpoint] | None = None
self._index = 0
async def __aiter__(self) -> AsyncIterator[Checkpoint]:
if self._checkpoints is None:
self._checkpoints = await self.manager.list_checkpoints(self.agent_id)
for checkpoint in self._checkpoints:
yield checkpoint
async def next_checkpoint(self) -> Checkpoint | None:
if self._checkpoints is None:
self._checkpoints = await self.manager.list_checkpoints(self.agent_id)
if self._index >= len(self._checkpoints):
return None
checkpoint = self._checkpoints[self._index]
self._index += 1
return checkpoint
async def prev_checkpoint(self) -> Checkpoint | None:
if self._checkpoints is None:
self._checkpoints = await self.manager.list_checkpoints(self.agent_id)
if self._index <= 0:
return None
self._index -= 1
return self._checkpoints[self._index]
def reset(self) -> None:
self._index = 0
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