Global durable
Root manifests, CAS objects, node graph, logical agent state, policies, evaluator versions, trajectories, audit records
State plane
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01 · System design
A durable checkpoint graph over a bounded execution pool.
The graph is the product-level source of history; execution attempts are disposable projections. LayerStack preserves workspace identity while OCI/Linux and WASI provide different ways to run it.
- Status
- Target design
- Scope
- 0.2.x architecture
- Primary decision
- Graph over sessions
- Portability
- OCI/Linux + WASI
Architecture decision
Persist nodes. Rent execution.
A SandboxNode is an immutable checkpoint reference plus logical state and provenance. It does not permanently own a container, mount, process, or worker. The scheduler activates only the frontier required by current work.
- Immutable roots
- A selectable node never changes after sealing.
- Private writes
- Every active attempt owns its writable delta.
- Bounded residency
- Live sandboxes are capped independently of graph size.
- Explicit integration
- Only OCC merge or promotion advances canonical state.
Reference architecture
Control, state, and execution remain separate.
The orchestration plane owns graph semantics. The state plane owns durable identity. Executors consume leases and return sealed results; they never become the source of checkpoint truth.
Workload controllers
Multiagent development
RL coordinator
MCTS controller
Orchestration plane
SandboxGroup service
Search / rollout state
Placement scheduler
Evaluator / verifier
Durable state plane
Logical manifests
Content-addressed storage
OCC · leases · journal
Trajectories · evidence
Bounded worker pool
OCI/Linux executor
WASI executor
Sealed result
Checkpoint · logs · patch · evaluation · provenance
Checkpoint graph
History can grow without keeping every branch alive.
Nodes share immutable roots and content identities. Activation allocates an execution attempt with a private delta; suspension seals that delta and releases the runtime slot.
root / N0
durable
candidate A
sealed
candidate B
active attempt
candidate C
sealed
B / child 1
active attempt
B / child 2
prunable
Fork accounting
- Logical child
- O(1)
- Parent RootId + new node metadata
- Hot local lower
- 0 payload bytes
- Lease an existing immutable native root
- Writable state
- Changes only
- Private upper/delta grows with actual writes
- Cold worker
- Hydration cost
- Materialize once, then share locally
Durable delta storage
Content-defined chunking makes the checkpoint graph space-aware.
Stable content identities sit beneath logical tree manifests and immutable B/L/S deltas. The capture path can reuse unchanged content and pack metadata without moving CAS reconstruction into commands, PTY, or stdin.
Lifecycle protocol
Checkpoint publication is an explicit transaction.
The critical path is expressed as a recoverable state machine so a crash can resume or abort without inventing a partially published node.
ControllerState planeSchedulerExecutorEvaluator
01Fork
Create child NodeId referencing an immutable parent RootId.
02Lease
Pin root and reserve one bounded execution slot.
03Activate
Build the backend view and allocate a private writable delta.
04Execute
Run commands or a rollout; stream evidence to attempt storage.
05Quiesce
Stop admissions, drain command/PTY work, and freeze the delta boundary.
06Seal
Publish manifest, logical state, provenance, and attempt result atomically.
07Evaluate
Run versioned tests or reward logic against the sealed root.
08Resolve
Promote, merge, backpropagate, retain, or prune idempotently.
State ownership
Each fact has exactly one durability owner.
Worker durable cache
Hydrated immutable roots, verified native extents, reusable image/runtime materialization
Worker cache manager
Attempt ephemeral
Mount namespace, private upperdir, workdir, PID/cgroup state, live PTY buffers
Executor lease
OCI/Linux projection
Mount over LayerStack materialization—not over user host volumes.
A worker hydrates or reuses an immutable native lower root, then composes a private writable view inside the sandbox mount namespace. The target image supplies no helper binary and never owns durable workspace truth.
Immutable lower root
Worker-local, verified, shared read-only
Private upper + work
Attempt-local writable delta
Overlay workspace
Mounted inside executor namespace
Command / PTY
Ordinary native file access