Preserve opencode sessions

Context

Craft sessions use opencode serve as the long-lived agent runtime inside a sandbox. Onyx persists the BuildSession.opencode_session_id in Postgres so a later turn can reconnect to the same opencode session instead of creating a fresh one every message.

That ID alone is not enough after a Kubernetes sandbox sleeps, is evicted, or is recreated. The opencode session rows live inside opencode's data directory in the sandbox filesystem. If the sandbox-level opencode data is not persisted and restored, the Postgres ID points at nothing.

The current implementation persists opencode history as sandbox-global state, separate from normal per-session workspace snapshots.

Goals

1. Preserve opencode's session history across Kubernetes sandbox sleep, recovery, and reprovision.
2. Keep durable storage ownership in the API server / FileStore layer, not in sandbox pods.
3. Keep normal session snapshots focused on per-session files.
4. Keep Docker workspace snapshots from carrying opencode data; opencode history persistence is currently a Kubernetes-only capability.
5. Be optimistic when a saved opencode ID is missing from a restored DB: mint a replacement ID and persist it. A later follow-up can replay saved chat history into that replacement session.
6. Treat opencode's session store as implementation data. Deleting an Onyx BuildSession removes the product-visible record and best-effort deletes the live opencode session when the sandbox is running; failure does not block Onyx deletion and does not prune durable history archives.

Storage Model

There are two distinct persistence surfaces.

Per-session workspace snapshots

Normal session snapshots capture only session-local user output:

• outputs/
• attachments/ when present and non-empty

They deliberately do not capture .opencode-data. These archives are created and restored by the sandbox sidecar through:

• POST /snapshot/create
• POST /snapshot/restore/{session_id}

The sidecar owns local filesystem access. The API server streams the archive into FileStore through SnapshotManager.

Sandbox-global opencode history

Opencode history is shared by all BuildSessions in a sandbox. In Kubernetes the pod is configured with:

• OPENCODE_DATA_HOME=/workspace/opencode-data

The opencode data root is:

/workspace/opencode-data

The durable FileStore object is deterministic per sandbox:

sandbox-snapshots/{tenant_id}/{sandbox_id}/opencode-history.tar.gz

The archive stores that directory under a stable archive root:

.opencode-data/

This keeps opencode persistence separate from session workspaces while avoiding a custom per-session opencode store that would not match opencode's actual sandbox-level data model.

Important Components

SnapshotManager

backend/onyx/server/features/build/sandbox/snapshot_manager.py

Owns FileStore persistence for both normal session snapshots and sandbox-global opencode history snapshots. Normal sidecar-created workspace snapshots keep the sidecar's archive and uncompressed-size checks. Opencode history snapshots use the deterministic storage path above and are not capped by workspace snapshot limits. Kubernetes still bounds the pod-local opencode data volume with an emptyDir.sizeLimit.

Sandbox sidecar snapshot endpoints

backend/onyx/server/features/build/sandbox/image/sandbox_daemon/server.py

The sidecar exposes local filesystem operations as signed HTTP endpoints. It does not upload to S3 and does not know tenant storage credentials.

For opencode history:

• GET /ready returns healthy only after the startup restore path has restored or explicitly skipped opencode history. This endpoint is used as the restartable init sidecar startup gate, not as the steady-state pod readiness signal.
• POST /opencode-history/create returns 204 when the opencode data directory has no content, otherwise streams a gzip archive.
• POST /opencode-history/restore accepts a signed, hash-verified archive body and restores the opencode data directory locally.
• POST /opencode-history/mark-restored marks a fresh sandbox ready when no durable history snapshot exists.

Opencode history archive helpers

backend/onyx/server/features/build/sandbox/image/sandbox_daemon/opencode_history.py

This module owns the opencode data archive logic:

• keep the opencode data path outside /workspace/sessions
• stage the opencode data directory before archiving it
• replace the staged opencode/opencode.db, when present, with a SQLite backup so the archive carries a coherent DB snapshot even if opencode serve is running
• restore the archive with Python's standard tar data filter, then replace /workspace/opencode-data with the extracted .opencode-data/ root
• ignore unrelated top-level archive entries outside .opencode-data/
• if the known current opencode/opencode.db is present but corrupt after restore, clear the restored opencode data directory so opencode serve starts fresh
• rely on signed sidecar endpoints and SHA-256 request verification for transport integrity
• write the startup restore marker under sidecar-owned managed state at /workspace/managed/.onyx/opencode-history-restored

This is separate from snapshot.py, which now remains focused on normal session workspace snapshotting.

Kubernetes sandbox manager

backend/onyx/server/features/build/sandbox/kubernetes/kubernetes_sandbox_manager.py

The K8s manager coordinates pod lifecycle, sidecar calls, FileStore streaming, and startup restore gating.

It is the only backend currently advertising:

supports_opencode_history_persistence = True

Craft's Kubernetes pod template uses a native restartable init sidecar, so Craft Helm deployments require Kubernetes 1.33 or newer. This is enforced at deployment/render time by the chart, not by a runtime backend version check.

Provision And Restore Flow

When a Kubernetes sandbox pod starts:

1. Kubernetes starts the firewall init container.
2. Kubernetes starts the restartable sidecar init container. Its health endpoint is available, but its startup endpoint stays blocked.
3. The K8s manager ensures the sandbox Service exists and publishes not-ready pod addresses so the sidecar can be reached before pod readiness.
4. If no durable opencode history snapshot exists, the manager posts a signed request to /opencode-history/mark-restored.
5. If a durable history snapshot exists, the API server reads it from FileStore into a temp file, computes its SHA-256, and posts it to /opencode-history/restore.
6. The sidecar restores the opencode data directory. If the restored current opencode DB is corrupt, the sidecar clears that data so opencode can start fresh instead of starting against known-bad state.
7. The sidecar marks opencode history restored.
8. The sidecar /ready endpoint succeeds, which releases the restartable init sidecar startup gate.
9. Kubernetes starts the sandbox app container. Its entrypoint runs opencode serve with XDG_DATA_HOME pointed at /workspace/opencode-data.
10. The K8s manager waits for pod readiness and opencode serve readiness.

The important property is that opencode serve never starts before restore has completed or been explicitly skipped.

When the K8s manager finds an already healthy sandbox pod, it reuses that pod without re-running startup history restore.

Snapshot Creation Flow

Opencode history snapshots are created before a sandbox sleeps and during best-effort recovery.

1. The K8s manager signs a request to /opencode-history/create.
2. The sidecar checks whether the opencode data directory has content.
3. If it has no content, the sidecar returns 204.
4. If it has content, the sidecar stages the opencode data directory, replaces the staged SQLite DB with a sqlite3.Connection.backup() copy, creates a tar.gz archive, and streams it back.
5. The API server streams the response into SnapshotManager.
6. SnapshotManager stores it at the stable sandbox-level FileStore key.

If the sidecar returns 204 for an empty live store, the manager preserves any existing durable history archive. That is important for idle/recovery paths: a transient live empty/missing DB should not destroy the last known good history.

Send Message Flow

The prompt path is intentionally optimistic.

1. The session row carries BuildSession.opencode_session_id when one has been persisted.
2. Before a turn, _ensure_opencode_session_id mints and persists an opencode session ID if the row has none.
3. yield_sandbox_events calls sandbox_manager.send_message with the saved ID and an on_opencode_session_resolved callback.
4. _send_message_via_serve calls OpencodeServeClient.ensure_session.
5. If the saved ID exists, opencode returns 200 and the same ID is reused.
6. If opencode returns 404, Onyx creates a fresh opencode session and invokes the callback so the BuildSession row is updated.
7. Non-404 lookup errors still raise. A runtime outage should not silently mint a replacement session.
8. The message is sent to the resolved opencode session and normal event streaming proceeds.

This means a restored sandbox with a missing opencode ID does not fail the user turn. It starts a new opencode session and records the new ID. The tradeoff is that opencode itself does not yet receive prior chat history in that newly created session. That replay behavior is intentionally out of scope for this change.

Delete Session Flow

Deleting a BuildSession deletes Onyx's durable session record. When the sandbox is running and the row has an opencode_session_id, Onyx also makes a best-effort request to delete that live opencode session. That cleanup is an optimization only: failures are logged and do not block deleting the Onyx row.

Opencode history remains sandbox-global implementation data, so session delete does not prune durable opencode history archives. If opencode still has a row for the deleted BuildSession, that row is orphaned and no longer reachable through Onyx.

1. SessionManager.delete_session acquires the session prompt slot.
2. If the sandbox is running and the BuildSession has an opencode session ID, the manager best-effort deletes that live opencode session.
3. Normal workspace cleanup and Snapshot FileStore cleanup proceed.
4. The BuildSession DB row is deleted.

For a sleeping or otherwise not-running sandbox, deletion does not try to edit or validate opencode history. The Onyx row is removed, so any stale opencode record left in a durable history archive is orphaned implementation data.

Idle Sleep Flow

The sandbox cleanup task handles idle running sandboxes.

1. If the backend supports opencode history persistence, it first attempts an opencode history snapshot.
2. If that snapshot fails but the sandbox still passes health check, the task leaves the sandbox running. Sleeping a healthy sandbox without fresh history would risk losing recent agent context.
3. If the pod is already unreachable, the task logs a warning and continues cleanup. At that point the live filesystem cannot be trusted or accessed for a fresh snapshot.
4. The task then snapshots each session workspace.
5. The sandbox can be put to sleep after required snapshots complete.

Recovery Flow

When Onyx detects an unhealthy running sandbox and needs to terminate/recover it, the lifecycle code attempts a best-effort opencode history snapshot before termination.

This path is best-effort because the sandbox may already be partially dead. A failure is logged but does not block recovery forever.

On reprovision, the normal restore flow restores the last durable opencode history snapshot if one exists.

Reset / Start Fresh Flow

User-requested sandbox reset is a destructive "start fresh" operation.

1. Delete the durable opencode history snapshot.
2. Terminate the sandbox resources.
3. Mark the sandbox DB row as TERMINATED in the caller-owned transaction.
4. Commit only after the durable history delete and sandbox termination succeed.

The durable FileStore delete is external to the DB transaction. If termination fails after history deletion succeeds, the API reports reset failure and rolls back DB state, but the durable history object is already gone. This preserves the "start fresh" invariant on the next successful provision.

If the sandbox row is already TERMINATED, reset has no live pod or DB status transition left to protect. In that case the durable history delete is best-effort: failures are logged and the reset still returns success. A later reset can retry the delete once FileStore recovers.

This is intentionally different from idle sleep. Sleep preserves history; reset removes it.

Why This Is Not A Normal Session Snapshot

The normal snapshot loop iterates session directories and stores each session's workspace. That is the right model for outputs and attachments.

Opencode history is different:

• opencode stores all sessions in one sandbox-level data store
• a per-session archive cannot safely represent the shared data store
• multiple BuildSessions can share the same opencode history store
• deleting one session can leave orphaned opencode rows because Onyx does not edit opencode's internal store on BuildSession deletion
• reset must delete the shared archive, not merge or preserve per-session stores

So the implementation reuses the same high-level snapshot infrastructure (SnapshotManager, FileStore, signed sidecar streaming), but keeps opencode history as a sandbox-level archive with its own create/restore endpoints and policy.

Operational Invariants

• The sandbox pod does not own durable storage credentials.
• The API server owns FileStore reads/writes.
• The sidecar owns pod-local filesystem reads/writes.
• Normal session snapshots do not contain .opencode-data.
• Opencode history is stored on a sandbox-global volume outside the /workspace/sessions tree.
• Opencode history snapshots contain the full .opencode-data/ archive root.
• A corrupt restored opencode/opencode.db is discarded in favor of a fresh opencode data directory.
• opencode serve starts only after startup history restore is complete.
• Craft Helm deployment fails fast on Kubernetes versions older than 1.33, before the backend starts provisioning sandbox pods.
• A missing saved opencode ID during send mints a new session and persists it.
• Runtime lookup errors other than 404 still fail the turn.
• Craft Helm deployment fails fast if ENABLE_CRAFT=true is paired with a non-Kubernetes sandbox backend.
• Session delete best-effort removes a live opencode session when possible, but still removes the BuildSession row if that cleanup fails.
• Session delete does not mutate durable opencode history archives.
• Reset deletes durable opencode history before terminating the sandbox so a failed delete does not leave a terminated sandbox with restorable stale history.

Known Follow-Up

If a restored sandbox does not contain the saved opencode ID, Onyx now mints a new opencode session and persists it. That avoids blocking the user, but the new opencode session does not yet contain prior chat history.

The planned follow-up is to detect this replacement-session case and replay the saved BuildMessage history into opencode before sending the next user prompt. That should live above the low-level snapshot/restore path. The snapshot layer should continue to restore the DB when possible and stay storage-focused.

Files Worth Reading

• backend/onyx/server/features/build/sandbox/image/sandbox_daemon/opencode_history.py
• backend/onyx/server/features/build/sandbox/image/sandbox_daemon/server.py
• backend/onyx/server/features/build/sandbox/snapshot_manager.py
• backend/onyx/server/features/build/sandbox/kubernetes/kubernetes_sandbox_manager.py
• backend/onyx/server/features/build/sandbox/opencode/serve_client.py
• backend/onyx/server/features/build/sandbox/serve_transport.py
• backend/onyx/server/features/build/session/streaming.py
• backend/onyx/server/features/build/session/manager.py