Portable VM Snapshots: Migrating Live AI Isolates Across Nodes 📸

1. What a VM snapshot contains

A KnotenCore isolate is a self-contained execution unit: it owns a register file, an operand stack, a call frame stack, a heap region for complex values, and a program counter pointing into its compiled bytecode. When knc_agent_snapshot is called, the VM is suspended at a safe yield point — it never captures mid-instruction state — and each of these regions is serialized in order using a length-prefixed binary format. The bytecode itself is stored as a content-addressed hash; the receiving node fetches the actual bytecode from the cluster's shared program store if it does not already have it cached locally.

The snapshot blob is intentionally compact. Only live heap cells reachable from the current register file and stack are included — dead values collected during the last GC cycle are not serialized. In practice, a mid-computation isolate running a moderately complex agent policy snapshots to between 4 KB and 80 KB depending on heap depth, making the blob trivially transferable over a standard JSON-RPC response body.

The snapshot format is versioned. The first four bytes encode a magic number and a schema version, ensuring that a v2.12.0 node will always reject a snapshot from an incompatible schema version rather than silently restoring corrupted state. This forward-compatibility guarantee is critical in rolling-upgrade deployments where nodes may temporarily run different minor versions.

2. The knc_agent_handshake & knc_agent_restore flow

Migration follows a three-phase protocol. In phase one, the orchestrator sends knc_agent_handshake to the destination node, advertising the isolate ID, schema version, and the content hash of the required bytecode. The destination responds with a capability acknowledgement and signals whether it already has the bytecode cached. If not, the orchestrator pushes the bytecode in a follow-up knc_program_upload call before proceeding.

In phase two, the orchestrator calls knc_agent_snapshot on the source node to obtain the binary blob and the current ledger hash. The source node suspends the isolate, serializes it, and returns the base64-encoded payload in the JSON-RPC result field. The isolate remains suspended — not terminated — until the orchestrator confirms successful restoration on the destination.

In phase three, the orchestrator calls knc_agent_restore on the destination node, passing the blob and the expected ledger hash. The destination deserializes the state, verifies the hash chain, and resumes the isolate from the exact instruction it was suspended at. Only after receiving a success acknowledgement does the orchestrator call knc_agent_terminate on the source node to release the suspended isolate. The result is a zero-downtime migration: from the agent's perspective, execution never stopped.

// Phase 1 — Handshake with destination node
{"jsonrpc":"2.0","method":"knc_agent_handshake",
 "params":{"isolate_id":"agt-7f3a","schema_version":"2.12.0",
            "bytecode_hash":"sha256:e3b0c44298fc..."},
 "id":1}

// Phase 2 — Snapshot from source node
{"jsonrpc":"2.0","method":"knc_agent_snapshot",
 "params":{"isolate_id":"agt-7f3a","suspend":true},
 "id":2}
// → result: { "blob": "<base64>", "ledger_hash": "sha256:a1b2c3..." }

// Phase 3 — Restore on destination node
{"jsonrpc":"2.0","method":"knc_agent_restore",
 "params":{"isolate_id":"agt-7f3a","blob":"<base64>",
            "expected_ledger_hash":"sha256:a1b2c3..."},
 "id":3}

3. SHA-256 cryptographic ledger chain for replay attack defense

Every KnotenCore isolate maintains a monotonically advancing ledger hash. Each time the isolate executes a state-mutating operation — writing a variable, calling a native function, yielding a result — the current hash is updated: new_hash = SHA-256(prev_hash || operation_descriptor). This forms a tamper-evident chain that captures the full causal history of the isolate's execution.

The ledger hash serves two purposes in the snapshot protocol. First, it acts as a state fingerprint: the source and destination both compute the expected hash independently, and a mismatch causes knc_agent_restore to return an LedgerMismatch error, refusing to resurrect a tampered or outdated blob. Second, it defends against replay attacks — an adversary who intercepts a valid snapshot blob cannot re-inject it later, because the destination node will detect that the ledger hash no longer matches the current cluster state for that isolate ID.

In high-security deployments, the orchestrator can additionally require a cluster-wide ledger epoch counter to advance monotonically, preventing any rollback to a previous snapshot even if an attacker has access to multiple historical blobs. This gives KnotenCore's state migration the same replay-resistance guarantees typically associated with cryptographic session tokens — applied directly to executable agent state.

4. Practical applications: live load balancing and fault recovery

The snapshot protocol unlocks two classes of cluster operations that were previously impossible: proactive load balancing and transparent fault recovery. For load balancing, an orchestrator monitoring per-node CPU and memory pressure can migrate hot isolates to underutilized nodes at runtime — without interrupting the agent's ongoing task. The agent program sees no discontinuity; it simply wakes up on a different physical host and continues from where it left off.

For fault recovery, nodes that receive a SIGTERM from a container orchestrator can emit a checkpoint snapshot for all running isolates before shutting down. A recovery controller monitors these checkpoints and restores them on replacement nodes within seconds, achieving effective RTO values far below what traditional process-level restart strategies can offer. Because the snapshot includes the full heap and call stack — not just the program's persistent output — the restored agent resumes mid-computation rather than from scratch.

Combined with the headless build profile introduced in v2.12.0, portable snapshots position KnotenCore as a first-class runtime for autonomous AI workloads that must survive infrastructure turbulence — node replacements, rolling upgrades, and cloud spot-instance evictions — without sacrificing execution continuity.