Spanda

Future Blockchain Support

Blockchain is optional in Spanda. The language core implements audit and provenance abstractions; ledger anchoring is provided by future community packages.

Architecture

flowchart LR
  Robot[Robot runtime] --> Audit[AuditBackend]
  Audit --> Local[LocalAuditBackend]
  Audit --> JSON[JsonAuditBackend]
  Audit --> Ledger[LedgerBackend trait]
  Ledger --> Mock[MockLedgerBackend]
  Ledger --> Eth[spanda-ledger-ethereum]
  Ledger --> HL[spanda-ledger-hyperledger]
  Ledger --> Sol[spanda-ledger-solana]
  Ledger --> Iota[spanda-ledger-iota]

Trait interfaces (`spanda-audit`)

trait AuditBackend {
    fn append(record: AuditRecord) -> Result<RecordId>;
    fn verify(record_id: RecordId) -> Result<bool>;
    fn export() -> Result<AuditExport>;
}

trait LedgerBackend: AuditBackend {
    fn anchor_hash(hash: Hash) -> Result<TransactionId>;
    fn verify_anchor(hash: Hash) -> Result<bool>;
}

Future packages implement LedgerBackend for their chain SDK. The compiler and interpreter do not reference chain-specific types.

Planned community packages

Package	Import path	Purpose
`spanda-ledger`	`ledger.mock`	Mock anchoring (MVP, included in registry stub)
`spanda-ledger-ethereum`	`ledger.ethereum`	Ethereum anchoring
`spanda-ledger-hyperledger`	`ledger.hyperledger`	Hyperledger Fabric
`spanda-ledger-solana`	`ledger.solana`	Solana anchoring
`spanda-ledger-iota`	`ledger.iota`	IOTA tangle anchoring
`spanda-did`	`identity.core`	Decentralized identifiers
`spanda-provenance`	`provenance.core`	Mission provenance helpers
`spanda-supply-chain`	`supply_chain.trace`	Hardware supply-chain traceability

Allowed uses of blockchain

Audit anchoring — periodic hash commits of audit log roots
Supply-chain traceability — component provenance for hardware modules
Device identity — DIDs and verifiable credentials for fleet devices
Tamper-evident mission records — signed, hash-chained logs with optional on-chain anchors

Forbidden uses

Safety-critical control loops — no blockchain calls in actuator paths
Real-time motion planning — latency-sensitive paths stay local
On-chain actuation — actuators accept only SafeAction from local safety.validate()

Mock ledger today

Programs can anchor audit root hashes via the built-in mock backend:

audit.record("mission_tick", robot.pose());
let root = audit.root_hash();
mock_ledger.anchor(root);
mock_ledger.verify(root);

This exercises the LedgerBackend interface without network access. Replace mock_ledger with a package-provided backend when real chain packages ship.

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