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21. Sidechains

21.1 Motivation​

quantos/src/sidechain/ contains an application-specific sidechain design. It explores custom runtimes, independent execution and L1 anchoring; inherited security is a target architecture, not a blanket guarantee of the current node.

┌─────────────────────────────────────────────────────────────┐
│                        Quantos L1                            │
│  ┌────────────────── Sidechain Registry ──────────────────┐ │
│  │  ┌──────────┐  ┌──────────┐  ┌──────────┐              │ │
│  │  │ Chain A  │  │ Chain B  │  │ Chain C  │   ...        │ │
│  │  │ (DeFi)   │  │ (Gaming) │  │ (NFT)    │              │ │
│  │  └────┬─────┘  └────┬─────┘  └────┬─────┘              │ │
│  │       └─────────────┼─────────────┘                    │ │
│  │               ┌─────▼──────┐                           │ │
│  │               │ Bridge Layer│  (asset locking)         │ │
│  │               └────────────┘                           │ │
│  └─────────────────────────────────────────────────────────┘ │
└─────────────────────────────────────────────────────────────┘

21.2 Shared-Security Model​

The documented sidechain model proposes a Proof-of-Stake bridge and L1 state commitments. The complete bridge, fraud-proof, validator participation and slashing path must be implemented and validated for a deployment:

  1. Staked participation: L1 validators opt in to securing a given sidechain by staking on its participation. They put L1-denominated stake at risk for honest sidechain operation.
  2. Periodic state commitments: Each sidechain posts a state commitment to the L1 every epoch, creating an immutable, L1-anchored history of the sidechain's state roots.
  3. Fraud proofs: Within a dispute window, any party may submit a fraud proof challenging an invalid sidechain state transition. A valid challenge reverts the disputed state.
  4. Slashing: Operators proven to have committed an invalid or fraudulent state transition are slashed, with the same economic finality as L1 misbehaviour.

If all commitment, dispute, validator and bridge invariants are implemented, this model could provide application-specific execution with L1 accountability. The current repository should not present that security inheritance as already established.

21.3 Asset Bridging​

Assets move between the L1 and a sidechain through a lock-and-mint bridge: tokens are locked on the source domain and a corresponding representation is credited on the destination domain, with the reverse on withdrawal. A lock-and-mint bridge is described as a target integration. Withdrawal security depends on actual state-root commitments, proof verification, relayer authorization, replay protection and key custody; these are deployment-specific and are not implied by the design description.

21.4 Custom Runtimes​

Each sidechain may define its own execution environment. A DeFi sidechain might run the full QuantosVM with the native token standards (Virtual Machine and Native Token Standards sections); a gaming sidechain might run a stripped-down, high-throughput runtime tuned for its specific transaction shapes. The L1 does not constrain the internal logic of a sidechain — it constrains only the commitment cadence and the fraud-proof / slashing discipline that keep the sidechain honest. This separation lets the ecosystem experiment with new runtimes without risking L1 consensus.