native-da v0.3+: §13 future-work tracking

[proofmancer]

Tracks the §13 future-work surface from native-da v0.2.

• Engineering-cost refinement (§13.1) — multi-quarter design + implementation + audit + bootstrap. v0.2 documents the design; future revisions refine cost estimates as the chain matures.
• Cross-DA bridging (§13.2) — during migration, attestations split across Celestia (legacy) and native DA (new). v0.2 sketches §11.2 hybrid mode; full specification deferred until migration is decided.
• Quantum-resistant commitments (§13.3) — KZG + Verkle depend on Shor-vulnerable schemes. §6.1 SHA-256-based Merkle trees are PQ-resistant under Grover. BLS aggregation in §6.3 needs PQ migration in lockstep. Cross-link Post-quantum cryptographic migration path for attestation-native chains #128 + Hybrid PQ signatures: Ed25519 default + Dilithium optional for v1 chain #50.
• Cross-chain attestation portability (§13.4) — native DA layer that doesn't bridge to other ecosystems loses composability. IBC-mediated proofs for cross-chain queries. Adds DA-layer protocol surface. Candidate for unified cross-chain follow-up paper.

Migration gates

§12 criteria: sustained throughput, light-client growth, fee-cost ratio. Until met, this paper is reference material; v0.3 is design refinement, not migration trigger.