chore: track unfinished Q1 2026 PRD items (PRD being retired)

[oskarth]

PRD-IPTF-PUBLIC-Q1-2026.md is being retired. This issue captures the items it
listed that never shipped, so they aren't silently dropped. Promote any item to
its own issue if/when prioritized.

Stream B — Compliance & Client-Side Proving

• Client-Side Proving pattern — patterns/pattern-client-side-proving.md
  Mobile/browser ZK proving strategies, device constraints, delegation fallback.
  Refs: PSE roadmap (Mopro, Noir acceleration), Aztec PXE, Miden edge execution.
• Payment Policy Enforcement pattern — patterns/pattern-payment-policy-enforcement.md
  Policy templates, approval workflows, limits, cross-border restrictions.
  Cross-refs: pattern-mpc-custody.md, pattern-erc3643-rwa.md. Regulatory-critical.

Stream C — Analysis & Comparisons

• Vendor Capability Matrix — enhance vendors/README.md
  15+ vendors mapped to patterns, sortable/filterable.
• MEV Protection Guide — approaches/approach-mev-protection-institutional.md
  Strategies compared, integration steps, cost/benefit.
• Migration from Enterprise Chains — approaches/approach-enterprise-to-ethereum-migration.md
  Decision tree, common pitfalls, anonymized case studies.
• Proving Infrastructure Comparison — domains/proving-infrastructure-comparison.md
  Prover matrix (Barretenberg, Winterfell, Halo2, SnarkJS, RISC Zero), resource
  requirements, proving time benchmarks with sources.

Stream D — Use Case Synthesis

Stub patterns:

• pattern-secondary-market-rfq-batching.md
• pattern-cash-leg-tokenization.md
• pattern-derivative-settlement.md
• pattern-performance-optimization.md
• pattern-eligibility-attestation.md
• pattern-key-management-threshold.md (verify not already covered by pattern-mpc-custody.md)

Use cases:

• use-cases/tokenized-deposits.md (or fold into private-stablecoins.md)
• use-cases/private-lending.md
• use-cases/liquidity-management.md

Backlog (was deferred, still deferred)

• PR-033 Nullifier Set Scalability — patterns/pattern-nullifier-set-scalability.md
  Refs: Zcash Tachyon, oblivious message retrieval research.

Tech debt called out by the PRD

• 7 patterns exceeded the 800-word recommendation (re-audit; may be obsolete after CROPS refactor).
• Verify Intel SGX consumer-deprecation warning is present in pattern-tee-based-privacy.md.
• Clarify MEV-Boost vs Flashbots relay coverage in pattern-private-transaction-broadcasting.md.