Add venue-neutral transaction composition

[tvolk131]

Summary

• add venue-neutral exact-in and exact-out execution intents with exact per-leg allocations
• bind adapter proposals to concrete confidential payment/receipt outputs and contribution-local blinding roles
• add a deterministic transaction composer with local symbolic IDs, one explicit network fee, global locktime intersection, resource limits, and a frozen unblinded-structure manifest
• compose non-issuance binary-market transitions at nonzero input/output offsets, including expiry locktime activation
• refactor the two-wallet confidential RFQ fixture through the production route/composer seam
• update the liquidity roadmap and ADR implementation status

Why

This implements roadmap item 4: a client-local transaction-composition boundary that is independent of whether a future fill originates from RFQ, DLOB, or AMM routing. It lets multiple independently prepared legs be assembled atomically without introducing a remote RFQ wire format or venue-specific PSET ownership.

The staging model prevents aggregate validation and final assembly from silently diverging: a validated route owns the exact prepared legs and network fee it composes. Cross-contribution blinding uses exact outpoints, and payer inputs must belong exclusively to the wallet contribution.

Safety boundaries

This remains a provisional normalization/composition API. Route validation authorizes declared trade claims, not wallet change, ancillary-output net effects, per-asset balance, proofs, sighash policy, or signing. Each participant must still validate the complete blinded transaction before signing.

Issuance contributions, output aggregation, remote quote validity/provenance, and AMM/DLOB-specific covenant delta/finalizer models remain deliberately deferred.

Confidential input rangeproofs are copied into the dedicated Elements PSET field so they survive serialized participant handoffs.

Validation

• nix develop .#default --command just ci-checks
  • formatting and strict workspace Clippy
  • 233/233 tests passed
  • documentation tests
  • WebAssembly build
• nix develop .#default --command just regtest-rfq-settlement
  • broadcast and mined the confidential P2TR settlement
  • spent both participants' received outputs

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