feat(platform-wallet): reserve DashPay payout addresses without Core funding

[PastaPastaPasta]

Supersedes #4614 (re-opened from the main repo so the Rust/Swift CI jobs run on it).

Issue being fixed or feature implemented

DashPay contact payments currently expose a combined address-resolution and Core-funded send operation. Wallets with Platform or shielded funds cannot obtain a fresh DIP-15 contact destination without selecting transparent Core inputs.

What was done?

Add DashPayView::reserve_payment_address and the Swift ManagedPlatformWallet.reserveDashPayPaymentAddress(fromIdentityId:toContactIdentityId:) wrapper through the C FFI. The operation completes the seed-verified deferred contact-crypto drain, consumes an address from the authoritative wallet/owner/contact external account pool, and persists and flushes its used flag before returning it.

Core sends and external payout reservations share the derivation helper and a per-wallet gate that keeps their pool snapshots ordered. Core broadcasts release the gate while awaiting the network, then reacquire it before a definitive rejection's address rollback. The Swift wrapper retains its mnemonic resolver throughout the FFI call and frees the returned string.

Callers reserve only when submitting a confirmed payment. Exposed addresses stay consumed after cancellation, rejected withdrawal, or an unknown outcome; this API does not submit the withdrawal or record payment history. The companion iOS change owns the submitted-withdrawal history.

How Has This Been Tested?

• Rust DashPay payments unit suite: 61 passed, including zero-Core-balance reservations, wallet/identity/contact scoping, persisted rotation shared with a subsequent Core send, store/flush failure, wrong-seed rejection, deferred contact setup, and preservation across a concurrent Core rejection.
• cargo clippy -p platform-wallet -p platform-wallet-ffi --lib (only pre-existing upstream warnings).
• cargo fmt -p platform-wallet -p platform-wallet-ffi --check and git diff --check.
• iOS simulator release FFI build and SwiftExampleApp Xcode build.

Real testnet validation used two registered DashPay contacts: a 0.02 DASH Platform withdrawal with zero Transparent balance and a user-submitted 0.1 DASH Shielded withdrawal paid the reserved addresses. Recipient receipt verification used a combined test build with the separate AssetUnlock discovery fix in dashpay/rust-dashcore#1004. Screenshots and exact build provenance.

The receipt fix needs a separate upstream SDK dependency update. This PR only adds address reservation and leaves the existing rust-dashcore dependencies unchanged.

Breaking Changes

None. The existing Core-funded send API remains available.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

This pull request was created by Codex.

[coderabbitai]

Warning

Review limit reached

Next included review available in 49 minutes.

Check out review usage here.

View limit details

Limit details: You’ve used the included review currently available.

You've used all free OSS reviews for now. Wait for the free limit to reset to keep reviewing this public repository.

Learn how review limits work.

Review configuration:

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Advanced

Run ID: 6085d4f6-2e2b-449b-8d09-8baf03aa2376

📥 Commits

Reviewing files that changed from the base of the PR and between 4993109 and d7d0224.

📒 Files selected for processing (4)

• packages/rs-platform-wallet-ffi/src/dashpay.rs
• packages/rs-platform-wallet/src/wallet/identity/network/payments.rs
• packages/rs-platform-wallet/src/wallet/persister.rs
• packages/swift-sdk/Sources/SwiftDashSDK/PlatformWallet/ManagedPlatformWallet.swift

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[thepastaclaw]

🕓 Queued for automated review — 56th in line, estimated start in ~77 h (commit d7d0224)
Estimated review time once started: ~2.8 h (two-phase automated review; median of recent runs).

• Request priority review — tick this box and the review moves to the front of the queue.