feat(platform): send memos with shielded transfers

[QuantumExplorer]

Issue being fixed or feature implemented

Dash shielded notes reserve a 36-byte DashMemo (4-byte kind tag + 32-byte payload) in every note ciphertext, and all the dpp builders already accept it — but the wallet hardcoded [0u8; 36] on every send, so there was no way to attach a note to a shielded payment. There was also no memo-kind convention and no incoming-side primitive that could recover a memo (the scanner's compact IVK decryption stops before the memo region).

What was done?

• dpp::shielded::ShieldedMemo (new packages/rs-dpp/src/shielded/memo.rs): structured memo with kind 0 = Empty (the all-zero memo every existing sender writes), kind 1 = UTF-8 text (≤ 32 bytes, zero-padded), and Other { kind, payload } so unknown kinds round-trip verbatim. to_bytes/from_bytes are total and lossless.
• Memo threading (Type 16 ShieldedTransfer): operations::transfer and PlatformWallet::shielded_transfer_to take memo: [u8; 36]; platform_wallet_manager_shielded_transfer FFI gains a nullable memo_text: *const c_char — null/empty → empty memo, over-32-byte text rejected with ErrorInvalidParameter; encoding lives in Rust (encode_memo_text), Swift only bridges.
• Swift SDK: shieldedTransfer(walletId:account:recipientRaw43:amount:memo:) with memo: String? = nil.
• SwiftExampleApp: Send screen shows a "Memo (optional)" field when the flow is shielded → shielded, with a live N/32 bytes UTF-8 byte counter that turns red and disables Send when over the limit. Gated on the flow (not just the recipient type) so the self-shield path — which has no memo parameter — never shows a field that would silently drop text.
• dash_sdk::platform::shielded::try_decrypt_note_with_memo: full (non-compact) IVK trial decryption over the 104-byte enc_ciphertext, returning (note, address, memo) — the receive-side primitive the compact scanner can't provide.

Other send paths (shield, unshield, withdraw, identity-create) intentionally keep the empty memo.

How Has This Been Tested?

• cargo test -p dpp shielded::memo — 11 unit tests (round-trips incl. multibyte UTF-8 at exactly 32 bytes, over-limit rejection, unknown-kind preservation, invalid-UTF-8 fallback).
• cargo test -p platform-wallet --features shielded --release memo_roundtrip — 2 round-trip tests: a real built transition's memo is recovered by the recipient IVK via try_decrypt_note_with_memo, and an OVK-encrypted note's memo is recovered via try_recover_outgoing_note.
• cargo test -p platform-wallet-ffi --all-features encode_memo_text — 5 tests for the FFI text→bytes rules.
• cargo check with --all-features --tests on dpp / platform-wallet / platform-wallet-ffi and --features shielded --tests on dash-sdk; cargo fmt --all clean.
• iOS: build_ios.sh --target sim (regenerated cbindgen header) + SwiftExampleApp xcodebuild clean.
• Manual UAT on the paloma devnet simulator: sent 0.05 DASH shielded→shielded with memo "Thanks for lunch" — over-limit memo correctly blocks Send with a red 40/32 counter; transfer succeeded on-chain (input note spent, recipient + exact-change notes scanned back in, balance down by exactly the 0.00162851 DASH fee).

Breaking Changes

None consensus-wise. platform_wallet_manager_shielded_transfer (FFI) and operations::transfer/shielded_transfer_to (Rust API) gained a memo parameter; all in-tree callers updated.

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

🤖 Generated with Claude Code

Summary by CodeRabbit

Release Notes

• New Features

  • Shielded transfers now support optional recipient memos (UTF-8 text with 32-byte payload limit).
  • Added memo input field in the send UI for shielded-to-shielded transfers with live byte-count validation.

• Tests

  • Added comprehensive memo encoding/decoding and round-trip recovery validation tests.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: c9ae04dd-3828-4ccb-9f70-ed45f602a5a0

📥 Commits

Reviewing files that changed from the base of the PR and between bfa8f68 and 2c30ac9.

📒 Files selected for processing (12)

• packages/rs-dpp/src/shielded/memo.rs
• packages/rs-dpp/src/shielded/mod.rs
• packages/rs-platform-wallet-ffi/src/shielded_send.rs
• packages/rs-platform-wallet/src/wallet/platform_wallet.rs
• packages/rs-platform-wallet/src/wallet/shielded/operations.rs
• packages/rs-platform-wallet/src/wallet/shielded/sync.rs
• packages/rs-platform-wallet/src/wallet/shielded/sync/memo_roundtrip_tests.rs
• packages/rs-sdk/src/platform/shielded/mod.rs
• packages/rs-sdk/src/platform/shielded/notes_sync/decrypt.rs
• packages/swift-sdk/Sources/SwiftDashSDK/PlatformWallet/PlatformWalletManagerShieldedSync.swift
• packages/swift-sdk/SwiftExampleApp/SwiftExampleApp/Core/ViewModels/SendViewModel.swift
• packages/swift-sdk/SwiftExampleApp/SwiftExampleApp/Core/Views/SendTransactionView.swift

---

📝 Walkthrough

Walkthrough

This PR adds shielded transfer memo support across Rust and Swift layers: a new 36-byte memo format, memo-aware note decryption, memo propagation through wallet and FFI transfer paths, IVK/OVK round-trip tests, and Swift example app memo input with byte-limit validation.

Changes

Shielded memo support

Layer / File(s)	Summary
Memo contract and codec packages/rs-dpp/src/shielded/memo.rs, packages/rs-dpp/src/shielded/mod.rs	Adds ShieldedMemo, memo size constants, 36-byte encode/decode logic, and public re-exports. Includes tests for round-trip behavior, UTF-8 trimming, overflow rejection, and unknown/invalid fallback handling.
Memo-aware note decryption API packages/rs-sdk/src/platform/shielded/notes_sync/decrypt.rs, packages/rs-sdk/src/platform/shielded/mod.rs	Adds try_decrypt_note_with_memo that parses full encrypted note fields and returns note, recipient address, and recovered memo bytes. Re-exports and module docs are updated accordingly.
Wallet transfer memo plumbing packages/rs-platform-wallet/src/wallet/platform_wallet.rs, packages/rs-platform-wallet/src/wallet/shielded/operations.rs	Adds [u8; 36] memo parameter to wallet and transfer operations and forwards it into shielded transition construction instead of using a fixed zero memo.
FFI memo input and validation packages/rs-platform-wallet-ffi/src/shielded_send.rs	Extends shielded transfer FFI signature with optional memo_text, decodes and validates UTF-8 memo input, encodes memo bytes, maps invalid inputs to existing error variants, and forwards memo to wallet transfer. Includes memo encoding unit tests.
IVK and OVK memo round-trip tests packages/rs-platform-wallet/src/wallet/shielded/sync.rs, packages/rs-platform-wallet/src/wallet/shielded/sync/memo_roundtrip_tests.rs	Adds a new shielded sync test module and tests proving byte-for-byte memo round-trip through incoming IVK decryption and outgoing OVK recovery paths, including helper construction of encrypted wire note data.
Swift SDK memo parameter wiring packages/swift-sdk/Sources/SwiftDashSDK/PlatformWallet/PlatformWalletManagerShieldedSync.swift	Extends shieldedTransfer with optional memo: String? = nil, updates docs, and conditionally passes memo as a C string pointer or nil to FFI.
Example app memo UI and send gating packages/swift-sdk/SwiftExampleApp/SwiftExampleApp/Core/ViewModels/SendViewModel.swift, packages/swift-sdk/SwiftExampleApp/SwiftExampleApp/Core/Views/SendTransactionView.swift	Adds memo text state and UTF-8 byte counting, enforces a 32-byte limit for shielded-to-shielded sends in canSend, forwards trimmed memo when sending, and renders a conditional memo input with live over-limit highlighting.

Sequence Diagram(s)

sequenceDiagram
  participant App
  participant FFI
  participant Wallet
  participant Ops
  participant Builder
  App->>FFI: call shielded transfer with optional memo
  FFI->>FFI: validate memo utf8 and length
  FFI->>Wallet: invoke shielded transfer with memo bytes
  Wallet->>Ops: call transfer with memo bytes
  Ops->>Builder: build shielded transfer transition
  Builder-->>Ops: return transition with memo payload
  Ops-->>FFI: transfer result
  FFI-->>App: ffi result

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• dashpay/platform#3802: Both changes touch shielded transfer operation wiring in operations.rs, where this PR adds memo propagation and the related PR adjusts transfer-related fee checks.

Suggested reviewers

• shumkov
• thepastaclaw

Poem

🐇 I tucked a note in moonlit bytes,
Through shielded paths and silent lights.
From Rusty burrow to Swifty glade,
The memo hopped, correctly made.
Carrot cheers for tests well played! 🥕

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely captures the primary change: adding memo support to shielded transfers across the platform.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/shielded-transfer-memo

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[codecov]

Codecov Report

❌ Patch coverage is 95.79832% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.05%. Comparing base (af5611e) to head (2c30ac9).
⚠️ Report is 1 commits behind head on v3.1-dev.

Files with missing lines	Patch %	Lines
packages/rs-dpp/src/shielded/memo.rs	95.79%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           v3.1-dev    #3836    +/-   ##
==========================================
  Coverage     87.04%   87.05%            
==========================================
  Files          2677     2679     +2     
  Lines        329918   330113   +195     
==========================================
+ Hits         287182   287372   +190     
- Misses        42736    42741     +5     

Components	Coverage Δ
dpp	87.43% <95.79%> (+0.01%)	⬆️
drive	85.99% <ø> (ø)
drive-abci	89.29% <ø> (ø)
sdk	∅ <ø> (∅)
dapi-client	∅ <ø> (∅)
platform-version	∅ <ø> (∅)
platform-value	92.20% <ø> (ø)
platform-wallet	∅ <ø> (∅)
drive-proof-verifier	49.55% <ø> (ø)

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[QuantumExplorer]

Reviewed

[github-actions]

✅ DashSDKFFI.xcframework built for this PR.

• Workflow run: https://github.com/dashpay/platform/actions/runs/27263172786
• Artifacts: DashSDKFFI.xcframework (folder), DashSDKFFI.xcframework.zip, xc_checksum.txt

SwiftPM (host the zip at a stable URL, then use):

.binaryTarget(
  name: "DashSDKFFI",
  url: "https://your.cdn.example/DashSDKFFI.xcframework.zip",
  checksum: "e0d9db421070a304509e11e694af1cda6cd205b17dd7efb0bc3b9c32db29802a"
)

Xcode manual integration:

• Download 'DashSDKFFI.xcframework' artifact from the run link above.
• Drag it into your app target (Frameworks, Libraries & Embedded Content) and set Embed & Sign.
• If using the Swift wrapper package, point its binaryTarget to the xcframework location or add the package and place the xcframework at the expected path.