refactor(rs-sdk-ffi): use the rs-sdk voting-key helpers instead of its own

[QuantumExplorer]

Completes the move #4340 started. That PR added the masternode voting-key facts to rs-sdk but did not remove rs-sdk-ffi's copies, so v4.2-dev currently carries two implementations of the same Platform behaviour — free to drift, and exactly the duplication #4340 existed to end.

What moves

Deleted from the FFI, now taken from platform::transition::masternode_vote_keys:

• fabricating the voting key Platform holds
• select_voting_key
• is_voting_key_failure (the diagnosis gate)
• diagnose_voting_key_failure

Net −340 lines.

What stays

The FFI keeps what it actually owns:

• pointer / CStr marshalling and null checks
• the byte-order conversion at the boundary — callers pass wire order, and voter_identity_id takes a typed ProTxHash, so the conversion happens once, here, where the FFI's contract is defined
• signer construction from the raw key (simple-signer is an FFI dependency, deliberately not an SDK one)
• rendering VotingKeyProblem into a user-facing sentence

That last split is the point: rs-sdk reports the typed fact, the binding phrases it. Formatting in the SDK would hand every caller English they cannot localise.

Tests

Tests follow the code. Selection, the gate and the diagnosis are covered by #4340's 10 tests in rs-sdk. What remains here covers only what remains here — that both messages name their identifiers, and that neither contains whitespace runs, which is the defect that once rendered them with blank gaps mid-sentence on device.

5 tests in the module, fmt and clippy clean.

Risk

Behaviour-preserving. The fabricated key, the gate's three signature variants, and the diagnosis logic are the same code, now called rather than copied — verified by the surviving message tests and by the fact that votes cast successfully on the merged stack.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved voting-key handling for more reliable vote submission.
  • Added clearer, more specific error messages when vote broadcasts fail due to voting-key issues.
  • Improved diagnosis of voting failures, helping surface actionable details to host applications.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 1050c1b1-1086-4571-a209-b86646f0aa0c

📥 Commits

Reviewing files that changed from the base of the PR and between f446428 and c779ca0.

📒 Files selected for processing (1)

• packages/rs-sdk-ffi/src/contested_resource/transitions/cast_vote.rs

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📝 Walkthrough

Walkthrough

The FFI now uses shared rs-sdk helpers to construct voting keys and diagnose typed voting-key failures after broadcast errors. Local identity fetching, key selection, and failure classification were removed. Tests validate diagnostic message formatting.

Changes

Voting-key diagnosis

Layer / File(s)	Summary
Shared voting-key construction packages/rs-sdk-ffi/src/contested_resource/transitions/cast_vote.rs	The cast-vote flow uses voter_identity_voting_key and shared voting-key diagnosis imports instead of local key construction.
Typed broadcast failure diagnosis packages/rs-sdk-ffi/src/contested_resource/transitions/cast_vote.rs	Broadcast failures use is_voting_key_failure, convert the hash to ProTxHash, and delegate diagnosis to rs-sdk. The FFI formats NoVoterIdentity and NoUsableVotingKey results and preserves unrelated errors. Tests cover diagnostic message formatting.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• dashpay/platform#4333: Both changes update voting-key construction and post-broadcast diagnosis in cast_vote.rs.
• dashpay/platform#4340: This change migrates the FFI logic to shared helpers introduced there.

Suggested reviewers:shumkov, lklimek

🚥 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 describes the main change: replacing duplicated FFI voting-key logic with rs-sdk helpers.
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.

✨ 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 refactor/ffi-use-rs-sdk-vote-keys

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.61%. Comparing base (f446428) to head (c779ca0).
⚠️ Report is 1 commits behind head on v4.2-dev.

Additional details and impacted files

@@ Coverage Diff @@## v4.2-dev #4341 +/- ##
============================================
- Coverage 87.79% 87.61% -0.18% 
============================================
Files 2677 2704 +27 Lines 342371 345211 +2840 ============================================
+ Hits 300578 302473 +1895 - Misses 41793 42738 +945 

Components	Coverage Δ
dpp	88.86% <ø> (ø)
drive	86.25% <ø> (ø)
drive-abci	89.66% <ø> (ø)
sdk	∅ <ø> (∅)
dapi-client	∅ <ø> (∅)
platform-version	∅ <ø> (∅)
platform-value	92.88% <ø> (ø)
platform-wallet	∅ <ø> (∅)
drive-proof-verifier	48.02% <ø> (ø)

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