feat(swift-sdk): public RawKeySigner one-shot raw-key signing

[QuantumExplorer]

Issue being fixed or feature implemented

Callers that already hold 32-byte key material (e.g. from a derivation-path lookup) had no way to sign without constructing a full KeychainSigner/KeyManager stack — the create-signer → sign → destroy FFI round-trip was private to KeychainSigner.ffiSign.

dashwallet-ios needs this entry point and has been carrying it on its platform pin branch; upstreaming it shrinks the pin (see DASHSYNC_MIGRATION.md there).

What was done?

• Extracted the dash_sdk_signer_create_from_private_key → dash_sdk_signer_sign → dash_sdk_signer_destroy round-trip into a public RawKeySigner enum (in KeyWallet/KeyManager.swift), with a typed KeyManagerError surface. The key copy is zeroed before returning.
• KeychainSigner.ffiSign now delegates to it, keeping a single implementation of the round-trip.
• Marshals only — no key-management decisions move into Swift; the signer handle binds as OpaquePointer, matching the current header import.

How Has This Been Tested?

• SwiftExampleApp builds for the iOS simulator on this branch (which exercises the SwiftDashSDK package including the delegating KeychainSigner).
• The same change has been exercised end-to-end on the dashwallet-ios pin branch, where RawKeySigner signs for the reveal-private-key flow.

Breaking Changes

None. KeychainSigner's public API is unchanged; RawKeySigner is additive.

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

• Improvements
  • Improved private-key signing reliability and error handling.
  • Added validation for private-key size before signing.
  • Enhanced protection of sensitive key material during signing.
  • Added clearer reporting when signer creation or signing fails.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: e1a822db-cb24-4250-811d-44d6689f07ca

📥 Commits

Reviewing files that changed from the base of the PR and between d7aee13 and 67bcff7.

📒 Files selected for processing (1)

• packages/swift-sdk/Sources/SwiftDashSDK/FFI/KeychainSigner.swift

📝 Walkthrough

Walkthrough

Adds RawKeySigner for one-shot ECDSA signing from raw private keys, including validation and secure cleanup. KeychainSigner now delegates signing to it and maps KeyManagerError cases to its typed signer errors.

Changes

Raw key signing

Layer / File(s)	Summary
Raw key signing utility packages/swift-sdk/Sources/SwiftDashSDK/KeyWallet/KeyManager.swift	Adds KeyManagerError.signingFailed, its description, and RawKeySigner.sign, which validates keys, performs FFI signing, frees resources, and wipes a defensive key copy.
KeychainSigner integration packages/swift-sdk/Sources/SwiftDashSDK/FFI/KeychainSigner.swift	Routes private-key signing through RawKeySigner.sign and maps creation, format, signing, and fallback errors.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Possibly related PRs

• dashpay/platform#3853: Modifies the KeychainSigner.swift FFI signing path and signer pointer handling.

Suggested reviewers: shumkov, llbartekll, thepastaclaw

🚥 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 main change: adding a public RawKeySigner for one-shot raw-key signing.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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 unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/raw-key-signer

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[thepastaclaw]

🔍 Review in progress — actively reviewing now (commit d7aee13)

[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/swift-sdk/Sources/SwiftDashSDK/FFI/KeychainSigner.swift`:
- Around line 716-732: Update ffiSign’s KeyManagerError.invalidKeyFormat catch
branch to return the error category intended for invalid signing input rather
than .ffiSignerCreationFailed, while preserving the original message and leaving
signerCreationFailed and signingFailed mappings unchanged.

In `@packages/swift-sdk/Sources/SwiftDashSDK/KeyWallet/KeyManager.swift`:
- Line 12: Remove the new public KeyManagerError.signingFailed case and update
the affected KeyManager error path to reuse an existing error case. Do not
expand the public enum API or introduce another case.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 67d3ea1c-bd23-4fb0-909d-2e39b6b7b67a

📥 Commits

Reviewing files that changed from the base of the PR and between 9c75a1c and d7aee13.

📒 Files selected for processing (2)

• packages/swift-sdk/Sources/SwiftDashSDK/FFI/KeychainSigner.swift
• packages/swift-sdk/Sources/SwiftDashSDK/KeyWallet/KeyManager.swift