[PM-40519] feat: Add passkey cipher storage and identity foundation to TestHarness

[morganzellers-bw]

🎟️ Tracking

PM-40519

📔 Objective

Adds the persistence and data-model foundation for passkey test scenarios in the TestHarness, split from PR #2945 for size.

• CipherStorageService persists SDK-encrypted ciphers across app relaunches, backed by UserDefaults.
• StoredCipher is a Codable mirror of the handful of Cipher/Fido2Credential fields these scenarios populate, since BitwardenSdk.Cipher isn't itself Codable.
• SyntheticIdentity/PasskeyKeychainItem model the throwaway identity persisted in the Keychain so the same crypto keys survive relaunches.
• PasskeyError and supporting fixtures round out the layer.
• No Fido2/SDK-client orchestration yet; PR [PM-40519] feat: Add SDK-backed passkey registration and assertion services to TestHarness #2945 builds the Fido2CredentialStore/Fido2UserInterface/PasskeyService layer on top of this.

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Stack: #2977 → #2945 → #2946 → #2947 → #2948

[github-actions]

🤖 Bitwarden Claude Code Review

Overall Assessment: APPROVE

This PR adds the persistence and data-model foundation for SDK-backed passkey scenarios in the Test Harness: a UserDefaults-backed CipherStorageService, a Codable StoredCipher mirror of BitwardenSdk.Cipher, SyntheticIdentity/PasskeyKeychainItem models, PasskeyError, SDK fixtures, and the XcodeGen/Sourcery wiring to link BitwardenSdk into TestHarnessShared. I reviewed the storage round-trip logic, the lossy-by-design Cipher reconstruction, keychain item protection level, secret handling, target/dependency configuration, and test coverage.

Secret handling looks correct for this context: only SDK ciphertext (Cipher.key, Fido2Credential.keyValue) lands in UserDefaults, while the synthetic identity material is modeled as a keychain item with kSecAttrAccessibleWhenUnlockedThisDeviceOnly. The lossy fields dropped by StoredCipher (notes, collectionIds, attachments, data, extra Fido2 credentials) are documented and match the fixed defaults these scenarios create, and both the nil-returning guards and the JSON round-trip are covered by tests.

Code Review Details

No findings.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.50%. Comparing base (f4b4283) to head (4d77e40).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2977   +/-   ##
=======================================
  Coverage   79.50%   79.50%           
=======================================
  Files        1169     1169           
  Lines       75028    75028           
=======================================
+ Hits        59650    59652    +2     
+ Misses      15378    15376    -2     

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