Fix PlayChain key data return semantics

[Kaua463]

Summary

Fixes PlayChain handling of keychain return semantics, particularly for kSecClassKey items requested with kSecReturnData.

Problem

PlayChain previously treated matched kSecClassKey items as SecKeyRef objects even when the caller explicitly requested kSecReturnData.

Google apps, including YouTube, perform queries such as:

kSecClass = kSecClassKey
kSecReturnData = true
kSecReturnRef = false

In this case PlayChain attempted to reconstruct a SecKey using key metadata such as kSecAttrKeyType and kSecAttrKeyClass.

Some persisted key entries do not contain those attributes, which could lead to a crash in PlayKeychain.copyMatching.

PlayChain also attempted to construct return values during SecItemAdd calls where the caller did not request a result.

Changes

• Respect kSecReturnData for key-class items and return the stored data instead of constructing a SecKey.
• Avoid constructing return values for SecItemAdd when no return value was requested.
• Handle data-only kSecMatchLimitAll queries.
• Treat queries without any kSecReturn* flags as existence checks.
• Preserve the existing kSecReturnRef behavior.

Testing

Tested with YouTube iOS 21.38.3 under PlayCover on Apple Silicon.

Runtime instrumentation confirmed calls including:

SecItemCopyMatching class=keys data=1 ref=0 attrs=0 pref=0
SecItemAdd class=keys data=0 ref=0 attrs=0 pref=0 resultPtr=0

With the final uninstrumented build:

• YouTube login persisted across 5 consecutive force-stop/relaunch cycles.
• Login persisted after fully quitting and restarting PlayCover.
• No PlayChain crash occurred.
• The project builds successfully with Xcode 27.0.

Related:

• [Bug]: Google apps can't retain login state. PlayCover#903
• [Bug]: PlayChain Causes Youtube Music to Crash Upon Pressing "Sign In" Button PlayCover#1799

[TheMoonThatRises]

@ohaiibuzzle you are the inventor of PlayChain, could you review this PR please?

[ohaiibuzzle]

Looks good. To be completely honest PlayChain makes a lot of assumptions when it was made, so these changes are to be expected.