Yattee v2 rewrite

Yattee/Services/Credentials/InstanceCredentialsManager.swift

@@ -0,0 +1,44 @@
+//
+//  InstanceCredentialsManager.swift
+//  Yattee
+//
+//  Protocol defining the common interface for instance-specific credentials management.
+//  Both InvidiousCredentialsManager and PipedCredentialsManager conform to this protocol.
+//
+
+import Foundation
+
+/// Protocol for instance-specific credentials management.
+/// Provides a unified interface for storing and retrieving authentication credentials
+/// across different instance types (Invidious, Piped, etc.).
+@MainActor
+protocol InstanceCredentialsManager: AnyObject, Observable {
+    /// Set of instance IDs that are currently logged in.
+    /// Used for reactive UI updates when login state changes.
+    var loggedInInstanceIDs: Set<UUID> { get }
+
+    /// Stores a credential (SID for Invidious, token for Piped) for an instance.
+    /// - Parameters:
+    ///   - credential: The credential value to store
+    ///   - instance: The instance to associate the credential with
+    func setCredential(_ credential: String, for instance: Instance)
+
+    /// Retrieves the stored credential for an instance.
+    /// - Parameter instance: The instance to retrieve the credential for
+    /// - Returns: The stored credential, or nil if not logged in
+    func credential(for instance: Instance) -> String?
+
+    /// Deletes the stored credential for an instance (logout).
+    /// - Parameter instance: The instance to log out from
+    func deleteCredential(for instance: Instance)
+
+    /// Checks if an instance has a stored credential.
+    /// - Parameter instance: The instance to check
+    /// - Returns: true if logged in, false otherwise
+    func isLoggedIn(for instance: Instance) -> Bool
+
+    /// Refreshes the login status for an instance from the Keychain.
+    /// Call this when a view appears to ensure UI is in sync with stored state.
+    /// - Parameter instance: The instance to refresh status for
+    func refreshLoginStatus(for instance: Instance)
+}