feat(flow): implement ABCD session policy and host return whitelist

- Scheme A: on-demand session start, inactivity-based expiry, handoff auto-recording
- Scheme B: cold-start overlay with swipe guidance and return alert
- Scheme C+D: HostAppURLRegistry (20 apps) and sourceApplication capture
- Settings: skip app switch toggle and inactivity duration picker
- Add LSApplicationQueriesSchemes for canOpenURL checks

Co-authored-by: Rocky <hkgood@users.noreply.github.com>

OSGKeyboardShared/Models/AppGroupConfiguration.swift

@@ -30,6 +30,10 @@ public struct AppGroupConfiguration: Sendable, Equatable {
         public static let detectedAppContext = "config.detectedAppContext"
         public static let detectedAppContextAt = "config.detectedAppContextAt"
         public static let personalDictionary = "config.personalDictionary.v1"
+        /// When true, the host app auto-returns to the source app after a cold-start handoff.
+        public static let flowSkipAppSwitch = "config.flowSkipAppSwitch"
+        /// Raw `FlowInactivityDuration` value; session expires after this idle window.
+        public static let flowInactivityDuration = "config.flowInactivityDuration"
     }
 
     // MARK: - Stored fields
@@ -49,6 +53,10 @@ public struct AppGroupConfiguration: Sendable, Equatable {
     public var cursorDragNavigationEnabled: Bool
     public var polishIntensity: PolishIntensity
     public var personalDictionary: PersonalDictionary
+    /// Auto-return to the host app after `startflow` cold start (default on).
+    public var flowSkipAppSwitch: Bool
+    /// Idle timeout before the Flow session ends; resets on each utterance.
+    public var flowInactivityDuration: FlowInactivityDuration
 
     // MARK: - Derived
 
@@ -145,7 +153,16 @@ public struct AppGroupConfiguration: Sendable, Equatable {
                 return defaults.bool(forKey: Keys.cursorDragNavigationEnabled)
             }(),
             polishIntensity: resolvePolishIntensity(from: defaults),
-            personalDictionary: decodePersonalDictionary(from: defaults)
+            personalDictionary: decodePersonalDictionary(from: defaults),
+            flowSkipAppSwitch: {
+                if defaults.object(forKey: Keys.flowSkipAppSwitch) == nil {
+                    return true
+                }
+                return defaults.bool(forKey: Keys.flowSkipAppSwitch)
+            }(),
+            flowInactivityDuration: FlowInactivityDuration.fromStored(
+                defaults.string(forKey: Keys.flowInactivityDuration)
+            )
         )
 
         let preset = LLMProvider.provider(id: config.providerId)
@@ -193,6 +210,8 @@ public struct AppGroupConfiguration: Sendable, Equatable {
         defaults.set(handednessPreference.rawValue, forKey: Keys.handednessPreference)
         defaults.set(cursorDragNavigationEnabled, forKey: Keys.cursorDragNavigationEnabled)
         defaults.set(polishIntensity.rawValue, forKey: Keys.polishIntensity)
+        defaults.set(flowSkipAppSwitch, forKey: Keys.flowSkipAppSwitch)
+        defaults.set(flowInactivityDuration.rawValue, forKey: Keys.flowInactivityDuration)
         Self.encodePersonalDictionary(personalDictionary, to: defaults)
     }
 

OSGKeyboardShared/Models/FlowInactivityDuration.swift

@@ -0,0 +1,46 @@
+// FlowInactivityDuration.swift
+// OSGKeyboard · Shared
+//
+// User-selectable Flow session inactivity timeout. The timer resets after
+// each completed utterance (and on session start).
+
+import Foundation
+
+public enum FlowInactivityDuration: String, CaseIterable, Identifiable, Sendable, Codable {
+    case tenMinutes = "10m"
+    case thirtyMinutes = "30m"
+    case threeHours = "3h"
+    case twelveHours = "12h"
+    case twentyFourHours = "24h"
+
+    public var id: String { rawValue }
+
+    public static let `default`: FlowInactivityDuration = .twelveHours
+
+    public var timeInterval: TimeInterval {
+        switch self {
+        case .tenMinutes: return 10 * 60
+        case .thirtyMinutes: return 30 * 60
+        case .threeHours: return 3 * 60 * 60
+        case .twelveHours: return 12 * 60 * 60
+        case .twentyFourHours: return 24 * 60 * 60
+        }
+    }
+
+    public var labelKey: String {
+        switch self {
+        case .tenMinutes: return "settings.flow.inactivity.10m"
+        case .thirtyMinutes: return "settings.flow.inactivity.30m"
+        case .threeHours: return "settings.flow.inactivity.3h"
+        case .twelveHours: return "settings.flow.inactivity.12h"
+        case .twentyFourHours: return "settings.flow.inactivity.24h"
+        }
+    }
+
+    public static func fromStored(_ raw: String?) -> FlowInactivityDuration {
+        guard let raw, let value = FlowInactivityDuration(rawValue: raw) else {
+            return .default
+        }
+        return value
+    }
+}

OSGKeyboardShared/Models/ProviderConfig.swift

@@ -171,6 +171,25 @@ public final class ProviderConfig: ObservableObject, @unchecked Sendable {
         }
     }
 
+    /// When enabled, the host app tries to return to the source app after a cold-start handoff.
+    @Published public var flowSkipAppSwitch: Bool {
+        didSet {
+            guard !isApplyingConfiguration, flowSkipAppSwitch != configuration.flowSkipAppSwitch else { return }
+            configuration.flowSkipAppSwitch = flowSkipAppSwitch
+            persistConfiguration()
+        }
+    }
+
+    /// Idle window before an active Flow session expires; resets on each utterance.
+    @Published public var flowInactivityDuration: FlowInactivityDuration {
+        didSet {
+            guard !isApplyingConfiguration,
+                  flowInactivityDuration != configuration.flowInactivityDuration else { return }
+            configuration.flowInactivityDuration = flowInactivityDuration
+            persistConfiguration()
+        }
+    }
+
     public var isConfigured: Bool {
         // Local engine uses on-device ASR + built-in DeepSeek polish and
         // does not need a user API key. Cloud needs base URL, key, and model.
@@ -218,6 +237,8 @@ public final class ProviderConfig: ObservableObject, @unchecked Sendable {
         handednessPreference = configuration.handednessPreference
         cursorDragNavigationEnabled = configuration.cursorDragNavigationEnabled
         polishIntensity = configuration.polishIntensity
+        flowSkipAppSwitch = configuration.flowSkipAppSwitch
+        flowInactivityDuration = configuration.flowInactivityDuration
         isApplyingConfiguration = false
     }