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>

OSGKeyboardTests/AppGroupConfigurationTests.swift

@@ -30,6 +30,8 @@ final class AppGroupConfigurationTests: XCTestCase {
         XCTAssertTrue(config.cursorDragNavigationEnabled)
         XCTAssertEqual(config.polishIntensity, .default)
         XCTAssertTrue(config.personalDictionary.entries.isEmpty)
+        XCTAssertTrue(config.flowSkipAppSwitch)
+        XCTAssertEqual(config.flowInactivityDuration, .twelveHours)
     }
 
     func testSaveAndLoadRoundTrip() {
@@ -49,6 +51,8 @@ final class AppGroupConfigurationTests: XCTestCase {
         config.handednessPreference = .right
         config.cursorDragNavigationEnabled = false
         config.polishIntensity = .light
+        config.flowSkipAppSwitch = false
+        config.flowInactivityDuration = .thirtyMinutes
         config.save(to: defaults)
 
         let loaded = AppGroupConfiguration.load(fromAvailable: defaults)
@@ -66,6 +70,8 @@ final class AppGroupConfigurationTests: XCTestCase {
         XCTAssertEqual(loaded.handednessPreference, .right)
         XCTAssertFalse(loaded.cursorDragNavigationEnabled)
         XCTAssertEqual(loaded.polishIntensity, .light)
+        XCTAssertFalse(loaded.flowSkipAppSwitch)
+        XCTAssertEqual(loaded.flowInactivityDuration, .thirtyMinutes)
     }
 
     func testTranslationEnabledDerivedFromTargetLocale() {

OSGKeyboardTests/FlowSessionPolicyTests.swift

@@ -0,0 +1,46 @@
+// FlowSessionPolicyTests.swift
+// OSGKeyboardTests
+
+import XCTest
+@testable import OSGKeyboardShared
+
+final class FlowSessionPolicyTests: XCTestCase {
+    private func makeDefaults() -> UserDefaults {
+        let suite = "group.com.osgkeyboard.shared.tests.policy.\(UUID().uuidString)"
+        let defaults = UserDefaults(suiteName: suite)!
+        defaults.removePersistentDomain(forName: suite)
+        return defaults
+    }
+
+    func testSkipAppSwitchDefaultsToTrue() {
+        let defaults = makeDefaults()
+        XCTAssertTrue(FlowSessionPolicy.skipAppSwitch(defaults: defaults))
+    }
+
+    func testInactivityDurationDefaultsToTwelveHours() {
+        let defaults = makeDefaults()
+        XCTAssertEqual(FlowSessionPolicy.inactivityDuration(defaults: defaults), .twelveHours)
+        XCTAssertEqual(FlowSessionPolicy.sessionDuration(defaults: defaults), 12 * 60 * 60)
+    }
+
+    func testTouchLastActivityExtendsExpiry() {
+        let defaults = makeDefaults()
+        defaults.set(FlowInactivityDuration.tenMinutes.rawValue, forKey: AppGroupConfiguration.Keys.flowInactivityDuration)
+        FlowSessionBridge.markSessionActive(defaults: defaults)
+
+        let staleExpiry = Date().timeIntervalSince1970 + 30
+        defaults.set(staleExpiry, forKey: FlowSessionKeys.flowSessionExpires)
+        FlowSessionBridge.touchLastActivity(defaults: defaults)
+
+        let refreshed = FlowSessionBridge.sessionExpiresAt(defaults: defaults) ?? 0
+        XCTAssertGreaterThan(refreshed, staleExpiry)
+    }
+
+    func testPendingHostBundleIdRoundTrip() {
+        let defaults = makeDefaults()
+        FlowSessionBridge.setPendingHostBundleId("com.tencent.xin", defaults: defaults)
+        XCTAssertEqual(FlowSessionBridge.pendingHostBundleId(defaults: defaults), "com.tencent.xin")
+        FlowSessionBridge.clearPendingHostBundleId(defaults: defaults)
+        XCTAssertNil(FlowSessionBridge.pendingHostBundleId(defaults: defaults))
+    }
+}

OSGKeyboardTests/HostAppURLRegistryTests.swift

@@ -0,0 +1,28 @@
+// HostAppURLRegistryTests.swift
+// OSGKeyboardTests
+
+import XCTest
+@testable import OSGKeyboardShared
+
+final class HostAppURLRegistryTests: XCTestCase {
+    func testWeChatLookup() {
+        let entry = HostAppURLRegistry.lookup(bundleId: "com.tencent.xin")
+        XCTAssertEqual(entry?.returnURLString, "weixin://")
+        XCTAssertEqual(entry?.displayNameKey, "hostApp.wechat")
+    }
+
+    func testUnknownBundleReturnsNil() {
+        XCTAssertNil(HostAppURLRegistry.lookup(bundleId: "com.apple.MobileSMS"))
+        XCTAssertNil(HostAppURLRegistry.lookup(bundleId: nil))
+        XCTAssertNil(HostAppURLRegistry.lookup(bundleId: ""))
+    }
+
+    func testQuerySchemesIncludesWeChat() {
+        XCTAssertTrue(HostAppURLRegistry.querySchemes.contains("weixin"))
+    }
+
+    func testEntriesHaveUniqueBundleIds() {
+        let ids = HostAppURLRegistry.entries.map(\.bundleId)
+        XCTAssertEqual(Set(ids).count, ids.count)
+    }
+}