Phase A logic: TabManager/TabItem/session store (TDD, 17 tests)

VideoDownloader.App/Browser/Tabs/TabSessionStore.cs

@@ -0,0 +1,38 @@
+using System.IO;
+using System.Text.Json;
+
+namespace VideoDownloader.App.Browser.Tabs;
+
+/// <summary>세션 JSON 저장소(T1-10). 종료 시 탭 URL 저장, 시작 시 복원.</summary>
+public static class TabSessionStore
+{
+    public static void Save(string path, SessionSnapshot snap)
+    {
+        try
+        {
+            var dir = Path.GetDirectoryName(path);
+            if (!string.IsNullOrEmpty(dir)) Directory.CreateDirectory(dir);
+            var tmp = path + ".tmp";
+            File.WriteAllText(tmp, JsonSerializer.Serialize(snap));
+            File.Move(tmp, path, overwrite: true);
+        }
+        catch { }
+    }
+
+    public static SessionSnapshot? Load(string path)
+    {
+        try
+        {
+            if (!File.Exists(path)) return null;
+            var snap = JsonSerializer.Deserialize<SessionSnapshot>(File.ReadAllText(path));
+            if (snap == null || snap.Urls == null || snap.Urls.Count == 0) return null;
+            var pinned = snap.Pinned ?? new List<bool>();
+            while (pinned.Count < snap.Urls.Count) pinned.Add(false);
+            return snap with { Pinned = pinned };
+        }
+        catch
+        {
+            return null;
+        }
+    }
+}