feat(headless): complete portable single-session host

src/AcDream.Runtime/Session/LiveSessionController.cs

@@ -556,7 +556,10 @@ public sealed class LiveSessionController
 
             CharacterList.Parsed? characters = _operations.GetCharacters(session);
             if (characters is null
-                || !CharacterList.TrySelectFirstAvailable(characters, out CharacterList.Selection selected))
+                || !TrySelectCharacter(
+                    characters,
+                    options.Character,
+                    out CharacterList.Selection selected))
             {
                 Console.WriteLine("live: no available characters on account; disconnecting");
                 StopCore();
@@ -755,6 +758,62 @@ public sealed class LiveSessionController
     private LiveSessionStartResult ConnectedResult()
         => new(LiveSessionStartStatus.Connected, _activeSelection);
 
+    private static bool TrySelectCharacter(
+        CharacterList.Parsed characters,
+        LiveSessionCharacterSelector? selector,
+        out CharacterList.Selection selection)
+    {
+        ArgumentNullException.ThrowIfNull(characters);
+        if (selector is null)
+        {
+            return CharacterList.TrySelectFirstAvailable(
+                characters,
+                out selection);
+        }
+
+        int selectorCount =
+            (selector.ActiveIndex.HasValue ? 1 : 0)
+            + (selector.CharacterId.HasValue ? 1 : 0)
+            + (!string.IsNullOrWhiteSpace(selector.CharacterName) ? 1 : 0);
+        if (selectorCount != 1)
+        {
+            selection = default;
+            return false;
+        }
+
+        for (int index = 0; index < characters.Characters.Count; index++)
+        {
+            CharacterList.Character character =
+                characters.Characters[index];
+            if (!CharacterList.IsAvailableActiveIdentity(character))
+                continue;
+            if (selector.ActiveIndex is { } requestedIndex
+                && requestedIndex != index)
+            {
+                continue;
+            }
+            if (selector.CharacterId is { } requestedId
+                && requestedId != character.Id)
+            {
+                continue;
+            }
+            if (selector.CharacterName is { } requestedName
+                && !string.Equals(
+                    requestedName,
+                    character.Name,
+                    StringComparison.OrdinalIgnoreCase))
+            {
+                continue;
+            }
+
+            selection = new CharacterList.Selection(index, character);
+            return true;
+        }
+
+        selection = default;
+        return false;
+    }
+
     private void ThrowIfDisposing()
     {
         if (_disposeRequested || _disposed)