Scenario conditions in dialogs: option if= hides choices, when moved here from stat checks; command schemas

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/Scenarios/Impls/WhenCommandStrategy.cs

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+namespace Cthangover.Mods.Dialog.Scenarios
+{
+    using System.Collections.Generic;
+    using Cthangover.Core.Localization;
+    using Cthangover.Core.Scenes;
+    using Cthangover.Mods.Dialog;
+
+    /// <summary>
+    /// A conditional jump in the middle of a dialog:
+    /// <code>when "stat(cha) &gt;= 5 &amp;&amp; door == 'open'" -> :persuaded [else=refused]</code>
+    /// evaluates the shared condition language (flags, quests, stats, equipment, GDScript
+    /// conditions — everything mods registered) at the moment the line runs, and jumps to
+    /// the arrow label when it holds, to <c>else</c> when it does not (or goes on).
+    /// <para/>
+    /// It is the RPG Maker "Conditional Branch" without a new syntax: the condition is the
+    /// same text a scenario header's <c>condition:</c> takes. Several words without quotes
+    /// are joined back with spaces, so short conditions need no quotes.
+    /// </summary>
+    public class WhenCommandStrategy : IScenarioCommandStrategy, IScenarioCommandSpec
+    {
+        /// <inheritdoc />
+        public string Command => "when";
+
+        /// <inheritdoc />
+        public int MinPositional => 1;
+
+        /// <inheritdoc />
+        public IReadOnlyList<string> AllowedNamed => new[] { "else" };
+
+        /// <inheritdoc />
+        public string JumpTargetNamedKey => "else";
+
+        /// <inheritdoc />
+        public void Execute(DialogQueue dlg, List<string> positional, Dictionary<string, string> named, string arrowTarget, ILocalizationProvider locale)
+        {
+            var condition = string.Join(" ", positional);
+            named.TryGetValue("else", out var otherwise);
+            dlg.IfGoTo(() => ScenarioCondition.Evaluate(condition), Label(arrowTarget), Label(otherwise));
+        }
+
+        private static string Label(string target) => string.IsNullOrWhiteSpace(target) ? null : target.Trim().TrimStart(':');
+    }
+}