feat(ui): integrate read-only Jev decision overlay

Initialize the Godot panel, poll the decision log in the background, and preserve inspection state during updates. Use a .conf file to keep local settings separate from mod manifests.

ui/JevOverlay/.gitignore

@@ -1,4 +1,4 @@
 bin/
 obj/
 # Local absolute path to the decision log.
-JevOverlay.config.json
+JevOverlay.conf

ui/JevOverlay/Core/OverlayConfig.cs

@@ -4,7 +4,7 @@ namespace JevOverlay.Core;
 
 public static class OverlayConfig
 {
-    public const string FileName = "JevOverlay.config.json";
+    public const string FileName = "JevOverlay.conf";
 
     public static string LoadLogPath(string modDirectory)
     {

ui/JevOverlay/Mod.cs

@@ -0,0 +1,105 @@
+using System.Diagnostics;
+using Godot;
+using JevOverlay.Core;
+using JevOverlay.UI;
+using MegaCrit.Sts2.Core.Modding;
+
+namespace JevOverlay;
+
+[ModInitializer("Initialize")]
+public static class Mod
+{
+    private static SceneTree? tree;
+    private static OverlayView? view;
+    private static LogTail? reader;
+    private static readonly DecisionHistory History = new();
+    private static Task<TailBatch>? poll;
+    private static double nextPoll;
+    private static double? lastRows;
+    private static bool keyDown;
+    private static string? configError;
+    private static TailBatch? lastBatch;
+
+    public static void Initialize()
+    {
+        if (tree is not null) return;
+        try
+        {
+            string directory = Path.GetDirectoryName(typeof(Mod).Assembly.Location)!;
+            try { reader = new LogTail(OverlayConfig.LoadLogPath(directory)); }
+            catch (Exception ex) when (ex is IOException or UnauthorizedAccessException or
+                                            System.Text.Json.JsonException or FormatException or ArgumentException)
+            {
+                configError = $"Configure log_path in {OverlayConfig.FileName}, then restart the game.";
+                GD.PrintErr($"[JevOverlay] Configuration unavailable or invalid ({ex.GetType().Name}).");
+            }
+            tree = (SceneTree)Engine.GetMainLoop();
+            tree.ProcessFrame += OnFrame;
+            tree.Root.TreeExiting += Shutdown;
+            GD.Print("[JevOverlay] Read-only decision viewer initialized. F8 toggles the panel.");
+        }
+        catch (Exception ex)
+        {
+            GD.PrintErr($"[JevOverlay] Could not initialize ({ex.GetType().Name}).");
+        }
+    }
+
+    private static void OnFrame()
+    {
+        try
+        {
+            view ??= new OverlayView(tree!);
+            bool pressed = Input.IsPhysicalKeyPressed(Key.F8);
+            if (pressed && !keyDown) view.ToggleCollapsed();
+            keyDown = pressed;
+            view.Resize(tree!.Root.GetVisibleRect().Size);
+            if (configError is not null)
+            {
+                view.SetStatus(configError);
+                return;
+            }
+            double now = (double)Stopwatch.GetTimestamp() / Stopwatch.Frequency;
+            if (poll is { IsCompleted: true })
+            {
+                // Only file I/O runs on the worker. All model and UI updates run here.
+                lastBatch = poll.GetAwaiter().GetResult();
+                poll = null;
+                History.Apply(lastBatch);
+                if (lastBatch.Lines.Count > 0) lastRows = now;
+                if (lastBatch.Reset || lastBatch.Lines.Count > 0) view.Render(History);
+                UpdateStatus(now);
+            }
+            if (poll is null && now >= nextPoll)
+            {
+                nextPoll = now + 0.5;
+                poll = Task.Run(reader!.Poll);
+                UpdateStatus(now);
+            }
+        }
+        catch (Exception ex)
+        {
+            // A broken viewer must not interrupt play or produce one error per frame.
+            GD.PrintErr($"[JevOverlay] Viewer disabled ({ex.GetType().Name}).");
+            if (tree is not null) tree.ProcessFrame -= OnFrame;
+            view?.Dispose();
+            view = null;
+        }
+    }
+
+    private static void UpdateStatus(double now)
+    {
+        string text = lastBatch?.Error ?? (lastBatch?.CatchingUp == true ? "Reading pending log rows…"
+            : lastRows is null ? "Waiting for complete log rows."
+            : $"Read-only log · no new rows for {Math.Max(0, now - lastRows.Value):0}s");
+        if (History.SkippedLines > 0) text += $" · skipped {History.SkippedLines}";
+        if (History.Notice is { } notice)
+            text += "\n" + (notice.Length > 110 ? notice[..110] + "…" : notice);
+        view!.SetStatus(text, text + "\nFile activity does not prove that the bot or game is running.");
+    }
+
+    private static void Shutdown()
+    {
+        if (tree is not null) tree.ProcessFrame -= OnFrame;
+        // The scene tree frees the controls. A pending bounded file read can finish independently.
+    }
+}

ui/JevOverlay/UI/OverlayView.cs

@@ -159,8 +159,11 @@ public sealed class OverlayView
         else
         {
             history.Select(index);
-            summary.Text = entries[index].Summary();
-            evidence.Text = entries[index].Evidence();
+            // Do not reset text selection or scroll when another decision arrives.
+            string nextSummary = entries[index].Summary();
+            string nextEvidence = entries[index].Evidence();
+            if (summary.Text != nextSummary) summary.Text = nextSummary;
+            if (evidence.Text != nextEvidence) evidence.Text = nextEvidence;
         }
     }