feat(a2b): first-pass texture render — full-screen event-CG layer

Wire asset resolution into a live Godot render. VM executes set-texture ->
ResourceMap resolves (scene,resId) -> files[section_base+resId] across all
archives -> pre-converted BMP -> composite behind the dialogue. The full-screen
event-CG layer (EV052*) renders end-to-end from the executed bytecode.

- Age.Engine/Sys4/ResourceMap.cs: Resolve + BMP TexturePath; Paths: asset JSONs
- GodotAdvHost: create/set/draw-texture -> TextureRect in a _stage layer
- IHost.DrawTexture + VM dispatch extended with dst x/y (draw-texture args 7/8)
- project.godot 800x600; convert_agf.py all-archive + --scene batch
- engine 8/8, C# --selftest still byte-matches vm0 trace (VM behaviour unchanged)

Known limitations (next chunk = graphics geometry/blend subsystem):
- sprites + BG* via the CG-load subroutine get garbage dst/size — native ops
  stubbed (0x208 get-texture-size + sprite position/anim chain)
- AE* fades draw opaque/instant (no alpha); no chromakey
- slot model approximates the game's immediate-mode blit-onto-slot-0 canvas
- AGF pre-converted to BMP offline (runtime decoder deferred)
See docs/phase-a-slice-plan.md (A2b section).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

engine/Age.Engine/Sys4/Paths.cs

@@ -8,6 +8,9 @@ public static class Paths
     public static string GameDir => Path.Combine(Workspace, "姫狩りダンジョンマイスター");
     public static string Build => Path.Combine(Repo, "build");
     public static string OpcodesJson => Path.Combine(Build, "opcodes.json");
+    public static string AssetSectionsJson => Path.Combine(Build, "asset-sections.json");
+    public static string AssetIndexJson => Path.Combine(Build, "asset-index.json");
+    public static string Textures => Path.Combine(Build, "textures");
 
     private static string FindRepo()
     {

engine/Age.Engine/Sys4/ResourceMap.cs

@@ -0,0 +1,63 @@
+using System.Text.Json;
+
+namespace Age.Engine.Sys4;
+
+/// <summary>One SYS4INI asset entry.</summary>
+public sealed record AssetEntry(string Name, string Archive, long Offset, long Size);
+
+/// <summary>
+/// Static asset resolver. SYS4INI's file list is sectioned (one per scene: SCxxxx.BIN + its
+/// cross-archive asset manifest); file_number is the index within a section. So a bytecode
+/// resId resolves as files[section_base(scene) + resId] -- unified for graphics and audio.
+/// See docs/asset-resolution-re.md. Built from build/asset-index.json + build/asset-sections.json.
+/// </summary>
+public sealed class ResourceMap
+{
+    private readonly IReadOnlyList<AssetEntry> _files;
+    private readonly IReadOnlyDictionary<string, int> _sceneBase;   // "SC0000" -> section base index
+
+    public ResourceMap(IReadOnlyList<AssetEntry> files, IReadOnlyDictionary<string, int> sceneBase)
+    {
+        _files = files;
+        _sceneBase = sceneBase;
+    }
+
+    public static ResourceMap Load(string indexPath, string sectionsPath)
+    {
+        var files = new List<AssetEntry>();
+        using (var idx = JsonDocument.Parse(File.ReadAllText(indexPath)))
+            foreach (var f in idx.RootElement.GetProperty("files").EnumerateArray())
+                files.Add(new AssetEntry(
+                    f.GetProperty("name").GetString()!,
+                    f.GetProperty("archive").GetString()!,
+                    f.GetProperty("offset").GetInt64(),
+                    f.GetProperty("size").GetInt64()));
+
+        var sceneBase = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);
+        using (var sec = JsonDocument.Parse(File.ReadAllText(sectionsPath)))
+            foreach (var p in sec.RootElement.GetProperty("scene_base").EnumerateObject())
+                sceneBase[p.Name] = p.Value.GetInt32();
+
+        return new ResourceMap(files, sceneBase);
+    }
+
+    public static ResourceMap Load() => Load(Paths.AssetIndexJson, Paths.AssetSectionsJson);
+
+    /// <summary>Resolve a scene-local resId to its asset, or null if out of range / unknown scene.</summary>
+    public AssetEntry? Resolve(string scene, long resId)
+    {
+        var key = scene.EndsWith(".BIN", StringComparison.OrdinalIgnoreCase)
+            ? scene[..^4] : scene;
+        if (!_sceneBase.TryGetValue(key, out var b)) return null;
+        long p = b + resId;
+        return p >= 0 && p < _files.Count ? _files[(int)p] : null;
+    }
+
+    /// <summary>Pre-converted BMP path for an AGF asset (see tools/convert_agf.py).</summary>
+    public static string? TexturePath(AssetEntry a)
+    {
+        if (!a.Name.EndsWith(".AGF", StringComparison.OrdinalIgnoreCase)) return null;
+        var bmp = Path.Combine(Paths.Textures, Path.GetFileNameWithoutExtension(a.Name) + ".BMP");
+        return File.Exists(bmp) ? bmp : null;
+    }
+}