fix(ui): D.2b-B — inventory panels render over the backdrop (#145 continuation) + captions

Visual verification surfaced two render bugs (controller LOGIC was already correct):

1. BACKDROP WASH-OUT (the big one — #145 continuation). The mounted backpack/
   3D-items panels inherited their sub-window root's ZLevel 1000 via the merge's
   zero-wins-base rule. The #145 ZOrder fold (ReadOrder − ZLevel·10000) turned 1000
   into ZOrder ≈ −10,000,000 — sinking the panels BEHIND the frame's Alphablend
   backdrop (ZLevel 100 → ≈ −1,000,000). The backdrop then overpainted the panels'
   captions/burden-meter/cells (the paperdoll root is ZLevel 0 so it escaped, which
   is why the previous session thought #145 was done). Fix: the sub-window mount now
   keeps each slot's OWN frame ZLevel, so panels sit in front of the backdrop.
   Root-caused via a one-shot sprite-segment-order dump (backdrop was painting after
   the panel content) + a live ZLevel probe.

2. CAPTIONS. The caption elements resolve to UiText; driving a nested child UiText
   didn't paint. AttachCaption now drives the host UiText directly.

Locked by InventoryFrameImportProbe (real-dat smoke: asserts each mounted panel's
ZOrder > the backdrop's). Visually confirmed by the user: dark backdrop behind,
Burden 17% + vertical bar + Contents-of-Backpack + full item grid all visible.
Build + App(532)/Core(1526) tests green.

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

src/AcDream.App/UI/Layout/InventoryController.cs

@@ -82,9 +82,9 @@ public sealed class InventoryController
             _burdenMeter.Fill = () => _burdenFill;
         }
 
-        // Captions: attach a centered UiText child carrying the known string. "Contents of
-        // Backpack" + "%d%%" are procedural in retail (gm3DItemsUI/gmBackpackUI PostInit/
-        // SetLoadLevel); "Burden" is the dat label. (Caption pass, spec §5.)
+        // Captions: drive each host UiText directly with the known string (the caption
+        // elements resolve to UiText). "Contents of Backpack" + "%d%%" are procedural in retail
+        // (gm3DItemsUI/gmBackpackUI PostInit/SetLoadLevel); "Burden" is the dat label. (Spec §5.)
         AttachCaption(layout.FindElement(BurdenCaptionId),   () => "Burden", datFont);
         AttachCaption(layout.FindElement(ContentsCaptionId), () => "Contents of Backpack", datFont);
         AttachCaption(layout.FindElement(BurdenTextId),      () => _burdenPercent + "%", datFont);
@@ -168,6 +168,30 @@ public sealed class InventoryController
     private void AttachCaption(UiElement? host, Func<string> text, UiDatFont? datFont)
     {
         if (host is null) return;
+
+        // The caption elements (0x100001D7 "Burden", 0x100001C5 "Contents of Backpack",
+        // 0x100001D8 "%") resolve to UiText (Type-0 inheriting a text base — confirmed live).
+        // Drive the host UiText DIRECTLY: it is already in the paint tree and renders, whereas
+        // a nested child UiText did not paint. Set it to a static centered single-line label.
+        if (host is UiText t)
+        {
+            t.Centered = true;
+            t.DatFont = datFont;
+            t.ClickThrough = true;
+            t.AcceptsFocus = false;
+            t.IsEditControl = false;
+            t.CapturesPointerDrag = false;
+            t.LinesProvider = () =>
+            {
+                var s = text();
+                return string.IsNullOrEmpty(s)
+                    ? Array.Empty<UiText.Line>()
+                    : new[] { new UiText.Line(s, CaptionColor) };
+            };
+            return;
+        }
+
+        // Fallback (non-UiText host): attach a centered label child.
         var label = new UiText
         {
             Left = 0f, Top = 0f, Width = host.Width, Height = host.Height,

src/AcDream.App/UI/Layout/LayoutImporter.cs

@@ -242,8 +242,21 @@ public static class LayoutImporter
         // (vitals/chat/toolbar). See ShouldMountBaseChildren + the B-Grid spec.
         if (baseChildren is not null
             && ShouldMountBaseChildren(d.Children.Count, self.StateMedia.Count, baseChildren.Count))
+        {
             result.Children.AddRange(baseChildren);
 
+            // The mounted slot's layer WITHIN THE FRAME is its OWN ZLevel, not the mounted
+            // sub-window root's. The gm*UI sub-window roots carry ZLevel 1000 (their standalone
+            // top-window layer); ElementReader.Merge's zero-wins-base rule made the slot (own
+            // ZLevel 0) inherit that 1000, and the #145 ZOrder fold (ReadOrder − ZLevel·10000)
+            // turns 1000 into ZOrder ≈ −10,000,000 — sinking the whole panel BEHIND the frame's
+            // Alphablend backdrop (ZLevel 100 → ≈ −1,000,000). The backdrop then overpaints the
+            // panel's captions/meter/cells (the wash-out bug; the paperdoll root happens to be
+            // ZLevel 0 so it escaped). Restore the slot's own frame-layer so the panel sits in
+            // FRONT of the backdrop. (B-Controller debug 2026-06-21; continuation of #145.)
+            result.ZLevel = self.ZLevel;
+        }
+
         return result;
     }